Relieving the exhaust bridge on a freshly bored 85 250R

[wonderboy]

I have my brother's 250R jug back from being bored and ported. I need to relieve the exhaust bridge. I understand it needs to be relieved 3 or 4 thousandths. To do this, is it fine to use a rotary tool or will this be too agressive? Also, I'm assuming that the relief is 3 or 4 thou at the midpoint of the bridge, and that it tapers back to nothing (no material removed) at the top and bottom of the bridge itself. Also, what surface finish am I looking for when done (same cross hatch as the rest of the bore, or smooth, etc).

I'm probably making more out of this than necessary, but any advice would be appreciated!

[barnett468]

I have my brother's 250R jug back from being bored and ported. I need to relieve the exhaust bridge. I understand it needs to be relieved 3 or 4 thousandths. To do this, is it fine to use a rotary tool or will this be too agressive?f you are determined to do it one approach is to use a dremmel with the white sanding/polishing tips.




Also, I'm assuming that the relief is 3 or 4 thou at the midpoint of the bridge, and that it tapers back to nothing (no material removed) at the top and bottom of the bridge itself.yes, but just .0015 is way more than enough. leave the bridge untouched 3/16" - 1/4" from both top and bottom so the rings will seal beyond those points.




Also, what surface finish am I looking for when done (same cross hatch as the rest of the bore, or smooth, etc).i would make it all as smooth as glass wherever you remove material. Hone it after, not before.




I'm probably making more out of this than necessary, but any advice would be appreciated!No, you are not, many people screw up their rings or cyl by doing it improperly.



You can color the bridge with black felt pen or dykem so you can see what you are doing better.

Instead of doing this or in addition to this you can also drill 2 1/32 holes in the center of the piston, one above the other 1/2" apart, starting at around 1/2" below the bottom ring. This forces gas/air/oil onto the bridge which cools and lubricates it which reduces the potential for a seizure on the bridge.

[82 250r]

Usually the machinst/builder who does the bore and hone will relieve the bridge for you.
Are you sure it's not already done?

[nstyle73]

An honest question, I know this is common practice on the Honda FL350, but is this pretty standard on the liquid cooled bikes?

[Super350]

Usually the machinst/builder who does the bore and hone will relieve the bridge for you.
Are you sure it's not already done?

I was going to say I have never done any relieving myself...I hope my machinist did it :wondering

[82 250r]

An honest question, I know this is common practice on the Honda FL350, but is this pretty standard on the liquid cooled bikes?
Yes...if you're referring to relieving the exhaust bridge.

[wonderboy]

Thanks guys. Barnett468, thank you for the details. That makes sense to leave it untouched before (rather than exactly at) the top and bottom, that way the ring is pushed back cleanly.

Unfortunately, the original machine shop that bored the cylinder didn't relieve the bridge. They also didn't even chamfer the ports (they are off my list now). The cylinder was ported by Jason Hall (after having it bored by another shop). Jason recognized that the ports weren't chamfered and did that, but didn't know if the bridge was touched or not, so he left that alone (especially figuring that I could easily take care of it)

Regarding weather or not to do it on a liquid machine: I think the problem was much worse on the air cooled machines (FL350 Odyssey) but most of the sources I read say to do it on all machines with an exhaust bridge. The way I figure, it can't do any harm as long as it is done properly.

I'll have to read up on the drilling of the holes in the piston. This sounds like a good idea too.

Thanks for all the good info guys, I appreciate it!

[atc007]

I've forgotten how many R motors I've built,and NEVER relieved it. I have always drilled 3 holes in every 250 and bigger 2 cycle piston there. Make sure your ports are chamfered smoothly,which yours are by Jason . And ride it.

[barnett468]

Thanks guys. Barnett468, thank you for the details. That makes sense to leave it untouched before (rather than exactly at) the top and bottom, that way the ring is pushed back cleanly.no prob, yes a shallow transition is better than a steep one.




Regarding weather or not to do it on a liquid machine: I think the problem was much worse on the air cooled machines (FL350 Odyssey) but most of the sources I read say to do it on all machines with an exhaust bridge. The way I figure, it can't do any harm as long as it is done properly.it's best not to do it on machines that are not known for seizing there. i did that and drilled holes on my old air cooled race bikes back in the 70's but they got the rings replaced often.

We never seized a stock kawi and the factory team rarely seized one. yes one might say that it's a bad comparison because the motorcycles are much lighter than a 3 wheeler and/or they are tuned by the worlds best tuners etc., but just the same, Jeff Ward, Larry Roessler and others subjected them to plenty of load I can assure you.




I'll have to read up on the drilling of the holes in the piston. This sounds like a good idea too. it is as ATC007 suggests. You can also put 3, 1 1/2" long narrow horizontal score marks around .0015" deep spaced 1/4" apart with the edge of a small fine triangle file on the ex side too if your worried. These help retain the fuel/oil mix adding additional lubrication to this area.

[barnett468]

post correction

never seized water cooled kawi.

[just ben]

I know wiseco pistons come with directions for drilling the holes In the piston. It's pretty simple,just Install the piston and trace the bridge on both sides with a pencil and drill the holes within the marks.

[Jason Hall]

Frank, I wish I would have known the cylinder was already honed to fit the piston, I would have done the bridge. I look at it this way, the bridge Will swell into the cylinder if ran lean. It only takes a couple seconds for the bridge to swell enough to trash your rings, and possibly stick the piston. Even if, and especially if your using a wiseco
Piston.. The Wiseco usually has the holes drilled to help cool/lube the bridge, but relieving it is extra Insurance that I like to have!! There are a lot of different opinions on pistons.. I like a cast piston. A wiseco is forged aluminum. That means when it was made it was poured into its mold and cooled under pressure, then machined. A cast piston is poured into its mold then cools naturally (not under pressure), then is machined. So IMO once the wiseco gets hot (Until it has some heat cycles to allow the aluminum to find its happy place), it wants to naturally expand like a Mo fo.. Lol. Even when I use a cast piston, I relieve the bridge and drill holes for the bridge. To much is never enough as I Hate to stick or melt my pistons.. Hope you understand what I'm saying, and I didn't confuse you.. Lol.

I use a 60 grit flapper wheel in my die grinder and check the clearance by laying a straight edge from the top of the cylinder to the bottom directly over the bridge. I have done a lot of them, and found this to be the easiest way. As stated earlier by someone, don't mess with the top or bottom to much, you just want to relieve the middle looking at it from top to bottom.. Good luck..

[wonderboy]

Thanks Jason! I was gonna call you and chat about it, but didn't want to bug you. No worries about leaving it alone, as you were just doing the porting job... By they way, check out my other thread showing off the 350x head you did. I put it side by side with a spare stock head I had. It is very cool... (I'm so excited to get these builds going) :)

I understand what you're saying about the forged versus cast pistons.

Also, back to early comments: I went onto Wiseco's website and downloaded their general piston instructions and they specifically say to do BOTH: relieve the exhaust bridge and drill the holes over the bridge. I found quite a few discussion about this on the net, including one that had comments by an official Wiseco rep saying that the only reason they don't drill the holes is that becuase many of their pistons cover multiple years and multiple cylinder configs (some without exhaust bridges). So wiseco just has the consumer drill the holes in situations like the 250R. Sounds like it is a very easy thing to do.

So, I'm planning on doing both steps.

Thanks again for everyone's input. It is greatly appreciated.

[barnett468]

Great jason posted, here's some more fun info.

1. A stock unmodified bridge is unlikely to swell especially if properly jetted as jsason suggests. this is also evidenced by the many cyls that atc007, factory kawi racing and i have run.

2. When a cyl with a bridge is modified/ported, it is common practice by many porters to narrow the bridge. when the bridge is narrowed it has lost some structural rigidity and therefore has an increased potential to swell/warp etc.

3. When the cyls are designed the engineers have this potential swelling in mind and make the bridge thick enough so that it should not swell providing it is left alone.

4. All the mfg's run the bikes through the wringer for a few hundred hours before production. all problems are fixed before production. if a bike ever seized for any reason the prob would be corrected before production. the mfg's HATE warranties so they really do try to build a reliable bike to start with.

5. The flapper paper he recommends is also good however it is easy to round the sides of the bridge quite a bit and/or accidentally catch the nicely honed cyl if one is not careful. You might consider putting masking tape around the ex port to protect those areas.

[Jason Hall]

All you said sounds great, but when they engineered the factory setup, I'm sure they used a Cast OEM piston?? Almost every person who just orders a piston from their local cycle shop will most of the time end up with a Wiseco piston. So I would Deffinatly not trust my piston and bore on an engineer that set up the cylinder 20 years ago with a cast piston that most likely used 2 times as much oil as most people would use today. Also, most people don't have there machines jetted correctly. A factory race team, or Very experianced person would probably not ever have to worry. I (knocks on Wood) have never had someone call me and tell me they just melted their piston, and I have done LOTS of cylinders for people. I Always tell people to call or message me and I will help them jet.. I don't narrow the bridge on the piston side, but do sharpen the outside edge. So to be safe I would always suggest to relieve the bridge.. Another thing to remember is as you bore the cylinder over, the cast iron sleeve gets thinner.

[82 250r]

Jason Hall knows his stuff.
I like to have the bridge relieved and always drill the holes even with a cast piston.

Marc

[barnett468]

All you said sounds great, but when they engineered the factory setup, I'm sure they used a Cast OEM piston??Yes.




Almost every person who just orders a piston from their local cycle shop will most of the time end up with a Wiseco piston.At least for a vintage bike like these, yes.




I would Deffinatly not trust my piston and bore on an engineer that set up the cylinder 20 years ago with a cast piston that most likely used 2 times as much oil as most people would use today.Well, as you know, in general the forged piston mfg's often recommend using a cyl to piston clearance that is slightly greater than what is recommended for a cast piston to account for the additional expansion that used to occur with all forged pistons. With new materials and mfg processes they now have forged pistons that can run nearly identical clearances as cast ones.

That being said, the bridge is what we are mainly referring to and it does not "swell" any more with a cast piston than it does with a forged one.

As atc007 mentioned, he has built many bikes and never relieved a bridge and never had a prob. Obviously we do not know what piston he used but as I mentioned the cylinder bridge does not care.

You may know that in the 70's Wiseco's had a propensity to seize. They have changed their piston so the cause of that problem along with the problem itself has been virtually totally eliminated.

As far as the oil ratios being greater in the 70's than they are now, I was running bel ray mc1 at 32:1 back then. While I was at Kawi, the mx race team used regular cheap old kawi 2 stroke oil in the recommended ratio.




Also, most people don't have there machines jetted correctly.lol, yes that is one of the worlds biggest understatements, plus how many have you seen or know of that had 200 million lbs of compression because his friend said that it would haul but if he shaved .100" off the cylinder head, then he puts 81 octane in it so he has enough money left over to buy that case of bud they have on sale and after pounding half of it down on the way to the riding area, eventually rides it totally oblivious to the engine pinging its death knell until the piston either vaporizes or grenades.




A factory race team, or Very experianced person would probably not ever have to worry.That is my experience with all water cooled bikes however even the factory teams and people like dg and fmf were melting or grenading pistons more frequently than they cared to. I seized several myself in those days.




I (knocks on Wood) have never had someone call me and tell me they just melted their piston, and I have done LOTS of cylinders for people. I Always tell people to call or message me and I will help them jet.. I don't narrow the bridge on the piston side, but do sharpen the outside edge. So to be safe I would always suggest to relieve the bridge.. Another thing to remember is as you bore the cylinder over, the cast iron sleeve gets thinner.Yes I've heard enough about you to have every confidence you know what you are doing.



I am certainly not trying to talk him or anyone out of doing this nor do I think it will do any damage other than possible premature ring wear which is no big deal, and I agree it is a reasonable safety precaution for most people in general for various reasons.

[Jason Hall]

Kawasaki usually had nicasil bore, so I would not argue that the bridge would not need as much relief. Honda has cast sleeve, so expansion would be different. Not really wanting to go on and on, I just feel safer with relieved bridge regardless. Can't hurt.

[RIDE-RED 250r]

Seems to be a highly recommended practice by just about EVERY reputable shop/builder that has worked with the 250r for any amount of time. I have it done on mine.

Side note: Jason, almost time to call you and talk over some "things"! ;) :beer

[Scootertrash]

Can someone post some pics of this bridge relieving you guys are talking about? Before and after etc? I'm not that big into racing 2 strokes, but you piqued my curiosity and I want to understand this better.....

Thanks!

[barnett468]

Can someone post some pics of this bridge relieving you guys are talking about?Unfortunately it's hard to see, but there are xlnt photos of it in the link below. I don't know how to post photos directly to the site, sorry.

http://www.pilotodyssey.com/ExhaustBridgeRelief.htm

[barnett468]

Here's a video.

ex port bridge relief and piston drilling and sanding.

http://www.youtube.com/watch?v=clwivP_riOY

[wonderboy]

Here is a pic of the exhaust port on the 250R cylinder. The divider running between the two ports is the bridge. This view is from the bottom of the cylinder looking up:
http://i1089.photobucket.com/albums/i356/frank-and-sara/IMG_0124_zps5e172dd3.jpg (http://s1089.photobucket.com/user/frank-and-sara/media/IMG_0124_zps5e172dd3.jpg.html)

Here is a shot of it from the top of the cylinder:
http://i1089.photobucket.com/albums/i356/frank-and-sara/IMG_0125_zpsf3ef0132.jpg (http://s1089.photobucket.com/user/frank-and-sara/media/IMG_0125_zpsf3ef0132.jpg.html)


So, after all the talk of having to drill the holes in the piston skirt to lube the bridge, this particula Wiseco piston is already drilled:
http://i1089.photobucket.com/albums/i356/frank-and-sara/IMG_0126_zps7ac16f7d.jpg (http://s1089.photobucket.com/user/frank-and-sara/media/IMG_0126_zps7ac16f7d.jpg.html)

This is the information on the model numbers, etc:
http://i1089.photobucket.com/albums/i356/frank-and-sara/IMG_0127_zpsa0db0bc7.jpg (http://s1089.photobucket.com/user/frank-and-sara/media/IMG_0127_zpsa0db0bc7.jpg.html)

[barnett468]

just curious, is the cyl photo after you relieved the bridge?

yeah, back in the jurassic days wiseco didn't have holes in their pistons, we had top drill them ourselves. they are a benefit even on cyls without a bridge.

if you want break in suggestions just ask, i've found most people do the same thing, it's pretty basic and honda has some in the manual too.

[barnett468]

if no one has checked your cyl head you can do the following.

get a full sheet of 400 wet sand paper.

place it on a granite counter, marble floor or tape it to a window next to the frame.

clean the gasket surface then color it with felt pen.

spray water or wd40 on the paper.

using moderate pressure rotate the head on the paper 4 times.

look at head and if all the black felt mark is gone it is flat, if not keep sanding.


hope the photos and videos i posted helped.

[wonderboy]

Hey barnett468,

I haven't touched the bridge yet. I'm pretty slow at working on these things (kids take up a LOT of free time).

Your advice on the cylinder head is excellent. At work, I have access to a large granite block (used in some way for setting up vehicle axles, or maybe just a general tool they have in that shop). I'll take your advice and check out the head to make sure it is nice and flat. That is really good advice.

As for break in procedure (please let me know your opinion), but from what I've read it is primarily about thermal cycles initially. Get some thermal cycles into it before really even running on the trail. And then when running on the trail, start at very light throttle and work up to higher throttle after a few tanks of fuel. (I'm paraphrasing the jist of what I've read...).

I'm pretty sure I'll be making a leak tester too, since I've had this thing completely torn down. I've found quite a bit of info on this site about making the leakdown tester (block off the intake, exhaust, pull a small vacuum and monitor the pressure over a long period). I want to make sure I got the crank seals in place perfectly and that all the case seams along the way are sealing properly.

Any additional advice is always appreciated!

[C.J]

I don't relieve te bridges on my bikes but we drill 2-3 holes in the piston for bridge lubrication/cooling.

As for break in.

My family has never done the "heat cycles". We ride easy for a bit, trying not to hold the throttle in one spot for too long. Run it easy twice then rap on it a little harder the next time out. The key to a proper break in is to get pressure on the rings and make them seat hard. If you do just heat cycles and put put put on it you'll just glaze the cylinder and rings and actually have less compression than a "rough broke" bike. My Suzuki has been together now for 2 years and I'm still at 187lbs of compression with a stock stroke, head gasket and base gasket, as well as stock head.

Ride it mildly for like half a tank then get on it good a few times, not really hanging it out through a feild, let it engine brake some too to get the force on the rings. It's all about getting those rings to seat ya know?

That's how my uncle broke our blaster in and it went 13 years on the same piston, rings, hone/bore and still had 13psi compression when I pulled it down for crank bearings.

I am by no means an expert engine builder or tuner but my family has been in the dirt scene since the 60's and my uncles have taught me all they know, plus my own experiences so far lol

[barnett468]

Hey barnett468,Your advice on the cylinder head is excellent. At work, I have access to a large granite block (used in some way for setting up vehicle axles, or maybe just a general tool they have in that shop). I'll take your advice and check out the head to make sure it is nice and flat. That is really good advice.

As for break in procedure (please let me know your opinion), but from what I've read it is primarily about thermal cycles initially. Get some thermal cycles into it before really even running on the trail. And then when running on the trail, start at very light throttle and work up to higher throttle after a few tanks of fuel. (I'm paraphrasing the jist of what I've read...). Any additional advice is always appreciated!
The following is the info you asked for. I don’t consider it the “best” technique, it is just what I have always done since the 70’s with no problems.


CYLINDER INSTALLATION

Before installing the cylinder I check for proper ring end gap then pour a little 2 stroke oil on the crank bearing then put a very light coat of 2 stroke oil on the inside and outside of the rings and cylinder. Harry Klemm assembles the cylinder dry, see article below.


OIL/GAS RATIO

I run between 20:1 – 28:1 pretty much even if the mfg says you “can” use 50:1 etc. See more on this in another Harry Klemm article online.


SPARK PLUG HEAT RANGE

Install a plug that is 1 step cooler than stock if the air temp is over 80 degrees or if your cylinder has been bored more than 1mm [.040”] over and it is over 60 degrees .


CARB JETTING

Jet carb slight rich, not excessively rich. Get specs from builder or others here with similar setups.


BREAK IN

Place a fan close to front of eng pointing at exhaust pipe then start, turn idle up slightly to around 1000 and let run by itself for 20 minutes, turn off and let cool for 20 minutes, repeat process at least one more time, then follow recommended Honda technique which is basically ride at no more than 1/2 throttle for around 20 minutes putting very little load on it [no hill climbs]. Do this at least 2 more times then let it rip.

Although this procedure is designed for motors with full rebuilds ie new crank bearings etc, it is still a safe and sound way to do it after rebuilding just the top end also.

For the riding portion of break in, install new spark plug using rating suggested above. Don’t use champions, their heat rating numbers are reversed. Check plug color after 30 minutes, white is bad [lean], light tan is good [just right], dark brown or black is bad[ too rich].

If you notice a significant flat spot with NO burble/sputter” upon acceleration then your jetting is too lean and should be corrected before continuing to avoid potential engine damage.


BREAK IN FALLACIES

Breaking in any engine at low rpm with no load for any length of time does not cause the rings to “glaze” preventing them from ever properly seating, they will still eventually seat just fine.





HARRY KLEMM TOP END SET UP AND BREAK IN TECHNIQUE

The following article was written by my friend Harry Klemm. Builder of many national and series championship bikes including one of mine. Hopefully this helps you.


About Proper Break-In Procedure

We have all met him …. The racer who boldly says “I break em in the same way I race em … just ride em full throttle”. Very sadly, there are a small few sets of circumstances were this bold guy is right.

Short Term Setups for short Term Break-ins - There are a number of engine builders who (for their own reasons) will set up the top end clearances of a high-performance two-stroke (piston & ring end-gap) considerably looser than factory spec. The most common reason for doing this is that the engine is prepared in a way that will cause very rapid wear to the piston and rings. Engines like this, often run very wide exhaust ports with very little radius for the rings. Such an engine would seriously wear the piston and rings before any break-in period could be completed, and so they are clearanced to go into immediate service with no real break-in at all.

In such engines, the loose piston clearances not only accelerate piston collapse and ring wear, but they also induce very heavy wear on the cylinder walls (especially around the exhaust port). While everything about this setup sounds short sighted and perishable (it’s both) there is an abundance of builders setting up engines in this way. At Klemm Vintage, we do not (and will not) build such an engine platform. Our engine sets are built for good long term wear and performance … and as such our setups “do” require break-in….. here is why.

A Bit of History - In the early years of high performance two-strokes, most piston rings were a raw cast iron material that very literally had to “wear-in” to perfectly seal on the new cylinder bore it was fit to. With such rings, it often happened that “full ring sealing” didn’t take place until the ring had been in service for a good number of hours. Getting any racer to run the engine easy for that stretch of time just wasn’t going to happen. To help ease this problem, manufacturers applied a soft Teflon “skin” on the outside of the ring sealing surfaces. This soft Teflon skin “sealed” to the new bore in a much shorter amount of time, making for faster break-in and true “sealed” performance in a shorter amount of time. The down side was that when the Teflon wore completely away, the ring end-gap became excessive for “ideal” performance, and the ring tension against the bore was also not ideal. This was a particular performance problem on high-rpm small-bore racing setups.

Wise engine builders began setting up these top ends with “much closer than spec” piston clearances in an effort to get proper ring-end gaps when the Teflon skin wore completely off the rings…. And it worked great as long as you had an oil with a very high film strength. What didn’t work out great was that the break-in time required for such setups was much longer … and no pro-racer could be trusted to “go easy” on the engine for that long.

The solution was to simply let the engine run 60-90 minutes on a stand at a high idle, with a fan or breeze blowing across the fins. This initial run-in wears away the majority of the “skin” off the piston rings. In addition, it gives the cylinder bore and piston-skirts time to “get familiar” with each other in a “low load” atmosphere. This is a procedure that we still use (and strongly recommend) today. It bears noting that after this “static” break-in running, there is still some “loaded” break-in operation needed. However the risk of a piston-scoring event during that break-in ride is greatly reduced.

About Wiseco Piston Break-in - There are an abundance of two stroke enthusiasts that speak with very little enthusiasm about Wiseco pistons. The common response is “you have to give them lots of clearance … otherwise they seize”. We couldn’t disagree more … and here is why.

In the 1970s, we made many attempts to use Wiseco pistons in two-stroke race motors…with very poor results. The truth is that Wiseco (at that time) had numerous materials and design issues that needed resolving. However, Wiseco has done a great job of evolving their materials and designs since the 70’s, and today’s Wiseco Pistons are an excellent choice for most high-performance two-stroke platforms. All that said, Wiseco pistons do have one design issue that they have intentionally have not tried to resolve … longer than average piston-ring break-in times.

The forged material that Wiseco uses for their forged pistons does require “a little” more clearance and a little longer break-in that typical “cast” type pistons … but that is not the unresolved design issue…. It’s the rings. The piston ring material that Wiseco uses is a very tough material that takes much longer than average to “seal” to the bores. While the Wiseco pistons themselves are not a particularly close clearance fit to the bores, the Wiseco rings are. In truth, the Wiseco rings are made brand new with an end-gap that is much too small for full temperature high rpm operation. However if a Wiseco equipped engine gets the slightly longer than average break-in period it deserves, the outer-skin will wear off the rings to result in an ideal “running” end-gap that will give excellent long term wear and service. If however, you try to run Wiseco piston rings prematurely hard, those rings will quickly expand until the ring ends make contact and literally “bite” the full bore diameter in the ring path. Some engine builders incorrectly give Wiseco pistons excessive piston clearance in an effort to resolve this ring end-gap issue.

We respectfully submit that Wiseco pistons can be fit with very close clearances, and offer great service … as long as you let the rings have their break-in time. Our 8500rpm Kawasaki Bighorn road race bikes are equipped with 82mm Wiseco pistons fit at .0035” clearance. These pistons never showed the slightest sign of piston scoring, even after 25+ hours of racing, dyno-passes and high speed testing. You cannot abuse a piston harder than we abused these…. But we did give the rings a long gentle break-in.

About “Dry Top End Assembly” - One step that helps reduce break-in times is to assemble the top end with no oil at all on the piston skirt or cylinder walls. This step has a history worth telling.

In the middle 1960s and early 1970s American muscle-cars were a very popular item on automotive showroom floors. At that time, it was standard procedure for Detroit manufactures to assemble all automotive engines with a generous helping of oil on the cylinder bores and pistons. When these muscle-cars were first fired up, the assembly oil on the bores would burn onto the bores as a glaze that took a very long time for the rings to wear through before sealing.

Unfortunately, this assembly process caused problems for salesmen in the showroom. When prospective buyers took a muscle-car out for a test drive, it was a given that there would be at least one full throttle blast involved. During that full throttle blast, the poorly sealing rings allowed considerable oil to pass, and the brand new muscle-car would leave a big plume of unattractive blue oil smoke that could be seen in the rear view mirror…. Buyers were understandably put off by anything that appeared to be “already burning oil”.

This was a very real problem that Detroit had to address. In time, they learned that if they assembled the top ends dry, with no oil on the bores or pistons, they could avoid this initial burned on cylinder glaze. The result was much shorter ring sealing times (because the rings didn’t have to wear through that glaze), and the absence of blue smoke from those important test drive blasts.

This same rule applies to two-strokes … vintage or not. Some owners shy away from this assembly process because they fear scoring the piston … but it is an unfounded fear. On such assemblies, we do apply assembly oil to all the lower end bearings. In the first moments of initial combustion, that lower end assembly-oil disperses on the bore in even quantities that are easily enough to avert any kind of scoring. In addition, it bears noting that the lubrication needs of an unloaded engine spinning at very low rpm’s are very minimal. We have been assembling high performance two-strokes in this way since the early 1970’s. It works … and it results in greatly reduced ring sealing / break-in times.

Hope this info helps.

[wonderboy]

Hope this info helps.

ABSOLUTELY! Thanks for taking the time to provide all the info. I really appreciate it. Realistically, it will probably be a month or two before we (my brother and I) attempt to get this motor bolted back up into his machine. However, I will try to reply and let everyone know how it goes.

[atc007]

That cylinder needs honed. Your cross hatch needs to be a "x" pattern. Nice ports :)

[wonderboy]

That cylinder needs honed. Your cross hatch needs to be a "x" pattern.

I'll take a closer look, but I think the problem is that the picture doesn't show the cross hatch very well. I still haven't washed the cylinder from all the machining debris. Once I do I'll try to get a better pic of the cross-hatch specifically.

[atc007]

No,it needs honed :) After it is honed to a x hatch. Wash it with whatever you like to use. Gas/degreaser,boil tank.. Then always final clean immediately with fresh 4 cycle oil. , Work the rag up and down until you can scrub the entire cylinder without a white rag and oil picking up ANY gray grit whatsoever. This is a step usually missed. All the degreasers and boil tanks in the world will not get the grit out of the cross hatch. Only scrubbing it this way with oil will get this done. Otherwise the microscopic grit stays in the cross hatch grinding away at your rings.

[wonderboy]

With you 100%. It's been honed. Just doesn't look it in the pics. I'll scrub it nice and clean once I'm ready to assemble. :)

[barnett468]

one way to do the pre oil cleaning is the following:

buy a small 12" x 12" rubber mat in the kitchen dept of the food store

Wait until the old lady is gone.

toss mat in sink

fill the sink 1/2 full with very warm water and dawn dish soap or something with citrus in it. you can also use old school tide clothing soap. this stuff is ultra nasty, wear gloves.

pour around 1" straight soap into a plastic cup etc.

toss the cylinder in the sink and get it all wet.

pull it out and dip someones tooth brush in the soap and start scrubbing one section at a time.

dip it in the sink then pull it out and scrub some more with straight soap again.

when finished, scrub while you rinse with warm water.

rinse and scrub with warm water.

dry with whatever the final dry with hair dryer.

wipe with white paper towel as described with pb blaster or kroil to remove "flash" rust.

wrap it up until installation.

before installation clean with flammabe brake cleaner and paper towel. the non flammable brake cleaner is water based.

clean with 2 stroke oil as i think atc007 is suggesting at this time or earlier if you want.

you will likely see 0 grit at this time.


i have been using this method or similar since the 70's. i found out early that if a newly bored or honed cyl is cleaned in a solvent tank that there will still be grit in it when doing the white paper towel test. i have never seen grit left after doing it the way o described. there will also be now soap residue using the soaps i suggested, just rinse it well.



the followingwith dawn dish soap in a high cosand a tooth brush in the sink while the old lady is gone. oe.iu csn clean it

[barnett468]

sorry for the typos, i do not have an edit button

[Dirtcrasher]

Where working on it buddy :D

[Jason Hall]

I put 2 stroke oil on the wrist pin bearing, and drip a bit of 2 stroke oil down into the crank bearing holes in the cases. Then spinn the crank a few times. Install base gasket, turn the crank so the piston is all the way up. Then flip the cylinder upside down, spray WD/40 in the bore, then quickly but carefully slide the cylinder down onto the piston and try not to get WD/40 on the base gasket. Done this to every 2 stroke I have built for Many years without problems. I have heard of the dry cylinder install, but have never done that myself. WD/40 burns off quickly. I have seen people unable to start 250r's because they used so much 2 stroke oil on the rings that the cylinder is so tightly sealed with oil that it will kick back and cripple your foot!!