I need a piston lesson (NEW ? VALVES!)11/14/12

[MRSOUND]

So I'm taking night classes for small gas engine repair and have taken an atc 90 in as my 1st 4 stroke project. Motor was free but no spark so I've haven't had it running yet. Anyway part of our "lesson" is to measure critical specs as we disassemble he motor. The specs for a 90 cylinder per the service manual is as follows:
STD -1.9685 - 1.9688
.25 - 1.9784 - 1.9788
.50 - 1.9882 - 1.9886
.75 - 1.9981 - 1.9985
1.0 - 2.0079 - 2.0118
My bore Measures 2.124! The cylinder is stamped 89cc. Which blew away my thoughts of it being a 110 cylinder.
I know i can't figure out the true cc's without the stroke dim. which I don't have yet.
Can anyone give me an educated guess?
Is this getting outside the "safe" limits of the cylinder?
Didn't get the valves cleaned up yet to take measurements yet but would they have had to change from stock as well?
Piston measured 2.123 X 2.117 - Instructor said this is to allow for heat expansion. It is stamped on top with 4.00.
Does this mean it is 4mm over std? Is this piston anything 'special" or just oversize?
Lots of carbon build up on the head, valves, and piston.
Here's a couple of pics. Talk to me fellow trikers!

154829154830154831154828

[hippyplz]

Yep, that a 54mm hc piston. Cool find.

[MRSOUND]

So Obviously I wont be able to use the stock head gasket that's coming in the gasket kit I ordered?

[hippyplz]

Yeah, i have a +5 in mine and the head gasket fit fine.

[hippyplz]

Well let me refraze that. A stock 90 head gasket will work, but if you ordered a kit for a 110 i dont know of it would be the same or not.

[Dirtcrasher]

Mike at VMS knows the sizes and requirements. Nice guy to talk to :beer

[atc007]

There is only one way you worry about measuring a piston. Skirt to skirt. No other measurement means anything. Generally the stamping on top of the piston is SAE,rather than metric. Like I told you,I'm no 90 expert. Mike,Shortline,,will see this,he can tell you the day and factory that piston was made lol and exactly what you can and can't do gasket wise. Very cool little piece for sure. I'm guessing a std 90 head gasket will work. But that is hogged out !

[blue27]

lesson #1 you never know what your are going to find until you open it up,lol High compression big bore 90,cool!!! Big overbore piston may be a little harder to find and pricey...If you need a stock cylinder to bore to a more common size piston kit I know we should have some around and I do know a shop local that can bore a cylinder at a reasonable price. LMK if I can help.

[MRSOUND]

Waiting for a shortline response Bill. Curious if it just a big bore piston or maybe something "special". I doubt it but hey, that would be cool.
Bruce- Thanks! I think both the cylinder and the piston are going to clean up fine. Wondering if there were other mods that typically would go along with a bore this big? What else if anything should I look for?

[shortline10]

Head gaskets are the same for the 90/110 after 1974 and I can see that your motor was made after 74 by the head configuration at the head gasket and yes its ok to use a stock head gasket with a big bore kit IMO . Your piston is 4mm over stock so that puts you at 55mm and 118 cc , if you have a stock atc90 crank . Piston looks like a Big Al's to me .

[MRSOUND]

Thanks for the info shortline! I'll get to the crank hopefully next Thursday. I'll let ya know if it is stock or not.

[oscarmayer]

do me a favor, take a pick of the bike and send it to oscar@mayer.net please.
Years ago I build a 90cc engine and did a 110cc bigbore setup with 110cc carb and a few other goodies tweaked cam and stuff. I get a nagging feeling on this particular bike you have that it may be that old 90 I had build up back in the early 90's. That piston loosk EXACTLY like the one I used.

following specs that I can remember were as follows:
Rockeymountain 12.5:1 big bore 110cc piston kit
stock jug bored to 110cc
cam was a web 110cc cam (back then the 110 cam had slightly bigger lobes and better overlap)
we had 3 angle valve job and stock valves with 110cc springs
125cc intake (was slightly bigger than 90 or 110)
110cc carb (re-jetted)
perforamce i think bassoni or supertrap exhaust i cannot remember which one
aftermarket exhaust studs. they were stronger than stocker that always snapped.
open air filter no airbox (uni filter if i recall)

i know there was a few other things. if it is that bike, it started out life in Southern Cali where I found it on autotrader for $350 smoking like a train. I was good friends with an old shop named "Sam and Ed's motorcycle and ATVs" in Azuza CA near West Covina and not too far north off arrow highway. (still trying to fine where they went as one of the borthers a few years after i left was killed in a bike accident (RIP my friend).
if you have photos of the bike before teardown, I can tell you for certain (if some of the specs I stated matched, which somethign tells me yours is fairly close)

[3wheelerfan1991]

do me a favor, take a pick of the bike and send it to oscar@mayer.net please.
Years ago I build a 90cc engine and did a 110cc bigbore setup with 110cc carb and a few other goodies tweaked cam and stuff. I get a nagging feeling on this particular bike you have that it may be that old 90 I had build up back in the early 90's. That piston loosk EXACTLY like the one I used.

following specs that I can remember were as follows:
Rockeymountain 12.5:1 big bore 110cc piston kit
stock jug bored to 110cc
cam was a web 110cc cam (back then the 110 cam had slightly bigger lobes and better overlap)
we had 3 angle valve job and stock valves with 110cc springs
125cc intake (was slightly bigger than 90 or 110)
110cc carb (re-jetted)
perforamce i think bassoni or supertrap exhaust i cannot remember which one
aftermarket exhaust studs. they were stronger than stocker that always snapped.
open air filter no airbox (uni filter if i recall)

i know there was a few other things. if it is that bike, it started out life in Southern Cali where I found it on autotrader for $350 smoking like a train. I was good friends with an old shop named "Sam and Ed's motorcycle and ATVs" in Azuza CA near West Covina and not too far north off arrow highway. (still trying to fine where they went as one of the borthers a few years after i left was killed in a bike accident (RIP my friend).
if you have photos of the bike before teardown, I can tell you for certain (if some of the specs I stated matched, which somethign tells me yours is fairly close)
Cool story, keep us informed.

[MRSOUND]

Emails sent oscarmayer... Don't sound like its the same trike though :(. This has the air box and stock exhaust unless the motor was plucked as a donor. (I could only hope!) How do I tell if it's a 90 or 110 carb? (remember I'm learning here) Here's pics for the rest of you in case your interested. Warning: this was really neglected and will need alot of tlc (and a new frame...cracked) Pics are "R" rated! (rusty):rolleyes:

155141155142155143155144155138155139155140

[shortline10]

Poor thing !!! Carb is def stock atc90 16mm

[MRSOUND]

Thanks shortline! Hopefully I can bring er back to life and give'er a makeover in due time. For now I need to see if I can her heart pumping again. Sure I'll be back with more questions and advice from anyone willing to chime in.

[oscarmayer]

take a measurement of the cam. see if in class they teach you abotu duration and lift ont he cam, if they do and it;'s not a stocker 90, then tehre's a decent chance it's th3e same motor. it does look liek it, the carb i thoguth was a 110 carb, but i could be wrong. The measure the inside of the intake, if it's bigger than 16mm it's the 125cc intake. (90 and 110 had same intake) it does look like a 125cc intake though. the best way is to pull the cam and check it on a cam machine to see what it says. (or check too see if it's stock markings). The reason why I'm asking is not only was it the last 90 that sam ever touched before he died, it was also the last "known" 110cc bigbore kit from rockeymountain they were able to find. i payed $145 for the piston back in 92 which is like shelling out about $350 in today's market for 1 piston. back then sinking $950 (which is what it cost me for the performance mods) was like $2500 today's market. That was actually the first trike motor I ever moded. Sam and I built it in the shop together and he taught me about the trikes back then.

anyway is you get a chance pull the head apart, check the valve seats, and the valves, if you see more than 1 angle on either one, that's another tall tale sign it's looking like it is the one we did. Not many peopel did them with multi angles.

I recommend trying to find anotehr "stock" jug and having it bored/hoend out to fit that piston. i think the 110cc piston rings with a slight "trim" woudl work on it but not 100% sure as like i said that was many years ago. if you can make it work, you'll have one hot rod of a setup that's for sure! At the river sand drags, it was the fastest thing under a 200cc bike (4-stroke). it out ran some 185s with upgraded carb and exhaust. ;)

[MRSOUND]

Looking through the text book it does show how to measure the cam and valves but just to compare it to the manufactures spec. I already have the cam and valves disassembled, but not cleaned up yet. The cylinder bore and piston both look unscarred, just need "cleaned up". I only got .001 difference between them. Now that was using a telescoping gauge/c-mic on the bore. Wish I had access to an intramic for a more confident measurement, but fairly confident in my results though (10 yr machinist in previous career). I'll update dim. as I get them.
By the way I do have downloaded service manual to refer to thanks to you;)

[oscarmayer]

n/p sir! keep me informed, I'd love for this to be the actual engine. That way I know it ended up in a good home. See when we moved to texas in 95, I sold it to help pay for my first home along with my 185s. We didn't make that much $ on them but it did help witht he down payment which hel;ped start our lives off so it was a fair trade.

[MRSOUND]

Well I got to measure the cam tonight....stock 90 per the service manual:(. Sorry oscar i don't think this one was yours. Didn't get to clean up the valves yet but he did show us how to grind and lap them as well as redo the seats. Didn't get much shop time tonight. It's killing me! I want to get i tore down and back together! Anyway here's pic of the cam & head (still not cleaned up).

155338155337

[MRSOUND]

Well here is before and after pics of my carb. This is a classic example i would assume of of leaving fuel in the carb for years. Still needs more cleaning as you can see. I do have a question on the slide. HOW DO I GET IT OUT? Soaked it in carb cleaner for about 1/2 hr. I thought when I unscrewed the top there would some way of releasing the cable. The instructor (more of a mower guy) thought everything should slide out. Is this true? What am I missing? Is it just seized in there? More soaking? Any help is appreciated!
Before
156368156369156370156371156372156373
After
156367

[shortline10]

Soak the carb in some mineral spirits over night and that should loosen the slide .

[MRSOUND]

Should it just pull out then? Not attached to anything else?

[shortline10]

Yes it will pull out .
Should it just pull out then? Not attached to anything else?

[Dirtcrasher]

Soak that puppy in gas for a bit, you did an amazing cleaning job on that carb!!.

[MRSOUND]

Soaked it in Gunk carb cleaner. Crap is expensive! $30 for a gallon can. But you do get multiple uses out of it. Even came with a basket inside so you drop your carb into the basket and let it soak (they recommend only 20 min). When time was up I just used a screwdriver to snag the basket handle and pull it out. Wipe down the outside with a rag and blew out the inside with air. Still need to go through all the orifices, Almost every one is clogged.

[86T3]

I used a bucket of that stuff on a real nasty 125M carb last winter. I pulled it out after 2 weeks and ran a wire through the fuel inlet and petcock inlets to get some on the crud out. After another 2 weeks it was completely free and clean. If i were you i'd throw it back in for a week or so. Also, the stuff i used (napa brand) said to wash it with water after you pull it out. Not sure if Gunk is the same. Good luck!

[TecateDan]

Make sure you do this step with a cigarette in your mouth for cool points


Soak that puppy in gas for a bit, you did an amazing cleaning job on that carb!!.

[MRSOUND]

Make sure you do this step with a cigarette in your mouth for cool points

Hmmmm...I do smoke but I think I'll pass on this tidbit of advise:D

[oscarmayer]

when i see these types of carbs, i will use the old "chemdip" it's a 1=gallon metal can you can buy at the auto-parts store of chemdip that eats it clean. soak the entire carb int he stuff over night and the enxt day it will be squeaky clean! even the palstic parts will be ok. then I take it and drop it into hot water to clean the cemdip off and sue carb cleaner to ensure all passages are clean. works like a charm and looks new.

[MRSOUND]

Ok Oscar.... Here's a pic of the valve seats. Hard to tell if there is a dual angle in there. Tried to feel it with my my finger nail but I cant really tell.

Shortline or anyone....Measuring the intake end of the carb I'm getting 18mm. If a stock 90 is 16mm what does it make this one? I had ordered a stock 90 rebuild kit. Will this have any effect on the carbs performance? (already rebuilt:rolleyes:)If I remember correctly the main jet was a 65 that came with the kit.
Help out here guys. Learning as I go.

[shortline10]

The carb in your pic is def a atc90 stock carb so the kit should be Ok .



Ok Oscar.... Here's a pic of the valve seats. Hard to tell if there is a dual angle in there. Tried to feel it with my my finger nail but I cant really tell.

Shortline or anyone....Measuring the intake end of the carb I'm getting 18mm. If a stock 90 is 16mm what does it make this one? I had ordered a stock 90 rebuild kit. Will this have any effect on the carbs performance? (already rebuilt:rolleyes:)If I remember correctly the main jet was a 65 that came with the kit.
Help out here guys. Learning as I go.

[MRSOUND]

Thanks Shortline! Next question is since this had the stock carb and stock exhaust with the oversized piston stuffed in there, can I assume thats why there was so much carbon deposits in the head and piston top? Lean condition? If it is any recommendations to even out the performance end? I have a cobra exhaust off a 110, will it mount up and help? Will changing the main jet be enough to get it the fuel it wants/needs? Open to suggestions.

[shortline10]

Could be a dozen reasons for the carbon build up. The carb is prob fine with stock jetting and the BB piston but if you put a HP pipe on it it will prob want a bigger carb or jets .

[MRSOUND]

Ok thanks again! :beer

[MRSOUND]

Valves - Went to grind my valves in class and the valve grinder they have wouldn't chuck down far enough to tighten on the stem! Its a 3 jaw friction chuck similar to cordless power drills, just it bottoms out turning it in before the jaws contact my stems. Put them in a drill to see how straight they were and seemed like they were running out of round just below the valve head. Decided to just go ahead and order new valves(Shindy).

Questions:
1) Do i need to grind the new valves when they come in or should they be ready to install? (I will be resurfacing the head seat with a cutter)
2) If I do need to grind the new ones, how can I get it chucked up running true in the school grinder? I thought about getting metal shim stock to insert at the contact surface of each jaw. Any other suggestions?
3) What angle are the valves usually ground at?
Thanks
Mike

[shortline10]

Yes you defiantly have to seat the new valves with lapping compound . Just use a short piece of rubber hose that's tight enough to slip over the valve stem and chuck the other side up in a cordless drill . Man I shouldn't be giving up any of my old school secrets :lol:

[MRSOUND]

First off I want to say thank you again for all your advice & knowledge sharing through out this thread. I don't think I'll be taking any engine building business from you anytime soon. lol So will I still need to grind them (on the valve grinder) or just lap them?

[shortline10]

Depends if the seats have any pits or groves . Most times a little lapping compound and your done , after laping them look for a nice grey looking seat to show that their mating up well .
A good test is to hold the valve in place after your done and see if they leak by pouring a little fuel down the port .


First off I want to say thank you again for all your advice & knowledge sharing through out this thread. I don't think I'll be taking any engine building business from you anytime soon. lol So will I still need to grind them (on the valve grinder) or just lap them?