85 250R Motor Teardown

[newby200x]

I'm getting ready to tear down my 85R motor, the left case has some damage and I want to send it out to BDT to be repaired. This is my first time ever splitting a case and was just looking for any tips or advice as to what to look for, do's and don'ts, tricks for disassembly/assembly, and so forth. Any input is appreciated.

[hatc200x1]

Best thing to do is have a clean bench, and be organized. Get sandwhich bags and a sharpie to label parts and assemblies. Here is a link to a manual that can help.
http://www.oscarmayer.net/atc/manuals/

[onformula1]

Grab a cardboard box lay your cases down on it trace it out with a sharpie punch the holes with a pick and pop the bolts though, label everything.

Musical bolts is no fun and can cause damage.

Clean everything to a inch of its life.

Sent from my SM-G386T1 using Tapatalk

[Red Rider]

Above all else, do not wedge anything (screwdriver) in between the cases to pry them apart. Be patient, methodical, and take your time, and they will come apart undamaged. Oh yeah, one other thing, have patience. Enjoy!

[newby200x]

225828

I'm worried about the exhaust bridge on this cylinder. I took a look at it last night, the cylinder is on the stock bore, has a few minor scratches that can only be felt w/ a finger nail. But the exhaust bridge looks like the sleeve is wore through? Can anyone shed some light on this?

[Red Rider]

It looks like the exhaust bridge has been relieved. Some builders do that to keep bridge from bowing out, and scarring the piston/rings, when the sleeve heats up & expands.

[atc300r]

It looks like the exhaust bridge has been relieved. Some builders do that to keep bridge from bowing out, and scarring the piston/rings, when the sleeve heats up & expands.
X2 . If you look at your piston there should be atleast 2 holes in it just below the bottom ring where it lines up with the exhaust bridge.

[newby200x]

Yes it does have the oil holes. Thanks guys, hopefully just a hone and it will be good to go

[atc007]

Grab a cardboard box lay your cases down on it trace it out with a sharpie punch the holes with a pick and pop the bolts though, label everything.

Musical bolts is no fun and can cause damage.

Clean everything to a inch of its life.

Sent from my SM-G386T1 using Tapatalk

Indeed, and 2 small hunks of a 4x4 board to support your cases on,and thick rags for cushioning if you're anal like me. I had a hole drilled down through my bench back in the day for the big 4 strokes with long cranks. But a R is about as easy as they come, behind a Banshee. They are fun :) Manual, patience and CLEANLINESS,and you'll be fine :)

[newby200x]

What's everyone's opinion on re-assembly? Use a small film of gasket sealer on the cases and covers? Or just gaskets?

[Red Rider]

The centercase tolerances are designed for a centercase gasket, as is the clutch cover. If the manual calls for a gasket, use a gasket. For me, I personally don't use any sealer on my gaskets, unless the manual calls for it.

[christph]

My advice is to use the right tool for the right job. I just rebuild my 250R engine--finished it just today. I split the cases with a Tusk case splitter and it worked great. But when I went to put it back together and pull the crank through the bearing (it is a press fit on the left side, slide fit on the right), I decided to rig a tool rather than buy a $70 crank installer I would use once every 5 years. I stacked large washers around the shaft and used the nut on the end to pull it through. It was working well until the tapered diameter of the shaft bottomed out on the hole in the washer before the crank was fully pulled through the bearing. One of the threads on the shaft started to strip before I realized what was going on. That would have been $200 for a new crank. Luckily I got a die and fixed the thread.

Here is the right tool for the job. https://www.rockymountainatvmc.com/p/989/17166/Tusk-Crank-Puller-Installer-Tool?term=tusk+crank+installer Check out the 3 part video at the bottom of the page; it goes through the whole process.

Also, if you are removing the bearings be sure to thoroughly heat the cases (and freeze the bearing) before you try installing the bearing. I think the magic number is around 240 degrees. I used a propane torch but others use an oven. I thought I heated by cases enough but the bearing only dropped half way down. It is hard to drop a bearing straight down without it getting cockeyed. I then had to use a large socket and hammer to force it the rest of the way. I just kept heating the cases and hammering until it was flush (do not hammer on the inside ring or you will pit the races). Anyway, more heat during the initial attempt would have spared me the hassle.

Finally, on the stator side, do not push the case seal too far in or it will bind on the bearing. It is easy to push in too far as there is no stop for it. It should be recessed about 6mm from the lip to accommodate the stator, but no more. On the clutch side the seal can be flush with the case.

[El Camexican]

My advice is to use the right tool for the right job. I just rebuild my 250R engine--finished it just today. I split the cases with a Tusk case splitter and it worked great. But when I went to put it back together and pull the crank through the bearing (it is a press fit on the left side, slide fit on the right), I decided to rig a tool rather than buy a $70 crank installer I would use once every 5 years. I stacked large washers around the shaft and used the nut on the end to pull it through. It was working well until the tapered diameter of the shaft bottomed out on the hole in the washer before the crank was fully pulled through the bearing. One of the threads on the shaft started to strip before I realized what was going on. That would have been $200 for a new crank. Luckily I got a die and fixed the thread.

Here is the right tool for the job. https://www.rockymountainatvmc.com/p/989/17166/Tusk-Crank-Puller-Installer-Tool?term=tusk+crank+installer Check out the 3 part video at the bottom of the page; it goes through the whole process.

Also, if you are removing the bearings be sure to thoroughly heat the cases (and freeze the bearing) before you try installing the bearing. I think the magic number is around 240 degrees. I used a propane torch but others use an oven. I thought I heated by cases enough but the bearing only dropped half way down. It is hard to drop a bearing straight down without it getting cockeyed. I then had to use a large socket and hammer to force it the rest of the way. I just kept heating the cases and hammering until it was flush (do not hammer on the inside ring or you will pit the races). Anyway, more heat during the initial attempt would have spared me the hassle.

Finally, on the stator side, do not push the case seal too far in or it will bind on the bearing. It is easy to push in too far as there is no stop for it. It should be recessed about 6mm from the lip to accommodate the stator, but no more. On the clutch side the seal can be flush with the case.

I've had great luck on my engines by putting the crankshafts in a freezer for a couple hours and then evenly heating the cases (with the bearings installed) just before assembly. I set the right side case flat on wood 2 X 4's so that the crank won't hit the bench then put either the gasket, or sealant in place, then the transmission and then wipe the frost off and drop the crank all the way into the right side case and then slip the left side case on as quickly as possible and tighten it up.

The down side to this method is that the crank sweats a lot, so you need to use the heat gun to remove the moisture and then get some 2 stroke oil onto the bearings ASAP. You can leave the engine on its side so that water doesn't get into the sealant before it's cured.

[250rRoostmaster]

You can make a case splitter very easily with a piece of flat steel and some all thread rod. No screw drivers, ever!. All good advice here, I used the freezer method personally with great success for putting it all back together.

[phantomtracer]

Take lots of pictures before taking apart the different assemblies

[newby200x]

Everything has been disassembled already. The left case should be back late next week. Then the fun begins putting back together. Thanks for all the tips everyone.

[newby200x]

So I finally have all the parts to put this motor back together. Installed all new lower end bearings last night, went w/ the updated 8 ball crank bearings. Then I took the frozen crank and slid it right in place, all is good. Slid the tranny back in, installed the forks, drum, and shafts, everything is going great. I drop the right side case on, bolt everything up, and everything appears fine, tranny spins good, as well as the crank. But then I notice the crank has a lot of side to side movement, the bearings are tight into the cases, the crank is sliding on the bearings. Is there something I'm missing here or is the crank shot? I don't have any of the seals or the spacer on the right side installed. I didn't check the side to side before teardown but I did check for vertical and horizontal play in the bearings and everything seemed tight. A new or used crank was not in the budget for this build, but I'm thinking it's going to have to be replaced.

[yaegerb]

Its OK to have approximately 1/16th play (or so) side to side and ZERO up and down.

[newby200x]

I'm getting confused on this crank to crank bearing install. From what I've read, the stator side of the crank & bearing should be an interference fit, so in theory, there shouldn't be any play side to side (left case to right case)? Or am I misunderstanding something?

[yaegerb]

I guess I am missing what you are referring to. Pics will help.

[newby200x]

227815

I can go both directions very easily as shown by my crude arrows. I think the shaft on the stator side might be too far wore since it is able to slide in the bearing and not pressed into it.