Replacing Main Bearings

DesertCR · Post by **DesertCR** » August 21st, 2008, 2:24 pm

Man Im having trouble replacing the main bearings in my 89 motor. I heat up the case and put the bearings in the freezer and yet they just wont go in smoothly into the case. I got one in but it wouldnt bottom out in the case and it sits a little high (not flush). What to do? Do I need dry ice to get the bearings colder? What should I do about the one that isnt all the way in, should I finish it with a press? BTW, I'm using a mapp torch so it does get pretty hot. Whatta think?

Post by **AlisoBob** » August 21st, 2008, 2:25 pm

I think you did it correctly.

Are these OEM bearings?

DesertCR · Post by **DesertCR** » August 21st, 2008, 2:44 pm

Yeah I'm using all factory bearings. How hot should I get the cases? Should the bearing just "drop in" when everything is done right?

teemtrubble · Post by **teemtrubble** » August 21st, 2008, 3:04 pm

I wouldn't heat your cases with a torch and I'd have someone press them in that knows what they are doing... and I'd only use OEM bearings period but, what do I know...

DesertCR · Post by **DesertCR** » August 21st, 2008, 3:07 pm

Yeah it looks like I will just have to have them pressed in because this is taking up too much time and not working. I too run only factory bearings and seals in all my bikes and cars.

teemtrubble · Post by **teemtrubble** » August 21st, 2008, 3:10 pm

HrcRacing · Post by **HrcRacing** » August 21st, 2008, 5:43 pm

Don't they sit a little proud of the cases? They did on the last bottom end I rebuilt (YZ250). That would give you some additional crank/case clearance.

iggys-amsoil · Post by **iggys-amsoil** » August 21st, 2008, 5:57 pm

Ya if I remember right, mine did sit high. Maybe .040? or close to it.

Dakota Boy · Post by **Dakota Boy** » August 27th, 2008, 11:01 am

Engine cases in the oven at 300 degrees for 30 minutes. Bearings in the freezer for at least 3 or 4 hours.

Retrieve both items and QUICKLY drop the bearings in.

They should drop right in.

dannygraves · Post by **dannygraves** » August 27th, 2008, 2:23 pm

I'd just bust out the BFH and a big ass socket

But I'm kinda ghetto!
actually, while we're on the topic, has anyone ever had a bearing come out of the cases, but stick to the crank? ISBBs did that to me, now I am wondering how to get the bearing off the crank without hurting anything.

ISBB · Post by **ISBB** » August 27th, 2008, 2:35 pm

I was thinking heat and a gear puller? Danny i talked to mike at TT and i think im going to get everything from him as soon as he gets me a quote along with main bearings.. that one that stuck kinda scares me a bit.. so i think we should just replace everything

We will have to hit up stieners when all is said and done and ill buy a few rounds, for all the help ya have given me

dannygraves · Post by **dannygraves** » August 27th, 2008, 2:46 pm

I was actually gonna suggest getting the mains after all. I replaced all the bearings in my 2 motors, except the large rod bearing in 1, and I'm starting to wish I has replaced that one too

if you replace the bearing, than I don't have to worry about damaging it during removal. That'll make things a lot easier.

BTW a round at steiners sounds like a deal to me

100hp honda · Post by **100hp honda** » August 27th, 2008, 4:03 pm

dannygraves wrote:I'd just bust out the BFH and a big ass socket But I'm kinda ghetto!
actually, while we're on the topic, has anyone ever had a bearing come out of the cases, but stick to the crank? ISBBs did that to me, now I am wondering how to get the bearing off the crank without hurting anything.

they should come off the crank first. hopefully the bearing didnt spin in the case

. i would carefully cut it off with dremel, but thats just me

. and like i said hopefully it didnt spin in the case , because once they spin just alittle the hole is wallered out and the case is junk

dannygraves · Post by **dannygraves** » August 27th, 2008, 4:24 pm

definitly didn't spin in the case, we had to muscle the hell out of the puller. I'm thinking about putting the whole thing in the freezer, then welding 2 nuts to each side of the outer bearing race (which will also get the bearing nice and hot) then hook up my puller and crank away

I've already got it soaking in some penetrating oil.

100hp honda · Post by **100hp honda** » August 27th, 2008, 4:55 pm

thats good news dude. while back i tore into one of my trannys and 1 bearing was spun, luckily it had just recently started to spin....i did some minor repairs and was able to salvage the case

Post by **AlisoBob** » August 27th, 2008, 6:36 pm

Weld a bead around on the OD of the bearing, as it cools, it will shrink ( A surprizing amount!), and the bearing should fall right out.

Nate · Post by **Nate** » September 8th, 2008, 1:05 pm

Heat cases in the oven and put bearings in the freezer. they should just drop in if you have the cases hot enough.

Post by **AlisoBob** » September 8th, 2008, 1:44 pm

Putting the bearing in Dry Ice works better.

dannygraves · Post by **dannygraves** » September 8th, 2008, 2:20 pm

we put some dry ice (that was later to be used for dry ice bombs) in the cooler with the food and EVRYTHING was frozen solid! even the ice turned into one solid peice! I had to put my mustard by the fire to thaw it so I could put some on my hotdog!

DesertCR · Post by **DesertCR** » September 8th, 2008, 9:53 pm

Ha thats funny, I need some of that stuff (dry ice). I just had a local shop press in the bearings, looks good. I'll have to try the oven thing next time. Now I just need to find some time to put the damn thing together and back in the bike for desert season.

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Replacing Main Bearings

Replacing Main Bearings