Pressing in new crank main bearings

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Brandon H.

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Mar 26, 2009
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What do I have to do to press the bearings in?? I just got the new bearings, and my friend has a press. I tried the heat and freeze method, with no luck. I am having trouble getting them to seat all the way.

So I want to press them on. But how do I do it?

What do I put under the case to protect it?

And what do I use to on the bearing to push it in the case?

Cost me $55 for these bearings, I dont want to fock them up :cool:
 
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julien_d

Member
Oct 28, 2008
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?

I don't understand. You should not have any trouble getting them in, provided you heated the case and froze the bearings. Perhaps you did not get things hot/cold enough? I didn't even need to use a press. Couple light taps with a rubber mallet and they were fully seated. If you're using a press, you'll have to just find something to put under the case. A block of wood, perhaps? If you want you can pay me to cut a piece of 2x4 to send you :)

J.
 
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Brandon H.

Member
Mar 26, 2009
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Can I use the back of a big flat socket?? I noticed the bearings were just a tad bit taller then the case.

Man, it seems I am needing a lot more tools then I originaly thought.
 

IndyMX

Crash Test Dummy
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Jul 18, 2006
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You should be able to lay them in the oven at about 300 degrees for a few minutes, and the weight of the bearing should be enough to get them to seat...
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
8,129
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Merrillville,Indiana
HOLD THE PRESSES! If you are having issues with them seating, they are probably crooked! Block from underneath with a big piece of wood, as long as the case is flat. A socket will work, but can you clean it enough not to knock debris into the bearing? Only drive on the outer race. Using the heat freeze method, properly, they should almost fall in. Most manuals just knock them out with a driver, very similar to the socket. NO PRESSES, no cracked cases! Vintage Bob
 
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Brandon H.

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Mar 26, 2009
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Ok well I got the bearings in, I had to reseat one, because it was going in a tad crooked. I ended up finishing them off with a friends press, they pushed in fairly easy, and I didn't really need the press for much.

I have the bottom end together now, but now the crank is pretty stiff to turn. I mean its smooth, just tough. Do I need to seat the crank? If so, how?

Or did I mess something up??
 
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helio lucas

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Jun 20, 2007
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sometimes when the seals are not good quality they do hold the crank. but in your case just tap both ends of the crank, gently but a dead shot, with a mallet will do the job. :cool:
 
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Brandon H.

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Mar 26, 2009
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Houston, I think we have a problem.

Well using a feeler guage did tell me it was uneven, a soft tap with a rubber mallet centered it. Its was pretty smooth after that, so I put the big spacer, gear, and bolt back on the other end of the crank (clutch side) and it pulls the crank right back where it was.

I don't get it, something aint right. One thing I just remembered, The crank pretty much slipped right into the bearing on the cluch side, not loose, but I didn't need a tool to get it in. Idk if thats bad. The bearing that was on there before had no problem staying tight, but once I got the bearing pulled, every bearing seem to pretty much slip on that side.

Its almost like I need to split the case, and use a very small .010" shim between the bearing and crank.

Also, I got my dial indicator, and set it up on the stator side where the crank tapers, and rotated the crank, and there is .004" wobble in the crank. idk if that matters any, or if the bearings are crooked..

Also, I noticed when I was checking the gap between the crank and case with a feeler guage, if I spun the crank it would get snugger on the feeler guage at one point then get looser. Almost like its not straight

God u guys make it seem like this stuff goes so easy, watching that ATVMC bottom end video on youtube looked like a breeze, I should have never touched the bottom end :|
 
Last edited:

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
6,958
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Brandon.

That is too much run-out on the crank. Remove the crank and put it between two centers. The run-out should be less than .001". If you have more than that, you will have to re-true the crank.

If the main bearing is too loose on the crank, you will have to replace the crank or at least the half that is loose.

The way I install main bearings is to heat the bearing first and then press it on to the crank using a deep socket against the inside bearing race. Seat it all the way down on the shaft. If you heat it the bearing will expand and slip on the crank without force.

Then let the bearing cool down and heat the cases until you can sizzle a drop of water on them. Don't heat them too much or they can melt. Then take the crank with the bearing installed and simply drop it into the case. With the weight of the crank the whole assembly should drop right in and seat all of the way down. Then heat the other case and assemble the cases.

IMO, you should never press bearings in or out of your cases without using heat. This will wear the aluminum bearing bosses and after a while your cases will be junk.

If you heat the cases correctly, you won't need a press or any tools at all. If you don't heat them, you will wind up with worn cases or a worn crank like you appear to have.
 
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Brandon H.

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Mar 26, 2009
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Ok so if I wanted to remove the bearings out of the case again, by heating the case and using a ratchet extension and a mallet to hit the inner race of the bearing, will the bearing still be usable after that?? When I say inner bearing race, I mean the area closest where the crank is.

I paid $50 for the bearings, I dont want to hurt them or get flat spots on them

sorry for so many questions too :)
 

IndyMX

Crash Test Dummy
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Jul 18, 2006
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My dad told me that back when he was racing.. (30+ years ago) The guy that did his engines had a hot plate in his shop that he'd lay the cases on, then once the case got good and hot, he'd drop the cold bearing on it, and it'd fall right in.

I like that idea.. Low stress.. ;)
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
8,129
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Merrillville,Indiana
How could the crank be pulled off center by the drive gear? The main bore is wore? Wrong collar between the gear and crank? Wore the collar into the crank too far? If the threaded end for the rotor is bent, it needs to be straightened/trued, and probably chase the threads. How did that get bent? While holding the rod up, the 2 edge flats at the horizontal center line is what you check for the flywheels being true. That is what will vibrate the engine and you to death if its off more than a couple thousandths. The only way I know of checking it is in between centers of an engine lathe. They make special jigs for holding and measuring them also. In the bike, highly questionable. You have no reason to remove the main bearings that I figure. They are flush, the seals are flush? Is the rod pressed properly, is the pin flush or the same on both sides? Fix the crank, and try it again. Vintage Bob
 
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Brandon H.

Member
Mar 26, 2009
199
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I have no idea, but something isn't right. I will hopefully be tearing into it tomorrow afternoon. I will split the case and check stuff out. Any idea how much a plane ticket is from IN to FL is???? ;)

The seals were never touched, so I am assuming they are fine (not sealing wise, but straightness wise) they look fine. I am 100% possitive its the right collar between the gear and crank.

When I was saying that it has about .004" wobble in the crank, I was setting the dial indicator at the very end of the crank, right before where the threads start for the flywheel. So I have no idea if the large crank weight thingy majiggers between the rod are off.

I am sure the rod is pressed properly, its at the right gap, and has no play verticaly. I never had the crank apart, I just fixxed the threads.


Hopefully its fixable....actually, hopefully its cheap :yikes:

I really do appreciate all the help so far guys, I have no idea where I would be without yall, I have learned a hell of a lot so far.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
8,129
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Merrillville,Indiana
Stop with the it looks good comments, please? Ditto what Indy said. Them seals are way to cheap. I am not going to get into how on earth you replaced the bearings without the seals???? Aye Carumba! If its the collar, no case splitting. If the rotor goes on, then true it, get the high spot and strike it with a dead blow, should get it back, no case splitting. Even the seal can be replaced without splitting. Unless the bearing is not seated all the way. 89er had a real good thread on this very subject, back in the day. It is not quite cold enough here yet, for me a Florida trip. When is the winter Olympics? Vintage Bob
 
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Uchytil

LIFETIME SPONSOR
Jun 29, 2003
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Based on your original post, and pictures, the crank looked beat from get-go. Like 89'r said you should have it checked between centers. Like I mentioned, I would have had the lower end bearing changed while it was out, maybe you should still consider that? Like everyone said, the seals are cheap and are a must to prevent air or oil being drawn into the case since 2 stroke engines rely on pressure to function. Tear it apart. Use the heat/cool methods mentioned for main bearings. Lets' see. I heat cases, freeze bearings - they drop in. Then I freeze cranks and I have a special (a few) aluminum slug that fits in the bearings inner boss. I heat the slug which transfers heat to the bearing then the crank drops in the mains, cases slide together. If the crank is slightly tight I gently tap each end with a brass hammer until it rotates. Never, ever, force anything.
 
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Brandon H.

Member
Mar 26, 2009
199
0
I didn't have a chance to work on it today and its buggin me.

Anyways I would like to check the crank and see if its straight and balanced. If it needs work, I will put a new lower bearing on at the same time. If it doesn't need work, I will just leave it how it is and save for a new crank/rod. I don't mind tearing back into the bottom end again in a couple months, I get joy out of working on these bikes. I can install a new crank/rod when I have the $$ in a couple months. If this crank is ok I will leave it, but it will make since if any work has to be done to this one to put a new bearing on :nod:

I already have the bearings in the case, I just don't know if they are fully seated I have a feeling the one on the stator side isn't...but who knows. I haven't check anything yet so all I can do is assume, and you know what happens when you assume :-).

Vintage Bob, when I said it "looks fine", I meant that the seal looks straight, and it "looks" like its not the problem, I have no idea if the seal is actualy bad, but if its the same one from 94' im sure it is.

I want to try a couple thing u guys mentioned, and if all fails, i will split the case again and inspect more.

Where could I have the crank checked?? Any engine machine shop?? I don't have anything to center it with, but I do have a dial indicator with a magnetic base :uh:
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
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Merrillville,Indiana
Eric at Forward Motion does mine. The last one, I drove though. I do not trust the mail. I have heard stories of brand new oem Honda crank halves being off .010". The flywheels spin way to easy on the big end pin. To me, any shop should have one. Any machine shop should be able to check, and align it. I would hate to see what a new set up to check them would cost. I steer clear of the automotive shops. You are doing seemingly well, better than my first! Everyone has been there, that has done this. Maybe except Rich, I do believe he was born with tools. He did have the original Mr. Know-It-All behind him, probably at all times the first few years? The way he harped over his bikes he would sell, I could not imagine him in the shop. Vintage Bob
 
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Brandon H.

Member
Mar 26, 2009
199
0
I have talked to Eric before, idk if I should call him or email, im sure call would be better since he seems busy. Still no time to work on the bike, hopefully tomorrow I will look at it more.

Been busy today, just bought a 1992 RM250 for $150!! Project #3 :cool: :ride:
 
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