Loose fitting main bearing in case....

[skiboyracing]

I split the case on my suzuki 250 and found that the right hand main bearing fits what I consider loosely inside the casing. I see where someone tried the old trick of center punching dots into the side of the case to grip the bearing but I can push it in and out with my fingers. There is probably a thousandth or two of play. I've been told to just clean it good and use some red locktight on about eight different points of the outside bearing race and put it all back together, When it cures all will be tight.. Anyone have an opinion. I don't want to spend 500 bucks on new cases but I don't like the idea of being able to install the main bearing into the case by hand with out a press fit.

 

[todd36]

Instead of red loctite get some green loctite that is a bearing sealer.

 

[whenfoxforks-ruled]

Green is permanent. Red is for stud and bearings. Clean both surfaces, and a light coating on the bearing outer surface and case bore. Very light, you can not seal the lube passage.

 

[todd36]

The green loctite I am referring to is a bearing sealant not a thread locker. You can use loctite 603 or 609. If you have any buddies that work in a machine shop they could knurl the bearing surface and rebore it out to a press fit. Here is a link to the loctite site
http://www.loctite.com/int_henkel/loctite_us/index.cfm?&pageid=19&layout=3

 

[whenfoxforks-ruled]

Knurl a bore, the size of the bearing? I would like to see the tool that does that. I have knurled plenty of shafts, never an internal bore. And then there is the fact it must remain dead on for being concentric. If the sealer does not hold, I would be looking on fleabay, and hoping it does not have to be a set!

 

[todd36]

The knurl is fixed on a holder that you run in a boring head. You then knurl so the bore is undersize. then you bore it out to the size required. Since you are using a boring head the centerline is already established. below is a picture of a I.D. knurl

 

[whenfoxforks-ruled]

How do you rotate the case to knurl it? Surely there is no way of turning that tool in a circle to achieve the knurl, so the case must spin? And yes, I do believe a guy could set it up to be on the money.

 

[Ol'89r]

How do you rotate the case to knurl it? Surely there is no way of turning that tool in a circle to achieve the knurl, so the case must spin? QUOTE]

foxforks.

You use a vertical mill and a graduated boring head. The boring head is indexed off of the original bearing boss ID just as though you were going to bore the ID bigger. But, instead of using a cutting tool, you use the knurling tool.

I see that as only a temporary fix since the bearing boss will only have partial surface support after knurling. The force of the crank will eventually pound the high surfaces down and the bearing will loosen again.

I would find a new set of cases and be sure to heat the cases when you install or remove the bearings. This will eliminate loose bearing bosses in the future.

 

[whenfoxforks-ruled]

If you can do this, then why not put a sleeve in it?

 

[Ol'89r]

then why not put a sleeve in it?

That is one option. If there is enough material in the bearing boss to bore it and still support the sleeve. Although, by the time you machine the sleeve and then bore the case you will have almost as much money in machine labor as a replacement case. Unless he has a friend in a machine shop that can cut him a deal.

 

[skiboyracing]

Thanks.. Unfortunatly I have no friends in the machine shop world :(

I see that it's a iron sleeve pressed into the aluminum casing from the factory. I have another case sitting here that has a blemish. I wonder if a machine shop could pull out the main bearing iron sleeve on both cases and press the good one into the one I have that's loose? You can't buy just the iron sleeve for it that I can find.

 

[whenfoxforks-ruled]

You one upped me there, I never knew they put sleeves on the bearings. If it can come out, then someone else can make it. Are you sure you are not looking at a machined surface?

 

[skiboyracing]

No it's an iron sleeve.. I even put a magnant on it to make sure it just wasn't rust off the old crank. It's actually a 92 lt250r quadracer engine that I'm working on. (so I can take my 3yr old for rides) All the dirt bike engines I've torn apart the bearings are pressed into the aluminum case, but this one has an Iron sleeve. I thought about trying to press the one out of my blemished case in the picture and reinstall it into the case I want to use but I've been told that the two case halves are a matched set that are line bored together, and that inserting a different sleeve would probably through the alignment off? Not sure..

 

[whenfoxforks-ruled]

I am wondering if you heated the case up, it may fall out.

 

[skiboyracing]

Thanks.. I am going to take it to a machine shop tomorrow and see if they can machine that down and put another sleeve inside it to press the bearing into. I'm guessing they will find dead center of the current bore, then machine it out from that. I would think that should keep the alignment correct. We'll see what they say since I'm not a machinist. They may just recommend using a locktite of some sort.. We'll see. Sure would be nice if someone made an oversized bearing for this kind of problem..