rod bearings, funky colors

They look kinda like demascus steel with copper mixed in on the outside of the bearing. None of them had spun. Was getting a knock at 50+, and under hard acceleration below that. Thr only thing obviously broke is the thicker of the chain guids held in place by three bolts. What is this discoloration from? Heat? Replacing these from what I've read is troublesome as you have numbers that mean little when parts are worn to figure out what color/number bearing is needed.

 

What does the other side of the bearing look like ?

 

Those bearings may not have spun, but they sure have been moving. That isn't discoloration; you're seeing the outer layers of the bearing having been worn through. You shoudn't be able to see one speck of the copper plating. Give us a pic of the other side and of the rod bearing journals.

 

The other sides are normal and burried in a bucket of oil at the moment. Here I believe is the other part you are looking for.

 

How many miles on this engine? Looks like it need the rods measured to see if the hole the bearings go is round or egged out. Rod reconditioning where the machine shop cuts the caps and machines the hole to spec.
If the rods need that kind of re-work the rest of the engine must need serious attention.

 

38k rest of the motor is in pretty good condition. Chain guid needs replaced (ordered) but other than that there isnt anything that stands out or is loose. Oh i replaced the auto cam chain tensioner and chain itself while I was at it.

 

Here is the crankshaft.

 

If it were me , I would take everything to a machine shop and have the guys mic everything up.
As long as it's all apart it would be a good idea to see what the clearances are before you order bearings and such. 38 Kis not that bad miles wise but if it has a lot of wear you can address it now if you plan to keep the bike

 

Ty

 

Looks like a 750 maxim. Make certain you take a good look at the starter clutch rollers and springs while you're in there.

Gary H.

 

Yes it is. What should i be looking for or testing?

 

Look for cracks in the starter clutch housing. If there aren't any then just replace the rollers and springs. If the housing is cracked then it will need to be replaced (it's the bronze casting that can crack). Replace the alternator chain guide as well.

 

Just got the chain guid in today. Rod bearings other side and miced the the rods and 3 are within .5 of a mm sadly the 4th is out by 1mm. Now to find a machine shop in this town...trans portation is dead.

 

Those bearings look bettter on that side, but still aren't great.

 

Imo the shells should be replaced. If not each shell should return to the journal it came from. Hope this helps.

Gary H.

 

The shells definitely need to be replaced. The backsides are not in any condition to be run. They will move again given the chance.

 

I would see what's available for parts before I would do anything. Not sure what undersized bearings are available and what sizes. The machine shop would need to know if they end up turning the crank. The rods will need reconditioning. Pistons and bores will need checking. If the pistons are toast that can get spendy pretty quick.
Maybe be look for another mill? Might be cheaper in the long run and generally a whole lot less work.

 

I have a machinist to redo the connecting rods but how do I know which bearings to order? I have seen a thread on here saying there isn't anywhere you can find the dimensions of the bearings by size/color. should I just make them out of oil impregnated bronze? I really cant afford to buy a set of bearings that wont work. the machinist can set the size of my rod to what ever I need...but what is it I need...

 

An engine machinist cuts the caps on the rods and re-bores the rods to make the rod bearing area round again. This is called rod reconditioning. With a micrometer he would measure the crankshaft and either turn the crank to an undersized bearing that is available or they can weld up each journal and resize it to stock. Any way you cut it this is going to be expensive.
Machine work is never cheap and parts are not sitting in the shelf at NAPA.

 

Not trying to be cheap about it but i don't want to spend 300 on a set of bearings i cant use. Have none of the sellers
thought to take measurements of them?

 

The difficulty lies in the fact that nobody to my knowledge has published a list of the bearing shell thicknesses cross-refrenced to color. There may be something out there, but I have yet to find it.

 

You can get the specs for the crankshaft in the service manual. Did you get your machinist to measure the crankshaft and the rods. Then you can get an idea from Chacal about undersized bearings and how long it would take to get them . I highly doubt it would be $300 for 4 rod bearing sets

 

He hasn't machined them yet. He wants to know what size to make them. Measured the crankshaft. They are all the same. And thank you for the responses. I thought i looked through the catalog and they were between 200 and 300 for 4. I could be wrong it was 3am.

 

Get ahold of xj4ever up in the right hand corner. See if his prices are any better.

Good Luck

 

There is a section in the catalog that explains how to use the scribed #'s on the case and the #'s on the end of the crankshaft to determine the location and calculate a one digit # which coincides with a specific color for the main and rod end shells. A # to color chart is also located in the catalog. The color will tell you which shells were installed by yamaha. k-moe stated he doesn't know of anything published which tells the thickness of the shells in relation to the color. Determine the color of the shells when they were new using the formula in the catalog then ask Chacal for thickness measurements and take those to your machinist. Hope this helps.

Gary H.

 

He's referring to the Xj4ever catalog.

Gary H.

 

Holy C**p $379.95 for 4 sets of rod bearings. I wouldn't think John Force would pay 1/2 that for his Funny Car engines. Guess I'm used to Sealed Power Chevy bearing prices. By the time you buy all the parts,gaskets and seals then pay the machinist it's going to be over $1000.00.

Now I'm just saying but you do what you want, but if it were me I would find a good used low mile engine and mothball that one till you can find reasonable priced parts. But that's just me.

MN

 

Have a machinest that will do it for 80 for all 4. Helped him out with stuff. Ill have to look up the gaskets tomorrow. To damned tired tonight.

 

Also, i dont remember seeing any when i took it apart. Will have to look again.