Main Crankshaft bearing colors / spec's - follow link please

[TownsendsFJR1300]

From a Yamaha motorcycle forum I frequent.

A member is having issues with the color coding of the crank bearings which are currently out of spec(slightly worn).
Its a 600cc, in-line 4 cylinder.

Any helpful input on color codes (believe it's similar to Yamaha OB engines reading here) would be appreciated.
Boscoe or anyone one else please chime in..


Post 157 and on: http://www.600riders.com/forum/fz6-g...tml#post636356


(I'll post a link to that member on that forum)..

Thanks..

[rodbolt17]

dunno about the mo mo sickles but the outboards are simple.
the crankcase has a number the crank journals have a number. you simply use the numbers and the chart to find the mains. then you use another set of crank numbers to find the rod bearing colors. then you plastigage them to double check. it aint difficult.
bad thing is unlike old chebby's and such they offer no undersize bearings if the journals are worn or damaged.

[boscoe99]

dunno about the mo mo sickles but the outboards are simple.
the crankcase has a number the crank journals have a number. you simply use the numbers and the chart to find the mains. then you use another set of crank numbers to find the rod bearing colors. then you plastigage them to double check. it aint difficult.
bad thing is unlike old chebby's and such they offer no undersize bearings if the journals are worn or damaged.

Correct. But I have been wondering.

The bearings are of different thicknesses. Let's assume a blue bearing is thicker than a red bearing. The red bearing is called for based on the calculations. But when the clearance is checked via the Plastigage it is slightly too much. Instead of a red bearing a blue bearing is installed. Clearance is checked. It is now within specifications.|

Do you see any problems arising?

Now what I have never understood is Yamaha using a bearing half shell of one thickness on one side and a bearing half shell of a different thickness on the other side. Anyone got any thoughts?

[99yam40]

are you saying you have seen these bearings installed in not matched sets or the instructions say to use them unmatched?

[walleye1]

That got me scratching my head in class at yamaha. It has to be in the machining, like theyer gear shimming there gear cases. p-f-r. Why cat'nt they make mashine them the same.

[boscoe99]

From a Yamaha motorcycle forum I frequent.

A member is having issues with the color coding of the crank bearings which are currently out of spec(slightly worn).
Its a 600cc, in-line 4 cylinder.

Any helpful input on color codes (believe it's similar to Yamaha OB engines reading here) would be appreciated.
Boscoe or anyone one else please chime in..


Post 157 and on: http://www.600riders.com/forum/fz6-g...tml#post636356


(I'll post a link to that member on that forum)..

Thanks..

If the guy has different coloured new bearings he could use a micrometer to determine the thickness of each.

Below is an illustration from a Yamaha F70 SM. It shows how to determine the bearing colour for the crank shaft main journals. I would start by recording the stamped letter for each journal. The J1 dimension. Should be either an A, a B or a C. Hopefully they will not all be the same. I would then measure the actual outer dimension of the main journal. Trying to determine if A means it is smaller or if C means it is smaller.

Once it is known which is smaller (say A is smaller than C) then I thick it can be deduced that bearing colour yellow is thicker than the other bearing colours. I think.

[boscoe99]

are you saying you have seen these bearings installed in not matched sets or the instructions say to use them unmatched?

In the back of my fading mind, I think so. Got to go and flesh this out. If I have to have some tasty crow pie I will come back and say so.

[boscoe99]

are you saying you have seen these bearings installed in not matched sets or the instructions say to use them unmatched?

What do you think? Am I misreading it?

[99yam40]

Looks like you were correct.
apparently a few thou difference between the top and bottom does not hurt anything

Back in the good old days there were people that would stick a piece of leather in to help the clearance out. would last for a little while

[zenoahphobic]

I'll declare my ignorance, never heard of such a thing, mix and match?
This would mean the crank would be slightly out of line, and must flex (is pushed up or down) to its new position. The thinking being more important that the overall fit around the journal more important than the alignment?

[99yam40]

actually the crank floats on a film of oil.
you get the tolerance correct to make sure there is enough oil film between metals.
too much clearance and oil will flow out to quickly.
too tight and not enough oil.
either way it is not good

[zenoahphobic]

actually the crank floats on a film of oil.
you get the tolerance correct to make sure there is enough oil film between metals.
too much clearance and oil will flow out to quickly.
too tight and not enough oil.
either way it is not good

Very good point.
Oil viscosity and oil pressure also play a part.
So I need not worry about misalignment as the mismatch still leaves space between the shaft and the bearing.

[dray0151]

You guys remember the article someone had on here about the wear pressure characteristics of oil that a mechanical engineer had done. That's the pressure that counts between that bearing and the rod or crank. Maybe we need to find that guy and have him do some studies of marine oil to get the best one?

[pstephens46]

You guys remember the article someone had on here about the wear pressure characteristics of oil that a mechanical engineer had done. That's the pressure that counts between that bearing and the rod or crank. Maybe we need to find that guy and have him do some studies of marine oil to get the best one?

There is a forum. "Bobistheoilguy". I bet they can carry on for days on the subject.

[dray0151]

I just slightly in my old age remember that Quaker State syn 0-20 had the best wear pressure rating in one of the studies. I was kind of surprised by that.