Bearing issues

[jbojo]

Also posted this in my build thread.

Ok, I checked the bearing clearances and its the main bearings that have the problem. The installed bearings are .010 so the crank was supposedly ground however when I used plastigage with a range of .001 to .003 range it didn't even begin to flatten it out. I torqued the main bolts to 105 ft/lbs. It appears that it might have just started to begin to flatten but couldn't really tell. By looking at it the clearance it may be around .005 to .006 or even more (max limit is .0026) so I was bleeding the oil by the bearings pretty badly. It makes sense that oil pressure cold was ok but as the motor warmed it began to drop rapidly.

Can someone tell me what the main journal size should be if the crank was ground .020 under? Do you just subtract .020 from the standard journal size?

The connecting rod bearings were spot on. The bearings for those are also .010 however the clearance is .0015 with the plastigage and that is the optimal clearance that my manual shows so I am ok there.

So bottom line now is that I need to measure the main bearing journals to see what bearing needs to be installed. If anyone know what the journal size should be if its .020 under please let me know. Lastly what is the max undersize a main journal can be ground to?

thx

 

[Jeff73Mach1]

You are correct, just subtract .020 from the main journal size of 2.749

.020 is all some machinists will go, though I have heard of .030 on occassion-if a stock crank, I would not turn it further than .020

a trick I will share is that most household aluminum foil is almost exactly .001 inches in thickness a few layers will help to confirm your measurements with the plastigage

 

[jbojo]

You are correct, just subtract .020 from the main journal size of 2.749

.020 is all some machinists will go, though I have heard of .030 on occassion-if a stock crank, I would not turn it further than .020

a trick I will share is that most household aluminum foil is almost exactly .001 inches in thickness a few layers will help to confirm your measurements with the plastigage

Thx Jeff,

I was going to get some plastigage (yellow pkg) which has a range of .009 to .020. If the bearings should have been .020 over then I should see about .0015 when I try the measurement, is that correct or is it better to use 10 pieces of aluminum foil and just check the measurement that way?

thx

 

[Jeff73Mach1]

honestly I would throw a drop of modelling clay in there, tighten the bearing cap and then cut the clay down the middle with a plastic razor or such and measure with my calipers

Remember your clearance is all around-tightening the cap should not appreciably compress the clearances opposite the plastigage or clay or whatever.

Are the clearances that loose on all of the mains?

 

[mjlan]

I've been following your threads, it sounds like you may have found your issue!

I think someone else mentioned rod side clearance- how is that? If it is excessive it can cause serious pressure loss...

 

[c9zx]

I haven't followed your thread however, I suggest you you have a well respected machine shop mic all the components for you. If that is not possible, it may be worth the money to buy inside and outside micrometers and measure the clearance yourself. Years ago we ran .030 undersized mains and rods without any problems. Everything depends on the precision of the machine work.

Chuck

 

[jbojo]

honestly I would throw a drop of modelling clay in there, tighten the bearing cap and then cut the clay down the middle with a plastic razor or such and measure with my calipers

Remember your clearance is all around-tightening the cap should not appreciably compress the clearances opposite the plastigage or clay or whatever.

Are the clearances that loose on all of the mains?

I only checked # 3 & 4 and got the same results and will check the other 3 today. I have another crank that I know has been ground .010 & .010 so I was thinking of trying to take measurements with that one to see if I get the same readings.