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View Full Version : bearing spec off .0002 What to do



posjr
03-05-2009, 10:09 PM
I'm installing my polished crank right now and got .0015in (specs .0005-.0023) for the first three which is good. The fourth bearing i got .003in (spec's .001-.0028in). I'm only off .0002in.

I'm trying to go for big #'s. At least 350hp.

I would rather not turn the crank. I'm on a budget here. So what you guys think. I my take the motor apart one day again to install pistons later but mybe a year or two from now which i can turn the crank than.

rzimmerl
03-05-2009, 10:13 PM
The journal is small resulting in the larger clearance, polishing or grinding will only make that number bigger.

Mike8675309
03-05-2009, 10:38 PM
I'm installing my polished crank right now and got .0015in (specs .0005-.0023) for the first three which is good. The fourth bearing i got .003in (spec's .001-.0028in). I'm only off .0002in.

I'm trying to go for big #'s. At least 350hp.

I would rather not turn the crank. I'm on a budget here. So what you guys think. I my take the motor apart one day again to install pistons later but mybe a year or two from now which i can turn the crank than.

That seems a bit loose on that one. You might want to verify the bearing is correct. Maybe get another set of bearings to get that one and try that. Manufacturing tolerances and all.

From Clevite:
http://mahleclevite.com/techbulletins/CL77-1-205R.pdf

For most applications .00075 to .0010 (three quarters to one thousandth of an inch) of clearance per inch of shaft diameter is a reasonable starting point. For example, a 2.000 shaft diameter would require .0015 to .0020 bearing clearance (.00075 X 2.000 = .0015 and .0010 X 2.000 = .0020). Using this formula will provide a safe starting point for most applications. For High Performance engines it is recommended that .0005 be added to the maximum value determined by the above calculation. The recommendation for our 2.000 shaft would be .0025 of clearance.

frdlvr30
03-06-2009, 12:29 AM
Sounds to me like that journal is "polished" too much. May have to get the crank turned. And purchase the .010 bearings. I would not run it that loose on the oil clearance...thats twice as much oil clearance as it needs.

Ddubb
03-06-2009, 01:35 AM
That is really close ... but slightly out of spec.

You measured it more than once right ?? Who did the polish ?

If youre going to grind, take it to Ed's crankshafts in San Leandro .. but that .010 turn is going to be the last grind for the crank. I think its another $90 for the grind, plus bearings .. like you havent spent a lot already. :rolleyes:

- Dan

posjr
03-06-2009, 02:27 AM
I have the correct bearing. I notice the old bearing was alittle worn out. Had three small grooves in it.

I'll recheck it tomerrow. I torqued it at 70lbs. I'll try 80lbs If i'm luckey i'll lose .0002in.


Dan-I took it to this old man over by san jose ave. He polished the crank for 30 bucks. But man he was super old. Can barely walk and does the work himself :eek:

Ddubb
03-06-2009, 03:20 AM
Sounds like that groove he polished was just .0002" too much. :D

I had Ed grind my crank .010", bearing clearances turned out to .001 for #1-3 and .002 for #4.

- Dan

Mike8675309
03-06-2009, 01:07 PM
.001 is a bit tight for most performance engine builds. .003 isn't all that bad, but being so different than the others is what would concern me more than anything. Oil flow in the crank may end up being uneven as the oil can get out too easy on that one journal.

How are you checking these? I hope you are using micrometers rather than plasti-gauge. You should be using the final torque. Here is a description of how to check clearance:
http://www.circletrack.com/tipstricks/4636_crankshaft_rod_bearing_installation_tips/index.html


Next we verify that the bearings have correct clearance to the crankshaft. This operation begins by taking measurements around the crankshaft journal. When the crankshaft measurement is set, it is directly transferred to the dial bore gauge. Using this method assures a specific crankshaft to main-bore measurement comparison for correct clearance.

Now, the bearings are set into place and the main cap is torqued down. Jackson noted that the main cap should be seated by tapping it into place with a mallet. Use of a mallet to seat the main cap is important, since seating the cap by torquing the bolts can result in a broken main cap. Once the cap is in place, it is ready to be torqued down.

With the bearings in place and the main cap torqued down, diagonal and vertical measurements are taken in the main bore. For complete accuracy, readings are taken in the vertical location as well as 1-inch diagonally right and left of vertical. This check determines that both the correct bearing clearance and correct bearing eccentricity exists. Jackson noted that if a decreasing number is obtained in the vertical to diagonal measurement, it is an indication of incorrect eccentricity. Should this condition exist, it is imperative to double check the housing bore and the bearings to determine the source of the problem for corrective action. Once the clearance and eccentricity are determined to be correct, this checking process is repeated at each main bore.


For those that have had their cranks ground .010 undersize, did the shops adjust the fillets so there is not a sharp transition there?

XR7 Dave
03-06-2009, 01:28 PM
That's too light on the torque spec. Crank it up to 85lbs and measure again. .003 isn't necessarily a deal breaker, but your .0015 on the front 3 is a little tight for a high performance application.

posjr
03-06-2009, 01:49 PM
I checked it with the plastercrap gauge. I'll see if i can get a ahold a of a dial bore gauge. I have a micrometer which i'll try also.

I post my new specs later today.

Mike8675309
03-06-2009, 04:29 PM
I checked it with the plastercrap gauge. I'll see if i can get a ahold a of a dial bore gauge. I have a micrometer which i'll try also.

I post my new specs later today.

yikes... that explains the wide difference. Do not use Plastigauge when trying to be certain of your dimensions. Sure, you could use it to check if you are at .005 vs .001. But all that tells you is if you need to take a closer look or not. For first time install, take a close look.

this is one of the benefits I had of just having my machine shop guys check everything, even though I told them i was going to do final assembly. They had the crank polished, and they checked all the bearing clearances for me, mains and rods. Of course, that means you need to have all of those parts for them. Note that you should call around. They might be willing to check it for you if you just drop by with the block, crank, and bearings while you wait. Depends on how busy they are.

BlackbirdSC
03-08-2009, 12:14 AM
Bearing clearance really is only for determining what weight oil to run and to produce proper bearing contact pattern (within reason). The factory spec of under .001" is for fuel mileage and to run with 10w30 or 5w30 oil and maintain adequate oil pressure. Which is why running 20w50 or 15w50 syn oil in a stock motor is not a good thing and will actually harm the bearings over time. Eccentricity in the bearing will affect the contact pattern (should be 1/2-2/3 of the lower main bearing shell) but all bearing manufacturers make there bearings a little different.

That said, I'd measure it with a dial bore gauge or take the block (with bearings torqued in place) and the crank to a shop and have them measure it. It'll only cost a couple bucks. If clearance is around .001"-.002", run 10w30 oil. If it's .002"-.003", run 10w40 or the euro spec 5w40. Having a 94-95 8 tooth oil pump for higher volume would be a good idea too if over .002".

It won't start rapping do to loose bearing clearances until over .004" clearance and/or low pressure due to improper oil selection (like .0035" clearance and 5w20 oil).