SBC - main bearing clearance question

[Belgian1979]

Anyone any input on the HXX bearing mentioned. Cannot finf these…

[Belgian1979]

Question: can you sand the back sides of the bearings a little to get the required extra clearance?

[FC-Pilot]

Question: can you sand the back sides of the bearings a little to get the required extra clearance?

If I am looking to squeeze out a few ten thousandths I sand the backs. I work hard to make sure it is even across the bearing shell. I am so use 1000 grit to make sure here is plenty of contact with the block for heat transfer. I don’t know if it is right, but that is what I do when in a pinch and have never had a problem. Have probably done it on 5 engines, so don’t have a wealth of experience doing it.

Paul

[lance flake]

Question: can you sand the back sides of the bearings a little to get the required extra clearance?

If I am looking to squeeze out a few ten thousandths I sand the backs. I work hard to make sure it is even across the bearing shell. I am so use 1000 grit to make sure here is plenty of contact with the block for heat transfer. I don’t know if it is right, but that is what I do when in a pinch and have never had a problem. Have probably done it on 5 engines, so don’t have a wealth of experience doing it.

Paul

I have done the same thing a few times. Most likely overthinking and overworking the whole time!!

[novafornow]

I have as well. The guys that do this daily may feel different, but I have not had any trouble because of it.

[mag2555]

When you sand down the steel backing you are also reducing the much needed level of as intended crush.

Your all playing with a real hot fire in my opinion.!
I would much sooner use 2000 grit wet or dry paper and soap & water to open up the face of the bearing even if it does take me 2 to 3 hours for a set of 8.

[V12MECH]

Always bolted pump on rear cap when checking with bore gauge, as Cowan mentioned, really never did a comparison with and without. May make a difference.

[Belgian1979]

When you sand down the steel backing you are also reducing the much needed level of as intended crush.

Your all playing with a real hot fire in my opinion.!
I would much sooner use 2000 grit wet or dry paper and soap & water to open up the face of the bearing even if it does take me 2 to 3 hours for a set of 8.

I agree with your comments, however I would be very hesitant to do anything to the coated surface and I'm out of options as no HXX is available despite they are mentioned in the link from Clevite I gave earlier.

[Belgian1979]

"The original bearing set that came out, had marks on the number 3-2 and a little on the number 1 (marks in the location where the journal is the smallest)."

Hi Belgian1979,

Got pix of the bearings that came out?
Were the marks on the insert from the block side of the bearing, or the cap side?
How small was the journal where it was "smallest" ? That location would have largest oil clearance, I;m guessing.

From rear to front






PS: very early on I had one instance where the pan was overfilled and at high rpm I saw oil pressure drop, after which I immediately pressed the clutch. Engine also had a low oil pressure at idle at that point (20 psi) After that I took the pan of and correctly reset the oil level after which I never had that problem again. Cannot be sure that this is a remenant of that instance. Could have been that my accusump saved me at the time

[Belgian1979]

Worked on it some more. Scotch brited the back of the number 2 but it yielded very minimal results. Still too thight.
I put back my old bearings and measured them and they are a larger by about .01mm (.0004") so still thight but better (.0236 vs the required .0024 which I wouldn't have sweat over but in view of the scoring I would have like them looser). I already use HX's on top and bottom, so I'm stuck here.
Measured the bearing shells with a caliper and the new ones seem .01mm thicker (in sofar as the caliper is correct). That would explain the difference I'm seeing. ( a good .0004" difference)

Have the crank polished a bit more?

[rebelyell]

Have the crank polished a bit more?

^^^this^^^

[novafornow]

There are various ways to go about this. You can grind the crank down or brush the saddles a little if they are not at max. I would not attempt to grind .0005” off of the crank, but have taken off .001” more than once.

[Lloyd klem]

I have never had a problem with .0027 to .0032 on rear ever.I live in temp range of -10 degs winter to 100 degs in summer.

[Belgian1979]

There are various ways to go about this. You can grind the crank down or brush the saddles a little if they are not at max. I would not attempt to grind .0005” off of the crank, but have taken off .001” more than once.

I couldn't leave it alone, so I went checking and basically it's a stacking of tolerances.
Crank is on the large size.
Bearings are on the large size (Clevite specifies +-.00015" per shell).
The main saddle bores are on the small side for 2,3 and 4 at 2.6405" so below or at the lower limit.
Saddle 1 and 5 are correct however...

Don't understand why the saddles are like this. These have been replaced when I bought the block. It had the 4 center caps replaced by steel splayed caps so the block should have been align honed. Looks like I need to have them align honed again and increase their size to that of number 1 and 5.
The previous time I assemble it I just squeezed by I presume because the bearings were thinner.

[novafornow]

I think that you have found something