SBC - main bearing clearance question

[Belgian1979]

I think that you have found something

Yes, but I still don't understand how that is even possible. If the caps would have just been thrown on there, the differences would be a lot bigger. But if you do bore and hone the mains, then they should be closer no?
BTW: I also measure about .02mm difference vertically vs the diameter at the parting line (.0008")
Maybe someone can explain to me how line boring/honing works and what results are typically and what the tolerances are that can be expected?

[Baprace]

Belgain1979 , Why not use some .001 brass shim stock between the main caps and the block ? from the last pics I have seen that engine is just too tight , if you don't want to do that then a line hone is your next fix. JMO

[Belgian1979]

Belgain1979 , Why not use some .001 brass shim stock between the main caps and the block ? from the last pics I have seen that engine is just too tight , if you don't want to do that then a line hone is your next fix. JMO

Hi Baprace, I agree it is too tight hence why I'm fretting about this.
I've tried to get shim stock over here before but that's next to impossible. In the US you really have a car culture and engine tuning history with everything that goes along with that. Not so much here.

[mag2555]

Something is not right with the bore!
With any bearing installed in a block the bearing width should be wider then the height!

This is what keeps the bearing from pinching in at the parting line when the cap under high loads pinches in at the parting line due to deflection.

I would not go with a brass shim since over time it will flow out and then you will loose all of your bearing crush.
Either have a shop polish in the extra .0005” to .001” to make you happy, or maybe use these.

My main concern is always what happens to those bores under high loads, not so much what the static clearance is if I am within .0005”.

[rebelyell]

so --- steel main caps retrofitted --- although were not align honed --- but have since sought perfection.
Not align honed --- Ay, there's the rub.

[Belgian1979]

Something is not right with the bore!
With any bearing installed in a block the bearing width should be wider then the height!

This is what keeps the bearing from pinching in at the parting line when the cap under high loads pinches in at the parting line due to deflection.

I would not go with a brass shim since over time it will flow out and then you will loose all of your bearing crush.
Either have a shop polish in the extra .0005” to .001” to make you happy, or maybe use these.

My main concern is always what happens to those bores under high loads, not so much what the static clearance is if I am within .0005”.

Not sure what you're trying to explain. The bearings still need a little force to be pushed in, so they are wider at the parting line than the diameter (I presume, not measured it).
Shims are not a direction I would want to go, so I'll just have to see if I can get it corrected. Again, no experience on the area of align boring/align honing. Let's hope this can be done.

[Belgian1979]

so --- steel main caps retrofitted --- although were not align honed --- but have since sought perfection.
Not align honed --- Ay, there's the rub.

Not sure if it's not align honed. It just looks odd to have the center caps at a smaller diameter than the 1 & 5. Also I would assume the bore would be bored/honed round, but this seems not to be the case, although after some searching here I find threads where comments are made this is not exceptional. Don't know. I'm not a machine shop, so not setup to check for main bore alignment. I used HX bearings on everything except 5 and it was ok, despite a bit on the tight side. So I was looking to get some more. When measuring the bearing wall thickness and comparing it to the old (with a digital caliper I find the new ones are .01mm thicker. So everything combined it seems to explain the no-go at this point.

[nwhp]

Post pictures of the bores of the 3 center main caps so we can see if they have been align honed.

Using a ball anvil micrometer to measure bearing shell thickness would more accurate and repeatable than a digital caliper.

I personally prefer the direct comparison method of checking clearance. Torque the bearings up in the bores, measure the journal with micrometer, lock the spindle, then set a bore gage with the micrometer and measure the inside diameter of the bearings. The bore gage reading is the clearance.

Good luck.

nwhp

[Belgian1979]

Post pictures of the bores of the 3 center main caps so we can see if they have been align honed.

Using a ball anvil micrometer to measure bearing shell thickness would more accurate and repeatable than a digital caliper.

I personally prefer the direct comparison method of checking clearance. Torque the bearings up in the bores, measure the journal with micrometer, lock the spindle, then set a bore gage with the micrometer and measure the inside diameter of the bearings. The bore gage reading is the clearance.

Good luck.

nwhp

There are honing marks (cross hatch) in all of them...Assume that's what you're looking for.

As for the method: that's what I use and I get repeatable results. I agree on the anvil micrometer but I don't own one.

Anyway, I measured a thickness of the bearing that came out at 2,37mm and the new one is 2,38 mm. The center caps are about .01mm smaller .
So a bearing which is .01mm thicker and a bore which is .01 mm smaller means I'm lacking ca. .02 mm (.0007") in these locations. So when I would like to get .0025" to .0027" I'm only getting around.002. Or .05mm in the worst location (.00196"). If the caps are corrected, I would end up with .06mm or .00236 theoretically. Or I could take out .02mm and would be at .07mm (.00275" which is what I have on 1 & 5).
Not sure if that can be done though.

PS: only torquing the caps to 70 lbs instead of 80 gave me another .01mm...

[af2]

PS: only torquing the caps to 70 lbs instead of 80 gave me another .01mm...

Something is wrong with the squish

[Belgian1979]

PS: only torquing the caps to 70 lbs instead of 80 gave me another .01mm...

Something is wrong with the squish

Can you explain AF?

[Belgian1979]

Line honed and now it's .0026-.0027". About .0004" from the center caps was removed.

[novafornow]

Perfect, but I do prefer the rear to be looser than the rest. It is quite a bit wider so in my mind it will not have the same flow. Also, I always file the parting edges for the thrust in high stall applications. Well done.

[Belgian1979]

rear is .00275. 2 HX's there would be .00325" and that seems a bit big in my book.

[FC-Pilot]

rear is .00275. 2 HX's there would be .00325" and that seems a bit big in my book.

I have no problem with the rear at .0032”. With the amount of surface area and therefore resistance to flow I actually like my small blocks in that range. It helps to get good flow to the thrust as well. Then again, that is just my theory. We all do it our own way. At the end of the day what matters is if it creates a problem, and if it does not then run it!

Paul