350 Main Bearing Clearance Assistance Needed

Hi
I am rebuilding a 350. Need to know how loose I can go with main bearing clearance. The original bearings had the .001 under marking. The crank was in good shape and was just polished. Got stock bearings from TA performance. Measurements of the crank journal, bearing shell thickness, and block main bearing bores show I should have the following clearances
Brg 1-.0028
Brg 2-.0026
Brg 3-.0022
Brg 4-.0027
Brg 5-.0022

The Buick manual requires main bearing clearance to be between .0004 to .0013. TA performance told me they set their main bearing clearances to .0022 to .0025.
Does anyone have experience run Buicks with main bearing clearance in the .0022 to .0028 range?

 

.002 max
.0028 to big
Your original bearings marked .001 were oversize from the factory, so they saw a too large a clearance, the reason for the .001 bearings.
If I were you, I'd have the crank turned undersize .010 to achieve .0015-.002 using a .010 oversize bearing.

 

It would run. Oil pressure will suffer. You would be building a new engine with worn out bearings.

 

Yep, just have the crank turned .010 from factory size (not what it is now, 2"rod 3" main if I remember right, someone correct if wrong) and use .010 bearings. Keep them TA bearings around in case you ever build another 350 with a standard crank or sell em.

 

And keep in mind, a crank turned will have LESS material so you need (thicker) bearings for an UNDERSIZED crank. The terms are confusing sometimes. ALSO, when ordering bearings online or in store, the buicks have a center thrust bearing so the thrust bearing will essentially look like a normal main bearing with a shoulder on it. it won't look like a double wide bearing like a Chevy 350 uses. Just looked on summitracing's site and had to weed through the "buick 340/350" listings for actual buick bearings. And they don't sell .010 main bearings. Lord.

Good luck to ya either way.

 

Get these to tighten up your clearances. You can use half standard and half .001 to dial your size in. JW does it....
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/332550594607

 

Awsome. Thanks for your help

 

Thanks all, you confirmed my thoughts. Will stick with the Buick manual recommended clearance range. Going with the .010 undersize bearings from TA performance and have the crank turned.

 

Really need to plastic gauge them .

 

Bore gaging & mic'ing torqued down pre-assembled parts/components is the best.
Would you really be that happy if your engine shop used plastic gage for checking all your bearing clearances....

 

I have not had an issue yet. Actual crush of bearing around crank. Measured . Obviously not all bearings are measured with plastic gauge . Nothing wrong with double checking clearance measurements

 

Plastigauge has been around a long time. Its fine imo in all but the most high dollar super race-y applications.

 

Nothing wrong with Plastigage, especially if your not well versed in precision measuring instruments like myself

 

If your line Bore checks out straight and your Crank run out is within range then I can see absolutely no need to run more then .002" main clearance in a motor that is more street then strip with a main journal size of a 350!!

 

.001 UNDER, or .001 OVER? Are you sure?

In anything but Buick, .0028 would not be unreasonable. Buick folks seem very allergic to clearance that loose.

Yes, I would Plastigage the assembly to verify clearance. How much material was removed when "polishing" the crank?

If those old bearings were .001 under, and they were in good condition, I'd re-use them. But they'd have to be in good condition.

 

if you rum 20-50 oil these loose clearances are fine

 

A problem I run into is bearing manufacturers have a specific journal size and clearance in mind when they make their bearings. If they see the original standard journal size was 2.5000", they will make the bearing to 2.5025" for a 0.0025" clearance. That is on the wide side for a Buick. The same thing happens with their underside bearings. On their 010 bearings they expect a journal of 2.4900" now, so they make the bearing to 2.4925" to give the same 0.0025" clearance....too wide. In other words: the crankshaft is always reground to a fixed size and the bearing manufacturer selects the clearance when they make the bearing. That doesn't work here.

So what I do is I give the crankshaft regrinder my own specified journal size after measuring the new bearings in the block. I write down the size I want the journals to be and I tell them I am running this engine with only 0.001-0.002" of clearance, so they better be very precise on the sizing and any taper or oval.

Or, I tell them to regrind one thousandth less, so instead of grinding the crank 010 undersize, I have them grind it 009. That one thousandth tighter clearance is usually just about right.

Then you have a Buick engine built the way Buick built it: tight, with 10w-30 oil.

 

Yes that is how all my engines are built. Assembled with bearings and then machine work is done to get the bearing spec. No plastigauge used only real tools.

 

Seems like plasigauge takes "human error" out of the equation. It doesn't get it wrong, and may account for things that can't be measured with a tool. Just a thought. It is what it is.