350 SBC Main bolt

[rdobbs]

I have a 350 30 over 2 bolt block and my son wants
to make a 383 out of it. Good block except the middle
main bolt seems to not want tighten up like it should
on one side. Is this something I can repair without
going to a machine shop?

[glennsexton]

When you say, “…the middle main bolt seems to not want tighten up like it should on one side…” do you mean is keeps turning when torqued or the bolt doesn’t come in contact with the main cap saddle? Is it possible that there is something in the bolt hole? Can you take the cap off and look down inside the bolt hole? I’d try chasing it with a thread cleaning tap and make sure you’ve got the correct bolt and give it another go.

It takes a bit to bugger these holes but it does happen and then it is best to have the machine shop examine and rework it. If you’re going to build a 383 the block will need to go to the shop anyway to grind the proper clearances for the longer stroke.

[rdobbs]

when I originally built the 350 the bolt would not torque up. It was like threads
were bad. Went ahead with it anyway and put about 10,000 miles on it with no
trouble,, but never did really trust it. Glen you mentioned grinding proper clearances on the 383. I don't recall doing that on the one I did back in the 90's.
I did have a 7 qt oil pan on it though, and never any problems. ThANKS

[glennsexton]

There are a couple schools of thought on overall clearances in building engines – I subscribe to the thought that there should be a minimum of .050" clearance between reciprocating assembly (the crankshaft and rods) and the fixed areas of the block. When building a 383 stroker there is a possibility of “metal to metal” in several areas, i.e., at the pan rail, the base of the cylinder bores and the camshaft in cylinder 1, 2, 5 and 6. Even with a small base circle cam the clearances need to be checked.

ARP makes a set of rod bolts specifically for stroker applications (Part Number 134-6026 - $75 from Summit - http://www.summitracing.com/parts/arp-134-6027 ) that give additional clearance in the factory (5.7”) rods. Money well spent.

In your earlier build, you may have used a 400 crank with 400 rods (5.565”) which would have allowed assembly without clearance issues but the trend has moved away from the short rods as the rod length-to-stroke ratio is not good and most 383’s are now assembled with the 5.7” rods.

[rdobbs]

Your right. I did use the 400 crank and 400 pistons with ARP rod bolts
as well as head studs. Did not know the trend had changed.