I’ve run into some clearance issues on my engine build. I have a 383ci small block Chevy with a 3.75 inch stroke crank and stock rods. I put the cam in and crank in everything is good. Then I go to put in the #1 piston. After I torqued it down I spin it around to check everything is still smooth and I have clearance issues where the connecting rod hits the cam lobe. It’s so bad that the crank just stops. The cam I have in (that I obviously can’t run now) is a Lunati Bootlegger PN 12224. It’s advertised as 0.485 inch lift.

I’m wondering if this is a common problem and if there is a solution like a smaller cam. I still want a good rpm range and a lopey idle. Stall and compression won’t be an issue as I have a manual transmission and the compression should be around 10.8:1. I’ve looked at the Summit Racing camshaft (part number SUM-1785) and it looks to fit the build at only 0.450 inch lift. Any help or advice here is welcomed.

A.B.

The first issue right out of the gate is that your photo shows that the cam is in with a gear but you do not have the crank timing chain gear or the chain installed. So the cam is not in the correct orientation with the crankshaft.

When building a 3.75 inch stroke (or longer) small block, this additional stroke moves the big end of the connecting rod very close to the camshaft with the piston near the top of its stroke. This is especially true when using stock connecting rods and stock rod bolts, which we will assume you are using. 

The first thing to do is to install your crank gear and timing chain with the dots aligned between the two gears. This will probably solve the problem with Number One connecting rod, but may only delay the next problem.

Most small blocks are very tight with the rod and cam on cylinders Number 1, 2, 5, and 6.

crankshaft installed in an engine
The builder included a photo of his engine when this problem occurred. You can see that the cam is not connected to the crank with the timing chain, so that’s the first thing to do when checking clearance. (Image/Jeff Smith)

Double check this but the rod that usually hits is #2 and/or #7. If this occurs, it might be possible to improve this situation by retarding the camshaft to see if this will create sufficient clearance. Any clearance will be enough—even 0.010 inch will work, but more is always better.

If that trick does not work, you could go with a camshaft with smaller base circle or you could use a different ARP stroker rod bolt with a trimmed rod bolt head offset to help clear the cam. This might affect balancing (assuming the rotating system was originally balanced—which you should always do), as the new ARP bolt will likely be not weigh the same as the original rod bolt.

You may be tempted to merely grind on the stock rod bolt head to achieve this same clearance. This is a dangerous game to play since any grinding on the head of the bolt will likely result in a bolt that will fail. So spend the money on the ARP rod bolts which are already stronger than stock rod bolts made of 8740 chromoly steel..

Package of ARP Engine Fasteners
ARP makes a special small block Chevy stock connecting rod bolt with a tapered head that improves the clearance between the rod bolt and the camshaft. (Image/Summit Racing)

These steps will also require degreeing the camshaft to check for clearance and may need a different timing set to allow you to change the timing more easily. Best bet is with moving the crank gear usually two degrees but sometimes four degrees.

Check for Clearance at the Bottom End Too

Do you have clearance at the block? Often the rod bolts on aftermarket rods will hit the area underneath the oil pan rail—so that needs to be checked as well to ensure you don’t have interference. If so, this work is best left to a machine shop to do correctly. This can be done with a deft hand and a high-speed die grinder. Shoot for minimal clearance here of 0.020 inch is all that is necessary. This clearance will not change regardless of rpm.

The best approach (which admittedly may be too late for you) is to use aftermarket stroker connecting rods that drastically improve clearance to clear the cam.

Keywords
383, Ask Away!, Clearance, Stroker
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.