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So I am looking for a crank bolt (harmonic balancer bolt, call it what you will) for my LT1. Summit doesn't seem to know which one I need. They have a listing for a regular 350 and for the LS1engine. When I got the engine, it was missing. Any one have a part number or idea where I can find one? Thanks!
 

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O'ya I need one too, the mechanic broke one, I guess, and replaced with non-GM, probably missbalacing it too!!!
 

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Hi, I am new to this forum. I am building a 65 chevy pickup but putting a lt1 motor our of a Camaro in it. I bought the engine and was told it had been rebuilt. Not so. One of the cylinders had a scar in it. I took the engine to the machine shop and had it bored 20 over. I also had a mild cam put in it. I put the heads on and replaced the stock rockers with rollers and the appropriate pushrods for the cam. My issue is, I tried to put my harmonic balancer on and the thread in the end of the crank seems to be the wrong size. I am at a loss. 7/16 X 20 is to big. I tried Metric and a 10MM x 1.25 will thread in but not tight and will easily wobble out. What the heck is wrong with my crank bolt thread? I am thinking of taking the crank out and having the machine shop drill and tap it to 7/16 X 20. I thought I would ask to see if anyone has had this issue or has advice for me.
Thanks in advance for the help.
 

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10mm bolts come in 3 pitches 1.5 , 1.25 , & 1.00. Did you use a pitch gauge to test threads of crank. That's all I can think of. No other inch or metric bolt size is near enough to work.

The 10mm bolt is .3937 in diameter. The 7/16 bolt is .4375

Welcome to the forum. Next time start a new thread instead of bringing back a 6 year old one.
 

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10mm bolts come in 3 pitches 1.5 , 1.25 , & 1.00. Did you use a pitch gauge to test threads of crank. That's all I can think of. No other inch or metric bolt size is near enough to work.

The 10mm bolt is .3937 in diameter. The 7/16 bolt is .4375

Welcome to the forum. Next time start a new thread instead of bringing back a 6 year old one.
Wow, only 6 years huh? Seems like only 5.
 

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The hole is definitely smaller than the 7/16 bolt. I got three metric bolts with all three pitches from the machine shop. None of them worked. I am thinking someone did something weird who owned the engine before. I am going to pull the crank and have the machine shop drill and tap it to 7/16. The only other think I can think of is to buy a new crank. Thanks for the comments just wanted to make sure that wasn't something odd with the engine that I was missing. It still seems really strange, I guess it could be possible someone stripped it out and put an insert in it. Just don't really know.
 

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The English used to have this strange bolt measuring system called "whitworth" it used inch sizes but the size was way different than US bolt sizes. That's the only other bolt measurement system I know of.
 

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It should be 7/16-20 threads. I used a 12 point SBC ARP bolt with the stock LT1 washer (which is quite thick, but smaller in diameter since it has to fit up into the hub). I machined clearance for ARP's fairly large radius under the bolt head on my lathe. Everything fit perfectly.
 
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