How does one determine bolt specs from the hole?

[Dabba]

So pretty much my worst nightmare just occurred. I had to have a starter bolt drilled and tapped because it broke off in the block. Now years later, the bracket rattled loose, as well as the oddball bolt and it fell out.

Now the truck won't start because it's missing the bolt and I haven't a clue as to the size. How do I measure this thing or even find one? I'd like to not have it towed.

Am I SOL?

 

[tRustyK5]

Trial and error, luckily there aren't a million sizes. Grab a 3/8" NC, a 7/16" NC, 10 mm to cover your bases and one of those three should be it I'd think.

 

[1-ton]

First thing is.What kind of vehicle is this? If this is a chevy truck with a V8, then any auto parts store should be able to get you the correct starter motor bolts in thier Dorman (A.k.A HELP line) of products.

 

[1-ton]

you will need to get the proper garreted style starter motor bolts for this vehicle, and then try to heli-coil to the correct size. Or else this will keep happening over and over again, unless you are OK with Gerry Riging as a way to fix a vehicle.

 

[Dabba]

Hey tRusty, what does NC stand for?

It's for the 86 cucv with the 6.2. Its not a stock starter bolt and that's the problem.

 

[nvrenuf]

NC = "national coarse" referring to the thread, coarse thread.

 

[Stomis]

I guess the million dollar question really is, does the block have a helicoil in it?

 

[Dabba]

No. They just drilled it out and used a larger size. Apparently the stock bolt is 10 x 1.5 x 9.8 metric. Trying to figure out what the likely next size up would be. 10mm is right between 3/8 and 7/16. So bet on 7/16? Is NC a universal thread width?

 

[Dabba]

So the only 7/16 option is about one inch longer.

Stock bolt was 113mm long which is 4.5in

7/16 NC, the next size up is 5.5in. Guess I'll get a handful and pray

 

[dyeager535]

No. They just drilled it out and used a larger size. Apparently the stock bolt is 10 x 1.5 x 9.8 metric. Trying to figure out what the likely next size up would be. 10mm is right between 3/8 and 7/16. So bet on 7/16? Is NC a universal thread width?

The only "standard" things we deal with in the US on a regular basis are course and fine.

I'm quite certain 10MM was never a standard starter bolt size, since they were the same at least back into the 70's, long before metric fasteners were seriously considered.

Your best bet, if you are guessing, is buy a handful of the cheapest bolts in each size +/- from the size you think the threads are, and see which threads in. Then get the proper length.

But I'd agree with the previous statements...if it fell out, you need to fix the hole. You are going to break the block (the furthest piece out will snap off) at some point if the starter isn't being held tight. This is one of those "fix it right or the wrong fix will cost you more" IMO.

There is a reason the starter bolts are designed differently than standard bolts.

 

[Dabba]

I don't think it ever had the proper bracket. It did have one, but not for the gear reduction. It must have fell off. So I'll be ordering that as well