1965 FI crank pulley center bolt

[Tony S.]

I'm in the process of restoring my original engine L84 car. The car last saw the road in the mid-1980s. I took this photo of the crank pulley assembly before tearing down the engine for rebuild.

I know the center crank bolt has a through-hole in the bolt head. I never knew why. Notice the wire connecting the center bolt with the 3 pulley attachment bolts. Factory wire? Or Bubba add on? If not factory, what's the purpose of the through-hole in the bolt head?

Thanks, Tony

[David H.]

Re: 1965 FI crank pulley center bolt

Tony

That would be Safety Wire. Expect your photo is of an owner modification. Doubt the General would spend money on drilled bolts.

Generally, safety wire is a twisted pair - your photo looks like a single strand.

Purpose - to keep bolts from loosening in the days before "Loctite". My first Harley-Davidson came with several components safety wired together - e.g. Primary to Motor. My second H-D used Loctite - much less expensive to build and repair.

Dave





024CCEF6-1728-447B-89B7-8DAC763A53E1.jpeg

[Tony S.]

Re: 1965 FI crank pulley center bolt

Thanks David. Actually, I believe that the center bolt with the through-hole bolt head is a production feature. It wasn't drilled after production. Just wondering the purpose of the hole then?

Thanks, Tony

[Terry M.]

Re: 1965 FI crank pulley center bolt

Tony,

I finished restoration of my 1965 Fuelie Coupe last Spring which you judged in Cedar Rapids and the following week in Bloomington. I have some good/nice parts left should you have the need. Just send me a list of things you might need and I'll see what I can do. You can contact me by email at tcmccarthy@mchsi.com.

Not sure if stock harmonic balancer bolts were drilled from the factory but have to agree with David. That hole is typically for the use of safety wire which prevents the bolt from loosening. This was also common in the aircraft industry, especially engine parts.

Terry

[Timothy N.]

Re: 1965 FI crank pulley center bolt

Hi Tony, I’m just going to comment on the wire job I think responding to your original question as I know or I think. The safety wire or also referred to as aircraft safety wire sometimes, is wired wrong on the front of your engine. It is designed to tug at the bolt or hold the bolt in a clockwise position so the the bolt won’t back off counterclockwise. The way someone wired yours would not hold it tight but would hold it after it backed out a 1/4 turn or so but wouldn’t be the purpose of the safety wire to begin with. On a different note in my mind but you would be far more experienced but just my observation, the wire after passing through the crank center bolt goes to the outer pulley bolts and seems to either be under the head or just wrapped around the head. Doesn’t seem proper. I would think that there would be a hole in the pulley bolts too for the wire to pass through. If they are under the bolt head that would seem like an engineering no no because the wire could break or get cut when the bolt tightens up and also create an uneven surface on bolt head contact to pulley. If they are wrapped around the bolt head that also would also seem like an unaccepted practice. Obviously the bolts would have been drilled before assembly. Kind of cool to explore these time capsules .. Just my thoughts, Tim

[Ray K.]

Re: 1965 FI crank pulley center bolt

Tony,

The GM part number for this bolt was 3815933. It definitely had a thru-hole in the head. Sold lots of these over the parts counter along with the special washer #3739422. My thought always was that this bolt was used in some other application whereby a safety wire would be required, but could never determine that application. Definitely not factory safety wired. I might still have one of these in my collection.

Ray

[Tony S.]

Re: 1965 FI crank pulley center bolt

Thanks Tim. This is just a curiosity to me. I've seen these harmonic balancer center bolts before with through-hole bolt heads. Not sure the purpose of the bolt head hole though? I've never seen the safety wiring before. Maybe an original bolt but added safety wire by someone after production? I don't know. Unless I'm mistaken, I believe that the bolt with through-hole is production. But I'm willing to listen to evidence to the contrary.

Tony

[Tony S.]

Re: 1965 FI crank pulley center bolt

[QUOTE=Ray Kimminau (8917);911354]

Tony,

The GM part number for this bolt was 3815933. It definitely had a thru-hole in the head. Sold lots of these over the parts counter along with the special washer #3739422. My thought always was that this bolt was used in some other application whereby a safety wire would be required, but could never determine that application. Definitely not factory safety wired. I might still have one of these in my collection.

Thanks Ray! Then that's the answer. The thru-hole bolt head IS PRODUCTION but NO safety wire. The safety wire must have been added along the way. I appreciate everyone's input!

Thanks guys!

Best regards, Tony

[Chuck B.]

Re: 1965 FI crank pulley center bolt

Tony,

The bolt on original engine 3542 is a TR grade 8 with the hole for a safety wire, but no wire was present. The big washer has what appears to be semi gloss black paint and the external tooth washer is visible as it is in your picture. Since I use the crank bolt to turn the engine when adjusting the valves, a safety wire would be in the way.
chuck

[Timothy N.]

[Tony S.]

Re: 1965 FI crank pulley center bolt

Thanks Tim! We never stop learning!

Tony

[Joe L.]

Re: 1965 FI crank pulley center bolt

Tony,

The GM part number for this bolt was 3815933. It definitely had a thru-hole in the head. Sold lots of these over the parts counter along with the special washer #3739422. My thought always was that this bolt was used in some other application whereby a safety wire would be required, but could never determine that application. Definitely not factory safety wired. I might still have one of these in my collection.

Ray

Ray------

Yes, I also feel pretty sure that this bolt had other applications requiring the hole for safety wiring which was never originally done on Corvettes. I've never been able to find the other application, either. It could be something very obscure like EMD or Allison application. However, the part number implies about a late 1962-early 1963 release.

The 3815933 bolt actually has another "special feature" besides the safety wire hole. It has a non standard thread length to total length. It is 2-1/4" in length but only has 1" of thread. Most "standard" 7/16-20 X 2-1/4" bolts have 1-1/8" or 1-1/4" of thread.

Curiously, as far as Corvettes go, the 3815933 bolt was used only for 1963-68 Corvettes with SHP small blocks (i.e. those with 8" balancer). Beginning in 1969 with the introduction of 350 cid small blocks for Corvettes, all small blocks were equipped with a balancer bolt but it was not the 3815933. For 1969-82 small blocks the balancer bolt used was GM #9428643. The latter bolt was the same 7/16-20 X 2-1/4" size as the 3815933 except that it had 1-1/8" of thread length and no safety wire hole. It was phosphate finished rather then zinc plated as was the 3815933.

[David B.]

Re: 1965 FI crank pulley center bolt

Joe, Your explanation is right on. You might have a typo in your last sentence regarding 9428643 size.

[Joe L.]

Re: 1965 FI crank pulley center bolt

Joe, Your explanation is right on. You might have a typo in your last sentence regarding 9428643 size.

Dave-----


Thanks, I corrected it.

[Ray K.]

Re: 1965 FI crank pulley center bolt

Joe,

Thanks for the update on the bolt. Always wondered why only listed for 1962 -68. It is odd that GM never cataloged the new number #9428643 for the later applications. Also, not referenced in any of my books, so am assuming that you were able to source the number from an AIM or other engineering document.

Ray