Question about an Original Harmonic Balancer Bolts with "TR" marking

[David L.]

In my 40-year collection I have five 7/16"-20 X 2 1/4" harmonic balancer bolts, GM # 3815933, along with the large washer (GM # 3739422) and external tooth lock washer that I bought at various swap meets. Three of these bolts have a "TR" marking with 6 radial line segments (grade 8) each with a 9-tooth external lock washer (possibly GM # 131718 as shown in the 1963 and 1964 Corvette AIM (Sections L-75,L-76, L84) . The other two harmonic balancer bolts have a "C" marking and a 12-tooth external lock washer (possibly GM # 138494 as shown in the 1965 Corvette AIM (UPC L76, Sheet 2). The change from the 131718 L/W to the 138494 L/W is listed in the 1965 revision records dated 2-23-65.

One of the large washers (GM # 3739422) is stamped with a "double S" (one "S" stamped over another "S").

I believe that the "TR" bolt was used on 1963 Corvettes with L-75, L-7 6, and L-84 engines.

My question: Were the "TR" harmonic balancer bolts used on all 1963-1967 Corvette with high H.P. engines?

Dave

[Alan D.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Can only verify the "TR" was used on my Mar64 FI car.

[Edward J.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Dave, My 63 has a TR bolt and has drilled holes through the head. my ia a SHP motor.

[David L.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

I have noticed that some "TR" bolts had the hole drilled thru the head and some did not. The NOS 3815933 bolt from the dealer that I bought years ago marked "LE" also had the drilled hole. What is the purpose of the hole?

[Gary B.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

David,

Safety wire?

Gary

[Joe R.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Regarding Bolts GM specifications for that and other bolts came from many sources. Many included TR, WB, AP and many others. As long as the suppliers met the minimum specifications GM bolts changed as supplies ran out and orders were filled by other suppliers. Looks like TR met those specifications and some had holes and some didn't.

JR

[John D.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Like David said the over the counter bolts had LE. When I new my 63 FI car was going to be judged I only had a TR bolt with no hole drilled thru it.
A local machine shop refused to drill it as he said the bolt was case hardened.
So I sent it to Don Baker and he drilled it. I did not know the bolt came two ways Joe.

[Alan D.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Finally got out to look at car, The "TR" bolt does have the hole - it's original in a Mar64 FI car
Did not think it had the hole so got surprised.

[Rich P.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

My VERY first attempt at a YouTube video addresses this.

https://youtu.be/XxurqdJibA0

[Gary B.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Rich,

Very cool!

Gary

[Chris H.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Rich,very informative. Nicely done.

[Joe R.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

My VERY first attempt at a YouTube video addresses this.

https://youtu.be/XxurqdJibA0

Each NCRS member should be required to view this video or sell their Corvette!
It answers the age old statement (I know my Corvette is Original) cause I'm the 6+ owner!

Thanks Rich,

JR

[Mark F.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

Interesting video.

But...

1. What is the hole for if it is not for a safety wire?
2. If it is for a safety wire, what is the wire wired to after it goes thru the "safety hole"?
3. If it's not for a wire, how is a hole in a bolt functioning as a safety feature?

[David L.]

Re: Question about an Original Harmonic Balancer Bolts with "TR" marking

I have the same questions as Mark.
I have 6 original Harmonic balancer bolts with various marking on the bolt heads but none have the hole for the safety wire. Most of the large
1 3/4" diameter washers are not stamped except for 2 of them that are shown in the photo below. The washer on the left has the "S" stamped on it while the one on the right has the "MCS" stamping.
BTW, very interesting video.
Dave

[Gary B.]

most of the original production-line balancer bolts had a safety-wire hole, and so did the Service replacements, until about 20 years ago.

Gary