A little help with Engine Mount Bolts

[Joseph A.]

I have a 1969 L89 Corvette with 23K original miles. I have owned it for 40 years. I decided to restore the car and I removed the engine and I noticed the engine mount bolts were grade 8 with an H and they had the stover lock nuts on them. Also they seemed to be gray phosphate as opposed to clear cad. Has any one seen this before as I am sure nothing was touched on the car. I am re-plating the hardware and want to plate them the correct color.

[Chris H.]

Re: A little help with Engine Mount Bolts

Joseph, this thread may be of assistance. https://www.forums.ncrs.org/showthre...ne-Mounts-Bolt

[Joseph A.]

Re: A little help with Engine Mount Bolts

There seems to be a change in the assembly manual for the bolt at the end of 1968. I have a January 1969 build so I believe it is the new bolt that was used.

[Ron G.]

Re: A little help with Engine Mount Bolts

I believe the grade 8 is correct. It is my opinion and experience that they were either black phosphate or black oxide. As far a the "H" logo is concerned, there were a number of hardware suppliers and we refer to them as "the family of GM hardware".

[Joe L.]

Re: A little help with Engine Mount Bolts

I have a 1969 L89 Corvette with 23K original miles. I have owned it for 40 years. I decided to restore the car and I removed the engine and I noticed the engine mount bolts were grade 8 with an H and they had the stover lock nuts on them. Also they seemed to be gray phosphate as opposed to clear cad. Has any one seen this before as I am sure nothing was touched on the car. I am re-plating the hardware and want to plate them the correct color.

Joseph------


Does the car have locking or non-locking style motor mounts? What is the length of the bolt? What is the build date of the car?

[Joseph A.]

Re: A little help with Engine Mount Bolts

The mounts I believe were non-locking, the bolt is 7/16-14X3 7/8, it also used a stover nut. Built Jan 21, 1969

[Joe L.]

Re: A little help with Engine Mount Bolts

The mounts I believe were non-locking, the bolt is 7/16-14X3 7/8, it also used a stover nut. Built Jan 21, 1969

Joseph------


Can you see an embossed part number on either side of the thick, rubber portion of the mount?

[Joseph A.]

Re: A little help with Engine Mount Bolts

I do not have the mounts in hand but the car has only 23K miles and I don't think they were changed. What should the mounts look like.

[Joseph A.]

Re: A little help with Engine Mount Bolts

Number is 3886466

[David L.]

Re: A little help with Engine Mount Bolts

Attached is a photo of a NOS 3888488 engine mount of left side of my 6/30/2011 photo.
Dave

[Joe L.]

Re: A little help with Engine Mount Bolts

Number is 3886466

Joseph------


Well, I was hoping that yours might have been a GM #3967767. This is a rather "mysterious" engine mount that was used for a very short time in 1969. It was once available in SERVICE but only for a very short time being discontinued in October, 1969 and replaced by locking style mount GM #3980701. The shame of it is that my original owner 1969 built in mid-September, 1969 probably originally had the 3967767 mounts but, unfortunately, I replaced the mounts with locking style mounts sometime in the mid-70's. If I saved the original mounts, I have no idea now where I stored them. I'd sure like to know how the 3967767 differed from the 3886466. The 3967767 was definitely a non locking style mount as I had to modify my lower RF ignition shields when I installed the locking mounts.

The through bolt was also changed during 1969. The first bolt was the GM #3817224 which was used from 1963-E1969. This is the zinc plated, GM 300-M (SAE grade 5). This changed sometime during 1969 to bolt GM #3958007. This is likely the bolt you have. It was never available in SERVICE so finding an NOS example is impossible. The 3958007 would have needed to be about the same length as the 3817224 and that's as you describe the length of your bolt. So, the two bolts differed by material grade and finish.

The AIM does not indicate a change in the nut used during the 1969 model year and shows only the GM #272876 which is the slotted type (marsden) locking nut. However, for 1970 the nut changed to GM #9422299 which is a distorted thread type (stover) locking nut. Since your car was apparently built with this type nut, the change from the 272876 to the 9422299 must have occurred much earlier than 1970 and, in fact, fairly early in the 1969 model year.

[David L.]

Re: A little help with Engine Mount Bolts

Attached are 2 photos of the NOS engine mount bolt, washers, and nut that I removed from a NOS 3980701 engine mount.
I assume the bolt is GM # 3958007, 7/16-14 X 4 7/16" (grade 8) with "R", "S", "C"" on the bolt head but this was wrong. The bolt is GM # 399803.
Dave

[Joe L.]

Re: A little help with Engine Mount Bolts

Attached are 3 photos of the NOS engine mount bolt, washers, and nut that I removed from a NOS 3980701 engine mount.
I assume the bolt is GM # 3958007, 7/16-14 X 4 7/16" (grade 8) with "R", "S", "C"" on the bolt head.
Dave

Dave------

The bolt could not be a GM #3958007. That bolt had to be shorter because it was used with non-locking style motor mounts. The bolt you have pictured is almost certainly a GM #399803. That is the bolt that was supplied with the locking style mounts and used in PRODUCTION for 1970-82 Corvettes. I posted a photo of an NOS GM #399803 in a recent thread and it is identical to the bolt you pictured even down to manufacturer's headmarking.

[David L.]

Re: A little help with Engine Mount Bolts

Dave------

The bolt could not be a GM #3958007. That bolt had to be shorter because it was used with non-locking style motor mounts. The bolt you have pictured is almost certainly a GM #399803. That is the bolt that was supplied with the locking style mounts and used in PRODUCTION for 1970-82 Corvettes. I posted a photo of an NOS GM #399803 in a recent thread and it is identical to the bolt you pictured even down to manufacturer's headmarking.

Joe,
You are correct. The bolt is GM # 399803, 7/16"-14 X 4 7/16".
I believe that the nut is GM # 9422299, l7/16"-14 lock nut (distorted threads), grade 301-M, Type EA as listed in my 1969 Chev. Parts Catalog in GR. 8.917.
I believe that the washers might be be GM # 9419276 as they measure 0.91" O.D., 0.49" I.D., 0.07" thick.

BTW, I removed the 1st photo with the tag that had the wrong part numbers.

Dave

[Joe L.]

Re: A little help with Engine Mount Bolts

Joe,
You are correct. The bolt is GM # 399803, 7/16"-14 X 4 7/16".
I believe that the nut is GM # 9422299, l7/16"-14 lock nut (distorted threads), grade 301-M, Type EA as listed in my 1969 Chev. Parts Catalog in GR. 8.917.
I believe that the washers might be be GM # 9419276 as they measure 0.91" O.D., 0.49" I.D., 0.07" thick.

BTW, I removed the 1st photo with the tag that had the wrong part numbers.

Dave

Dave------


The nut is definitely a GM #9422299.