Motor mount bolts

[Tom L.]

When I removed the mounts there was an assortment of bolts in both the block and onto the frame. Does anyone know what are the correct lengths of each and what the appropriate head markings are??? I have a bunch of stray bolts and was hoping some might match. Thanks!!

[Joe L.]

Re: Motor mount bolts

When I removed the mounts there was an assortment of bolts in both the block and onto the frame. Does anyone know what are the correct lengths of each and what the appropriate head markings are??? I have a bunch of stray bolts and was hoping some might match. Thanks!!

Lynn-----


The motor mount-to-block bolts were 3/8-16 X 15/16", black phosphate, and trimmed (i.e. non-"indented") head. I don't recall headmarkings. I'm sure there were at least several.

The through bolt is 7/16-14 X 4-7/16". It is zinc plated or electro-galvanized and has a trimmed head. It also has a pilot tip.

[Joseph M.]

Re: Motor mount bolts

Joe, is the through bolt also zinc plated for a 67? What type of nut was used on the through bolt? Thanks.

[Alan S.]

Re: Motor mount bolts

Hi,
The original mount to engine bolts on my mid-January 71 are a bit different than you descrbed Joe.
They're indented head with a captive split lock washer.
Did the style of bolt vary over the years?
Thanks,
Alan

[Patrick H.]

Re: Motor mount bolts

Hi,
The original mount to engine bolts on my mid-January 71 are a bit different than you described Joe.
They're indented head with a captive split lock washer.
Did the style of bolt vary over the years?
Thanks,
Alan

I agree Alan - my 71 and 72 are exactly as you have pictured including same headmark.

Patrick

[Joe L.]

Re: Motor mount bolts

Joe, is the through bolt also zinc plated for a 67? What type of nut was used on the through bolt? Thanks.

Joseph------

I'm not sure of the finish on the 1967 bolt. It was shorter than the 70+ bolt due to the fact that the pre-1970 engine mounts were of the non-locking variety. I'm not sure about the nut but I think it was a zinc-plated, lock nut.


ADDENDUM: From what I can determine from specs, the nut used for the through bolt was a 7/16-20 slotted locking nut, zinc plated, and 11/16" across-the-flats (wrench size). A slotted locking nut is a rather unusual configuration on GM cars. This nut was used through 1969 but not thereafter.

[Joe L.]

Re: Motor mount bolts

Hi,
The original mount to engine bolts on my mid-January 71 are a bit different than you descrbed Joe.
They're indented head with a captive split lock washer.
Did the style of bolt vary over the years?
Thanks,
Alan

Alan-----


I was incorrect on my description of the bolts. My recollection was that they had a trimmed head but on further checking I find the GM #3748038 did have an untrimmed ("indented") head. They also did have the captured lockwasher. Of course, the captured lockwasher is a PRODUCTION-related convenience. For a restoration it's not necessary to use a bolt with a captured lockwasher. No one will ever know that the bolt and lockwasher are not an assembly.

[Alan S.]

Re: Motor mount bolts

Hi Joe,
Thanks for the reply.
I was curious because I DO value your knowledge on parts, fasteners, and finishes!!!!
Regards,
Alan

[John H.]

Re: Motor mount bolts

ADDENDUM: From what I can determine from specs, the nut used for the through bolt was a 7/16-20 slotted locking nut, zinc plated, and 11/16" across-the-flats (wrench size). A slotted locking nut is a rather unusual configuration on GM cars. This nut was used through 1969 but not thereafter.

Joe -

As I recall, those were Marsden nuts, and that was the only Corvette application for that unique style of locking nut; they were also found on many 1st-generation Camaro and Chevy II rear leaf spring rear shackle plate bolts.


MarsdenNut3.jpg

[Patrick H.]

Re: Motor mount bolts

Joe -

As I recall, those were Marsden nuts, and that was the only Corvette application for that unique style of locking nut; they were also found on many 1st-generation Camaro and Chevy II rear leaf spring rear shackle plate bolts.


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Mine are the "deformed thread" nuts that are sort of shaped like a triangle internally.
I'm sure there is a proper name for them.

The same style is used to hold the power brake booster to the firewall on the inside. Worst nuts to remove on the whole car.

Patrick

[Joseph M.]

Re: Motor mount bolts

Thanks for the info re the nut. Does anyone have a comment on the finish of a through bolt for a 67?

[Joe L.]

Re: Motor mount bolts

Mine are the "deformed thread" nuts that are sort of shaped like a triangle internally.
I'm sure there is a proper name for them.

The same style is used to hold the power brake booster to the firewall on the inside. Worst nuts to remove on the whole car.

Patrick

Patrick-----


They are called stover type lock nuts. 1970+ Corvettes used this style lock-nut on the through bolts. These are 7/16-14 whereas earlier used 7/16-20 slotted locking nuts.

[Joseph M.]

Re: Motor mount bolts

Does anyone know what finish is on the through bolts?

[Joe L.]

Re: Motor mount bolts

Does anyone know what finish is on the through bolts?

Joseph------


I'm pretty sure the GM #3817224 bolt used for most 63-69 was zinc plated, just like the longer 70-82 bolts. However, I'm not 100% sure as the 3817224 was never available in SERVICE.

By the way, 1965 with L-78 used a different bolt----GM #3832465. Why? Well, it probably had something to do with the fact that application was also supposed to have used unique, side-specific motor mounts. How were the mounts and bolt different? I do not know and neither the mounts nor the bolt were ever available in SERVICE. Were these parts actually used in PRODUCTION? I do not know that, either.

[Joseph M.]

Re: Motor mount bolts

Joe, thanks for the info.