1970 Corvette Q-Jet bolts

[D S.]

Some time back there was a discussion here about the long bolts on 1970 Q-Jets and having the built in washer. I didn't read anywhere as to the headmarks on them and I assume there were more than one manufacturer of them. I have two pair of them with one pair having a P headmark and the other a C headmark. Are these the ones being referred to as being correct for 1970 Corvette Q-Jets?

[Alan S.]

Re: 1970 Corvette Q-Jet bolts

Hi Scott,
As a matter of comparison; a few months ago I put the original Q-Jet back on my 71 350/270. I found the bolts to have a 'P' head mark with 3 slashes; the head flared out in the shape/size of a washer.
If only I'd bagged a couple of other parts I took off the car in 1971.
Hope this helps in some way.
Regards,
Alan

[D S.]

Re: 1970 Corvette Q-Jet bolts

Thanks, Alan. It does! The archive discussion here previously went into detail about the appearance, length, thread size, head configuration, etc but no mention of any specific headmarks. There was a photo posted of a carburetor with those type bolts but I could not see details. I asked a friend in Oklahoma who makes his living in salvage yards if he could find those bolts. He found two pair for me off of '70s GM cars. He said they were hard to find as most of the vehicles were devoid of carburetors. I would have guessed that the C headmark would have been used but since I also have a pair with the P headmark I may use those. I guess it really doesn't matter which.

[Clem Z.]

Re: 1970 Corvette Q-Jet bolts

i have seen those flanged bolts on GM cars BUT never on chevys including corvettes. when i rebuild those carbs i always give the owner 2 SAE washer to put under the front bolt heads to keep them from cutting into the casting. JMHO

[D S.]

Re: 1970 Corvette Q-Jet bolts

i have seen those flanged bolts on GM cars BUT never on chevys including corvettes. when i rebuild those carbs i always give the owner 2 SAE washer to put under the front bolt heads to keep them from cutting into the casting. JMHO

Clem, from a post dated November 2008 by Lyndon Sharpton and Joe Lucia's response:

Lyndon-----


Here's the deal: 1970 Corvettes with Q-Jet carbs used unique-to-that-year front retaining bolts for the carb. These were special bolts of GM #3967476. These bolts were 5/16-18 X 3-5/8". They had a flanged (washer) head. I do not know the material grade, finish, whether or not the head was trimmed or untrimmed, and what the across-the-flats (wrench) size was for these bolts.

So, why did they use these bolts for 1970? Well, it had to do with the NA-9 (California emissions) option. For cars equipped with this option, the front carb bolt holes were equipped with insulators. I expect that to improve retention of the insulators, the flanged head bolts were used. However. perhaps to simplify things, the same bolts were specified for all Q-Jet applications and not just those equipped with NA-9.

For early 1971, these bolts were replaced by GM #9432450. These are, from what I can tell, very similar bolts except that they are 3-3/4" long. They have a flanged head, phosphate finish, GM 280M material grade (SAE grade 5--3 lines), and untrimmed ("indented") head. I believe these are also the bolts used on the Oldsmobile applications that clem referred to.

In later 1971, these bolts were replaced in PRODUCTION by GM #9419047. These bolts are the same thread size and length as the 9432450. However, they are a NON-flanged head bolt. They were phosphate-finished and of GM 280-M material grade. I do not know if they had trimmed or untrimmed heads.

Why GM went back to the non-flanged head bolts during 1971 or why they ever used them for 1968-69 Q-Jets, I will never know. I TOTALLY agree with clem; the flanged head bolts should ALWAYS have been used with Q-Jets to avoid damage to the carb air horn. It was a DUMB thing for GM to use non-flanged head bolts for this application----just as dumb as using non flanged head bolts for small block intake manifolds and non-flanged head bolts for head bolts on both small and big blocks. DUMB!

By the way, all of the above-referenced bolts are discontinued and, as far as I know, not reproduced.

[Clem Z.]

Re: 1970 Corvette Q-Jet bolts

could this have been when oldsmobile switched to chevy engines ???

[D S.]

Re: 1970 Corvette Q-Jet bolts

Could be that 1970 Corvettes had those type bolts installed that year although Alan Struck reports that the original bolts on his 1971 Corvette are like those.

[Joe L.]

Re: 1970 Corvette Q-Jet bolts

could this have been when oldsmobile switched to chevy engines ???

clem------


That happened quite a bit later. In fact, the Oldsmobile engines were actually used in cars for much longer than I once thought. In any event, the first year for Chevrolet V-8 engines in Oldsmobiles was 1977. However, Oldsmobile V-8's continued to be used in some Oldsmobiles at least until 1981.

By the way, I still say that Chevrolet's use of the non-flanged head bolts on most Q-Jet applications was DUMB. TOTALLY DUMB.

[Dave S.]

Re: 1970 Corvette Q-Jet bolts

clem------


That happened quite a bit later. In fact, the Oldsmobile engines were actually used in cars for much longer than I once thought. In any event, the first year for Chevrolet V-8 engines in Oldsmobiles was 1977. However, Oldsmobile V-8's continued to be used in some Oldsmobiles at least until 1981.

By the way, I still say that Chevrolet's use of the non-flanged head bolts on most Q-Jet applications was DUMB. TOTALLY DUMB.

FWIW, I've seen a lot of Q-Jet Corvettes and never seen one with the "built in washer" on the front bolts. They are typically Grade 5 bolts with varying headmarks and no washers at all.

[Dennis D.]

Re: 1970 Corvette Q-Jet bolts

Some time back there was a discussion here about the long bolts on 1970 Q-Jets and having the built in washer. I didn't read anywhere as to the headmarks on them and I assume there were more than one manufacturer of them. I have two pair of them with one pair having a P headmark and the other a C headmark. Are these the ones being referred to as being correct for 1970 Corvette Q-Jets?

Not the ones on my 70. The washer is almost undetectable being its diameter is the same as the bolt head. Just a machined thin circle at the top of the shaft on the underside of the bolt head When the bolts installed its hard to see. Think there's an "A" on them

[Alan S.]

Re: 1970 Corvette Q-Jet bolts

Hi,
Here's a picture of the bolts on my 71, mid- January build, #6589.
These bolts came off the engine in 1971 and were in the box with the carb until I put the carb back on a couple of months ago. My belief is that they're what was on the carb when it left St. Louis. BUT.... they have been off the engine so.....?
Dave, is this a 'built-in washer' headed bolt?
Regards,
Alan

[Clem Z.]

Re: 1970 Corvette Q-Jet bolts

Hi,
Here's a picture of the bolts on my 71, mid- January build, #6589.
These bolts came off the engine in 1971 and were in the box with the carb until I put the carb back on a couple of months ago. My belief is that they're what was on the carb when it left St. Louis. BUT.... they have been off the engine so.....?
Dave, is this a 'built-in washer' headed bolt?
Regards,
Alan

that is them same as used on oldsmobiles

[D S.]

Re: 1970 Corvette Q-Jet bolts

Hi,
Here's a picture of the bolts on my 71, mid- January build, #6589.
These bolts came off the engine in 1971 and were in the box with the carb until I put the carb back on a couple of months ago. My belief is that they're what was on the carb when it left St. Louis. BUT.... they have been off the engine so.....?
Dave, is this a 'built-in washer' headed bolt?
Regards,
Alan

That's them! Exactly like those I have. Thanks, Alan.

[Dave S.]

Re: 1970 Corvette Q-Jet bolts

Hi,
Here's a picture of the bolts on my 71, mid- January build, #6589.
These bolts came off the engine in 1971 and were in the box with the carb until I put the carb back on a couple of months ago. My belief is that they're what was on the carb when it left St. Louis. BUT.... they have been off the engine so.....?
Dave, is this a 'built-in washer' headed bolt?
Regards,
Alan

Alan,
Yes, that is a bolt with a built in washer. It may very well be original but it is not what I'm used to seeing.

[Joe L.]

Re: 1970 Corvette Q-Jet bolts

Hi,
Here's a picture of the bolts on my 71, mid- January build, #6589.
These bolts came off the engine in 1971 and were in the box with the carb until I put the carb back on a couple of months ago. My belief is that they're what was on the carb when it left St. Louis. BUT.... they have been off the engine so.....?
Dave, is this a 'built-in washer' headed bolt?
Regards,
Alan

Alan------


That is the configuration of the bolt I would expect on 1970 Corvettes with Q-Jet and early 1971 Corvettes with Q-Jet. I expect the same bolt was used for other 1970-71 Chevrolets with Q-Jet, but I don't know that, for sure.

I do not know if this is a GM #3967476 or a GM #9432450. However, I think they were the same in configuration except for a slight difference in length.