VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 39 Exhaust Manifold

My exhaust manifold has two bolts - one on each end of the manifold set bolting it to the engine in addition to the bolts, washers and "do-hickies" attaching the manifolds to the engine. Can't remember the name of the do-hickies...

My question - Are the bolts correct? I've looked at a number of 6 cyl motors from 39 thru 61 - some have bolts like mine (1948), some have treaded studs with brass nuts, some have treaded studs that aren't long enough for nuts (1959), and some have studs with no treads sticking out of the manifold like a pin (1961).

Which are correct and specifically which is correct for 1939?

The 1939 has studs with nuts on the ends and bolts at the other locations. Around 1949 the ends got dummy locating studs and no nuts.
Chevrolet NEVER used brass nuts at any location. Often brass was used by mechaniics for a replacement.

I've checked a couple of books and it's not really clear. Best I can tell is they use studs that are 3/8x1-3/4" USS thread. (16 TPI) Quantity listed is "as required".

My '38 has the studs & brass nuts. Here I'd always thought that was factory original. I wonder what the perceived advantage would be for putting brass nuts at that location?

When I'm looking for the studs, they only seem to be with brass nuts. However, I have plenty of regular nuts. It sure will be a lot easier to reassemble with locating studs, rather than all bolts!

BTW - the two nuts on my exhaust head pipe at the exhaust manifold are brass. Guess that's incorrect...

Yes, Chevrolet used steel there also.

Using brass nuts on the exhaust manifold (complete exhaust system) makes undoing next time easier as the brass doesnt corrode (weld) to the stud.
It isnt factory correct but much easier during future repairs which is the way I look at the situation.
Tony

I find this discussion about the brass nuts very interesting. I can't remember one of my older six cylinders that had anything but brass nuts on the end studs of the exhaust/intake manifold or exhaust pipe studs. That includes some 20+ vehicles.

That got me to do a little research. According to the listings in parts books from 1929 to September 1938 the part number for the nut was 355827. In the August 1, 1939 parts book another nut is listed in group 3.277. For part number 355827 the description reads "Nut, ends to cyl. hd. & exh. flg. stud (3/8"-16 x 5/8" high)". The second part number 838780 is described as "Nut (3/8"-16 x 11/32" thick)". The February 1940 parts book only shows the 838780 number for 1929-40.

My interpretation of the part book listings is that the brass nuts were used through 1938 and beginning in 1939 steel nuts were installed.

So my question would be, why did they stop using a fastener on the outside ends? The previous exhaust manifold on my 38 was cracked, on one of the inner runs. I wonder if clamping down the ends can enhance the probability of a crack developing.

Seems to me that if the head is planed straight and the manifolds are also straight then the end nuts are not needed because the other nuts will be sufficient to draw the exhaust and intake manifolds up tight enough to crush the gasket and, thus, defeat intake/exhaust leaks.

As to the question about the nuts at the exhaust manifold to exhaust pipe flange, take it from Chipper and Gene that we don't really know for sure. Chipper is right about the nut siezing to the studs. If they have been on there more than two weeks (a fortnight forTony and our other friends down under You, too ) then you will wring the studs off if you need to remove the manifold. Don't worry none, though, the machine shop will install new ones and throw in a couple brass nuts to avoid the job in the future.

Charlie