Exhaust gasket straight eight

[Guest sherlok]

Hi folks,

It appears that I'm going to have to replace an exhaust gasket on my 47 Roadmaster. It's leaking toward the front of the engine and getting worse.

Any surprises I should be prepared for. I understand the manifords are prone to warp over time. I also don't want to break a bolt or something.

Any sage advice would be appreciated.

Thank you,

[Bill Stoneberg]

They usually warp from ham fisted mechanics cranking down on the nuts that hold them on. Tighten from the middle out a little at a time. After running it for a bit, recheck the torque.

I never have a problems getting them off but if they haven't been off for a while you might want to use some please PB Blaster. Be careful, you dont want to break the studs. If you pull the studs out, you can get them at Ace Hardware.

[Guest Straight eight]

Also do NOT remove them if you have been running the engine. To be safe wait 24 hours after running the engine to remove them. Gentle is the word when installing. One crack and its trouble. <img src="http://forums.aaca.org/images/graemlins/tongue.gif" alt="" />

[Guest sherlok]

Thanks guys for your help. We'll give it a try.

Regards,

Sherlok

[Bill Stoneberg]

Here is a quote on how to do it......

David Corbin provided this

Dear JBoros:

The big series Buicks started in about 1933 with 3 piece exhaust manifolds as the cast iron of the time couldn't stand the heat over a 30+inch length and cracked in all kinds of places. The 3 piece exhaust manifold as used on the 1936-1952 320 engine improved the situation considerably, but it's still not great. The usual point of failure is in the center manifold section, where it splits parallel to the length of the engine. This is caused by swelling of the end pieces as they heat and cool. What I have done quite successfully is to buy a new NODULAR iron center section, (Skip Boyer or CARS) very carefully eliminate the sharp machined corners with a small radius both inside and outside of the holes where the front and rear sections fit in. (The sharp corners are where cracking starts.) I then carefully grind down the slide-in part of the front and rear sections so that it slides in as a snug hand fit. (Care and Patience REQUIRED on this!!) Be sure to check the operation of the heat riser flap valve. As I'm ready to assemble it to the engine, the center section is already bolted to the intake manifold, the end pieces have been coated with high temperature sealer and inserted into the center sections, adjusted by hand to an approximate fit and the new intake and exhaust gaskets put on the little rings inserted into the head and everything already cleaned of old gasket material. Put the assembly on, adjust everything to a snug FINGER tight position and tighten from the center out, alternating from the front of the engine to the back of the engine and tighten in several steps of about 1/4 of a turn of the nuts or 10 ft-lb of torque increments per step, just like putting on a straight 8 cylinder head. This will get you a lasting fix on the exhaust manifold problems. I hope this description doesn't scare you, but this addresses ALL the problems with the original design and the original cast iron materials.

Regards, Dave Corbin

[Fred Rawling]

You should check the intake/exhaust port side of the head to see if it is straight. Also check to see if the exhaust manifold is straight. It may be advisable to have a machine shop do a clean up cut on them to be sure that they mate together properly. If you put on a new set of gaskets and they blow, this is something you should seriously consider

[Guest sherlok]

Thanks Fred,

I went ahead and pulled everything and discovered that the center section had indeed cracked fore and aft and someone had brazed it back together very out of round. No way to get a good seal. Since a reproduction center section from Bob's is $300.00, I figured I had some room to try to repair the original. Asking around I located a top-notch machinist who says he can remove the brass, reweld and fit it to the other sections. After seeing some of his work, I'm confident he knows what he's doing. When he's done we may have to level everything up before re-installing. The head surfaces look good.

In the meantime I'm doing a few things I've postponed like sending the heater control out for overhaul, repainting the engine, etc.

I haven't done this much mechanicing since my hot rod days in the early 60's.

Regards,

Sherlok

[Guest DaveCorbin]

Dear Sherlok:

I'm glad you found a machinist you have confidence in, but I think you're wasting your money. The problem is in the basic Buick cast iron material, which he can't change and a design that needs more strength in a critical area, which he also can't change.

Regards, Dave Corbin

[Guest DaveCorbin]

addendum.

Dave Corbin

[sledheader 48381]

Bobs in Ca. is now selling a copperclad manifold gasket, their not cheap but are worth the money.

Don