Info on exhaust manifold gasket fix?

[CCCC]

All of these old small and large blocks with high miles and have never blown or had to replace an exhaust gasket until now after a recent 4000 mile trip in 1972 C30 Motorhome - engine is 402BB with 108k miles. The leak is at the front end of the passenger side manifold.

I have purchased the supposed "heavy duty" (leaded?) Fel Pro gasket set at NAPA and am getting ready to go at it.

Are there any cautions about what not to do or any old tricks to make this go well? What should a guy use on the bolts to make sure they loosen properly without breakage? Any cautions about lining up the new gasket?

And, any ideas on why the gasket might have gone out? Should I be looking for possible manifold warpage after all these miles? Is there any chance that 1000 miles with a minor, but progressivly bigger, leak at that place could cause valve deformation? The outside air temps were warm.

Just being cautious on a first-time fix. Thanks for any info.

[silverstreak]

Are you sure it's the gasket? I'd keep an eye out for a cracked manifold as well.

It's kinda hard to get penetrating oil to the bolt threads, but it's worth a shot and can't hurt anything.

As far as breaking off the bolts, it's kinda like rolling dice sometimes with exhaust manifolds. I definitely reccomend using a 6 point socket instead of a 12 point.

I like using a breaker bar and giving the handle a few raps with a metal hammer (in the direction of removal). It saves my knuckles, back and helps to "shock" the rust loose a bit.

As far as lining up the gasket, you can use two short pieces of all thread ( about the length of the bolt) and file (hacksaw) a slot in one end to accept a flatblade screw driver. Install them in the two outermost bolt holes in the head finger tight. Install the gasket then manifold and hold it in place using the 4 center bolts. Using a flatblade screwdriver, remove the two pieces of allthread from the outermost holes and reinstall the outer two bolts. Tighten all the bolts to proper torque using the proper sequence. This method is not required, but can help in certain situations.

[CCCC]

silverstreak, thank you. This is exactly the kind of experienced info that helps.

Am rather certain that it is a blown gasket - leak came on very gradually and have used the "listening hose" method to identify the precise location - and actually can see/feel the remaining loose shreds of gasket on the top side. Of course, will thoroughly check the manifold for cracks. etc. when it is off the head.

Most of the concern is about removal of the original bolts - they never have been out of there - and really do not wish to deal with a broken bolt. I will do the usual soaking with PB Buster or such with occasional tapping to try to work the stuff down along the threads, but had not thought about the 6 pt. vs. 12 pt. issue. Good idea. Usually I do a good bit of tapping and easy persuasion (like rapping the breaker bar) before putting the muscle to task. The all-thread technique makes perfect sense. Thanks again.

If one (or more) of the bolts twists off I probably will be back here for more advice.

CCCC

[geezer#99]

Another tip.
When you loosen the bolts alternate from loose back to tight when removing them. Loosen a bit then snug em back up a hair. That lessens the chance of galling the threads or breaking a stud off. If it gets hard to loosen then tighten back up and try to loosen again.

[1-PU70]

Well the SB did not come with an exhaust gasket from the factory. I dont know about the BB but probably not. As far as getting a good seal take the exhaust manifolds to the machine shop and have them but a nice surface on them. The last ones I had done they just put them on a big belt sander and it gave them a nice true surface. I have never used exhaust manifold gaskets and have never had a problem. Good luck.

[dwcsr]

Originally Posted by 1-PU70

Well the SB did not come with an exhaust gasket from the factory. I dont know about the BB but probably not. As far as getting a good seal take the exhaust manifolds to the machine shop and have them but a nice surface on them. The last ones I had done they just put them on a big belt sander and it gave them a nice true surface. I have never used exhaust manifold gaskets and have never had a problem. Good luck.

I agree. I don't use gaskets for exhaust unless there is a problem with the manifold or head. I always use Red RTV and rarely have a leak

[CCCC]

Thanks geezer#99 for the added advice on old bolt removal - now that you say it, seems like my smart dad told me something like that once, but oh how easy we forget. I have fixed a ton of stuff on these trucks and a lot of other older cars when I was really poor, but never an exhaust manifiold issue.

So, 1-PU70 and dwcsr are adding to my education - seriously - I never noticed the absence of exhaust manifold gaskets on any of the SBCs around here or on other older Chev V8 cars I owned. Because this BB is the first such problem encountered I just figured it was like a lot of other older vehicle heads with gaskets. The fact that the 402 BB originally had none must mean that the one PO encountered a warp or distorion issue with the manifold and used the gasket as a fix.

Thanks again guys. CCCC