mclark68442

Seeking advice / tips / what to look out for in replacing both LH & RH exhaust manifold gaskets on stock 400 with stock exhaust manifolds on my 68 442. I've developed an exhaust leak on both sides now, LH side has been developing over past couple of years. I was hoping it was the head pipe-to-manifold donut gasket, but inspection on the rack while running at an exhaust/muffler shop tells me it is likely the manifold gaskets. And since it is both sides now, I'm thinking cracked manifolds are less likely.
Can this work be done with engine remaining on it's mounts, and if so is access better from below with car on a rack, or from above, or probably a combination of both?
Any recommendations to minimize breaking a bolt that's frozen stuck? The manifolds have not been removed since the engine was rebuilt 30 years ago. I'm envisioning those manifold bolts being seized well to the block. Hopefully not.

Thanks for any tips, advice. I'll probably take the car to a local shop whose owner used to race a 68 442 for this work, as I know he'll take care and is knowledgeable with it, I just want to know myself some info about the job and what's involved.

66SportCoupe

Simple. Undo all exhaust bolts. Leave outer 2 in. Slip gasket in and reinstall the other bolts. 30 min tops

Sugar Bear

Use Kroil to soak the bolts multiple times on a warm (not hot) engine and let it cool wicking the Kroil in as it cools. Repeat, repeat, repeat...the more soaks the better on the manifold to head bolts and the exhaust pipe to manifold bolts. Patience pays on this job.
​​​
Should have a fire extinguisher nearby when doing this in the unlikely event the Kroil ignites.

Good luck!!!

oldcutlass

Just note there was no gasket there from the factory.

matt69olds

As already mentioned, don’t even attempt to take it apart until you have throughly soaked all the bolts. The “environmental loctite” can easily make a hour long project stretch out for several days when a bolt breaks off.

The factory didn’t use a gasket. They relied on a perfectly machined flat surface to seal the ma manifolds yo the head. After 50plus years, things aren’t perfectly machined anymore!

Hopefully all the bolts come out. Remove all the old gasket, assuming somewhere in it past one was installed. Leave the 2 outer bolts in place, slip a new gaskets in, and reinstall. You can replace the gaskets with the engine on its mounts, without much hassle.

Greg Rogers

This is true, if you are working on your 68 in 1968, not 53 years later. Expect bolts to be shrunk, I hammered on a 13mm socket to get some loose, and then replaced with high quality new 3/8 bolts. If is goes easy you can definitely do it in car, but if siezed/shrunk bolts then be ready for a project. Let us know how it goes!

acavagnaro

Since you're effectively removing the exhaust manifolds anyway, I would highly recommend you check the mating surface for flatness before just dropping in gaskets. There's a reason you have leaks now after the rebuild 30 years ago. There are many reasons why the sealing surfaces may no longer be flat and new gaskets may not solve your real problem.
If they are warped (manifolds, not heads), a machine shop can skim the surface to level them back up easily/cheaply. If the bolts are tight, the only reason you would have leaks are if they're no longer flat or if you've developed cracks.