455 exhaust manifold monster

[the_boat]

I have a 74 98 that is in the shop once again for both sides blowing out the exhaust manifold gaskets. I have replaced the thermostat to a mid-range (160 degree, I think) and replaced the fan clutch. Is there anything else that I should look for, replace, try, etc? I love my baby, she is in great shape (original paint and still looks good), but my pockets aren't that deep to keep taking her in every two or so years to get the exhaust manifold leaks fixed. Sometimes it is one side, while others it is both. The previous owner mentioned they "fixed" the problem about 12 times: I am on number eight. She likes to warp them and go through the exhaust manifolds if I let the problem go too long. She is just driven locally now and no long trips (over 1 hr) because she can over heat in the summer with the a/c on, and I am so paranoid about blowing the gaskets over and over. Will someone help me please?

[J-(Chicago)]

If your timing is too far retarded your exhaust will run hotter.
I'm only on my second set of gaskets

[the_boat]

Thanks. I will look at that as well!

[Rallye469]

-What kind of gaskets are you using? (paper/metal)
-Do you torque, then re-torque your manifolds?
(then check them every month or so-they're not hard to get to)
-have you thought of new manifolds or even headers?

Can you lay a straight edge across either the block or the manifold surface?

[Oldsmaniac]

Hmmm...Do you know that the factory did not use gaskets on the exhaust manifolds? It was a metal to metal fit on the head. To blow gaskets it is possible the bolts are not tight enough or are coming loose. You can also buy a solid copper gasket that should not fail as easy as the metal fibered ones. You could try and have your manifolds milled smooth and dont use any gaskets.

[joe_padavano]

As noted, factory manifolds did not use gaskets. First, have the manifolds inspected for cracks. Second, have them checked for flatness and ground if necessary. Third, use a straightedge and feeler gauge to check the exhaust flange surface of the head for flatness. Finally, if all is good, install the manifolds without gaskets. Torque the bolts per spec. Use the factory style lock tabs to prevent the bolts from loosening. Drive.

[Olds64]

Make sure you fix your overheating problem. Even an older car shouldn't overheat in the summer with the AC on. Unless you live in Death Valley. Or do you mean it just gets really hot inside the car?

[the_boat]

Originally Posted by Rallye469

-What kind of gaskets are you using? (paper/metal)
-Do you torque, then re-torque your manifolds?
(then check them every month or so-they're not hard to get to)
-have you thought of new manifolds or even headers?

Can you lay a straight edge across either the block or the manifold surface?

I have tried paper, copper, metal, and about anything out there as well as no gaskets. I admit, I have not been as keen as I probably should on the upkeep on torquing. I have literally been through 4 sets of manifolds since '96. I have toyed around with the idea of headers, but I like my car quiet. I want to feel the engine and hear her roar to life like a sleeper when I romp on the gas pedal. What would you say the pros/cons of headers vs manifolds are?

[the_boat]

I know! I think that may be part of the underlying exhaust gasket problem. No matter how plumb the heads, manifolds, gaskets or not, she still leaks and I fear it is something else that is causing it and I do not know what. I fear to think of the damage other places the years of getting too hot (hot enought to blow the gaskets and not push the exhaust out and away) has done. I am desperate to find the true culprit and not keep band-aiding it.

[the_boat]

I have had no success on finding good exhaust manifolds. Does anyone know where I would be able to get them? The current ones are too warped to be machined and I am having a hell of a time finding them for a 1974 98. It seems like everything is '71 and older or '77 and newer. Why?
Thanks everyone for the help!

[88 coupe]

Manifold surfacing is part of a quality head job. Gaskets are band aids.

Originally Posted by the_boat

........ The current ones are too warped to be machined ........

I do not think that is possible. Sounds more like you found someone who can't, doesn't want to, or doesn't know how.

Look around for a competent shop.

Norm

[VWBeamer]

Is it possible that you have too much back pressure in the exhaust system?

I've had good luck with the copper gaskets, annealed in an oven on other cars. The gasket is heated in an oven to about 400 degree, then left to slowly cool. This makes them soft. The heating/cooling cycles when installed will make them hard again.

[Oldsmaniac]

I doubt the manifolds are the problem since you have tried so many sets already....are you sure the bolts are correct size and correct threads?...Maybe the threads in the heads need to be "chased"....am thinking the bolts are causing the manifold to become loose and causing the gaskets to fail....either that or head surface is bad...

[DennisG.]

You obviously have another problem some where and it`s not the manifolds. I`m guessing it`s the exhaust side of the head is either coroded or who ever is changing the manifolds or gaskets, are not cleaning things very well. Maybe both. If you can afford it and really want to solve the problem I would pull the heads and have the exhaust side milled enough for a clean surface. Probably just have the heads reconditioned while they are off. I`m a firm believer in preventive maintainance. Or, buy another set of heads, J,G, Ga etc, have them reconditioned and have the exhaust side milled. Find another set of manifolds, or machinest, or buy a set of new reproduction WZ manifolds.

[rocketraider]

All 71-4 455 dual exhaust cars used W and Z manifolds. If your car is a factory DE car, that's what it should have. Make sure someone hasn't installed a set of smallblock manifolds somewhere along the line. Those have numbers instead of letters and ports are smaller.

Joe P mentioned the lock tabs. They're aggravating, but they're critical for keeping the manifold bolts tight and not allowing them to back out from heating/cooling cycles. You can get reproductions from Fusick.

[the_boat]

Originally Posted by Oldsmaniac

I doubt the manifolds are the problem since you have tried so many sets already....are you sure the bolts are correct size and correct threads?...Maybe the threads in the heads need to be "chased"....am thinking the bolts are causing the manifold to become loose and causing the gaskets to fail....either that or head surface is bad...

You hit my delima right on the head. Welcome to my headache. I have no idea about the bolts/threads. I do not know how long they have been used on the car or anything. I have no idea about the head surface, but since I am getting so much gracious advice to look at it I will pay special attention to it this time around. Do you happen to know if there are special (dumb question I know ) bolts for the exhaust manifolds or where to get them? I miss my car so much, but I want to be very thorough this time.

[the_boat]

Originally Posted by VWBeamer

Is it possible that you have too much back pressure in the exhaust system?

I've had good luck with the copper gaskets, annealed in an oven on other cars. The gasket is heated in an oven to about 400 degree, then left to slowly cool. This makes them soft. The heating/cooling cycles when installed will make them hard again.

When copper gaskets where on her, those lasted the longest at 2.5 years before the put-put-put came back.

Funny you should ask. I got the casting numbers off of the exhaust manifolds on her now and the LH is from an '81-'85 260, 307, '86-'87 442. No wonder she can't breathe. I didn't bother looking at the RH. I think I may have found some repro exhaust manifolds at Thornton Reproductions. Would anyone mind commenting about them please or directing me to a company where I can purchase the exhuast manifolds. I finally have the correct casting id's.

[the_boat]

Originally Posted by DennisG.

You obviously have another problem some where and it`s not the manifolds. I`m guessing it`s the exhaust side of the head is either coroded or who ever is changing the manifolds or gaskets, are not cleaning things very well. Maybe both. If you can afford it and really want to solve the problem I would pull the heads and have the exhaust side milled enough for a clean surface. Probably just have the heads reconditioned while they are off. I`m a firm believer in preventive maintainance. Or, buy another set of heads, J,G, Ga etc, have them reconditioned and have the exhaust side milled. Find another set of manifolds, or machinest, or buy a set of new reproduction WZ manifolds.

I am a believer in preventative maintenance as well. Whenever a friend needs a ride, who do they turn to -- me because my cars are always running! I have had a close friend give your same advise. Right now, I don't have the fundage to do that but would love to. I have decided that if this current go does not take, then I will start pulling off stuff. I also has a friend comment that my cam might be outta whack due to the years of her not getting all the hot exhaust out from the leaky/warping manifolds. With the cam off, my timing would never be right and it just leads to another cyclical problem. Validation on that thought process please?
I am searching now for a set of repro manifolds. Any comments as to where to go?

[the_boat]

Originally Posted by rocketraider

All 71-4 455 dual exhaust cars used W and Z manifolds. If your car is a factory DE car, that's what it should have. Make sure someone hasn't installed a set of smallblock manifolds somewhere along the line. Those have numbers instead of letters and ports are smaller.

Joe P mentioned the lock tabs. They're aggravating, but they're critical for keeping the manifold bolts tight and not allowing them to back out from heating/cooling cycles. You can get reproductions from Fusick.

I didn't know they made those. For as many problems times this one boat has had this problem I am investing in the lock tabs.

Regarding the small block manifolds, see reply post below. (I was so irritated when I found that out!).

[Oldsmaniac]

The bolts should be 3/8 16 which is a coarse thread. They are about an inch and a half long I believe. The bolts should tighten and remain tight and have threads all the way or enough threads so they dont bottom out before getting tight.

[the_boat]

sweet. you are awesome. thank you!