Cracked header repair (Page 2/2)
Joseph Upson OCT 14, 07:26 AM
I doubt there are any problems with the motor unless the OP failed to mention that the engine light is on. Let's not forget that the V6 has a blower motor and supporting duct/tubing to blow cool fresh air directly on that area of the engine bay for a reason. Fresh air has a path up and over the inboard header area thanks to the deck lid vents, which should afford it a better cooled environment than the aft location, although I still suspect there's a crack somewhere in the inboard header also.

Exhaust temps from when I actually ran an EGT sensor were around 1600F on the high side under sustained load, but generally 1-1200ish under moderate driving loads.

These are aftermarket headers, in place of stock manifolds that were also known to crack and shear off exhaust bolts, so this is to be expected in my experience with tubular exhaust manifold runners that are relatively short, with little to no provisions made for stress relief from heat expansion. Tubular manifolds have far less capacity for heat absorption and dissipation unlike the cast iron manifolds, so they will get very hot and stressed when pushed, especially in the Fiero, which is why heat wrap on a manifold of this design without expansion joints is a no-no. I warped cast iron manifolds by wrapping them after all the expanding and contracting worked the bolts loose allowing more movement.

This is an easy fix with a MIG welder. Remove the exhaust gasket, torque the manifold directly to the head with appropriate spacing at the exhaust bolt holes, don't forget to loosen the bolts at the "Y" pipe connection to release the tension from removing the gasket, take the car to a trusted muffler shop if you can't weld and I bet they'll tack weld the crack as needed to hold positioning before removing to complete and if possible, repair it on the car if there is room, if not, it's the easiest of the the manifolds to remove.

If you have an extra cylinder head as already mentioned, that would be even better, take it to someone who can weld and they should be able to fix you right up. This is the approach I used to repair my warped exhaust manifold, I cut it between the exhaust ports while bolted to a cylinder head, welded it back together with flanges flush against the head and used shielding instead of heat wrap, along with studs in place of the exhaust bolts and never had another problem with the exhaust, for the remaining 4 yrs I had the car before selling it.
pmbrunelle OCT 14, 12:11 PM

quote
Originally posted by Joseph Upson:
This is an easy fix with a MIG welder.



I would say a return to a like-new state; not a long-term fix.


quote
Originally posted by Joseph Upson:
These are aftermarket headers, in place of stock manifolds that were also known to crack and shear off exhaust bolts, so this is to be expected in my experience with tubular exhaust manifold runners that are relatively short, with little to no provisions made for stress relief from heat expansion.



Restoring the manifold back to its stock-style state is likely to result in stock-style reliability. Dismal reliability, in other words.

People assume that there's some underlying engine problem behind cracked manifolds, but I think the factory Fiero exhaust design was just marginal.

This is my Fiero:


I suggest bellows on the stock manifolds, and it looks like bellows could be retrofitted to the Sprint pieces.

Here is the Dorman Jeep 4.0 exhaust manifold:


I guess for OP in California, my main concern about installing bellows would be the smog inspection. Maybe this modification would cause the car to fail smog.

[This message has been edited by pmbrunelle (edited 10-14-2020).]

Joseph Upson OCT 14, 03:18 PM

quote
Originally posted by pmbrunelle:


Restoring the manifold back to its stock-style state is likely to result in stock-style reliability. Dismal reliability, in other words.

People assume that there's some underlying engine problem behind cracked manifolds, but I think the factory Fiero exhaust design was just marginal.

...
I guess for OP in California, my main concern about installing bellows would be the smog inspection. Maybe this modification would cause the car to fail smog.




I'm with you all the way, especially with the bellows install which GM FWD crossover pipes have incorporated for a few decades now. Just keep in mind that you are "idealing" in terms of those like you, me and others who can actually perform these modifications ourselves. He was considering JB Weld so modifying the headers to include bellows is quite a jump from that and beyond keeping it simple and functional, considering as manufactured they may have provided several years of proper service before finally having enough. The pics suggest they're about 14 ga steel which is very good for the job it's doing.
DrXtreme OCT 14, 05:56 PM
I remember seeing that on cars back in the 80's. Not sure how thick that tube wall is but looks very thin. You may weld the cracks and stop the leak, but it will likely crack in another spot. Your long term solution may be to go with a beefier header set up.

Dr Xtreme
pmbrunelle OCT 14, 07:24 PM

quote
Originally posted by Joseph Upson:
Just keep in mind that you are "idealing"



Yes, that's right to some extent.


quote
Originally posted by Joseph Upson:
considering as manufactured they may have provided several years of proper service before finally having enough.



Forum member GTDude was a GM dealer mechanic, and he stated he that he did many 2.8 Fiero exhaust manifold replacements (more than on other cars), while the cars were on warranty (3-year warranty?).

So I'm not convinced that a repair without changing anything in the header's design will yield an "acceptable" service life.

Of course this depends on OP's expectations for reliability after the repair.


quote
Originally posted by Joseph Upson:
modifying the headers to include bellows is quite a jump from that



Yes and no... if OP is ready to bring his headers + a head (or RD welding jig) to a local welder/fabricator, it wouldn't be much of a stretch to bring four bellows, and ask the welder to add them in.

[This message has been edited by pmbrunelle (edited 10-14-2020).]