Exhaust doughnut
- Thread starter udidwht
- Start date
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If the donut leaks, the hot exhaust will burn through it. They cannot leak AT ALL and have any longevity.
The old donut has to be totally removed; and sometimes that's a biitch.
First Guess: You need new springs, the old ones have lost tension from heat and age. If you can move them when the nut is tight, they're worthless. The springs are what puts pressure on the flange, to keep it sealed. The idea is that the engine can move--a little--and the springs allow just enough flex in the exhaust system to prevent cracking of manifolds and/or pipes.
Verify your engine mounts, and make sure the engine doesn't misfire. Verify the exhaust hangers. The engine better not be wobbling around on ruined mounts, and the rest of the exhaust system needs to be secured in OEM hangers.
Yes, I suppose if the catalyst is getting plugged there'd be extra exhaust gas pressure trying to blow-through the donut.
Is the ignition timing, and timing advance working properly? Retarded timing makes for ultra-hot exhaust gas.
How about fuel pressure? Lean fuel mix makes for hot exhaust gas.
The old donut has to be totally removed; and sometimes that's a biitch.
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First Guess: You need new springs, the old ones have lost tension from heat and age. If you can move them when the nut is tight, they're worthless. The springs are what puts pressure on the flange, to keep it sealed. The idea is that the engine can move--a little--and the springs allow just enough flex in the exhaust system to prevent cracking of manifolds and/or pipes.
Verify your engine mounts, and make sure the engine doesn't misfire. Verify the exhaust hangers. The engine better not be wobbling around on ruined mounts, and the rest of the exhaust system needs to be secured in OEM hangers.
Yes, I suppose if the catalyst is getting plugged there'd be extra exhaust gas pressure trying to blow-through the donut.
Is the ignition timing, and timing advance working properly? Retarded timing makes for ultra-hot exhaust gas.
How about fuel pressure? Lean fuel mix makes for hot exhaust gas.
udidwht
I'm Awesome
This is a 94 Fleetwood Southwind Storm P3X chassis 454 TBI w4L80E trans.
udidwht
I'm Awesome
I rebuilt the entire ignition system HD ceramic 8.5mm wires, cap, rotor, ICM, pick up coli, ignition coil, MAP, IAC, PVC, Purge valve, Idle control solenoid, O2 sensor (all Delco parts) plugs as well.
No sign of lean condition power is good and no misfire/s. Timing is at 4 BTDC while unplugged.
This particular manifold the donut sits in the manifold steel ring end first with gasket facing down towards pipe. I'll get some pics of it installed.
udidwht
I'm Awesome
Heres a link to a pic of the passenger side manifold/donut...the springs and nuts were replaced 1,607 miles ago. There no movement with them when tightened down. Should they be tightened down 100 percent? I passed all emissions tests done on engine. As of 2 years ago Wa. does not require emissions anymore.
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Frank Enstein
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The springs go between the nuts and the pipe flange.
The idea is to have the same tension hot or cold and allow some movement.
The springs shouldn't be in coil bind but close.
I would back off 1 turn from coil bind and put a jam nut on it so the nuts can't loosen.
The ones I've seen--and it's been awhile--have shouldered studs. The nut tightens against the shoulder, leaving the shoulder length to set the spring preload distance.
If the springs get weak, the preload suffers even at the specified distance.
Point being, you don't "adjust" spring preload. You'd just run the nut down tight on the shoulder and hope the springs are in good condition.
If the springs get weak, the preload suffers even at the specified distance.
Point being, you don't "adjust" spring preload. You'd just run the nut down tight on the shoulder and hope the springs are in good condition.
udidwht
I'm Awesome
I do recall the first time I did this job the old springs had no tension at all when the nuts were torqued down. They could be easily spun and wiggled up/down under the nut.
The springs and nuts now are fairly new 1 year with 1700ish miles on them. Once torqued down 100 percent there is no movement with the springs.
I retorqued them down 100 percent but backed them off 1/8th a turn. Im leaning that I should just torque them down all the way.
The springs and nuts now are fairly new 1 year with 1700ish miles on them. Once torqued down 100 percent there is no movement with the springs.
I retorqued them down 100 percent but backed them off 1/8th a turn. Im leaning that I should just torque them down all the way.
udidwht
I'm Awesome
Went ahead and torqued them down all the way. The springs are good and tight no movement.
udidwht
I'm Awesome
Update:
My return trip from southern Ca. was cut short in Chiloquin, Or. (97 hwy) for a few hours. Damn donut on drivers side this time. This was after replacing both on the trip down in Bakersfield, Ca. Exactly 1072 miles they held up. I had used Fel-pro donuts. Once I had the pipe down the passenger side donut looked great. The drives had about a third burned thru. But the burned area was not on the pipe side it was the outer edge near the manifold. When I installed them in Bakersfield I had noticed they fit rather loose. I had to use a smear of copper paste to hold it in place. I'll post some pics of the donut.
I'm beginning to think it's crap parts. Anyone know the part number from GM? Or how about some pics comparing the GM vs 3rd party brand?
My return trip from southern Ca. was cut short in Chiloquin, Or. (97 hwy) for a few hours. Damn donut on drivers side this time. This was after replacing both on the trip down in Bakersfield, Ca. Exactly 1072 miles they held up. I had used Fel-pro donuts. Once I had the pipe down the passenger side donut looked great. The drives had about a third burned thru. But the burned area was not on the pipe side it was the outer edge near the manifold. When I installed them in Bakersfield I had noticed they fit rather loose. I had to use a smear of copper paste to hold it in place. I'll post some pics of the donut.
I'm beginning to think it's crap parts. Anyone know the part number from GM? Or how about some pics comparing the GM vs 3rd party brand?
