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#1 |
Registered User
Join Date: Mar 2007
Location: San Pedro River, SE Arizona
Posts: 734
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Info on exhaust manifold gasket fix?
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.
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CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp |
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#2 |
Registered User
Join Date: Mar 2009
Location: USA
Posts: 255
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Re: Info on exhaust manifold gasket fix?
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. |
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#3 |
Registered User
Join Date: Mar 2007
Location: San Pedro River, SE Arizona
Posts: 734
|
Re: Info on exhaust manifold gasket fix?
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
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CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp Last edited by CCCC; 09-25-2010 at 12:19 PM. |
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#4 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: Info on exhaust manifold gasket fix?
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. |
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#5 |
Registered User
![]() Join Date: Apr 2000
Location: Bradenton, FL
Posts: 1,036
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Re: Info on exhaust manifold gasket fix?
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.
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1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters |
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#6 | |
Hollister Road Co.
Join Date: Apr 2005
Location: Houston
Posts: 6,134
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Re: Info on exhaust manifold gasket fix?
Quote:
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#7 |
Registered User
Join Date: Mar 2007
Location: San Pedro River, SE Arizona
Posts: 734
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Re: Info on exhaust manifold gasket fix?
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
__________________
CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp |
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