2F intake issues - vacuum leak??!! (2 Viewers)

[crewzerdog]

Previously posted the "symptoms" of my recent cruiser rebuild -- problems with idling after warm up. (here's the link the the previous posts https://forum.ih8mud.com/index.php?board=1;action=display;threadid=15306).

Anyway, seems I might have chased down the problem --the dreaded manifold leak. A "cold" manifold seems to be sealed up 'tight' but once the engine gets to full operating temp the intake must warp enough to leak-- I sprayed starting fluid around the intake and no increase in RPMs except for one area around #1 and #2 cylinders-- definite and immediate response. Yeah, I have retorqued the bolts a few times to no effect. Is this a typical scenario of the intake leak occuring after the engine heats up?

So I guess my options are: 1) to take the thing off and have it 'trued-up' a the local machine shop or 2) give the 'two-gaskets' approach advocated by many on this board a try. From what I've read posted here - having the intake/exhaust machined is not a sure fix -- many folks say they still had to use two gaskets to get a good seal. If using two gaskets do you use some hi-temp 'copper' gasket sealer in between gaskets and on the block/intake sides as well?

What's the advice folks? I would prefer to do this only once...
Thanks for the help!
Tom

 

[IDave]

I forget if you said you have headers or not. If headers, I would go the double gasket route. You might have a shop true it up as well.

If you don't have headers, and I am thinking you don't, I would just have the manifolds milled and forget the 2 gasket approach. It very good sense that a warped manifold would not respond to retorquing and would open up at high temps to me.

 

[crewzerdog]

IDave, no headers - using the stock intake and exhaust set-up including the exhaust pipes from the exhaust manifold out. I'm going to check the vacuum leak with a guage today to see if my theory that it begins to "open up" after the intake gets hot.

Sure hate to pull all of the stuff off - especially after chasing down all the original smog equipment and installing all the vacumm lines.

Any other tips from others in this same spot? Also, if I take it back off wouldn't this be the time to replace all the gaskets inbetween the stock intake/exhaust manifold - i.e. below where the carb mounts?
thanks, Tom

 

[mallred]

Tom, use carb cleaner works just as good chasing down vacum leak with less of a chance of a big boom than with starting fluid. Using the 2 gasket system here with no glue, Myrle

 

[Tinker]

You have to pull the manifold anyway, so check it with a straightedge & have it milled if warped. You'll have to mill the exhaust manifold the same amount unless you can arrange some kind of shims. I installed a MAF 6-2-1 exhaust manifold with an SOR gasket (because it was thicker than MAF's & the original), torqued it, & had no leaks on my 83 FJ60.

 

[fsusteve]

[quote author=IDave link=board=1;threadid=15665;start=msg149025#msg149025 date=1083498621]
I forget if you said you have headers or not. If headers, I would go the double gasket route. You might have a shop true it up as well.

If you don't have headers, and I am thinking you don't, I would just have the manifolds milled and forget the 2 gasket approach. It very good sense that a warped manifold would not respond to retorquing and would open up at high temps to me.
[/quote]

Ditto, I would have a machine shop mill regardless of how good they look, why do it twice?

 

[crewzerdog]

Myrle, yeah - the safer bet is the carb cleaner - had me a little worried using the other stuff but the RPMs really picked up!

Well - confirmed the vacuum leak. I hooked up a vacuum guage to one of the intake hoses and on a cold start the gauge held really steady at 18 in Hg. Truck ran great, idled smoothly. As the tech article says, the vac gauge dropped to near zero and then up to 25 when the gas pedal was depressed but leveled out quickly again at 18 in Hg. No leaks huh?! It's unusually cool here today and the truck stayed on smooth idle for over 10-15 minutes so thought it was time to take it around the block for a drive. Ran great - started to think it "healed itself" - no hesitation, no stall at stop lights,etc. Life is good right -- not quite.. after it got up to full operating temperature the rough idle and stall returned -- hooked up the vacuum gauge again and readings all over the place. :'( That vacuum gauge is the trick - really a great tool and simple.

Next few 'nights' will be a tear down of the truck to take the manifolds to the local machine shop - with luck I'll be back running again this weekend?? Thanks to all for the advice and tips.

Tom

 

[Beehanger]

Myrle, yeah - the safer bet is the carb cleaner - had me a little worried using the other stuff but the RPMs really picked up!

Well - confirmed the vacuum leak. I hooked up a vacuum guage to one of the intake hoses and on a cold start the gauge held really steady at 18 in Hg. Truck ran great, idled smoothly. As the tech article says, the vac gauge dropped to near zero and then up to 25 when the gas pedal was depressed but leveled out quickly again at 18 in Hg. No leaks huh?! It's unusually cool here today and the truck stayed on smooth idle for over 10-15 minutes so thought it was time to take it around the block for a drive. Ran great - started to think it "healed itself" - no hesitation, no stall at stop lights,etc. Life is good right -- not quite.. after it got up to full operating temperature the rough idle and stall returned -- hooked up the vacuum gauge again and readings all over the place. :'( That vacuum gauge is the trick - really a great tool and simple.

Next few 'nights' will be a tear down of the truck to take the manifolds to the local machine shop - with luck I'll be back running again this weekend?? Thanks to all for the advice and tips.

Tom

Gold of a thread.