Dumb question about checking heads

[78waygone]

Umm, so does that mean...I'm...ok?

I know I don't want to pull the heads just yet (re-using my MLS Cometic head gaskets scares me, and they're damn expensive ..at least for my 3800)


Just a FYI for anyone reading...

***This is a Series II 3800 in my '97 GP that I am asking about***

....not that engine design/make/model makes much difference for the question at hand, I just figured I'd throw it out there.

 

[Doober]

I'll be honest, only thing I read regarding a leakdown test was a magazine article. It did say that anything up to around 20% isn't anything to be overly concerned about, because you're never going to have a cylinder that seals 100%.

 

[StreetBu]

Leaks past valves are VERY common. I've never checked mine, but I'm sure they leak. Your trying to seal two pieces of metal with no gasket, It cant be done 100%. The problem you run into is if they are really bad like a burnt valve, bent valve etc. If you do a leakdown test and all cylinders are close in compression and leakage, Dont worry about. BUT you have to do the leak down test to be sure, dont assume they are ok...

 

[Dyno Donny]

A quick check with the heads assembled is to turn the head with the combustion chamber up. Put a small amount of fluid around the head of the valve. Blow shop air from the runner side and watch for bubbles. You may see a few but if you see a lot then you have a problem. I do this as a quick check on all of the heads I build. The advantage is you see immediately where the valve is leaking at. I tried the vacuum check process and even though it works you still don't know were the valve is leaking. You just know which one is leaking.
Lapping the valve in after blueing the seat sometimes will show the seat to be good. But the air check will show otherwise. Being able to see exactly where the problem is enables us to fix it.
As pointed out don't get to concerned by a small amount of leakage on a head that has been run, it could be carbon or trash between the valve and seat. Tapping lightly on the valve stem with a soft hammer will usually fix this.
BTW I use well over $40,000 worth of equipment and several thousand dollars worth of custom designed profiled cutters (Some of the profiles that we use have as many as 7 angles on them.) to do the best job I can on valve seats.... and a few minutes of the engine running negates a lot of this. :?

Sorry I got so long winded on this Just ignore what you want to.
My wife says that every time someone ask me what time it is... I start trying to tell them how to build a clock.

One other thing as others have said. "The only Dumb Questions are the ones not asked".

 

[Robert1320]

A quick check with the heads assembled is to turn the head with the combustion chamber up. Put a small amount of fluid around the head of the valve. Blow shop air from the runner side and watch for bubbles. You may see a few but if you see a lot then you have a problem. I do this as a quick check on all of the heads I build. The advantage is you see immediately where the valve is leaking at. I tried the vacuum check process and even though it works you still don't know were the valve is leaking. You just know which one is leaking.
Lapping the valve in after blueing the seat sometimes will show the seat to be good. But the air check will show otherwise. Being able to see exactly where the problem is enables us to fix it.
As pointed out don't get to concerned by a small amount of leakage on a head that has been run, it could be carbon or trash between the valve and seat. Tapping lightly on the valve stem with a soft hammer will usually fix this.
BTW I use well over $40,000 worth of equipment and several thousand dollars worth of custom designed profiled cutters (Some of the profiles that we use have as many as 7 angles on them.) to do the best job I can on valve seats.... and a few minutes of the engine running negates a lot of this. :?

Sorry I got so long winded on this Just ignore what you want to.
My wife says that every time someone ask me what time it is... I start trying to tell them how to build a clock.

One other thing as others have said. "The only Dumb Questions are the ones not asked".

X2 for good info.