Non-traditional leak down test?

Mac_49

Mac_49

Member
Hey all, so I have a racing friend that asked me about a test I'd never really heard of and wanted to get your opinion.
He was told to take the head off, have it upside down with the spark plug in it and pour gas into the combustion chamber. After about an hour (maybe less) he could feel gas on the intake and exhaust ports (not much but some). Basically he's wondering if this is a valid test for leakage? Note: this was done on a new head that hadn't been run yet.
Thanks for the help!
 
Valve seal was tested that way for years, it really does not give you the information or sense of leakage the leak down tester shows. The cost of a leak down tester is soon consumed by gaskets when you need a quick diagnoses.
 
Kart43 said:
Valve seal was tested that way for years, it really does not give you the information or sense of leakage the leak down tester shows. The cost of a leak down tester is soon consumed by gaskets when you need a quick diagnoses.
Click to expand...

Is it accurate enough in these heads to consider a "leak"?
 
Look at it this way.
What is the pressure in the combustion chamber (when the spark plug has fired ant 30* BTDC and a millisecond later) when the piston is 10* ATDC?
What is the pressure on this gasoline poured in the combustion chamber?
What is thinner Gasoline or air?
 
Jimbo said:
Look at it this way.
What is the pressure in the combustion chamber (when the spark plug has fired ant 30* BTDC and a millisecond later) when the piston is 10* ATDC?
What is the pressure on this gasoline poured in the combustion chamber?
What is thinner Gasoline or air?
Click to expand...

To your point...if gasoline is able to seep through at normal atmospheric pressure then it sure seems like it'd definitely leak through once under compression. On the contrary, under compression, you could argue that extra force is helping seal the valves and there be no leakage which could make the test results seem false. That's why I'm curious if it's an accurate test to consider or not. I'm only trying to help someone that wanted me to present it to you guys. So no offense but your answer does me no good.
 
To answer your question it does not indicate head gasket leak (not uncommon on these engines) it does not indicate ring seal. It is not an easy test to do, it shows a gross leak quickly but a small leak takes time to appear. especially on the exhaust side as the solvent gets absorbed in the carbon and is hard to detect. I used to wad up a rag with a piece of fuel ine shoved into the port and the blow as hard as I could if bubbles appeared I knew I had a leak.
 
I would agree with the previous two posts.
It might give you a "general idea" if the valve is sealed, no differently than shining a flashlight over the valve & seat and looking inside the port for light, but it is not nearly as accurate as a good pressure test.

Now, if we're going to argue cylinder pressures under combustion; how many psi is that? Shouldn't we then test with an equal pressure?



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Thank you thank you for the answers. I suggested to just do a normal leak down test with a gauge but thought I'd definitely ask about this "method". I wasn't aware of it but can definitely say I'm happy to have learned about it with some insight!! Thanks again everyone!!
 
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