Spark Plug and Compression Test Talk and Evaluations

[HotRodPC]

i prefer to do things once, and know whats wrong with it. bring the cylinder to TDC, install leakdown tester, apply shop air. you now know what is bad, and how bad it is. it will diagnose a lower end problem, a head gasket, and valve to seat seal all in one shot, and tell you how bad it is. i was always told to work smart not hard, if you're running a dry compression test, and a wet compression test, the leakdown tester is already ahead of the game. now throw in a leaky valve or a bown head gasketl, and you have more diagnostic work to do, where the leakdown tester is done.

You're right, but the average shade tree mechanic, or your average DIY guy doesn't have a leak down tester. But, I can usually be right, just from experience, a compression tester and vacuum guage. Sometimes I can even tell with just a vac guage and don't need the compresssion tester.

 

[Irishman999]

You're right, but the average shade tree mechanic, or your average DIY guy doesn't have a leak down tester. But, I can usually be right, just from experience, a compression tester and vacuum guage. Sometimes I can even tell with just a vac guage and don't need the compresssion tester.

Your like the Chuck Norris of square body repairs Hotrod.

 

[RetroC10Sport]

Hence my sig addition...

 

[HotRodPC]

Your like the Chuck Norris of square body repairs Hotrod.

Hence my sig addition...

hahahaha, You guys might be sorry some day. I'm not alwasy right you know. I just throw alot out there, and if wrong, hoping someone corrects the info. Nice to have to the vote in confidence though.

 

[Old77]

I was thinking hrpc was more like Chuck Norris' James Trivett on Walker Texas Ranger

 

[HotRodPC]

I was thinking hrpc was more like Chuck Norris' James Trivett on Walker Texas Ranger

And I don't wipe my ass with 80 Grit sandpaper either.

 

[crazy4offroad]

I checked out GD's link earlier in the thread, he's got a cool how-to on how to make your own leakdown tester. One of the main reasons more people run a regular test as opposed to a leakdown test is the expense of the tool, or dont own an air compressor. And for the record I always heard 150 psi was the baseline for a new or newly rebuilt engine, regardless of CR.

 

[GreaseDog]

You're right, but the average shade tree mechanic, or your average DIY guy doesn't have a leak down tester. But, I can usually be right, just from experience, a compression tester and vacuum guage. Sometimes I can even tell with just a vac guage and don't need the compresssion tester.

then they need to go down to your local chain auto parts store, and get the one they have in their loan a tool program... costs nothing, other than the deposit, which you get back when you take it back.

 

[GreaseDog]

I checked out GD's link earlier in the thread, he's got a cool how-to on how to make your own leakdown tester. One of the main reasons more people run a regular test as opposed to a leakdown test is the expense of the tool, or dont own an air compressor. And for the record I always heard 150 psi was the baseline for a new or newly rebuilt engine, regardless of CR.

too many variables for what the peak cyl pressure should be in static compression, and cam profile variations. one engine could be good @ 140, while another is trash @ 210. the leakdown test will give you a definite number on the percentage of leakdown. by putting 100psi through the orifice, the second gauge will show you a drop in pressure. if the second gauge reads 85psi, you have 15% leakdown, period. and by listening to where it is escaping, you can pinpoint your issue.

 

[89Suburban]

 

[Old77]

You guys are definitely talking way over my head now...

 

[89Suburban]

You guys are definitely talking way over my head now...

The little guy mirror sig thing is getting old dude....

 

[HotRodPC]

Still I see your point GD. I think its just a matter of preferance. If I ever felt stumped, or I thought a tear down could be avoided to fix a problem, I'd sure use your method, and waste my time, gas and energy to go get a loner leak detector. You are also right about the variable on static compression and if I did have a big cam motor that I was diagnosing, that had alot of valve overlap, then yes, to get a proper diagnosis, I'd likley choose the leak down tester for the purpose of doing the leak test with both valves closed, this way you are working around the dynamic compresion factor and any valve overlap or intake valve still being open at the time of compression stroke. For stockers, I'lll likely stick to what have I have done for years and been correct 98% of the time.
Just curious. Do you think a leak down test can ever be wrong? And if so what scenario would can it be wrong? I'll just tell you it can be wrong in the right scenario, and I have seen someone make a wrong diagnosis using a leak down tester.

 

[89Suburban]

Fixed the broken spark plug.

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[RetroC10Sport]