Leakdown resuts question for the pros

It's a good test. If it was properly done with good equipment you are done.

If the method was wrong or the equipment is faulty doing it over and over and manipulating engine parts will not arrive at a better conclusion.

If there is a doubt have it done by someone knowledgeable with known good equipment.

 

+1

The thing is with these static tests is that since there is no "wind" blowing through the engine all it takes is a little piece of carbon/dirt to become dislodged and cause a valve to hang open just a bit and you have a bad leak down. Crank the motor over again, the garbage fall out and the valve seats correctly and there you have it. It's important to understand that none of these tests are necessarily "one and done". Recall the car that Dr. Bob looked at and decided not to buy. The compression test was repeated several times, with some driving in between, to confirm the bad numbers were not from an erroneous test.

 

A lot of that going on here.

 

What there is a lot of in this thread is people diagnosing a problem from long distance with little though. This thread has gone from "documenting" bad steel guides to potentially bad liners to "it won't hold until the next major before becoming symptomatic" to just abut everything else under the 355 sun. Mean while the dearly departed (from FChat) Dave Rocks and I have been privately encouraging Mark not to panic and to thoroughly diagnose the problem by performing additional tests to verify the results of the initial test, and hopefully a compression test to further diagnose any potential problem. Now we have two additional tests and we have gone from comments like "Do it right, do it now " to "I could not justify taking the motor apart. "

I think it should be obvious exactly what this thread documents.

 

Are you guys taking all the spark plugs out and then doing the leak down test? I mainly work on Porsche 911's but with those engines I put the cylinder on TDC first, then pull the plug only for the cylinder I am testing eliminating any chance of carbon from the spark plug threads falling on the exhaust valve and preventing it from closing fully. I learned this many many years ago, a typical rookie mistake. Any chance this could be happening on your 355?

 

This thread is a microcosm of Fchat. No?

 

I asked mark from the very beginning if he had compression numbers. The first set of data that was posted was leak down numbers with a 20% leakage in one cylinder. In my albeit limited experience with this issue having only owned my car for two years, a properly done compression test from the start may have avoided all of this concern on leak down as it may have been benign.

Again my understanding on this and from my experience a leak down is done if there is a compression issue to be diagnosed as to where and how much leakage is occurring causing the suspect compression problem.

My point is that all of this may have been a non issue with a compression test done first.

 

I just jump on the pile for the fun of it. Always liked a good beating when I was a kid

 

It would be interesting to know what the compression numbers are You can't get it in neutral when its out of the car?

 

OK I forgot it was an F1

 

Pull the pumpkin, pretty quick and easy and you'll probably want to make sure there's no wetness in there anyway.

 

If it were my car, and my compression test numbers are that good, I stop testing.

Button it up.

 

If you saw those numbers on a PPI CC that would need no further leakdown analysis.

 

can we say….documented, another 1998 without valve guide problems?

 

I think we can say do a compression check on your prospective purchase and go from there regardless if year and of guides.

A poor compression number in a cylinder indicates an
Issue in that cylinder which may or may not be extrapolated over the rest of the engine.

Some have dismissed the value of a cc before purchasing. If anything these results show the validity of doing a CC and going from there.

 

VERY educational thread!
Drive it like ya stole it and it'll be fine!

 

Would it anger everyone to hear I would still do the guides?

 

I think many would enjoy seeing this done. It perpetuates the FCHAT wisdom!!

DRIVE IT LIKE YOU STOLE IT. STALLIONS NEED AN ITALIAN TUNE UP ONCE IN A WHILE TOO.

 

Right. All the pros jumped to a conclusion that the guides were bad, maybe a liner was shot.....and on and on to every possible tangent based on the initial set of numbers. Not one suggested that Mark check his numbers. No one but a couple of us armatures suggested (off board) that Mark retest with a different instrument and at different pressures. Let's all hear it for the pros! Apparently they never heard the phrase, "measure twice, cut once". This kind of BS is exactly why I don't ask for help on FChat. Learn something...when things don't come out the way you expect, check your work.

Makes me wonder how many engines you guys have torn down and done guides on that really didn't need them. And how many actually bother to check the clearance on the guides before you replace them? Yes, let's hear it for the FCrap pros.

Face facts. This is social media. Not MIT or Cal Tech. It's not even Wyo-Tech. It's barely Shade Tree Institute.

 

I've been following this thread because.. drama.

When I read the initial numbers I had PRESUMED that they were checked twice. As with any garbage in garbage out that is an internet forum... you get the result out of it that you get from the input that you put into it.

Interestingly.. none of the pros said "WOW that's an unusual number!" So what I read from THAT is that these numbers are common enough due to valve guides that given conclusion is drawn. Either MANY mechanics use a bad tool and there are hundreds of good cars having their guides changed unnecessarily... OR this is a common enough occurrence with this model that the conclusion offered by the "experts" is justified.