Compression test and leak down test

The valve is 26.7mm or 1.05" That would equal 86.54 pounds on the valve at 100 PSI, 34.6 at 40PSI. Give that, 100 PSI can overcome the spring, 40 cannot. Regardless, Brian says it don't mean sh*t

 

So what material are stock 355 valve seats make of that they rust?

Personally I think that is leak down tests performed at different pressures show substantially different results the test isn't reliable for defining the condition of the engine.

 

And that I can't argue with.

Ferrari calls it cast iron. But there is cast iron and there is cast iron.

 

I really doubt it's cast iron since that won't harden well.

 

Yeah I sort of wonder what type of steel Romeo and Juliet (the robot which installs valve seats at the factory) installs. I started using Tucker valve seats not long ago and they are just obsessively knowledgable regarding the subject. If you ever want to ask about rust and valve seats then I'm sure they're not a bad party to ask.

 

I agree. The translations in the manuals can be pretty misleading. They have often used ESL students to do the translations so not only is the grasp of the language iffy there is no technical expertise.

Once in a while I'll read the Italian version and understand it better.

 

All steel that can be hardened, including 440 stainless will rust. But, most have higher chromimum content and if oiled, won't rust like plain carbon steels.

 

I do that often (read the Italian version) to really understand what they are saying

Thanks for posting your experiences with leak down/compression tests.

 

The math is correct but the application of it is not. If there is a bleed off of air as in a non-seating valve the 881 force of the air pressure leaks out the hole and you don’t have enough force to close the valve to stop the bleeding. If you could fire the 100psi in fast enough to offset the bleed to overcome the valve spring that would be a different story. That all sounds sort of difficult to wrap one’s head around until you think about what happens at a tire store when the tire monkey have a difficult bead to seat on say a race tire they overcome pressure with delivery volume of air to seat the bead. We are not doing any of that with a 100psi FAA leakdown test.

[ame=http://www.youtube.com/watch?v=PONJgC3EZDA]Quad tire bead seating with maximum ease - YouTube[/ame]

This also explains why Brian finds no difference in the 2 tests in his experience. Someone here also got me fired up about the low pressure test. I also did both tests for about a year. Then abandoned the low pressure test and just went with the FAA test with a certified FAA tester since my low pressure tester was HF junk. I just found it did not matter and figured the FAA guys and the pro auto race teams were smarter than me so I just copy them.

 

When you consider that actual max cylinder pressures under load can run above 50 bar......

 

Note that as Brian pointed out, I was doing this in a hurry and ignored the actual valve diameter which greatly reduces the force. And I do agree that the force will be less in a non sealed system (high leak rate)

 

I was factory trained too and was shop foreman at what was then the largest dealer in existence.

So what? Don't be too impressed by any of that.

Ever consider the fact that one or both leak testers was defective? And there are a whole shopping cart full of variables beyond that.

Additionally I can pretty much make the tester say anything I want it to say depending on my motive.

Also In case you didn't catch it a low pressure test will often fail a motor with slightly stick rings, rings that work perfectly in the real world.


Want a good motor to fail a test...no problem I can do that for you if that is your motive.

 

So what's the point of the test then? And, it's difficuit to get accurate information since so many disagree. Who is to say you are right, or Tony at Algar is right? I ask that with no motivation - just making a point. No disrepect or judgement to you at all.

As a side note, when I started as an engineer, I worked with a couple of fantastic guys, my best friends to this day. The one would always make 3 calls to different people when it came to technical issues and then he would make his decision based on merging the pieces togther or dismissing the obvious poor advice. I've learn to follow the same process, and it is frustrating but usually works.

 

I am not going to tell anyone on the internet to buy or not but any given car. Personally I consider the internet part of the problem and not part of the solution. I would consider it a victory if people ignored everything they read here, me included. The signal to noise ration is clear off the charts.

This case is an example of that. We are creating yet another falsehood and people will come to my shop expecting me to perform based on what they read here at which point they will be shown the door.

 

This might be the single best post I've ever read on this site...

 

I guess you should have bought the car but still unsure. That post is what I always liked and appreciated from Brian, Dave and others. They did not always agree but they also did not bull**** you. Not to put words in Brian's mouth but I think he once said the 355 was a more troublesome model than most others. He will correct me if I'm wrong.

 

Bob, thank you for starting this thread and keeping it informative for all. I look forward to reading about your future test results.

 

Nope.

Most just want their version of reality to be validated. I have no need to do that.

 

I look forword to the results as well. Another question does anyone have compression and leak down test results for any of their daily drivers just curious?

 

Grant
82000km compression 195 to 215 cold

 

If you are using a screw driver and observing it going up and down visually without the aid of a dial indicator, you are just guessing. It could be 3-5 degrees off. It would not be accurate enough for valve timing, but OK for the purpose of testing leakdown.