PPI 355 Compression and leakdown #'s

Starting with the first line: 225 27 / 28%, what relevence does the number 27 hold?

At any rate I'll give ya my $.02 worth of thought. The engine in a 355 costs every bit as much to overhaul as a big Continental turbo in a Bonanza. No one in thier right mind would pay top money for an airplane with leakage on any cylinder above 5%. At 10% you would be grounded and in need of a top overhaul. I know some have claimed a 355 with loss to 10% would be acceptable, but I would never pay much for one.

But if the loss that you are showing is 25 - 29%, I think someone did the test wrong. Compression is even, which is more to the point, so probably they screwed up the leakdown test. Have someone else do it again and see what numbers you get.

 

what??????
for a leak down a specific pressure of air is fed into the cylinder via the spark plug hole, BOTH valves should be closed. the rate of loss is read of the second gauge. this is a simple explination btw.

the only relevancy intake or exhaust has is where the air is leaking from. try and get clarification or use another shop/dealer. and from what i've read here it's not so much the %loss unless you're really loosing air but how even it is across the cylinders. from those numbers i'd say it's very even wear, but i'm not sure if an average of 25% is good or bad.

 

Get another test done by someone that has a clue. The people that did that one are idiots.

If EVERY cylinder is not above 200 lbs and below 5%, run.

 

I am used to the pressure regulator/Moroso type of leakdown tester like Rifledriver uses, where you zero the input pressure, and read the outlet (leakage) directly.

I think this is a different kind, where you look at the difference. If so:

1 1%
2 2%
3 4%
4 4%
5 5%
6 5%
7 4%
8 5%

Just a guess, but a good guess.

JM

 

Carbon build up on the intake valves IS common on 355's, but several techs/mechanics will tell you that is most likely caused by oil getting past those pesky (and worn) valve guides...so run!

 

Hey Brian, Question..Isn't it odd to have such hi compression #s and then those leak down #s the way they are? Those compression #s are excellant but I would think that motor would barely run with leak down #s like that. those valves must be shot and even consistant in their shotness(I know that isn't a word but it sounds good) I mean their wear is so consistant. Regards, Vern

 

If the car has 37,000 miles...wouldn't the valve guides have been replaced already?

Those are some fantastic looking compression numbers, especially with 37,000 miles, no?

 

Thats why I commented the way I did. The results are nonsense, mean nothing and cannot have been generated by someone that knew what was what.

The comp #'s are a little high. Maybe a gauge a little off and that is ok but the leak down information is so nonsensical and it has to bring the entire thing into doubt.

If I go in for a physical and the Doc says "your blood pressure is great but there is a little problem with your respiration, you don't have any" I'm sorry, I'm looking for another Doc and I'm not paying much attention to his position on my blood pressure.

Throw it away and start over.

 

Good doc. analogy. Hahaha. Who's the guy in your avatar?

 

One of the greats, Joe Leonard.

A local boy. Rocket on 2 wheels and 4. One of the few who was successful on both.

 

That describes an invalid test. Test is the same on diesel, gas, or steam, 4 stroke, 2 stroke or rotory.


Good luck to you.

 

How is it that you get the 2 numbers? I am guessing that on a large diesel they dont pump it up to 100 psi, as the motor would almost certainly flip over.


Are they only putting it up to 30 psi, and running the test? If thats the case, wouldn't you multiply by 3 to normalize up to 100 psi?

ie. 26/30 is "4" if you subtract. But as a percentage (30-26)/30=13%.

Just guessing...anyone understand this?

 

Nothing to understand. Not a valid test. Period.

 

agreed, those numbers just don`t make any sense.

Good engine Leakdown percentage should be under 10%.

regards, Jim

 

Get another test at a different shop, and specify you want someone who knows what they are doing. For something that is so simple there sure are a lot of people who can screw one up.

It is true that on a large bore engine 100 PSI can become difficult to hold back. We use 80 PSI on aircraft, and let me tell you, even on a 80 inch prop it can take all your wieght out on the tip to keep that bugger from getting away. Starting with the base pressure, the cylinder pressure that is holding is your percentage of the base pressure. If you have 100 PSI on the main, and the second guage is holding 90 psi, you have 10% loss. With 80 PSI, 72PSI would basically be the same percentage of loss.

You could look through aircraft ads over the last 30 years, or talk about aircraft at an airport, and everyone uses the same procedure and figures. Numbers like 80/76, or 80/74. Why everyone around cars has to have some different way of relaying information is beyond me.