leakdown test

[adi]

does the engine have to be turned over to do a leakdown test? or can it be done on an engine which is on a stand etc?

[dude]

Normally you use compressed air to presurise a cylinder and see how long it takes to 'leak down' !!!

Dude:thumbs:

[adi]

okay cheers.. thought so.. :D

adi

[scooby_doo_do]

Cool, I always wondered what one of them was....

[Digsy]

Originally posted by dude
Normally you use compressed air to presurise a cylinder and see how long it takes to 'leak down' !!!

Dude:thumbs:

I think nitrogen is used most often. Probably for safety.

[Adam W]

How do you know how long it's meant to take to leak down by a certin percentage? ie if you pressurise the camber to 5 bar and then five minutes later its down to 4 bar, how do you know if that's good or bad?

[Digsy]

If I remember next week I'll try to get a specification for you. Not sure it there is a generic one or not, but I should be able to turn up something.

[Ian C]

Originally posted by Darren Blake
I think nitrogen is used most often. Probably for safety.

Don't Lotus use oil? :D

-Ian

[Digsy]

TERRY! IAN'S MAKING FUN OF PEOPLE IN THE TECHNICAL FORUM!

:baa:

[Ian C]

Priceless :respekt:

-Ian

[adi]

I think any more than 20% loss is bad.. i had my 1J done a while back and it was between 10 and 20% on all cylinders, which i think was borderline pass.

[Digsy]

I just spoke to one of our development guys who's out here with me. As with all things, its not as simple as it first appeared.

The full nitrogen leak test is done to find out whether the cylinder head gasket is working, and if not where the leak is. Procedure is to plum all the spark plug bores up to pressure guages, as well as the oil galleries and water jacket in the cylinder head. Lock off the engine so that it can't turn using a purpose build tool - and this must be absolutely 100% secure because of the next bit.

Then you pressurise each cylinder in turn up to peak firing pressure - something in the order of 70bar??? and hold it there, looking for signs that gas is escaping into any of the other chambers you have plumbed up with pressure guages.

The bummer is that because of the high pressure, this test is really dangerous to do. Also, because you are holding peak firing pressure for meny seconds on end (instead of the split second at a time that the engine seems during normal running) then you are putting a LOT of stress on the engine do one test.

The alternative is to use normal pneumatic line pressure air such as you may get in a highstreet workshop, and pressurise the cylinders with that. For some reason I had trouble getting a spec for leak down out of the guy although he did say he had seen meters in use that had simple OK and NOT OK indicators on them?

His final comment was that for the latter type of test you would probably be just as well of doing a compression check while the engine was running.

Probably not the level of detail you were looking for, but hope it helps anyway.

[adi]

nope that explains a lot, cheers.