4722 replies to this topic

[Nev]

Hmmm, I'm in a bit of a quandary now, though on the whole things are looking good, so I'd appreciate any input from anyone with experience of doing pressure/leak down tests please...

PROCEDURE
1. I did my test in a similar fashion to: https://www.youtube.com/watch?v=jc3j4ShE-tk
2. Leak down tester from eBay arrived. It's quite a good bit of kit apart from having the wrong bayonette (which I have now adapted).
3. Left the car in neutral (as I didn't want the compressed air to 'drive' it off the ramps!).
4. Took the plastic cam cover off (so that I could turn the engine over by hand using the cam hex bolt).
5. Used the leak down tester on all the cylinders about 3 times each.
6. In order to find TDC I pressurised the cylinder with compressed air and turned the engine over by hand until feeling the compression resitance. I also used my ear to detect when the leak went from "rushing" to a very slight hiss.


OBSERVATIONS
1) All cylinders were showing similar leak at approximately 20 PSI of inlet pressure. When retesting the same cylinder a variance of +/- 2% to 3% occurred. The figures shown below are the best I could get by moving the cams around. On my gauge Green=10% to 40%, Orange=40% to 65%, Red=65% to 100%, so all the figure below show theoretically healthy cylinders:
Number #1: 18%
Number #2: 21%
Number #3: 15%
Number #4: 15%
2) If I tried to increase the pressure, the engine just turns over at around 25 to 30 PSI, and then the valves open and let the pressure out.
3) I can hear the air roaring through the engine when the pistons are not at TDC.
4) When at TDC there is a consistent whisper of air noise, so clearly some minimal air is getting past the valves or rings.
5) This whisper noise level is the same for all cylinders at TDC.


QUESTIONS
1) Even though my tester "setting point" was done at around 20 PSI, presumably this means that all cylinders are operating with minimal leak?
2) I know it not really indicative of a great deal, but is approx. 25 PSI normal to turn a 4 pot engine over (without plugs in), seem like minimal ring friction to me (which is good in some ways!)?


POSSIBLE EXTRA TEST
As an additional test, would it be sensible to chock the car up very well and:
1) Put it gear to stop the engine turning.
2) Blast 100 PSI directly into each cylinder and see if the escaping air makes a similar amount of noise for each clyinder?
3) Presumably this test would be closer to the real life approx 200+ PSI that the cyclider actually sees when the engine is running?
4) Would this be a good test or am I trying to invent a test that wouldn't offer viable evidence?


CONCLUSIONS?
1) Is this enough info to conclude that the pistons + valves + HG are good health, or is that wishful thinking ?!

I have to say it's tempting to whack the refurbed turbo back on and drive it !

Edited by Nev, 16 April 2013 - 06:38 PM.

[Nev]

Well I've rung up Simon "Chip" Comins (one of my key mentors on this crazy project) and he thinks I should plonk the turbo on and see if the problem is fixed. However, any input from other is still welcome :)/>

Edited by Nev, 16 April 2013 - 07:02 PM.

[Arno]

Agree.. Just re-fit the turbo, disconnect any crankcase ventilation hoses from the intake and (temporarily) vent to the atmosphere so you eliminate any oil ingestion into the intake tract from that source and see if it still smokes or not.

If it's OK then and you get sick of the oily fumes then you can look into a catchtank or something like a MANN Provent 200 ( http://www.mann-humm.../ProVent-en.pdf ) to capture them..

Bye, Arno.

Edited by Arno, 17 April 2013 - 07:04 AM.

[vocky]

my last engine had between 5 and 6% leakage across all four cylinders, so 21% seems quite high

[cnrandall]

21% is quite high, have you put a bore scope down that bore?

[oakmere]

Nev Did you do the test warm or cold as your forged pistons will leak much more than std when cold?

[Nev]

Thanks for the input guys. In answer to a few questions: 1. I don't have a bore scope or know anyone who has one I could borrow from, so though I'd like a look look iwth one I haven't been able to do this. 2. The tests were done on a cold engine that had been idle for approx 2 weeks, so maybe the losses would probably be less if it was warm and had more oil on the rings. 3. The pistons (C20LET ones) are not fully forged, just hot pressed crowns, thus I think they might only expand like normal non forged ones (though I am guessing). Unfortunately I can't remember the piston to bore clearances on them. It's worth bearing in mind that all leak down testing guages vary. The hole size between the guages will vary, as will gauge accuracy etc surely? Maybe I should put the turbo on, fire it up till it's warm and then retest to see if the % values drop a fair bit.

[Bargi]

Check eBay, you can get USB bore scopes with adjustable LEDs for lighting for less than £20

[CocoPops]

Check eBay, you can get USB bore scopes with adjustable LEDs for lighting for less than £20

JG bought one recently from ebay

[CocoPops]

Like this I think: http://www.ebay.co.u...=item19dad90d50

[techieboy]

If you want to go for a USB one, then this looks decent. It's a 7mm thin head, so you can get into places that some can't and it's got the mirror attachment so that you can inspect the valve faces as well as whatever is below the camera head when inserted (you can't bend them 180 degrees and insert it through the spark plug holes).

[JG]

thats roughly what i've got. 7mm tube. its brilliant and shite all in one. but i used it to inspect all the fuel lines (more as toy really). suppose i could upload a vid to youtube.

[Zoobeef]

I just see how far I can get mine in my ear or down my throat Id put the turbo on and try it. Its not that much extra work.

[techieboy]

suppose i could upload a vid to youtube.

Go on, you know you want to.

[JG]

I'll have a go later.

[techieboy]

We probably don't need all 2 hours of footage though. 20 seconds is probably sufficient, unless you discovered something really interesting?

[JG]

erm no, it was so uninteresting that i didn't even bother uploading it to my project thread, and i'm not scared of posting uninteresting things in there!

[techieboy]

No pot of gold at the end of the rainbow, or similar, then? How disappointing.

[JG]

no, though i did poke it down a sill, and that provided a moment's entertainment, as thats really the only place in my car i haven't seen.

[techieboy]

We need footage of the innards of your Milltek back box to settle the is it chambered, or not, question?