Compression test results...

[X@V]

I tested the compression on my 1.9lTD this afternoon.

The results are: 420-520-520-400

It was rebuilt 100,000km ago.

What do I do?

It's my daily driver and I work with my car... I can't work on it a lot.

Please help me  :?

[chrissev]

I tested the compression on my 1.9lTD this afternoon.

The results are: 420-520-520-400

It was rebuilt 100,000km ago.

What do I do?

It's my daily driver and I work with my car... I can't work on it a lot.

Please help me  :?

cyl 4 is a bit low, and 2 and 3 are high.  1 is within spec.  Are you sure you are getting 520?  that is a lot.

[X@V]

Yes, I'm sure. We tested them two times to be sure.

Same results.

The first went to 430 after 30 seconds. The last one, it was 390 and after 30 seconds, it went until 400...

 

[Master ACiD]

you mean after 30 seconds of cranking each cylinder?

that seems like an awful low of time to crank just for a compression test.

[X@V]

After two minutes, the indicator decreased of 40 PSI  :?

There was a check valve on it.

But I know there's a bif difference.

I had lots of trouble while starting the engine when it's cold now (tonight). I think there's something that causes trouble into the injection pump.

[Justin]

try cranking it over no more than 5 times and see what the numbers are, with numbers 400 and over it should start really easy even in the cold, unless your glowplugs are bad.

later
Justin

[X@V]

Yesterday I started it at -8*C without the glow plug relay (4 hours stopped) and it started. I didn't worry about the compresison but I tested it today.

The results are not as I was thinking. I tought about 450-480 at the 4 cylinders with the 3-notch headgasket...

I don't understand why the two cylinders in the middle have better compression that the two others (1 and 4). Does someome know why I had these results?

Thanks

[DieselMonkey]

Its very unlikely, but maybe due to the decreased amount of air flow to cylinders 1 and 4 has caused a build up of carbon on the piston top, increasing the compression ratio to this degree.

This is a known issue, but with only 100K Km on rebuild, it would seem unlikely.

Maybe the piston projections are different. You used a gasket in relation to the highest piston, maybe 2 and 3 were not sitting as proud.

Matt

[Wingaman]

Did the mechanic use new heat shield to test de compression ?

From the Bentley A2:

4.   Thread the compression tester, with an injector heat shield, into the first cylinder's injector hole. Thread the gauge in tight enough to seal.
5.   With the transmission in neutral, crank the engine with the starter. The gauge reading should increase with each engine revolution. Continue until the gauge reading stops increasing (about 4 to 5 revolutions). Record the highest value indicated by the gauge.
6.   Release the pressure, either with the gauge valve or by slowly removing the gauge, allowing the pressure to bleed off while threading it out of the injector hole.
7.   Repeat the test for each of the other cylinders. Record the data and compare with Table c.
8.   Reinstall the injectors with new heat shields. Torque the injectors to 70 Nm (51 ft. lb.). For correct heat shield installation position, see FUEL SYSTEM-DIESEL.

I will test the compresion with new heat sheild. They are cheap, under 1$ each like i did with my engine.

[Justin]

check your valve lash if its a mechanical lifter head. often times with a new rebuild the valves will "seat in" after a break in period and they will hang open a little more taking away some of your compression.

later
Justin

[chrissev]

the signature indicates his engine is a 1.9TD.  Did they have different compression from the 1.6 engines?

[fspGTD]

Given you've got a 1.9, you've got hydraulic lifters so there is no valve lash to check.

I'd guess the bulk of the compression variance from one cylinder to the next is due to ring leakage.  This could be isolated by performing a dry and then a "wet" leakdown test; any difference would be the leakage past the rings.  Remaining leakage would be from "other" sourecs (valve most likely, but also sometimes cracked head, leaking head gaskets, etc can allow combustion chamber pressure to escape.)

Ring sealing is a pretty complicated topic, and there are a multitude of reasons that could explain why some cylinders have better sealing rings than others.  It could be as simple as some cylinders happen to have rings that have spun around such that their end gaps are all lined up while others have staggered end gaps.

Keep in mind that starter motors aren't designed to run continuously for more than about 10 seconds.  That should be also all it takes to get a good compression reading on one cylinder.  I'd recommend limiting your cranking during the compression test to maybe 10 seconds at a time... and allow a minute or so at least in between cranking to let the starter motor cool.

[X@V]

An other thing: my turbo leaks oil and I added about 500mL for 5000km. I don't thing the rings are leaking.

AN other thing, the breather tube was located near the firewall this summer because of the p-flow. There was no oil on the firewall. I think there's no compression un the crankcase.

[Mark(The Miser)UK]

Given you've got a 1.9, you've got hydraulic lifters so there is no valve lash to check.

I'd guess the bulk of the compression variance from one cylinder to the next is due to ring leakage.  This could be isolated by performing a dry and then a "wet" leakdown test; any difference would be the leakage past the rings.  Remaining leakage would be from "other" sourecs (valve most likely, but also sometimes cracked head, leaking head gaskets, etc can allow combustion chamber pressure to escape.)

Ring sealing is a pretty complicated topic, and there are a multitude of reasons that could explain why some cylinders have better sealing rings than others.  It could be as simple as some cylinders happen to have rings that have spun around such that their end gaps are all lined up while others have staggered end gaps.

Keep in mind that starter motors aren't designed to run continuously for more than about 10 seconds.  That should be also all it takes to get a good compression reading on one cylinder.  I'd recommend limiting your cranking during the compression test to maybe 10 seconds at a time... and allow a minute or so at least in between cranking to let the starter motor cool.

IIRC 'climbing' high compression values can be a function of poorly opening exhaust valves and I'm sure hydraulic followers could produce this effect by going 'soft' which is why they should be checked for excessive gaps AND valve seatings could 'sink' effectively making them too long and no valve gap and valve leakage. Hydraulic lifters fail from day one of installation [ie defective] onwards... (not in this case however)...
Ring gap alignment is my favourite culprit for general variations though.

[Wingaman]

fspGTD:
From the Bentley and it's true. A friend did this and the gage has ben blow. Lucky the guy was alone to do the test, so it was cranking and not checker the gage.

CAUTION- Do not attempt a wet compression test on a diesel engine. The oil in the cylinder may be ignited by compression pressure.

The warning is not there for nothing.

I'm thinking you are talking about leak down test.