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#1 06-13-2011 14:46:47

ned
Helper
From: Williamsburg Ky
Registered: 01-11-2010
Posts: 20

Compression Test

I just re-seated the head on my 2.1l Renault turbo diesel and have a question. If I turn it over by hand without the valves opening at all, I can hear air hissing out the bottom of the cylinders. Is that a sign of worn piston rings or do I need to re-do the head gasket again?


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06-13-2011 14:46:47

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Re: Compression Test

#2 06-13-2011 15:05:55

scooter
Helper
Registered: 10-05-2008
Posts: 16

Re: Compression Test

The air has got to go somewhere, and slowly turning it by hand is poor representative of running conditions.  I would think a true leakdown test would give you a better answer.  I would also squirt a bit of oil in the cylinders and see if sounds different or is harder to turn over by hand.

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#3 06-13-2011 15:06:31

ned
Helper
From: Williamsburg Ky
Registered: 01-11-2010
Posts: 20

Re: Compression Test

I'll squirt in some oil this evening and turn it over again


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#4 06-13-2011 15:07:54

evad
Enthusiast
Registered: 10-05-2008
Posts: 136

Re: Compression Test

I agree and then the engine is also cold so the forged pistons did not have
a chance to swell up some. ;-)
As long as you don't hear the air leaking out between the head and the
block, or in your case.....from the valves since they are closed.


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#5 06-13-2011 19:15:38

sucram
Rookie
Registered: 02-20-2010
Posts: 85

Re: Compression Test

Be glad you can replace the heads on those. Here on the XJ's with the VM Motori turbo diesels that have a head for each cylinder, they state once removed must be replaced with a new head at $1200 each!

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#6 06-13-2011 19:16:55

ragnar
Helper
Registered: 10-05-2008
Posts: 19

Re: Compression Test

Sounds like old times.

I always think it is realy a sucka$$ed way to do business.
Build and sell stuff that can't be fixed or tell you to buy new if you take it apart.

What year is it?
If they can't fix it why do they think it is OK to sell it?

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#7 06-13-2011 19:27:48

ned
Helper
From: Williamsburg Ky
Registered: 01-11-2010
Posts: 20

Re: Compression Test

I have confirmed what it going on.

The piston rings need to be soaked in oil to completely seal, this is actually a common diesel thing, the oil scraper ring is 2nd from the top seal, and the oil normal coats the inside to boost compression. That and the fact that the rings have been dry and cold for so long (around 4 years) just means its feeling unused.

The only things left to do are:

-Re-mount and seal water pump and thermostat.

-Prepare the wiring harness (Consisting of 8 wires: Temperature Gauge, Oil Pressure Gauge, Fuel Cutoff Valve, Turbo Boost Gauge, Alternator Linkage, Starter Wiring, Ground)

-Install new valve rockers and re-mount rocker bar.

-Time engine

-Remove V6 from XJ

-Mount Everything

-Test Drive!


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