Does anyone know where compression numbers should be. Im looking at a 98 xjr. Jaguar dealer said 150 to 170, another jag dealer had no idea. The compression came back at 135 across all cylinders . My local import guy said that is low as well. Anyone have the actual numbers they can point me to?
Worried about the start of a nikasil issue

 

The SC engines have a lower compression and I think your numbers are good.
A nikasil issue is unlikely unless the engine was overheated. The problem was caused by high sulfur fuel and that's long gone. Your block should outlast a steel lined one.

 

I don't have the actual numbers in front of me, but most posters that have measured compression on XJR's have viewed 120psi as good compression. The 150 to 170 range is probably for the higher compression (naturally aspirated) versions of the same engine.

 

In general, it's probably more important to be within a narrow range than to be a a specific number. If they are all 135, then that's probably what they should be.

 

The compression test should be performed on an engine at NORMAL OPERATING TEMP.

Performing the compression test on a cold engine will not be accurate but a reading of all cylinders within 10% of each other is GOOD.

A cylinder leakdown test is probably more accurate.

bob

 

Thanks. Really happy to hear that. We did the test on a warm engine. Should have a new old jag soon