Rb25 neo with poor compression readings

[Jbp]

Hi, I’ve got a r33 with a rb25 neo engine fitted. Just had a compression test done as it is running a bit rough and it come back with poor results ( cylinder 6 as low as 60) is there anything I could check that could be causing this before I suspect the worst.

[Ben C34]

Could be lucky and could be cam timing related. But if one cylinder is alot lower than others that won't be the case.

If one cylinder is substantially lower than others its head off at the least. Options are burnt valve, blown gasket, damaged piston.

What were the results of the comp test?

cold/warm?

[Jbp]

Yeah that’s what I’m thinking now.

cyl 1-160, cyl 2-150, cyl 3-120, cyl 4-140 

cyl 5-100, cyl 6-60

just took covers off now and checked valve clearances and all seem fine except cyl 6 exhaust side is at .35 instead of .5 which might have a little to do with it but not that much I wouldn’t think 

cam timing is all good 

 

Edited March 17, 2018 by Jbp

[KiwiRS4T]

Before you pull the head off you could do a leak down test which should show whether compression is getting past the valves or the rings.

[GTSBoy]

But the back half of the motor is definitely sad compared to the front half, so I would not think this motor has a long future without being opened.