Compresson test results 3.5 V8 - comments/advice please

[Mark2]

I did a compression test last night on the motor from my project car.
Motor and box on the floor so these results are for a cold engine. Its an 8:1 motor from a mid eighties range rover. None of the plugs were oilly, most had a brown electrode, a couple were sooty black (not the low ones)
Looking from the front of the motor:

LEFT
155
150
120 (135 wetl)
150

RIGHT
150
150
135 (150 wet)
150

I was fairly happy with the 150's? what about the 2 low results - both second cylnders from the rear. Is it worth pulling the motor down or should I just put it back in, given I'm not that confident in this area?

Thanks

[Simo63]

I did a compression test last night on the motor from my project car.
Motor and box on the floor so these results are for a cold engine. Its an 8:1 motor from a mid eighties range rover. None of the plugs were oilly, most had a brown electrode, a couple were sooty black (not the low ones)
Looking from the front of the motor:

LEFT
155
150
120 (135 wetl)
150

RIGHT
150
150
135 (150 wet)
150

I was fairly happy with the 150's? what about the 2 low results - both second cylnders from the rear. Is it worth pulling the motor down or should I just put it back in, given I'm not that confident in this area?

Thanks

Hi Mark2. I've had a bit to do with the rover motors and they generally don't push big numbers due to their low compression. Assuming the motor was a good runner before (do you know the history?) then what a comp test will show is just what this one has shown, a variance in the cylinders. Anything more than 10% variance could be signs of an impending problem.

Different comp readings like you got could be to do with a few things, the wear on piston and rings, valve and valve seat condition, headgaskets (in extreme cases) or cam. I would hazard a guess from the readings above that maybe the cam is a bit worn or the valves aren't seating too well on a couple of cylinders.

What are your plans for the motor in the project car? If it's out on the ground then it could pay to whip the heads off and get them serviced and replace the cam, lifters and timing chain. Whilst you have the heads off, check the bore for wear. If that is alright then a top end job like listed above should keep it going for a few years more.

Cheers
Simo

[justinC]

Hi Mark,
If you had the $$$ I would do it now while the engine is out. The 130's are getting down to the Min, and the 120 is definately a worry. BUT, If the motor has been not running for some time, and the cranking speed during comp test wasn't particularly fast, then all these readings will be a whole lot lower than reality. Cold will always be slightly less also. If you feel strapped for $$$, then just bung it in and try it. Don't forget to look at the camshaft too, this could be more of a concern than the compression figures.

JC

[Simo63]

Hi Mark,
If you had the $$$ I would do it now while the engine is out. The 130's are getting down to the Min, and the 120 is definately a worry. BUT, If the motor has been not running for some time, and the cranking speed during comp test wasn't particularly fast, then all these readings will be a whole lot lower than reality. Cold will always be slightly less also. If you feel strapped for $$$, then just bung it in and try it. Don't forget to look at the camshaft too, this could be more of a concern than the compression figures.

JC

Yeah Justin has a couple of good points here I forgot to mention about the cold reading, maybe slow cranking as well and also if it's been sitting for a long time. All these things will give lower readings although they should still be pretty consistent if the testing was consistent.

[Mark2]

Thanks guys, I think I will pull the heads off for a valve grind at least and have a go at replacing the cam. I have heard these motors respond well to new cams after highish mileage.......


Should I drain the coolant from the block while the motor is in 'storage' to prevent internal alloy corrosion? I think there is a drain plug on the block somewhere?

[roverlux]

like simo63 said, later rovers (ie Range rover, rover motors) have lower compression about 8.0:1 i think, and the older (as in 70s car) have higher compression about 10:1.

if you are looking at the older motor i think you may have problems, but if its a later model, you may be in the ballpark???

Joe.

[peter r]

G`day Mark2

Agreeing .

In my experience it`s always best to get as much infomation from the engine as possible before pulling it apart .

I`d suggest you give the other cylinders a wet test , to see if they come up 15 as the low ones have , as i think you know it will tell the condition of the rings over all .

Also take the rocker covers off and measure the movement of the valves on the dud cylinders and compair it with the movement of the good ones , then you can judge if the lobes/lifters are at fault .

Also have a close look at the valley/inlet gasket for any distortion , can be a sign of leaking h/gaskets .

As you say i`d be happy with the 150 cold and dry too and it would certainly be good time to do the cam and gaskets while its out and i`d also suggest you get a manual or CD as it will pay for its self in time and piece of mind .

All the best , peter .

[Philip A]

I take it that this is a motor that has not been run for a while.
I think the compression tests would be pretty meaningless as some of the tappets may have leaked down and some not. They rely on oil pressure.

I would look at the cam lobes on the cylinders that are low.

But you cannot tell much on an hydraulic lifter engine if it has not been run for a while.
Maybe a leak down test which does not depend on valve opening would be more meaningful.
Regars Philip A

[Mark2]

Its probably only been four or five weeks since it was run.

It wont be a big job to get it running on the floor - basically I would just need to hook up the fuel line which is still connected to the pump and probably stick a garden hose in the lower? radiator hose or one of the heater hoses?

Sounds like it might be worth running it for a few minutes and redoing the test