P38, 4.0 petrol, 2002, Bosch - no start

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I'm confused. With any compression tester I've used, you screw it in place of the spark plug, for on throttle, turn engine with key for at least 3 revolutions (to make sure you get peak compression). Take a reading then release the pressure and repeat, then move to the next cylinder.
You mention an initial pressure that drops to zero.
Unless your tester is leaking, it should retain the max reading, regardless what that reading might be, until you release it with the button.
Am i missing something? Does your tester not work like this?
 
This is one of mine, the pressure release button at the bottom 15914509214780.jpg
 
kermit_rr said:
I'm confused. With any compression tester I've used, you screw it in place of the spark plug, for on throttle, turn engine with key for at least 3 revolutions (to make sure you get peak compression). Take a reading then release the pressure and repeat, then move to the next cylinder.
You mention an initial pressure that drops to zero.
Unless your tester is leaking, it should retain the max reading, regardless what that reading might be, until you release it with the button.
Am i missing something? Does your tester not work like this?
Click to expand...

+1 on that.

Assuming it does stay up, did you try with a spoonfull of oil?

Starting to sound like the crank has sheared in half. Hard to believe, although thinking about it you said it blew past your thumb so cannot be that.

Next step after is to make something up so you can connect an airline / compressor / bike pump up and then turn to TDC (piston at the top) and listen to where the air is escaping. Exhaust manifold, inlet manfold or oil breathers.
 
Could the camshaft be broken causing valves in back half to stay open? Probably worth whipping the rocker covers off and cranking it to see if the rockers are moving.
 
kermit_rr said:
I'm confused.
Click to expand...
Haha, me too!

No, my tester is similar to the one described above. It'll sit and hold at a higher reading like 120 no bother (or 150 on my car when I tested it on that) but I think when it's very low compression such as the problem ones it''ll only pulse up a bit then drop back to near zero with an occasional outlier. In a nutshell I can't hold my thumb on four cylinders but I can on the back four so somethings obviously very wrong.

Grrrrrr said:
Don't scare him too soon! He'll bolt!
Click to expand...

Don't worry, I've done it all before on other cars! I was just hoping I wouldn't have to do it on this one. It's got service history going out the door so I thought I was relatively safe but doesn't look that way.

I'll do a leak down test and take the rockers off and see what's what. As always, i appreciate the input.
Ed
 
Bit of a long shot my dads P38 Gems would run rough and stall. It turns out the battery was undersized and knakered it couldn't provide the correct voltage to all the sensors. We thought engine damage. Fitted new battery and all went back to normal. Is the battery in good nick?
 
Lukas018 said:
Bit of a long shot my dads P38 Gems would run rough and stall. It turns out the battery was undersized and knakered it couldn't provide the correct voltage to all the sensors. We thought engine damage. Fitted new battery and all went back to normal. Is the battery in good nick?
Click to expand...

Good call. First rule of any Rangie troubleshooting is a decent battery. Seem to recall something about the earth-strap on tge GEMS too.
 
Well, it looks like a depressing result after all. It took a while to get the fan and rocker covers off but I finally stripped it down to get a view of the cam (?) and valves and although all eight pistons move the full travel as expected only the front four valve rockers (2 on both sides) actually move. The back four don't seem to rock at all nor do the pushrods so that finally explains the weird compression results. I think Grrrrr noted a snapped crankshaft as a possibility and that's how it looks, assuming the crank moves the pushrods. How all the pistons still move though I don't know. Anyone have an explanation how that's a possibility?
 
Jock85 said:
Well, it looks like a depressing result after all. It took a while to get the fan and rocker covers off but I finally stripped it down to get a view of the cam (?) and valves and although all eight pistons move the full travel as expected only the front four valve rockers (2 on both sides) actually move. The back four don't seem to rock at all nor do the pushrods so that finally explains the weird compression results. I think Grrrrr noted a snapped crankshaft as a possibility and that's how it looks, assuming the crank moves the pushrods. How all the pistons still move though I don't know. Anyone have an explanation how that's a possibility?
Click to expand...
The possibility was a snapped camshaft, not crankshaft, it's fairly simple to replace once you've got the rockers off. You need to replace the hydraulic lifters at the same time
 
Jock85 said:
Grrrrr noted a snapped crankshaft as a possibility and that's how it looks, assuming the crank moves the pushrods. How all the pistons still move though I don't know. Anyone have an explanation how that's a possibility?
Click to expand...

if the pistons move it’s not the crank.
If the valve don’t move it’s possibly the cam has snapped, is that what he said? (The cam is driven from the crank by a chain)
Problem is what damage has that done? Will an open valve touch a piston?

I have been reading this with interest and now, I feel it’s about to get very expensive:( sorry.

J
 
marjon said:
if the pistons move it’s not the crank.
If the valve don’t move it’s possibly the cam has snapped, is that what he said? (The cam is driven from the crank by a chain)
Problem is what damage has that done? Will an open valve touch a piston?

I have been reading this with interest and now, I feel it’s about to get very expensive:( sorry.

J
Click to expand...
If the camshaft had indeed snapped, the all valves will be shut so not much damage. The biggest chance of damage is from any bits floating around getting into bearings. Hopefully it's a clean break
 
kermit_rr said:
If the camshaft had indeed snapped, the all valves will be shut so not much damage. The biggest chance of damage is from any bits floating around getting into bearings. Hopefully it's a clean break
Click to expand...

will they? Please explain.

some will be open/closed or halfway?

J
 
kermit_rr said:
That was my thought, without the chain keeping it in place, the valve springs would turn the free end so most of not all valves would be closed
Click to expand...

Whithout the weight of the spinning crankshaft to turn the camshaft the springs would be the strongest part of the top end...inlet manifold off and have a look me thinks...
 
Shippers said:
Yes...but maybe not enough to open fully hence the lack of compression and the readings he's getting possibly?
Click to expand...

I haven’t checked valves open closed when or tried to get technical about lift and piston touching valves (it’s too late at night) or even if it could.

But engine needs out and a bit of money right now, which is sad to hear:(

it don’t need to be open much (or bent) to loose compression.

J
 
kermit_rr said:
That was my thought, without the chain keeping it in place, the valve springs would turn the free end so most of not all valves would be closed
Click to expand...
some would be open some shut some half way ,it wouldnt suddenly turn under spring pressure ones balanced by another,you only get good compression if valves operate correctly
 
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