Lack of compression on one cylinder, Think its the cam.
Turbo Mini Forums

I got my turbo engine started today for the first time in about 6 years, It was bought in unknown condition for the basis of a rebuild.

I got it started today for the first time, but before that. There appeared to be no compression when cold on number 2 cylinder and there is compression on the rest, I have yet to do a propor test as i need a diffferent spark plug fitting for the tester.

So pulled the head off, reground the valves, taken wire wool and white sprit to the block and head faces, and adjusted tappet clearences. also new head gasget. still no compression on 2 cylinder. I also put on another head to check the head was not warped, and replaced the gasget again

I then got it started and up to normal operating temperature and repeated the test of thumb over the cylinder, still no compression. Tthen bunged loads of oil down the bore and got compression for about 5 strokes of the engine before it was down to pathetic again.

There was no smoke at all at idle, or at about 1500 rpm I couldn't get it to rev higher than that because it would then die - fueling related I think

I will do a propor compression test tomorrow when I have the right spark plug fitting, However I am concerned that there is more wrong here then just goosed rings, such as warped block face.

Will a proporly goosed piston ring really loose all that pressure to the point where a thumb can resist it.

That is all I could think of, sorry for the long winded post.

Edited by minimole23 on 8th Jun, 2007.

Are the cam lobes for that cylinder round instead of spiky?

Edited by Tom Fenton on 21st May, 2007.

I will have to check the lift on them, However in desperation I even adjusted the clearences to about 3mm to see if that made a difference due to incorrect grind in the first place.

Edited by minimole23 on 21st May, 2007.

3mm!!! That will make things worse not better.

i would turn the engine over with the rocker cover off and see if all the valve move right.

put it in 4th gear on the flat, ignition well and truely off and push it along to see what all 8 valves do.

if you have no feeler gauges, you want a small movement, i.e. just feels like it moves. that would see if the compression is ok anyway but wants adjusting correctly to approx 0.015" or .38mm.

feeler gauges are usually about a pound and a worthwhile investment

Edited by minimole23 on 21st May, 2007.

well if the valves are seating correctly and there isnt a big hole in the piston it has to be rings.

Although saying that i would expect some compression with completley shagged rings.

The piston goes up and down on that cylinder with the rest doesnt it?

Hi,
The fact that you did get some compression with the oil in the bore would suggest rings. I would expect it to breath heavy / smoke when running though....
Cheers,
Gavin :)

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thats exactly why I am so confused, because there is no smoke at all. it isn't under load though, but still i would expect some.

at least the turbo's good

Hi,
Well that's something!
Comp test got to be the way to go now, leak down even better
Cheers,
Gavin :)

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I also thought i'd add there is no smoke out of any of the brethers. something that has just sprung to mind, when i fired it up originally I did so without water and got smoke or steam out the thermostat housing. I gave up trying to figure which of the 2 it was, though there was abosultely no water in it. it had been running for 30 seconds. then i shut it off and filled it with water.

Hi,
That could well be some water lying in the bottom of the water jacket getting boiled off.
Cheers,
Gavin :)

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RINGS!............... take the engine out get it bored

why not go to 1380cc

I should have expected that comment from Benross!

Edited by minimole23 on 22nd May, 2007.

Hi,
Post up the results when you're done
Cheers,
Gavin :)

Edited by Bat on 22nd May, 2007.

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I have just carried out the test and it has come out as expected, it does indeed require a rebuild.


1- 150
2- 40
3- 170
4- 190

oh well I did state in the ad i placed, it doesn't matter if it needs a rebuild. Never mind its not as if i paid a stupid price for it £170 quid last year. No nasty rattles either from the bearings. and a turbo that doesn't smoke.

Infact i am so confused as to why it is not smoking, could the compression rings have broken but the oil control survived? - just clutching at straws now.

I'll get a leakdown test done before i rebuild it, but it can go back under the work bench now for 2 years till i can afford to rebuild it and the insure it.

Edited by minimole23 on 7th Dec, 2007.

Sounds like cam lobe, had the same problem a few years back. I thought mine was the rings as it had the same symptoms so I went out and bought all the parts I needed for a turbo conversion, as I would be stripping it all down anyway. It was only when I took everything apart I realised the cam lobe was worn (Inlet IIRC).

Thats how it became a turbo. Lol

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1/4mile in 13.2sec @ 111 terminal on 15psi

yeah i wouldnt say its rings yet. measure the lift on each rocker, its farily easy. infact you would probably notice this just by having the rocker cover off and comparing to the next whilst pushing it along...

I will whip the rocker cover off now, I can't push it as the donar car is non existant!

socket on the crank pulley nut then even better!

ideally you want to measure the lift with a dial indicator on the pushrod but a roughly estimate should do if your that far down on compression.

I will whip the rocker cover off now, I can't push it as the donar car is non existant!

Right, I checked and the lift is about 4-5mm which I compared to the other cylinders. Its a crude measurement as I had to use a ruler as I do not posess the correct instruments

Second edit: what the hell happened there?

Edited by minimole23 on 22nd May, 2007.

and in comparision to the other cylinders is...

i cant think off hand whether 4-5mm is a lot of not a lot. i'm thinking its not enough so points towards valve train, i.e. goosed cam, sticking/damaged cam follower etc.

Sorry I can't count, the lift was 5-6mm the intake was about 0.5mm below the rest on the offending cylinder.

Mabie I should invert the engine and slot another cam in I may be able to retrieve the cam followers with some careful magnet work from number 2 cylinder.

Edited by minimole23 on 22nd May, 2007.