4 replies to this topic

[beentheunseen]

Hey everybody,

I have a 1989 998cc mini, which has been suffering from an unfortunate rattlely/tappetty sound for a long time now. A year ago I eliminated all of the obvious things, i.e. setting the valve clearances, replacing the timing chain/rockers/water pump/cam followers, and I have had the head off and fully inspected the valves etc. From what I could tell, everything on the top end looks fine.

I have been out of the country for the last 12 months, and so she has been sitting unused in the garage for a long time. However, she appeared to start up fine the other day. Last time she was was on the road, other than the tappetty sound and slightly low oil pressure she ran fine. For this reason, I was starting to suspect that one of the main bearings was on the way out so I was gearing myself up to take the engine out.

However, I just got hold of a compression tester for the first time, and the readings came out as 110 PSI on cylinders 2, 3, and 4, but no compression on cylinder 1!

As I recently had the head off and removed all the valves, so I know that all of the valves, seats and springs are in good shape, and as far as I could tell there was no significant wear in the valve guides. The head gasket is brand new, and head isn't cracked. What should I check for next? I'm thinking it must be valve related, as I cant imagine the bore could possibly be worn enough to cause zero compression... If one of the valves is leaking for some reason, would the engine still appear to run relatively smoothly? I definitely didn't notice any loss of power last time it was on the road which is what makes this kind of confusing...

[lrostoke]

Seems odd to have no compression, did you redo the test to be double sure.

[beentheunseen]

Seems odd to have no compression, did you redo the test to be double sure.

I did, and I went back through the other cylinders just to make sure the gauge was still working, but I agree it seems odd... Going to recharge the battery and give it another go tomorrow. I'm familiar with the problems that could cause LOW compression, but is there one thing in particular that NO compression would point to?

[zef]

I bet you it's the same problem we've just fixed by swapping the head. The next time it rattles whip the rocker cover off and you'll probably notice 1 valve stuck down. Reason it's stuck? Bet you the valve seat has fallen out and rattles round the valve jamming it open. Ours was intermittent, rattling and poor running then a click and it was fine. Might be worth checking.

[beentheunseen]

Ok, just found the problem - one of the rockers was too tight and was holding the intake valve slightly open... I must have made an error when I put the head back on. Loosened it up and now the compression is the same as the other cylinders. False alarm everybody, looks like the main bearings are still the number one culprits for the rattle.

Edited by beentheunseen, 12 January 2010 - 08:07 PM.