71 replies to this topic

[Cooperman]

You need a 'leakdown' test, not a compression test. A leakdown test will indicate ring condition.

It does seem as though it is piston ring/bore related. It is not difficult to break a ring, especially if the engine overheats or runs with too much ignition advance.

I am surprised you have 28 cc combustion chambers with what I think are flat-top pistons. The 28 cc chambers are for raised D-top pistons where the raised tops take up 4 cc of volume, so with flat tops the chamber volume should be c.24 cc (subject to measurement & calculation). Not that this has any bearing on the smoking.

The only real option is to remove the engine and strip the pistons out for inspection. I would bet you will find either a cracked/damaged piston, a broken ring or a badly scored bore.

Just a thought, but if the manifold has a leak it could have been running too lean and if it was retarded as well that would cause a build up of heat in the bores and thus, possibly, the damage.

[BronkoMini]

Thanks for the reply I shall have to see what happens tomorrow, it's not really looking good. At least I have my brothers mini to drive while I sort this out.

[BronkoMini]

Just got back from the garage and the compression test result are as follows
Cyl1: 140
2: 150
3: 40
4: 35 I think it was in psi

Also looking at piston 3 and 4 there appears to be oil on the top of the pistons, the garage said the next step is to take the head off, but I think I shall wait and try to get it to Combe. Garage thinks it may be the piston rings, head gasket or maybe valve guids, he couldn't be sure unless the head gets taken off.

[BronkoMini]

Oh and his leek down tester broke so couldn't do that test.

[silve1999]

not good... to be honest I wouldnt be driving it like that :-(

[Nick Warwick]

Very low on 3 & 4, i personally wouldn't drive is without knowing what it is as your risking more damage if its more than just a head gasket or valve guide.

 

Head gasket could have gone between the two cylinders with them compression results. It only takes around 3 hours to change a head gasket.

 

Have you done a wet compression test? two squirts of oil down the bore you are testing to see if its the rings.

[BronkoMini]

Very low on 3 & 4, i personally wouldn't drive is without knowing what it is as your risking more damage if its more than just a head gasket or valve guide.
 
Head gasket could have gone between the two cylinders with them compression results. It only takes around 3 hours to change a head gasket.
 
Have you done a wet compression test? two squirts of oil down the bore you are testing to see if its the rings.

Will have a look at how to do a head gasket change, and no didn't do a wet compression test.

[klivins]

It clearly isnt healthy enough to drive somewhere. may be limp home mode only. Something was bad from the start if the smoke was present, I would go back to the seller.

[Cooperman]

With those compressions and the smoking I would not even drive it to the local shops.

If, for example, it is a cracked piston, it could easily break up and the pieces drop into the gearbox with the con-rod seriously damaging the bore and possibly the camshaft as well.

Head off before driving it again, the probably engine out and strip for inspection & repair.

[BronkoMini]

It clearly isnt healthy enough to drive somewhere. may be limp home mode only. Something was bad from the start if the smoke was present, I would go back to the seller.

I'm not sure what the seller could do.

[BronkoMini]

With those compressions and the smoking I would not even drive it to the local shops.
If, for example, it is a cracked piston, it could easily break up and the pieces drop into the gearbox with the con-rod seriously damaging the bore and possibly the camshaft as well.
Head off before driving it again, the probably engine out and strip for inspection & repair.

I'm going to take the head of and go from there.

[BronkoMini]

Also there wasn't that much smoke when it first started up just a bit from the tappet breather, I just presumed that was normal as the rocker cover that came with the engine had breather points.

[Cooperman]

It could well just be a head gasket, but that won't be known until the head is removed for inspection. The fact that the compressions are down on two adjacent cylinders points to HG.

It really is pointless speculating and only inspection will give the correct answer. It really is VOR until the head is off and the problem resolved.

[BronkoMini]

Also it's a bit annoying, only just out it in, at least it's still fresh in my mind. The problem is as I'm off to uni I won't have much time to fix it.

[BronkoMini]

It could well just be a head gasket, but that won't be known until the head is removed for inspection. The fact that the compressions are down on two adjacent cylinders points to HG.
It really is pointless speculating and only inspection will give the correct answer. It really is VOR until the head is off and the problem resolved.

Will take it off later I'm just reading up in the Haynes manuel on how to do it.

Edited by BronkoMini, 24 September 2014 - 04:29 PM.