22 replies to this topic

[Dan]

Normally I'd agree, a leakdown test is far more useful than a compression test which will often hide many serious problems. If there's not enough compression to make a serious result on the compression tester though, a leakdown test of that cylinder won't be possible I don't think.

[Kerrin]

By the sounds of it there is a hole somewhere, Valve, Piston, or Head Gasket or possibly a bent valve.

A small leak will still give some compression. I havent personally seen holed or damaged pistons on a mini engine, but I worked on an MG Metro engine which was running very lean and had burnt out a valve.

Its still worth a look in the plug hole with a torch, in case you can see any damage.

[sam_o]

If you've never done this before I wouldn't bet on being able to use the car on Monday. Anything can go wrong and when you do find the actual problem it may prove to be something you can't fix. If you don't have at least a new gasket set, oil, filter, coolant, Hylomar, all the tools and enough space to do this on your own drive (bearing in mind that this is actually illegal to do on the public highway now) then I wouldn't even start it on Sunday. When you know what you're doing you can replace a head gasket in about 1 1/2 to 2 hours but the first time it can take you hours and hours even if it all goes to plan. If I were you, I'd be planning on a different mode of transport for next week and spend tomorrow getting together what you'll need to do the job properly.

Im not planning on driving the car monday because its not taxed or insured yet lol. I think i have most of the tools i need and its parked in a lot of garages behind my house so theres plenty of space to work on it. I just dont have the knowledge of mini engines to know what to do on them.

[sam_o]

get a cylinder leakdown test done, will tell you whats wrong before you start

How do you do that mate? What tools do i need to do it?

[sam_o]

By the sounds of it there is a hole somewhere, Valve, Piston, or Head Gasket or possibly a bent valve.

A small leak will still give some compression. I havent personally seen holed or damaged pistons on a mini engine, but I worked on an MG Metro engine which was running very lean and had burnt out a valve.

Its still worth a look in the plug hole with a torch, in case you can see any damage.

Right okay then, well i think im going to take the head off tomorrow and have a look in the plug hole to see if its damaged.

[ANON]

get a cylinder leakdown test done, will tell you whats wrong before you start

How do you do that mate? What tools do i need to do it?

to do it as a diy job all you need is a small compressor and a rubber wheel valve.

you need to get both valves closed on the dodgy cylinder, take the plug out and you pressurise the cylinder, the valve will seal over the plug hole but you need to keep it pressed on.
as you've got very low compression you should be able to hear the air escaping. if you can hear it through the oil filler then rings/bores, if you can hear bubbling through the rad/cooling system then head gasket/crack, inlet will be inlet valve and exhaust will be exhaust valve.

[Dan]

Oh I see what you mean. Yes that would work but it's not what I would call a leakdown test. That would be using a leakdown test rig and give a percentage of leakage for each cylinder, if it's not making compression the leakdown tester will just register 100%. Your method would work well Anon.

[sam_o]

get a cylinder leakdown test done, will tell you whats wrong before you start

How do you do that mate? What tools do i need to do it?

to do it as a diy job all you need is a small compressor and a rubber wheel valve.

you need to get both valves closed on the dodgy cylinder, take the plug out and you pressurise the cylinder, the valve will seal over the plug hole but you need to keep it pressed on.
as you've got very low compression you should be able to hear the air escaping. if you can hear it through the oil filler then rings/bores, if you can hear bubbling through the rad/cooling system then head gasket/crack, inlet will be inlet valve and exhaust will be exhaust valve.

Alright then, cheers for your help guys. I'll try and give that a go today, i'll let you know what happens.
Thanks