Compression Test

[Masekwm 2]

Decided to do a compression test on my 205 as it's sounds like it has a missfire and one of the plugs had oil on it, during a service a while ago.

 

I let it get to temperature with the throttle held open and using a push in connector. All the readings gave a good first jump followed by smaller rises.

 

1 Drivers side wing - 105

2 110

3 105 - This is the plug with oil on the thread

4 150

 

 

What do they mean? I meant to put some clean oil in but was beaten by the darkness

 

I'm thinking HGF from the Haynes notes?

Edited September 24, 2008 by Masekwm

[welshpug 1,666]

150 sounds reasonably healthy, but the rest definitely a bit low, try with a bit of oil as you mentioned.

 

not sure about the 8 valver but a fresh 16 valve is usually around the 200-220 mark.

[Cameron 16]

Check them again when it's light.. like Weshpug says do a dry compression test like you have done, then squirt a little bit of oil down the plug holes and test it again. If it's a noticeable difference it would point to worn rings.

[mickie 3]

and if compression still doesnt go up its valves..

 

a drop like that between cylinders is bad tho.. guesstimate i would say between pistons the compression drop shouldnt be more than 25psi

 

oil on the spark plug can only be piston rings, valve stem seals or the cylinder head gasket..

 

drop some oil into the cylinders through the spark plug and do a compression test again, if compression goes up, its rings, if it doesnt then it may be head gasket or valves..

 

either way i'd be re-building what ever is wrong with it

[Masekwm 2]

Erm... How can I put this, I screwed up

 

1 - 195

2 - 200

3 - 205

4 - 205

 

Now, the worrying thing, cylindar 3, whilst testing occasionally blew a fine mist of oil. Would that be the Stem Seals?

[mickie 3]

Erm... How can I put this, I screwed up

 

1 - 195

2 - 200

3 - 205

4 - 205

 

Now, the worrying thing, cylindar 3, whilst testing occasionally blew a fine mist of oil. Would that be the Stem Seals?

 

with those compression results i'd say yes.. thats if you have done a compression test again with a drop of oil in them and making sure you aint over full with oil..

 

really easy to change valve stem seals without taking the cylinder head off, drop some rope down the bore through the spark plug hole and either buy a tool or make one to take the valve springs out in place.. obviously a little more too it than how im explaining but not too much more

Edited September 25, 2008 by mickie

[Masekwm 2]

with those compression results i'd say yes.. thats if you have done a compression test again with a drop of oil in them and making sure you aint over full with oil..

 

Those results were without putting any oil into the cylinder.

 

 

really easy to change valve stem seals without taking the cylinder head off, drop some rope down the bore through the spark plug hole and either buy a tool or make one to take the valve springs out in place.. obviously a little more too it than how im explaining but not too much more

 

I think a post in wanted is in order

[Cameron 16]

Drop rope down the bore?? What tee eff?

[wardy18 33 1 Cars]

I assume the rope is to cushon between the valves and the piston so that when you tap the valve when sat on top of the piston to release it you dont bend it by hitting metal on metal....

 

may be wrong thou

[Cameron 16]

What the clucking bell? Do people actually do this!?

 

Gimme a C.. an O.. a W.. a B.. another O.. You know the rest..

[RINRIN 1]

Check them again when it's light.. like Weshpug says do a dry compression test like you have done, then squirt a little bit of oil down the plug holes and test it again. If it's a noticeable difference it would point to worn rings.

 

So the compression should go down with oil drope?

[Anthony 1,003]

What the clucking bell? Do people actually do this!?

 

Gimme a C.. an O.. a W.. a B.. another O.. You know the rest..

Actually it works suprsingly well using that and a suitably adapted valve compressor - I've seen it done and I was impressed. Remember that all you're doing is stopping the valve dropping into the chamber - nothing more, nothing less.

 

Personally, I'd pull the head off as normally if the head has done enough miles that the stem seals are shot, then the chances are the rest of the head could do with a rebuild - but if it's purely the stem seals you're doing, then the rope in the cylinder trick works fine, and obviously there's no risk of snapped headbolts and the like that way either.

[Anthony 1,003]

So the compression should go down with oil drope?

No, often if the rings are worn, the compression test will be noticeably higher with a few drops of oil down the bore (the oil effectively stops the air leaking past the rings)

[mickie 3]

I assume the rope is to cushon between the valves and the piston so that when you tap the valve when sat on top of the piston to release it you dont bend it by hitting metal on metal....

 

may be wrong thou

 

changing valve stem seals this way is too easy, get a rope, about 1M long, tie a knot in it so it doesnt fall into the cylinder, push it down the bore through the spark plug hole, turn the rope a few goes till it spirals up.. doing all this with the piston at the bottom.. once the rope is in, turn the engine going for TDC untill it hits the valves, or stops the engine turning..

 

this will stop the valve dropping, if the valve did drop you may have to take the head off..

 

what i do once the rope is in, push down on the valve seat top and if the spring moves but the valve doesnt, that means the rope is doing its job and its safe to take the spring out..

 

using what ever tool you are using, take the valve spring out as you would using any normal valve spring compressor..

 

valve will be stuck there, pull off valve seal and replace, easy as that

[mickie 3]

Actually it works suprsingly well using that and a suitably adapted valve compressor - I've seen it done and I was impressed. Remember that all you're doing is stopping the valve dropping into the chamber - nothing more, nothing less.

 

Personally, I'd pull the head off as normally if the head has done enough miles that the stem seals are shot, then the chances are the rest of the head could do with a rebuild - but if it's purely the stem seals you're doing, then the rope in the cylinder trick works fine, and obviously there's no risk of snapped headbolts and the like that way either.

 

i'd do a leak down test first, even tho the engine may have worn 1 or 2 valve seals, piston rings and valves may be ok..

 

doing the leak down test and a proper compression test should tell you how bad the engine really is and what work needs to be done

[Cameron 16]

If it works then fair enough.. personally I'd rather put my balls in a vice than go sticking foreign objects into my cylinders! Just imagine how many bits of grit and s*ite could be on that rope, even if it's new. Might as well go sticking some rubbing compound down there for good measure.

[mickie 3]

If it works then fair enough.. personally I'd rather put my balls in a vice than go sticking foreign objects into my cylinders! Just imagine how many bits of grit and s*ite could be on that rope, even if it's new. Might as well go sticking some rubbing compound down there for good measure.

 

first i knew they made rope out of bits of grit..

 

buy a soft rope, somethink like climbers use. theres probably more grit in the oil than on rope

[Masekwm 2]

Would someone like to show me the rope trick?

 

Otherwise it looks like I'm stripping the head off.

[mickie 3]

 

take all the spark plugs out, get a long screw driver and stick it down through the spark plug hole, you wanna get the piston between TDC and BDC

 

take the timing belt off, making sure its marked up, so making it easier to put back.

 

take the cam cover off, then the camshaft caps and camshaft, making sure you know where it goes back, number them or something..

 

buy some soft rope, i got some from B&Q, push it down through the spark plug hole, twist it up, making sure its at BDC.

 

now turn the engine from the crank untill it stops, whatever cylinder your rope is in, take a valve lifter out of that part you're working in, to make sure the rope has the valve stuck in place, push down on a valve spring and look to see if the valve stayed in place, if it didnt, pull the piston back down, play with rope, push it back up and have enother go..

 

when you're happy get your overhead valve spring compressor and take a spring out, use a magnet to collect the collets and other bits, take the valve seal out with some long pliers or valve stem seal pliers.

 

put some silicone grease on the new seal, push it over the valve all the way down to the valve guide, using a socket, maybe 12mm, i cant remember, push the seal right down, untill you can feel its all the way down..

 

put the spring and everything back and start on the next valve..

 

its a lot easier to understand with pictures but if you search the internet, there is loads of info

 

 

ohh and the rope i used was black when i pulled it back out, theres more carbon in cylinders and durt than on my clean peace of rope

Edited September 29, 2008 by mickie