16 replies to this topic

[stubbsy]

Hi guys and gals

Got a suspicion that head gasket has gone so think i need to do a compression test??? are there any tutorials on how to do it or is it generally cheap enough to get a garage to do it??

Thanks in advance

Duncan

[Cooperman]

It's a 10 minute job if you have a Gunson (or other suitable) compression tester.
Get the engine warm, take out all the plugs, undo the coil to distributor lead and fit the comp. tester to cylinder no. 1. Push the throttle to the floor and crank the engine for about 5 seconds. Record the reading. Repeat for cylinders 2, 3 & 4, recording each one. If you then need another opinion, post the figures on here.
Re-fit plugs and coil connection and it's all done.

[stubbsy]

Thats great thanks, sounds straight forward. what kind of numbers am i looking for on a 998 ? does Stage one kit affect numbers???

Sorry i really am a novice

[AndyMiniMad.]

Anything above 140-150 will be fine...So long as there is no more than a 5-10 per cent difference between bores.

[bcjames]

To add to the above, label your HT leads 1 to 4 as you disconnect them so you don't get stuck putting it back together. Apologies if that is pointing out the obvious!

[Cooperman]

To add to the above, label your HT leads 1 to 4 as you disconnect them so you don't get stuck putting it back together. Apologies if that is pointing out the obvious!

That's a good point. I usually put some dots of yellow paint on the plug caps to identify which is which.
A 'Stage 1' kit will only affect the figures if it includes a modified head with a raised compression ratio. The expression 'Stage 1' really has no meaning in engineering terms, as it's a sales expression, so it's impossible to say. However, if you get anything over about 145 psi it'll be fine. Just make sure the throttle is fully open when doing the test and that the engine has just been run so it's at operating temp.

[ZKruly87]

To add to the above, label your HT leads 1 to 4 as you disconnect them so you don't get stuck putting it back together. Apologies if that is pointing out the obvious!

good advice. many a time i have full rebuilt an engine to put the plugs back on wrong.

[bushy46468]

just out of interest how much is it for a garage to do / how much in the compression kit to D.I.Y.

[Cooperman]

A Gunson Compression Tester should cost about £25 from Halfords or any good motor factors.
All you need as well is a plug spanner.
A garage would probably charge around £30.

[leroy26]

screwfix do them for seventeen!

[minidazza]

Great thead guys. I want to do a test on my 998 engine. Its nice that we can do jobs like this ourselves, than pay some cowboy to tell it is a gaskit, when it is just a spark plug. I will refer to this thread when I have bought a tester.

[daenesh]

sorry to butt in but what happens if you do a compression test but don't open the throttle fully? i think i might have made that mistake.. as in i forgot to open the throttle fully..

[minimadles]

You get an inaccurate result as the throttle butterfly causes a restriction to the incoming air that is subsequently compressed

[Tamworthbay]

To add to the above, label your HT leads 1 to 4 as you disconnect them so you don't get stuck putting it back together. Apologies if that is pointing out the obvious!

good advice. many a time i have full rebuilt an engine to put the plugs back on wrong.

Did that on my first clubman when I serviced it for the first time. I think it was 2 and 3 I mixed up. It still ran (I got about half a mile) but rough as anything.

[daenesh]

You get an inaccurate result as the throttle butterfly causes a restriction to the incoming air that is subsequently compressed

 

I think i definitely made a mistake there.. haha didnt even warm up the engine as well.. too many rookie mistakes