compression ? spark plug ?any idea

[bigmike35]

been told my engines compression reads 130,130,130,75 bere in mind its been stood for 5 years got it started quite easly but i thaught it sounds like its missing so i took a spark lead off at a time 1,2,3,4. 1,2,3,made a lot of differance number 4 didnt alter any thing so it seems to be running on 3 would low compression do this? my way of thinking is it must be a sticking piston ring making comp low as i been asured engine in fab working order last used so if spark plug knackerd not getting spark to ignight petrol to get any chance to burn this crap away any other ideas greatly welcome

[Matt]

Try quicksilver powertune - in case it's gummed up rings etc. Otherwise, with that much difference in pressure, time to pull the head and see what's going on!

[SultanOfSoltron]

have you tried removing the spark plug, holding to the engine block and turning the engine over, and seeing how strong the spark is?

Also when you remove the plug, is it wet as if mixture is getting into the cylinder - or is it bone dry.

I would thought even if little compression as long as there is fuel and spark you should get some firing on the cylinder, not as you say, make no difference when the plug lead is removed.

[ashbypower]

Some answers here http://www.rib.net/forum/showthread.php?t=13174

Brian

[tue]

The genaral rule when it comes to compression is a maximum tollerence of 15psi variance between cylinders. You will almost certainly notice a cylinder down if it is only running at 75psi when the rest are so high. You could try powertune, but as its the lower cylinder I would tend to just jump in and get the head off (any moisture in the engine will drop to lowest cylinder). You may be lucky and just need new piston rings, bbut also check for scoring of the cylinder bore itself and if you can feel the scratches when you run your finger around the bore then its off for a rebore and oversized piston .

Just noticed the pic of your engine. That one has no head gasket, and checking of the piston rings/bore requires a powerhead off and strip job

[Matt]

Boroscope/Endoscope down the spark plug hole then to see what the bore is like!
There's usually a few on ebay!

[bigmike35]

what are these scope?

[bigmike35]

changed plug no difference.Is the engine worth spending on as must be honist havnt got much spare cash and dont want to spend if thay not much good but on the other hand under the covers is spotless looks like new

[tue]

IMHO no. Its certainly not woth paying for a engineer to do the work. On the other hand if you are prepared to do the work yourself then you will have a motor that runs and the bits should only cost you around £150 (unless you need a re-bore).