Engine compresion testing questions?

[172lover]

Hi folks

My friend is calling up with his car tomorrow.
He was told there's something wrong with cylinder 3...
also theres a bit of black smoke with it hits 6,300rpm.


when I do a compression test(spark plug out, tester in...crank for 10 seconds)


Whats the other way of checking it?
drop a bit of petrol down the spark plug hole and then do the test.....?

what does the second way prove?


(also is it best to remove spark plugs one at a time or all 4 when testing??)

(car is a vzr pulser)

thanks

 

[MG cup]

Either have them all out when doing each cylinder or take them out one at a time so the test is equal.

putting drops of 'oil' into the cylinder helps to show wether its rings or valves/ head gasket.

Make sure to remove the coil pack plug.

 

[Dan@SJM]

On the pulsar you'll need to hold it at full throttle.

 

[172lover]

Either have them all out when doing each cylinder or take them out one at a time so the test is equal.

putting drops of 'oil' into the cylinder helps to show wether its rings or valves/ head gasket.

Make sure to remove the coil pack plug.

Ah oil!
i got mixed up with petrol

So if the psi raises after dropping a teaspoon of oil in.... More then likely it's rings?

If it stays the same it valve stems..

Correct?

On the pulsar you'll need to hold it at full throttle.

Thanks dan
how come only some cars need the throttle open?

my f7r was compression 195,190 without touching the throttle

 

[MG cup]

Ah oil!
i got mixed up with petrol

So if the psi raises after dropping a teaspoon of oil in.... More then likely it's rings?

If it stays the same it valve stems..

Correct?

Yes typically but its quite common to see f4r's with compression down due to the piston ringland.

It could also be a leaky valve or knackered fire ring on your head gasket (not likely on a Clio I'm told)

EDIT: im forgetting its for a pulsar

 

[172lover]

Thanks for the help,

dry compression was,

240-250-250-260

Wet was,

280-255-250-265

so something is off with the first cylinder...

​

 

[Dan@SJM]

No, they're acceptable on dry, however the wet test has highlighted 2,3 and 4 have issue elsewhere than the rings.

 

[MG cup]

Shouldn't be a massive running problem with those figures IMO

 

[Dan@SJM]

Shouldn't be a massive running problem with those figures IMO

Tbh I don't think there would be an issue with compression. They're bloody good figures, I do know the VZR does run something like 13:1 static CR.

 

[172lover]

I was impressed with the psi!

The car is 175bhp standard...
went on a rr and made 145bhp.
(4 branch manifold,decatted and exhaust)

The mechanic/dyno fella said there was a problem with Cynder 3.

Spark plugs were changed 1 week ago and already there black as feck!

So the friend is on about rebuilding it at the head of the year.
(197bhp vzr head and a Alicia bottom end)


would a leak down test be worth buying?

 

[Dan@SJM]

Tbh black plugs sound more like a fuelling issue. Got a copy of the graph? Does it show the AFR?