Hi,

 

Does anyone have a link to a write up on the correct way to do a compression test?

 

Cheers

 

Vijay

found one http://www.twinturbo.net/nissan/300zx/FAQ/FAQpages/compression.html

 

How much oil do you pour in if compression is low and what's a low figure?

 

Vijay

bump

about a teaspoon i would say?

if you get a low reading, what could be the cause?

Worn rings, head gasket, stuck valves, piston damage, cracked head

A few pointers - there is plenty more to add, and nothing is conclusive without further tests...but gives you some ideas -

 

150+ is a good strong engine

Getting a bit tired at around 130

 

A poor dry test, but good wet test would indicate worn rings and/or bore damage. Will often see excess pressure through crankcase such as fumes out of oil filler cap, or pushing dipstick out.

 

A very low figure or zero compression will usually indicate a holed piston.

 

No significant difference between wet and dry, but 2 adjacent bores with low figures can indicate head gasket. WOuld need further investigation to prove though - such as Losing water, overheating, gasses in Cooling system..etc

 

Heads (alloy) can warp

Block (iron) can crack

Cheers guys :)

Once you do a compression test and find a low reading.

Do a cylinder leakage test and find the leak.

 

Bubbles in the rad = head gasket

hissing from the exhaust = outlet valves

Bubbles from the rocker = piston rings / cracked piston or bore scratch.

Hissing from the intake = inlet valves

Edited July 24, 200817 yr by SMW1
added inlet valves

Once you do a compression test and find a low reading.

Do a cylinder leakage test and find the leak.

 

Bubbles in the rad = head gasket

hissing from the exhaust = outlet valves

Bubbles from the rocker = piston rings / cracked piston or bore scratch.

 

And from the intake? inlet valves?

yup

I sometimes get hissing from my backside.. what would that be then?

I sometimes get hissing from my backside.. what would that be then?

 

IIA valve / idle control valve , they often fail/leak, and result in a poor idle

I sometimes get hissing from my backside.. what would that be then?

 

You have been eating your own cooking :D:nelson:

cylinder leakage test, take it I need a bit of equipment for that??

 

Vijay

I sometimes get hissing from my backside.. what would that be then?

 

as said - worn ring! :rofl:

IIA valve / idle control valve , they often fail/leak, and result in a poor idle

 

haha legrath with the serious post :D

haha legrath with the serious post :D

 

it was too easy to make a joke reply :p