Compression test

[moggiethouable]

Morning all,
I thought as a matter of course I would attempt a compression test.
The engine is a 1098, bog standard, can anyone tell me what sort of readings in p.s.i. I should look for ?
Thanks.

[philthehill]

150 lb is a good average.
All plugs out - throttle fully open (brick on the pedal) and turned over on the starter to build up to max pressure.

[svenedin]

150 psi is what I got with my absolutely standard and rather worn out 1098cc. Since rebuild, 170 psi.

Although a useful test, a compression test only tells you what happens at the relatively low cranking speed. I found that although it gave good, completely consistent compression readings, in use especially at speed (e.g 50-60 mph) my worn engine used a lot of oil.

Stephen

[moggiethouable]

Thankyou people, how much does it matter if the engine is hot or cold?

[moggiethouable]

My final thoughts are this.
Number 4 cylinder is well down, the rockers are worn, the front oil seal leaks and she does not have yet a lead free head or duplex chain..
So I think I am going to plumb for a reconned engine with everything sorted.
At 98k miles without major repairs I think its time.
She is worth it.

[Bernie-the-Bolt]

Ran a test on my 1098 J reg Traveller last week, results were :-
141, 139 , 135 , 135.
I didn't do a "wet " test because I thought they were OK figures at the time , but reading this they seem quite low.
I guess I ought to do it again with a wet test to prove if a problem with rings / bores ?
I am planning on reconditioning the cylinder head over the winter and fit new valve guides and the newer type seals , as she is burning a bit of oil on overrun.
I have no history of the engine though , except it is a silver seal factory replacement. Speedo showing 60k + ( probably been around at least once )
Mpg is about 29mpg. Drives OK though.

[TonyTorque]

Those four readings are nice and even, which matters more than the absolute figure. I'd do the wet test like you say, just a squirt of oil in each bore, and if the numbers jump by 20 psi or more that points at rings rather than valves. Was the engine warm and the throttle held wide open when you did it?

[Bernie-the-Bolt]

Hi Tony ,
Yes engine was warm ,all sparkplugs removed . Throttle pedal,held down with a block of wood.