when to compression test a newly built engine??

[cantfindausername]

Hi everybody... I'm just wondering after how many miles should you compression check a freshly built engine?

Thanks in advance for any advice
Ant

[Guy Croft]

You'll see about the highest it's going to achieve on a compression test within a very short time, 20 miles is the lowest I've done that, though that's not to say at all that the rings will have bedded in fully by then (and oil consumption stabilised). That takes way longer. The valves and seats bed in seconds.

For info: Hot engine, all plugs out, wide open throttle, isolate injection/ignition otherwise you might pump gasoline straight into the catalytic converter and light it up when you restart.

It should take no more than 2 or three strokes to achieve peak pressure, don't stop cranking until the gauge stops climbing. There are reasons for slow rate of climb if that is what you find.

GC

[cantfindausername]

Thanks Guy. I've done about 25 miles on the engine so far (still not legal), but that will go up considerably over the weekend and next week as I'm getting my MOT and Tax later today.

I think I'll wait till maybe next weekend and do the test then and report back with my figures.

Thanks,
Ant

[mack124]

Hi Guy,
I've just read this thread and was wondering what sort of pressure you would be looking at for a relitavley standard 2ltr Fiat TC? with 9:1 CR and the GC recomended valve/seat work.

Would a highly tuned motor have any more compression at cranking speed or does most of the modfications come into place once the engine is actally running?

I have ghad a quick test of my compression. It seemed a bit low but the engine is still very fresh. The pressures were all very even though.

Regards
Gill

[cheitane2003]

Hello:
In my new rebuilt 1919 ccm Beta motor with 50 ccm combustion chamber, after 400 km road test , I found the following compresion numbers. I don‚´t know if they are very good or not, but are very similar.
Cylinder 1 2 3 4
Static 195 192 192 185
Idle 50 70 50 55


All are psi.

Best regards,

Siro,