1098 compression test figures

[ratrodmog]

Good evening all.

I need clarification as I'm questioning my methods and results.

Comp test done on my 1098 with a low mileage crank. Engine hot, all plugs out, throttle wide open and getting 170psi on all four cylinders (give or take 1 or 2 psi). Hoping this is the correct method? I'm getting a bit of blue smoke on startup and when left at idle but not when driving at road speeds. My best guess is worn valve seals (top hat type fitted on the inlet) or possibly slightly worn guides. The engine is running a little rich (HS4 SU fitted with an AAU needle) which could add to the smokey exhaust.

Trusting the reading isn't too high?

Ta

[Chipper]

Sounds very healthy to me. Anything around 140psi above is OK.

[Chipper]

Sounds very healthy to me. Anything around 140psi above is OK.

[oliver90owner]

Crank condition will have no bearing on compression results. Pressure gauges on these tools are not always very accurate - they don’t need to be as results are used as a comparison, not an absolute value.

Simply, the results being of less than a 5% range is good.

Seems like you have followed the proper instructions for carrying out this procedure.

The engine would ‘pink’ under load if the compression was too high. It is not going to be too high if the engine is in standard condition?

[mogbob]

Compression figures sound great. Nothing wrong with your technique either.
Worn guides might eventually be the cause but eliminate everything else before making an appointment with Engine machine shop !

First of all you say it's running a bit rich. So check the timing first of all and the state of the points, HT leads ,
plugs,etc. Are the valve clearances OK , no tappet noise ? What state are the valve seals in , still sound or in the process of disintegrating. If they are knackered , replace , set up the clearances again after reassembly.Then tune the carb. ( I assume the carb is in reasonable nick , not covered in oil grease and grime to give a clue as to how clean the internals are ? ) .
Good luck with it.
Bob

[ratrodmog]

Thanks for all the replies and it's god to know that I've followed the appropriate procedure (I know everyone has slightly different methods).

First of all you say it's running a bit rich. So check the timing first of all and the state of the points, HT leads ,
plugs,etc. Are the valve clearances OK , no tappet noise ? What state are the valve seals in , still sound or in the process of disintegrating. If they are knackered , replace , set up the clearances again after reassembly.Then tune the carb. ( I assume the carb is in reasonable nick , not covered in oil grease and grime to give a clue as to how clean the internals are ? ) .

Valves could do re checking again as I've not done them since setup and that was a couple of 1000 miles ago. Stem seals look alright although I can only look through the valve springs so access isn't great.

Sounds very healthy to me. Anything around 140psi above is OK.

In the clear then!

Crank condition will have no bearing on compression results. Pressure gauges on these tools are not always very accurate - they don’t need to be as results are used as a comparison, not an absolute value.
Simply, the results being of less than a 5% range is good.

I guess I'm just looking to see how close each cylinder is to one-another rather than a definite value on the gauge.

Now to wait until this rain eases so I can get the car out and start tweaking the engine without gassing out the garage!