While looking for the reason why the top speed of my 7 is too low I did a compession test with the following results:-

No1 100psi
No2 85psi
No3 85psi
No4 100psi

This is outside the limits given by Mac in an earlier thread - any suggestions as to what is the problem is and wether this could account for a loss of at least 10mph from the expected top speed?

The engine was fully re-built less than a thousand miles ago and has never preformed as expected.

Dave Griffith

Check the valve clearences first. recommend set at 8 thou.inlet and exhaust. if they are closed up this could be the answer, also try a "wet" compression test. Do your compression test again ,then introduce oil in to each bore in turn. if the low ones improve it points to ring or piston tolerence.

Mac,
Thanks for your reply, I have checked the valve clearences and they are all 6 thou.

I have redone the compression test with a few squirts of oil in each cylinder the results are now all within +/-5 of 150psi. Is this good or bad?

Dave Griffith

I think...Its all in the bores/piston rings. so....The wet test indicates that when it is running they may well balance,but any way not a lot you can do. I would suggest perhaps a bit more mileage before you make a final judement and after a fine ignition settings check.Also check you are getting full throttle. Not so daft,I had a ruby in recently that had been driving with a maximum throttle opening of 2/3 for years! A revelation when we set to open fully... Mac

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Just nicely run in then!


Mike