Peggy's got legs - I got her going

[Steve in Cairns]

Happy to report that after not to much trouble I got her engine running so I decided to push on and do a compression test. All the plugs had black powder on them, so I guess that's the fuel/air mixture.
The compression results were a little confusing. With no throttle all were between 105 and 110, and with the throttle open they were 155 to 160.
Which pressures do I use and what does it tell me?

image.jpg

Please help.

[pop058]

IIRC, cylinders pressures are taken with open throttles.

[Steve in Cairns]

Looking at the figures in the Haynes manual this would mean I have an 8:1 engine as the results are higher than the 145 lb/in for the 7:1 engine. Am I wright to assume this?

[JDNSW]

Have a look on the cylinder head, just next to the rocker cover beside the carburettor. There should be a square raised block cast into the cylinder head, and on top of it should be a stamped number.

'8' indicates an 8:1 engine, '7' or no number means 7:1, as does no number, and no raised block means an early 7:1 head, which, at least in theory, does not have enough metal to allow it to be skimmed to raise the CR.

This information may be incorrect, as the head may have been skimmed at some time in the past raising the ratio of the head. The stamped number may be very light.

John

[Ozdunc]

As John says the stamped number can be very light, I had no idea my engine was 8:1 until I wire brushed the square block above the manifolds

[Phil B]

Peggy's compression is very good though with consistent and high figures.
Sounds like it may be time to put a new kit in the carb or fit a new carb.
That will make a huge difference from experience.

Phil.