69S Compression Test Results

[Scott72]

Hi,
We did a compression test today on our 69S and the results seemed odd to us.

On the right bank:
#1 135
#2 135
#3 140

On the left bank:
#1 160
#2 170
#3 166

Never seen this before - such a large difference between banks. We retested it twice to make sure we didn't make an error. Engine supposidly has less than 1000 miles since rebuild. Have a stack of receipts confirming this. Has anyone seen this before?

Thanks,
Scott

[Flieger]

Perhaps the cams are not timed close enough to each other. There is a spec for the lift when setting one cam, and the other should be at the same lift and within that spec. It is a few tenths of millimeters, IIRC. Perhaps you have a few too many tenths of difference, leading to the different compression patterns.

[MarkS]

I think Max is on to something.

[Neil '67 911S]

Does it drive in circles?

[Scott72]

I wish it did. Between this and the bad bearing in the tranny it doesn't really move much at all.

Thanks for the responses.

[chiroracer]

sometimes I have done a compression test when the throttle blades are closed and it effects the reading, with the overlap the readings may also change a bit depending on how fast you spin it over, ie' the difference between static and dynamic compression. S

[Flieger]

Yes, the throttle linkages could be mis-adjusted so that only one side is getting full throttle. I have also heard of people finding that they have two different cams in the engine, though that is usually when buying a used project engine, condition unknown.