Hitchcocks Forum

Greetings fellow tinkerers,

I have fitted a new timing 12T sprocket to my 1959 Connie engine and the valve timing now appears to be 5 degrees advanced. Exhaust closes 30 degrees ATDC, inlet opens 35 degrees BTDC. However the timing details in the workshop manual are also confusing. The manual gives super meteor inlet valve opening 30 degrees BTDC but gives the Connie inlet valve opening at only 24 degrees BTDC. I would have thought that the higher performance camshaft would open the inlet valve earlier. Does anyone have any more info or experience? Thanks in advance for any info or feedback.

Regards Alan

Alan,
Are you using the timing marks?

I would not rely 100% on the figures in the manual as I have measured a few engines over the years and not one matches the manual exactly. Also do you have the Constellation "R" cams fitted? as all the twin cams are interchangable (except the S11 Interceptor) and there are a few variations of inlet cam sprocket

Hi,

Thanks for the feedback Norm and Chevy. The engine as I bought it several years ago was a mixture of sm and connie parts but worked quite happily for many years with a good turn of speed. It had connie cases, SM heads, SR2 magneto and I don't know what crankshaft. It also came with INR and EXR camshafts. After a bottom end meltdown caused by a hole in a piston I rebuilt it. It now has a different crankshaft, constellation heads and the same cams. The old 12T sprocket was cracking up so I fitted one from Hitchcocks but the timing marks did not quite line up but I chose the closest position and took it for MOT. It ran but there was a lot of spitting back through the carb and little power. I checked the timing was still about 10.5 mm btdc and fitted a carb slide with smaller cutaway to richen the mixture as you lift from tickover. It improved but still spat back and little power. Thats when I started chasing valve timing. I bought an OEM 12T sprocket which seemed to differ by a few degrees. The timing marks now match up well but still spitting back and misbehaving. Next I am going to try to get the inlet opening as close to the 24 degrees quoted in the book for Connies and see what happens, regardless of timing marks.

Alan

Alan,
timing marks don't line up all that well depending on shain wear etc

Hi, I couldn't get the inlet opening any where near 24 degrees so I bought a new camshaft from our hosts, expensive but the keyway is at a noticeably different angle in relation to the cam lobes compared to the old one. The old one has also been reprofiled, 0.2 off the base circle 0.6 off the peaks, and that has obviously altered the valve timing. So hopefully after reassembly my problem will go away. I don't know how it ran so successfully for so many years, maybe the old 12T sprocket was at a different angle in the old crankshaft to compensate. thanks for the helpful comments, regards, Alan.

Alan,
It is a problem with these things that people have butchered and modified over the years but glad to hear you have it sorted. Don't throw the old cam out but see if you can mark the cam the same as the new one relative to the keyway so that in another 50 years the next owner of the cam doesn't get caught with the same problem. In another 50 years Mr H may not have any left