Hi All,
Just rebored and fitted new piston. Cylinder head still off.
I'm just in the process of setting the timing and checking valve timing with a timing wheel i attached to the timing side of the crank. I have a dial gauge set onto the piston crown. As a matter of interest i checked the degree rotation of the ignition (7/16" BTDC measured on the gauge) this equates to 42- 43degrees BTDC on crank rotation! It sounds very advanced to me as most bikes I've timed tend to be 37-39 degrees. Am I somehow measuring wrongly or is this correct - is it due to longer stroke and lower compression than most bikes I've timed?
Pete.
If you have the head off , stick a ruler down the bore and measure it as the manufacturer intended.
Also, make sure that you rotate backwards well past the point of max advance and then forwards again to eliminate backlash.
Cheers,
Bernie
Yes thank Bernie and Idie,
I will do it by measurement as you say
But also what i was concerned about is that 42 or 43 degrees seems a long way advanced, and wondered if anyone could explain why this engine needs to be so far advanced compared to say a 1960s twin that's typically 38 degrees BTDC?
Pete
The BSA data books show 7/16inch BTDC or 38 degrees BTDC full advance for the B31.
Below from the 1952 data book.
I measured this on my B31 and got 38° BTDC. Then I dumped the degree disc and stuck to measuring 7/16 with the head off.
cheers
Pete
Thanks to all of you for your help with this!
Pete
Hi All,
Further on this topic...
After more careful use of a dial gauge and a degree disc attached to the timing end of the crankshaft I can confirm and I measured myself that 38 degrees BTDC equates to 7/16" to set full advance on the timing.
I'm also using the disc to confirm opening and closing times for the valves.
Pete