Timing and valve clearance - 903cc

tomnj

tomnj

Old fogie stogie
I just want to clarify the procedure and specs for timing and valve clearance on a stock 903cc. I've been reading conflicting info and observing things differently than described.

Valve Clearance - my shop manual says to set intake and exhaust valves at 0.15mm. However I read on a forum elsewhere that with the 903cc the intake is set to 0.15mm while the exhaust valves should be 0.20mm. Which is correct?

Timing - using the static method, when lining up the timing marks on the centrifugal oil filter housing with the one on the timing cover, I read that you would rotate the distributor clockwise until just when the light goes out, that would be 0° BTDC. With that setting, my engine won't even run. It needs to be rotated more clockwise to get it to idle. Am I doing something wrong or just use a timing light and try to match up the marks?

Question: does rotating the distributor CW or CCW advance the timing?
 
Valve clearance may be set by the cam manufacturer. Which cam do you have?
Static method is only for starting. Use the timing light once it’s running.
Can’t remember on which way but if idle speed increases you’re advancing.
 
The factory workshop manual for the 843 engine says 0.006" for both intake and exhaust
Some other engines from Schmidt's book:
A112 A0 or A5, 127 (so later, low performance engines) 6 thou intake, 8 thou exhaust
A112 A1 (1000CC) (higher performance engine) 8 thou intake, 10 thou exhaust
A112 A2 (1050CC) (higher yet performance engine) 10 thou intake, 12 thou exhaust

0.15mm = 0.0059", which would be consistent with the 843 engine
0.20mm = 0.0078", so that would also be reasonable.

Probably doesn't make any difference other than 8 thou giving you a longer time period between adjustments before the clearance gets too small.

Jim
 
Thanks. I was reading the same thing, 0.15mm for both on 843 (and 817), but it seems the 903 is 0.15mm intake and 0.20mm for exhaust.

The engine runs CCW (Anti-clockwise) and the rotor rotates CW so that means rotating the Distributor CCW advances the timing.

I just bought a timing gun and will set the timing this weekend.
 
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