Timing gears

[DJ]

I just noted something interesting that I've never heard before and wondered if anyone here can shed some light.

IAP's catalog specifiies different timing gears for carbureted and injected engines. Additionally, for carb engines they specify the same gear as the exhaust but for injected engines they specify a totally different gear for the aux shaft.

1. What's so special about the aux gear on the FI engines? (Mostly just curious here because I've cutoff the fuel pump lobe and am not worried about timing it.)

2. What's so different about the intake and exhaust gears between carbed and injected engines? Upon inspecting a set of each I find 2 differences. The carb engine gears have retaining shoulders on the sides where the injected gears have none at all (the phenolic that was on my aux shaft does have a shoulder). Additionally, the injected engine gears are wider than the carb engine gears, even with the shoulders on the carb gears (1 1/16 inch versus 1 1/8 inch). The FI gears have teeth that run the entire 1 1/8 inch width whereas the carb gears have teeth only 13/16ths wide.

I expect to use the FI gears that came on my head because they show no wear at all. But I want to replace the aux gear and am really curious about why a totally different part number is specified for the FI aux gear.

I should note that I don't find any difference in timing between any of the 1800 carb and 2000 FI gears I have. I seem to remember that others have stated in the past that there are differences but I haven't seen any in the 12 plus gears I have in hand.

FWIW, I'm using a set of Monte cams from Italy in the engine and a Zagato FI setup with Weber big-throat throttle body.

Any ideas, thoughts, or comments? And before anyone suggests it, I don't intend to buy an expensive set of adjustable wheels.

[Wallace]

Dunno. I'd have to think LONG and HARD over that.. . . but - more to the point - I know they're expensive - but changing the cam timing can make a real difference to the engine. Croft does them (adjustable cam wheels that is ) - and Kent Cams as well in the UK - or if you have two spare steel ones, it's not impossible to get an adjustable pair machined up from all 4 if that makes sense.

Havn't done it myself - but it should be a simple lathe job to get the centre of one to fit the outside of the other - and then onto a mill to do the rotary slots.

A few degrees either way on my engine made a very noticable difference to when the power came in, when it ran out and how much there was of it !

And after all - you wouldn't buy a carb or FI system that couldn't be adjusted - so why not have adjustable cam timning as well ?? !!