Cam timing

[ianh1968]

360 degrees divided by 40 teeth is surely 9 degrees per tooth?
I think that this is also the figure in Mr V's books...

Ian

[mk1]

Depends if you are talking crank or cam degrees.

m

[Jono]

..it always surprises me how it's the most innocuous threads which seem to gain legs

Anyway, one for Spider - yes, a nice tool - I will have to make one of those. What you say about allowing for chain stretch rings a bell with me which is why I raised it earlier in the thread. I will use my IWIS chain - would you suggest allowing the same amount of advance allowance for stretch if using that chain (which is sold as limited stretch).

Or put another way, if I am 5.5 degrees advanced already and I use the IWIS chain what offset do I need on the woodruff key?

Cheers, it's all interesting stuff.

I hope that I like the engine when it's all finished and running

Jon

[R&R]

360 degrees divided by 40 teeth is surely 9 degrees per tooth?
I think that this is also the figure in Mr V's books...

Ian

Ian,ask yourself what, and how, you are measuring the timing. Your potractor is on the crankshaft, the crank pulley has 20 teeth, you are measuring crank degrees, so one tooth is 18 crank degrees. The cam wheel (40 teeth) turns once in 720 degrees of the crankshaft. I'm sure you get the picture! Anyway, why would 9 degree reversible offset keys be available?

[ianh1968]

Baffling...

I've never seen reference to 18 degrees before, only 9...

I've mostly used belt drives with adjustable pulleys over the last few years, so my
experience with chains has been rather limited. The last chain I did was a few years
back and I was timing a 643 into what is now my Marcos engine. On checking it out
I found it to be 100 degrees ATDC full lift, No.1 inlet. I switched the gear one tooth
and re-checked and it was close enough to the specified 110 degrees that I left it as
it was.

Fortunately, there is someone amongst us that has an engine in bits and can
verify the effects of changing the timing by one tooth.

Jono, if you would be so kind?

Ian

[Spider]

That's a good idea!!

Yes and no.

Yes - because it is simple and very quick to attach / remove and it does work well for turning the engine over. I also slip a short pipe over the handle when the engines facing up and then let that pipe swing around to the leg of the engine stand to lock it for tightening up the Cam Nut and The Harmonic Damper Bolt.

No - because for do the Cam Timing, it's at the wrong end, I find it a bit awkward watching the degree wheel which I mount to the front of the engine, but the handle is at the back of the engine. I'll get around to making one that fits to the front of the engine one day,,,,,,

Chris, I've said this to you before on another thread... you have a nice tool.

Why thank you my good man

[ianh1968]

... Yes, I'd say at least 14",
and it looks quite stiff, as well

[Spider]

... Yes, I'd say at least 14",
and it looks quite stiff, as well

Oh, I've been caught out,,,,,,,,,,,,,,,,,again,,,,,,,,,,,,,,,