timing the engine - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-25-2005, 05:08 AM   #11
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Now you're talking...
Thanks, Raymac, I was hoping there were an easier solution to keep this cam gear from moving.
I apreciate all the helpfull hints and all the suggestions, as always.

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Old 05-10-2009, 11:53 AM   #12
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Re: timing the engine

I have a saito 80 I had apart and had the same problem. Once I reset the idle mixture to stock (turn out flush with the throttle arm) I then could
start fresh and had idle and high speed again. Don't know if this helps or not.
Or hopefully you have already solved your problem.
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Old 05-10-2009, 12:30 PM   #13
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Re: timing the engine

Rotate the engine through the exhaust stroke. You'll see the exhaust valve open, then start to close. As the piston comes up to top dead center you will see the intake valve just start to open. At top dead center both valves should be just open just a bit. If you see this, then you've probably got the timing set correctly.
Are you sure? At TDC of the firing stroke surely both valves should be closed tight. At TDC of the exhaust stroke should not one valve be open and the other closed?

When setting OS timing I place the piston at TDC. I position the cam timing mark at 6. o-clock or 12. o-clock whichever is easiest. It makes no difference. There is a 2/1 ratio between the shaft and cam gear.

I believe the Saito mark is on the front of the gear. If the mark on the gear cannot be seen at 6 then install it at the 12 position. with the piston at TDC of course.

If I am wrong please educate me.

Ed S
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Old 05-10-2009, 06:28 PM   #14
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Re: timing the engine

The valves on any four stroke be it a model engine or lawn mower or automobile, should be equally open at TDC (end of the exhaust stroke and beginning of the intake). This is called overlap. The amount of overlap depends on the operating characteristics of the engine and the lobe shape of the cam. Generally, the higher the operating RPM of the engine, the greater the overlap.
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Old 05-10-2009, 06:34 PM   #15
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Re: timing the engine

Thank you, that explains that detail.

Ed S
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