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Old 05-12-17, 08:55 PM   #1
Rookesy
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Default Help needed with a JAP 5 please.

Gents,
I have a JAP 5 that was on a generator and I cannot get it to start. I did the usual checks - petrol was getting through and it had a good spark etc.
I took the head off to check the timing and this is what I found - https://youtu.be/CPa3q9jR68Y .
The timing for the piston seems to be 180 degrees out with the valves opening at the wrong times. Can anyone help please as to how to change it over to run correctly? I think once that is sorted the mag should just slot in with the correct timing. Thanks in anticipation
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Old 05-12-17, 09:10 PM   #2
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Looks right to me. Assuming the exhaust valve is closest to the camera?
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Old 05-12-17, 09:23 PM   #3
air-cooled
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Rotate the mag shaft 180 degrees and put it back on the engine.

Phillip
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Old 05-12-17, 11:46 PM   #4
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I agree with Phillip.

Last edited by 1956ld1; 05-12-17 at 11:46 PM. Reason: mistake
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Old 06-12-17, 05:03 PM   #5
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Default looks fine!

Taking another look at your video! Information from the web confirms the inlet valve will be the larger! This is the valve nearest the camera!

Quote! 'Because engine efficiency depends upon VOLUMETRIC EFFICIENCY of a combustion chamber. The inlet valve is larger than the exhaust valve as inlet mixture arrives at lower pressure ...whereas exhaust gas leaves the cylinder at higher pressure so can pass quickly through a smaller outlet! Inlet air (or) air-fuel mixture has less pressure as compared to exhaust gas!

If we look at your video the inlet valve appears to be open during the UP stroke of the piston! THIS IS INCORRECT....as the Inlet should be open with the piston travelling down!

You need to re-check your valve timing!

Can you get at the drive gearing from the crankshaft to camshaft? There should be timing marks on these which should align when correct timing!
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Last edited by ahg_allcroft; 14-12-17 at 03:24 PM.
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Old 06-12-17, 05:41 PM   #6
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Quote:
Originally Posted by 1956ld1 View Post
I agree with Phillip.
Doesn't the Wico A magneto have an "idle" spark? Certainly sound like the impulse clicking every TDC, so I don't think turning the mag will make any difference.
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Old 06-12-17, 06:19 PM   #7
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The larger valve is always the inlet, even on these industrial engines, and if the magneto is running at engine speed, then as Charles says, changing it by 180 degrees won't make any difference.

Just out of interest, the Ruston 6AP magneto also runs at engine speed.

Peter
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Old 06-12-17, 06:40 PM   #8
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Have you got the correct specification of magneto to suit the engine? Are you turning it in the correct direction?

Dan
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Old 06-12-17, 06:54 PM   #9
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Quote:
Originally Posted by Appletop View Post
Looks right to me. Assuming the exhaust valve is closest to the camera?
What am i missing here Rob, i'd have said its correct if the closer valve was the inlet.
Suck, squeeze, bang, exhaust and repeat.

Neil.
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Old 06-12-17, 07:17 PM   #10
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'Fraid not - go and watch an engine; exhaust immediately before inlet.

MP
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