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Old 06-26-2019, 08:03 AM   #2
Mart
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Join Date: May 2010
Location: Solihull, England.
Posts: 8,732
Default Re: piston stop bolt confusion

Whoa. Not on a flatty. The spark plug hole is not over the cylinder.

A piece of flat bar bolted to the deck face across the center of the bore is good, the crown on the piston is a reasonable distance for the piston to stop before top dead center.

You need a pointer on the crank pulley.

Bolt the stop over No.1 piston.

Rotate the crank clockwise until the piston contacts the stop. Mark the pulley (temporarily) at the pointer. Rotate the crank anti-clockwise until the piston contacts the stop. Mark the pulley (temporarily) at the pointer.

Put a permanent mark half way between the two temporary marks. When the pointer aligns with that mark, that is as close to TDC as you can get it by all practical means.

To find whether you're at the ignition TDC or at the end of the exhaust stroke, look at the firing order and split the first and second halfs.
1548
6372

No 6 is at top dead center at the same time as no.1.

Look at the valves. As no.1 piston rolls past tdc on it's ignition stroke (when it should be firing) the exhaust valve on n0.6 should just be closing and the inlet on no.6 should be just about to open. This is called "rocking".

When no.6 valves are rocking, no.1 should be firing.

As the exhaust valve is visible through the plug hole, this method can be used when troubleshooting the ignition on a built up engine.

Any questions just ask.

Mart.

Last edited by Mart; 06-26-2019 at 08:20 AM.
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