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Discussion Starter · #1 ·
For a portruding spark plug,

what is the clearance at tdc of the cylinder ? fsm doesn't seem to indicate this dimension.

The plugs i want to run match the ngk b8s... except the tip portrudes 1.2mm further.

Seems fine until i saw they request a minimum gap of 1/1000th of an inch between piston and plug tip. I had no idea we were dealing in such small numbers.

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1/1000 of an inch sounds like a typo, the connecting rod will stretch farther than that at high rpm. Even the piston dome will swell more than that when it gets to operating temperature. Screw the plugs in, without any washers, and see if the engine will turn over without the piston hitting the plug end.
 

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Discussion Starter · #3 ·
1/1000 of an inch sounds like a typo, the connecting rod will stretch farther than that at high rpm. Even the piston dome will swell more than that when it gets to operating temperature. Screw the plugs in, without any washers, and see if the engine will turn over without the piston hitting the plug end.
Great idea! See if it fits without the washer!!!

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Be careful or you could be buying a new spark plug as it's easy to kiss a plug with the piston when doing these experiments. Bring your piston up to tdc, put a thin dab of heavy grease on the end of the plug, screw the plug in gently, when it stops reverse and check to see if the grease has transferred to the piston.

I'm all for trying things but was wondering if you have run the numbers? One dyno test I read saw an increase of 7 hp .... on a motor that had 425 on old plugs. Now if I was a racer running wot I would be pleased as this is a 1.6% increase. The comparison to new plugs vs these special plugs was down to 1%. Again if I am racing I will try for any gain but for street .... well 1% isn't going to do much.
 

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Discussion Starter · #5 ·
Be careful or you could be buying a new spark plug as it's easy to kiss a plug with the piston when doing these experiments. Bring your piston up to tdc, put a thin dab of heavy grease on the end of the plug, screw the plug in gently, when it stops reverse and check to see if the grease has transferred to the piston.

I'm all for trying things but was wondering if you have run the numbers? One dyno test I read saw an increase of 7 hp .... on a motor that had 425 on old plugs. Now if I was a racer running wot I would be pleased as this is a 1.6% increase. The comparison to new plugs vs these special plugs was down to 1%. Again if I am racing I will try for any gain but for street .... well 1% isn't going to do much.
Right... this is purely out of fascination with the design of a multi spark plug. I don't expect to notice a performance increase.

The bike was in really rough shape when i bought it... so i hace no idea how good the performance should be anyway.

Ill put it on the bacl burner and focus on what matters. Going to adjust the valves and work on timing tonite.

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