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Old 01-09-2012, 01:02 AM
BarelyAWake's Avatar
BarelyAWake BarelyAWake is offline
Motorized Bicycle Elite Member
Join Date: Jul 2009
Location: Maine
Posts: 7,212
Default Re: Spark Plug reach-why not use longer?

A potential issue is it seems both piston dome height & combustion chamber clearance is inconsistent amongst these engines - for example a BPR6HIX (which is about a thread longer than the B6HS) just taps the top of the piston on one of my motors (stock generic) whereas it clears fine on another, despite having a thinner head gasket & lapped head (grubee).

I do think matching the plug depth to your particular engine is not a bad idea - but when recommending plugs to others it's prolly best to roll with what is known to fit w/o problems, I don't think anyone has had an issue w/the NGK B6HS (or other heat ranges) with any of these motors w/a stock head...

...jus' some thoughts - but I suspect to get a plug that perfectly matches may be limited to a case by case basis

Last edited by BarelyAWake; 01-09-2012 at 01:05 AM.
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