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Old 01-12-2010, 03:35 PM
wildemere wildemere is offline
Motorized Bicycle Elite Member
Join Date: Feb 2008
Location: Newcastle
Posts: 269
Default Re: Shorty Spark Plugs

Using the NKG part number guide available here,

NGK Spark Plugs USA

A BPM6A decodes as 14mm plug with projected tip and 3/8 long threads

The B6HS Is the same as the stock plug, 1/2" threads

BP6HS has the projected tip as well.

The shorty plug will leave exposed thread in the chamber, not good for many reasons. Especially when you try to install the correct 1/2" plug and the threads are full of carbon or burnt away.

The shorty plug may fit better without its washer or if the head is machined to accept 3/8" plugs. The quality of the alloy used here might not be good enough for only 3/8ths of thread though.

One of my engines blew out a shorty plug once.

A helicoil insert fixed the issue though.

Last edited by wildemere; 01-12-2010 at 03:38 PM.
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