Spark Plug Question

A friend and I were hanging out in his shop discussing bikes. He said that he was checking over one of his bikes and noticed that one of the spark plugs was not torqued to spec. In fact, the crush washer hadn't been crushed.
Bike has 4 plugs, spec is about 25 ftlbs per plug. He said it had about 15 ftlbs on it but when he torqued it to spec he felt the crush washer crush. No noticeable effect on the engine running before or after the re-torque. Anyone know what this would do to an engine? He is using a NGK B8ES. We were thinking that the spark plug wouldn't reach as far and cause it to act like a B9ES. Thoughts?

From what I have read an under-torqued plug doesn't seat in the head fully and therefore doesn't transfer the amount of heat, to the head, that it is designed to. This will cause the plug to run hotter which could lead to denotaion or pre-ignition. So, in fact a B8ES would probably run like a B7ES.

ive never torqued a sparkplug in my life and ive installed more than i can count,the differance in the b8 to b9 is te length of insulator.b9 is actually a colder plug;)

Spark Plug Overview

u could also have a compression leak and run the risk of damaged threads.

My car manual recommends different spark plug torque for different driving.

Loose plugs for stop & go - it keeps the plugs hotter.

Tight plugs for long range or hauling.

this is a new one,,you need to tighten the plugs until the washer crushes, anything less could cause the plug to back out and leak, I have never torqued a plug down either

Ive never torqued a plug down either, rule of thumb is hand tight, then another 1/4 turn. Never had a problem.

The FSM soes have a torque spec value, but I've always chickened out before the "click". I'm too fearful of stripping out the threads in the head as sparkplug threads are generally the most abused.

i put a little anti-seize on the plug threads also;)

HerrDeacon wrote:

From what I have read an under-torqued plug doesn't seat in the head fully and therefore doesn't transfer the amount of heat, to the head, that it is designed to. This will cause the plug to run hotter which could lead to denotaion or pre-ignition. So, in fact a B8ES would probably run like a B7ES.

This strikes my interest. I had a bike that was detonating and when I pulled the spark plug, it was grey (from the piston) and the crush washer was not crushed on the plug. I couldn't find any other issues with the carb/timing on the bike and have wondered if this was it. Do you know where you read that?

PLUMMEN wrote:

ive never torqued a sparkplug in my life and ive installed more than i can count,the differance in the b8 to b9 is te length of insulator.b9 is actually a colder plug;)

I reason I thought this was because I thought that the reach of the spark plugs varied to make them hotter or colder. Reading Pattons link helped me understand better what is happening with the plugs.