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piston hit spark plug?

  • Thread starter Thread starter gs850cafe
  • Start date Start date
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gs850cafe

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i had gapped my plug to the proper gap a while ago....i pulled my number 1 plug out earlier and something has knocked it shut a hair...enough to where it has maybe a business card or gap...

any ideas?
 
not sure if po had any headwork done. the plugs i got in it are ngk b9es now...not sure what was in the bike
 
For 1980 and newer the stock plug should be a B8ES. The B9ES is actually a colder plug and should only be used if you have issues with a B8ES. http://ngksparkplugs.com/tech_support/spark_plugs/index.asp

Neither plug should hit the piston. My GPz has about a 10.75:1 compression (Wiseco 810 kit and milled head) and the B9ES plugs (stock plug) have not had such an issue.
 
ok i went an checked, i got the b8es...maybe i did hit that number 1 plug?

everything looks ok...the bike did run ok before that had happened
 
If I remember, off of the top of my head, the factory piston to valve clearance is .030"
The spark plug to piston clearance is probably pretty close to that spec as well.
Did something get into the combustion chamber for the spark plug tip to hit?
Usually a small piece of something metallic is involved.
Are all of the plugs damaged?
If the piston itself hit it, usually all of the pistons would hit all of the spark plugs if the head/cylinder was milled.
A worn wrist pin could also cause the impact as well as many other less likely items. (loose con-rod bolts, worn rod bearings, etc.)

Daniel
 
gs850cafe said:
i had gapped my plug to the proper gap a while ago....i pulled my number 1 plug out earlier and something has knocked it shut a hair...enough to where it has maybe a business card or gap...

any ideas?
Click to expand...

A business card is close to the correct gap, what gap did you set them to in the first place?
 
gs850cafe said:
i had gapped my plug to the proper gap a while ago....i pulled my number 1 plug out earlier and something has knocked it shut a hair...enough to where it has maybe a business card or gap...

any ideas?
Click to expand...

How long was 'a while ago?'

I've never heard of a B8ES hitting a piston on standard plug or even a larger plug gap. What makes you think that it has done so? The closed gap on the plug?

If the piston had hit the plug you would see damage on part of the electrode of the plug. If there's no damage to that its not the plug.

What other work have you done recently to the bike? Valve clearance check possibly?

SM
 
Unless you dropped it on the floor before installing it,
something INSIDE the combustion chamber hit it.

Daniel
 
How many miles on the bike? Burn any oil or running really rich? Is it possible there is enough carbon built up on the piston crown to do this?

I've never ever had a plug contact the piston. I've used stock B8s, and 7s and 9s and never had an issue. Can you look down into the plug hole and see what the piston crown looks like?
 
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