Spark Plug Gap Changing Every Time Motor Starts

cprince · May 11, 2010

Have a friend who has a 9.9hp Rude. Every time he starts it, the plug gaps change (get smaller).

Sounds like a piston head is slapping the plug to me. If the plug is the correct one, what would cause the pistons to travel too high? Crank shaft bent?

(I know that this is thin on info, but this is how I got this problem sent to me!)

Craig

walleyehed · May 11, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

Carbon build-up possibly...What plugs?

cprince · May 11, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

Thanks for the reply walleyehed.

I am still trying to get more info from him!

Post more when I get more!

Craig

walleyehed · May 11, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

The only other thing, if they are the correct plugs, would be potentially bad needle bearings, but you'd have other issues there.

tschamp20 · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

walleyehed said:
The only other thing, if they are the correct plugs, would be potentially bad needle bearings, but you'd have other issues there.

exactly what i was thinking.your friend should really take off the head and look for any pieces of metal.if the bearing goes,so could the connecting rod,piston,cylinder wall and head potentially. trust me i know.

a70eliminator · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

cprince said:
Have a friend who has a 9.9hp Rude. Every time he starts it, the plug gaps change (get smaller).

Sounds like a piston head is slapping the plug to me. If the plug is the correct one, what would cause the pistons to travel too high? Crank shaft bent?

(I know that this is thin on info, but this is how I got this problem sent to me!)

Craig

Thats a very big "IF"

R.Johnson · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

If it effecting both plugs' I would check for wrong spark plugs with a longer threaded shank.

noelm · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

OK, lets assume the motor is OK, it is possible the head has been machined at some time and then done again, and is now too thin, try to fit another washer (or two) on the plug and see how you go, a bent rod is not going to cause your problem (it will actually cause the opposite) and a bearing that bad will certainly be audible when running.

Vic.S · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

You dont tell us the year but:

1974-76 UL81C
1977-94 QL77JC4 or QL82C
1995 and newer QL82C

They are all the same length reach ... defined by the letter "L"

Not lost the sealing washers ?

wilde1j · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

Easy to confirm the piston is whacking the plugs ... remove the plugs and shine a light on the piston top. If it's hitting the plugs, you'll see the marks on the piston tops.

cprince · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

You guys are tops!!

Turns out, much to my horror, he put in any old spark plugs! Too long...

Now to add to the atrocity, someone put washers on them to act as spacers.

I warned him about too hot or too cold causing possible damage to his motor. Hope he takes the warning.

This all leads me to this question, if the piston slaps the plug and the piston is now marked, what kind of affect is there on the engine performance?

Thanks!

Craig

PS
Motor is a 69 'Rude, 9.9hp

Craig

R.Johnson · May 12, 2010

Re: Spark Plug Gap Changing Every Time Motor Starts

If the piston hit the plug only enough to bend the ground strap with out completey closing the gap, probably nothing. If the piston smashed the gap shut, the engine would not have started.

Spark Plug Gap Changing Every Time Motor Starts

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