Rebuilt G1 sounds like piston/plug contact

Garga39 · 08-09-2008, 12:54 AM

Well I just got the engine back running...well kinda. The problem is it sounds like the piston is hitting the spark plug. When I turn the engine over by hand it clanks right at top dead center. I can turn the engine forward and back by hand and it clanks right at the top. When I pull the plug it doesn't. Is it possible to overtighten the head? I torqued it at about 20lbs. Book calls for 18lbs. I put in a ngk bp6hs plug. Engine has a new piston, rings, bearings, seals. The engine will run, but I'm afraid to run it with the noise. I don't want to damage it. Does anyone have any ideas! I'm at my wits end.

scottyb · 08-09-2008, 08:09 AM

Get a plug with a shorter 'reach' and try it?

Garga39 · 08-09-2008, 08:16 AM

What plug do you think would work? Or do you know a site that has plug specs?

scottyb · 08-09-2008, 08:19 AM

Sorry I do not. What about your local supply house? Napa?

BigBlockMan · 08-09-2008, 08:33 AM

If the piston was actully hitting it would close gap and not run, It may be the lower rod bearing making noise due to more compression from rebuild, That pretty common if you don't replace it.

Garga39 · 08-09-2008, 08:34 AM

Thanks anyway...I just found some specs on my ngk bp6hs plug. 14mm thread 1/2" reach. I will try a ngk bm6a which has a 3/8" reach.

Garga39 · 08-09-2008, 08:36 AM

If it were the lower rod bearing wouldn't it still clank when I remove the plug and turn the engine over?

scottyb · 08-09-2008, 10:17 AM

When you remove the plug you remove the compression so no pressure on the rod? Maybe?

Garga39 · 08-09-2008, 11:00 AM

I think your right. Time to tear it back down Thanks for your help!

smallblock450sl · 08-09-2008, 11:49 AM

Quote:

Originally Posted by Garga39

Well I just got the engine back running...well kinda. The problem is it sounds like the piston is hitting the spark plug. When I turn the engine over by hand it clanks right at top dead center. I can turn the engine forward and back by hand and it clanks right at the top. When I pull the plug it doesn't. Is it possible to overtighten the head? I torqued it at about 20lbs. Book calls for 18lbs. I put in a ngk bp6hs plug. Engine has a new piston, rings, bearings, seals. The engine will run, but I'm afraid to run it with the noise. I don't want to damage it. Does anyone have any ideas! I'm at my wits end.

So sorry to hear the bad news. An NGK-BP5HS is the standard plug for Yamaha 2 cycle (G1's) and there would be no way it would hit the piston. When considering rebuilding a G1 engine (if it runs) I listen for noises first (ie: rattling/clatering) ,from the ("top end", noise-worn cylinder/piston, call it piston "slap"), from the ("bottom end"-crank bearings bad or lower crank/rod bearing bad). If you take the cylinder off, "pull" "up and down" on the rod...there should be no movement, there can be some "side to side" movement. Good luck and keep us posted. Dave

08-09-2008, 12:54 AM	#1
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16	Rebuilt G1 sounds like piston/plug contact Well I just got the engine back running...well kinda. The problem is it sounds like the piston is hitting the spark plug. When I turn the engine over by hand it clanks right at top dead center. I can turn the engine forward and back by hand and it clanks right at the top. When I pull the plug it doesn't. Is it possible to overtighten the head? I torqued it at about 20lbs. Book calls for 18lbs. I put in a ngk bp6hs plug. Engine has a new piston, rings, bearings, seals. The engine will run, but I'm afraid to run it with the noise. I don't want to damage it. Does anyone have any ideas! I'm at my wits end.
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16

08-09-2008, 08:09 AM	#2
scottyb Happy Carting Join Date: Dec 2007 Location: Southern California Posts: 73,406	Re: Rebuilt G1 sounds like piston/plug contact Get a plug with a shorter 'reach' and try it?

08-09-2008, 08:16 AM	#3
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16	Re: Rebuilt G1 sounds like piston/plug contact What plug do you think would work? Or do you know a site that has plug specs?
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16

08-09-2008, 08:19 AM	#4
scottyb Happy Carting Join Date: Dec 2007 Location: Southern California Posts: 73,406	Re: Rebuilt G1 sounds like piston/plug contact Sorry I do not. What about your local supply house? Napa?

08-09-2008, 08:33 AM	#5
BigBlockMan Gone Wild Join Date: Feb 2007 Location: Southwest Georgia Posts: 1,469	Re: Rebuilt G1 sounds like piston/plug contact If the piston was actully hitting it would close gap and not run, It may be the lower rod bearing making noise due to more compression from rebuild, That pretty common if you don't replace it.

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08-09-2008, 08:34 AM	#6
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16	Re: Rebuilt G1 sounds like piston/plug contact Thanks anyway...I just found some specs on my ngk bp6hs plug. 14mm thread 1/2" reach. I will try a ngk bm6a which has a 3/8" reach.
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16

08-09-2008, 08:36 AM	#7
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16	Re: Rebuilt G1 sounds like piston/plug contact If it were the lower rod bearing wouldn't it still clank when I remove the plug and turn the engine over?
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16

08-09-2008, 10:17 AM	#8
scottyb Happy Carting Join Date: Dec 2007 Location: Southern California Posts: 73,406	Re: Rebuilt G1 sounds like piston/plug contact When you remove the plug you remove the compression so no pressure on the rod? Maybe?

08-09-2008, 11:00 AM	#9
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16	Re: Rebuilt G1 sounds like piston/plug contact I think your right. Time to tear it back down Thanks for your help!
Garga39 Not Yet Wild Join Date: Jul 2008 Posts: 16

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