73 johnson 115.. piston hits spark plug.

[naturallysmashed]

Re: 73 johnson 115.. piston hits spark plug.

i agree with the fact that electrode or no electrode,the eng should accept either,based on what was posted with the ql77jc4 being an alternate and having put many in for guys that trolled alot,now,you have 1 cy,with the problem,and it likely a small measurement of trouble,what comes to my mind is age of motor,if that head has been dressed up many times over the yrs ,he could very well have a head that has been machined down too much,next question would be why one cyl and not the 2.well,ive seen guys do all sorts of crazy stuff,from holding the head on a belt sander,not the little hand sander a bench sander,attempting to get warp out,so,its possible,the head was sanded,milled whatever while either not flat,or a warp so bad ,with a sanding so excessive ,he now has a head over milled.I suggest,take the head off,measure it up and compare to spec.or try another head,now,if the eng block was decked and too much the same result could apply.I believe an oversized head gasket may be available,I know the 6 cyl had them to reduce cmp.but as for the 4.Maybe someone else knows.My opinion is mine only and I say its not the plug or rod or piston but head or block.If there was that much slop,the eng would be short lived

I like the way this sounds. I'm still going to try different plugs because that's what many people are suggesting.. but the head was probably milled down the wrong way. A shorter plug should work just as well as a thicker gasket in theory. Let me try different plugs first, i will post back.

 

[naturallysmashed]

Re: 73 johnson 115.. piston hits spark plug.

the ql77jc4 are the same size as the plugs i have now, they didn't help.. i put an extra washer on the spark plug that kept getting hit and it was fine.. the engine is running beautiful.. i just wish i knew exactly why it was hitting without the extra washer.

 

[emdsapmgr]

Re: 73 johnson 115.. piston hits spark plug.

If the head had been milled too much, or the block decked on that side-you should have the clearance issue on both plugs on that side, not just one.

 

[emdsapmgr]

Re: 73 johnson 115.. piston hits spark plug.

If the head had been milled too much, or the block decked on that side-you should have the clearance issue on both plugs on that side, not just one. How does the compression on the one hole compare with the three?

 

[naturallysmashed]

Re: 73 johnson 115.. piston hits spark plug.

When I checked a few weeks ago it was the same as the others.. they were all right around 120. I'll check again to see if anything changed.

 

[Daviet]

Re: 73 johnson 115.. piston hits spark plug.

This topic has been talked to death. It looks like you have 3 options, tear the engine down, use the surface gap plugs and suffer a poor idle or use 2 gaskets and have a proper running engine.
There have been other posts on this and they ended up using 2 gaskets with sucess, just as I have.

 

[HybridMX6]

Re: 73 johnson 115.. piston hits spark plug.

He's already got it running fine by using 2 washers instead of the 1. I believe at this point his problem is most likely going to be bearings on the cylinder are getting worn out, causing excess piston play up and down.

 

[ezeke]

Re: 73 johnson 115.. piston hits spark plug.

Let the different plugs tell the story; click the thumbnail, please.

 

[ilovefroggin]

Re: 73 johnson 115.. piston hits spark plug.

He's already got it running fine by using 2 washers instead of the 1. I believe at this point his problem is most likely going to be bearings on the cylinder are getting worn out, causing excess piston play up and down.

I am confused. This reply makes absolutely no sense to me. Maybe I am stupid....

1st of all Cylinders do not have bearings. Crankshafts do.

2nd if a crank bearing was bad allowing extra up and down play by the piston how does that make the piston hit the spark plug electrode???

Maybe more likely to hit a valve but not the spark plug.

 

[crb478]

Re: 73 johnson 115.. piston hits spark plug.

I am confused. This reply makes absolutely no sense to me. Maybe I am stupid....

1st of all Cylinders do not have bearings. Crankshafts do.

2nd if a crank bearing was bad allowing extra up and down play by the piston how does that make the piston hit the spark plug electrode???

Maybe more likely to hit a valve but not the spark plug.

There are no valves so it can not hit them, If there is too much play in the bearing the piston will go up into the head too high and hit the electroid which is the closest thing to the piston.

 

[HybridMX6]

Re: 73 johnson 115.. piston hits spark plug.

I was referring to bad rod bearings on the crank for that particular cylinder.
As stated above, there are no valves in a 2 stroke motor.

 

[R.Johnson]

Re: 73 johnson 115.. piston hits spark plug.

I would take the head, and intake by-pass cover off, and check the piston, rod assembly for end play. Check the head for pryor macine work, take some measurement's, and the fix would be up to the owner. This is the 51st post. You could guess at this forever

 

[ilovefroggin]

Re: 73 johnson 115.. piston hits spark plug.

I was referring to bad rod bearings on the crank for that particular cylinder.
As stated above, there are no valves in a 2 stroke motor.

I know why I was confused. I was confusing spark plug placement with an conventional auto engine where the spark plug enters the cylinder from the side where as on an outboard it enters more like a hemi, on the top.

I told you I might be stupid.

 

[naturallysmashed]

Re: 73 johnson 115.. piston hits spark plug.

There really has been a ton of posts on what it could be. I definitely have a place to start. After I'm done using the boat this year (not too long from now).. I'll tear the engine down and check things out. I'll posts updates on what I've found, or what I change. If it looks like the heads been machined down too much, I will double up on the gasket. I'll find out for sure what the problem was and post the update so that all of you that helped me could at least get some satisfaction from helping me! who knows maybe this thread will actually help somebody if they read it to the end!

 

[mikesea]

Re: 73 johnson 115.. piston hits spark plug.

oh come on,I went out of town and this is still goin,great.as for the spark plug comparision,i understand the point and see the differanve of length,however,both plugs can be used per some specs,they are fine on other side ,and I still stand on my idea of bad mill or deck job,as for the bearings,possible,however at 5500 rpm,it would be history already with that much slop,in my opinion,with respect,i would like to see the poster replace the head and test run,so we dont have to wait til next yr.just kiddin,have a nice winter,ill do the same in south fl.