95 Johnson 140 (recently rebuilt)

[mrcoop]

I have a 1995 Johnson 140 the head was totally rebuilt and I may have a total of 20 hrs on the new head. I ran double oil during a break-in phase.<br /><br />Twice running FOT at 5200 rpm the engine dropped rpm to 3500. I checked to see if I had lost a cylinder and learned that I had a fouled plug on the bottom port side. This was caused by an accumulation of metal flakes that gathered around the spark plug. (not a good sign) <br /><br />A compression check was done on all cylinders without a significant change in pressure upon comparrison. The carbs were rebuilt and the plug was replaced. <br /><br />The motor again ran well for about 2.5 hours and then it dropped rpm again from 5200 to 3500. This time it was the upper port plug that fouled in the same manner (aluminum flakes around the plug). I again performed a compression check on all cylinders and got this result <br />right top port cyl = 115 <br />all other cyl = 122. <br /><br />I also inspected all piston heads and saw that the top port side was starting to get a small hole in the center of the piston (all others were fine and flat)I did not see any other damage.<br /><br />I realize that this could be an ignition problem and that I am running lean on the port side, but what could cause this is my question ?<br /><br />I run spec oil and good (new) fuel. Plugs are gapped correctly and are champions for this engine.<br /><br />Help on this subject would be greatly appreciated.<br /><br />mrcoop

 

[Walker]

Re: 95 Johnson 140 (recently rebuilt)

Burning a hole in the center of the piston I'd say was caused by pre-ignition, You timing is advanced too far or your fuel octane is too low (which I doubt)

 

[mrcoop]

Re: 95 Johnson 140 (recently rebuilt)

walker,<br />thanks for the reply....the timing was checked and was within specs - according to the man who built the engine. fortunately it's his engine for 90 days so he's trying to work the issue out.<br /><br />Tell me what you think of the compression readings I got....and how would you tell if the piston head was damaged to the point that it can no longer be of use?

 

[Walker]

Re: 95 Johnson 140 (recently rebuilt)

Compression sounds okay but that or those 2 pistons are damaged and are going to fail if you keep running them.

 

[mrcoop]

Re: 95 Johnson 140 (recently rebuilt)

walker,<br />I agree that damage will continue if problem is not solved. <br /><br />Damage is appearant on only the top port piston...what else could cause that port side to run so lean....octane im using is ok...the timing is within specs...is there anything else that could cause a pre-ignition problem so great as to bore a hole in the top of the piston.

 

[ob]

Re: 95 Johnson 140 (recently rebuilt)

The aluminum flakes you mention around the plugs in your first post will cause preignition by absorbing cylinder temps and storing heat.Cylinder needs to be devoid of any metallic particulates.There is a possibility that one of the carbs has a restriction causing a lean condition but at this point the guy that performed the work will have to make good.

 

[mrcoop]

Re: 95 Johnson 140 (recently rebuilt)

carbs were checked and rebuilt no restrictions found.<br /><br />timing within the specs.<br /><br />Im thinking a diode in the power pack is bad allowing the plug to continously spark and burn hot in turn causing the pitting effect to start in the piston head. Fortunately I caught this before real damage occured and the piston burned through or to the point of replacement. This engine only has one power pack (not individual/cylinder)<br /><br />Anyone's opinion on the power pack idea is appreciated.

 

[mrcoop]

Re: 95 Johnson 140 (recently rebuilt)

anybody got an opinion on the power pack as a possible cause

 

[Hooty]

Re: 95 Johnson 140 (recently rebuilt)

You can check your powerpack idea with a timing light. Put a mark on the flywheel at the pointer when the nr. 2 (top port) piston is at tdc. Connect the timing light to nr. two and if it fires somewhere on the flywheel other then where your mark is, it's hitting twice.<br /><br />c/6<br /><br />Hooty