#6 Piston Damage w/Pics (1 Viewer)

[medikateme]

Pulled the head earlier today and found pitting on the #6 piston. One decent ding at the edge of the piston. Pic with red straw shows the location. Straw is 2mm in diameter for scale. Was hoping to get feed back on whether or not this piston needs to come out.

Also included is a photo of the #6 spark plug. Specifically there appears to be no insulation left. Was it incinerated?

Thoughts on next steps appreciated.

 

[medikateme]

Pic of #6 SparK Plug

 

[scottryana]

Yes piston is no good as it is, might be able to clean it up, but all those sharp edges will cause detonation. Looks like the spark plug came apart, could have been from detonation (chicken or the egg) and then it damaged the piston.

 

[FJ40Jim]

The piston doesn't concern me as much as the bore. The porcelain could have scratched up the bore quite a bit. Turn the cylinder to BDC and run fingers around the bore to feel for any irregularities

 

[medikateme]

Thanks for the quick replies. Is there a technique for dealing with the chain and sprocket while turning the motor? I have the chain zip tied to the sprocket.

 

[n0rth]

Here's a pic of how I dealt with my timing chain zip tie is around the guides.

 

[flintknapper]

I'd want to check the cylinder bore to see that it wasn't damaged. The piston would not concern me much. Clean it up, removing as little material as possible to get rid of the raised up portions of the pitting. And a small amount of the depth, but carbon is quickly going to fill the remaining divots.

IF the bore is scratched or damaged, then the piston will need to come out to correct that issue and might as well replace it at that juncture.

 

[medikateme]

Thanks for the pic. Here is how mine is configured. Do I need to remove the zip ties on the sprocket? I am concerned the position of the chain will change and I will not be able to get it back in the proper position.

 

[medikateme]

Just realized how bad that pic is. Sorry about that. 2 zipties up near the the white mark which indicates the correct position at tdc.

 

[CRSHR]

Just realized how bad that pic is. Sorry about that. 2 zipties up near the the white mark which indicates the correct position at tdc.

I would use a paint marker or touch up paint. Mark a link in the chain and the sprocket for reference. Then you can undo the zip tie and rotate the engine. That’s what I would do anyway.

 

[CRSHR]

Like this

 

[medikateme]

Thanks for taking the time. That white dot is from a paint pen and it corresponds to the divot in the side of the sprocket. If I understand you correctly, as long a those two marks match-up again next time the link comes around i'm good to go.

 

[medikateme]

First two pics are of the cylinder wall. There are visual imperfections but the surface feels smooth. There is a detectable difference to the touch as you get to the top of the cylinder in the area that looks gold in color.

Also included is a pic of cylinder #1 with water in it. #6 look like this as well.

 

[Tools R Us]

Those dents look relatively small, insignificant? I would remove, smooth, the high points and run it.

 

[bigredmachine]

is the cross hatching still visible on the cyl walls?

 

[AJP]

when you replace the valve guide seals (and now you are this far - hopefully you will) you might want to inspect the valves, seats and guides for that cylinder very carefully. It is possible that the damage was not caused by the spark plug insulation but rather by something else that got into the cylinder (which also destroyed the plug insulation — while bouncing around etc) ... just a thought fwiw

 

[-Spike-]

Thanks for taking the time. That white dot is from a paint pen and it corresponds to the divot in the side of the sprocket. If I understand you correctly, as long a those two marks match-up again next time the link comes around i'm good to go.

Don't count on it. Those marks only line up at long intervals, depending on the ratio between the two sprockets.

 

[medikateme]

Tools-R-US: When you say remove, do you mean remove the piston or just the surface pitting? Any recommended grit or grinding tool to smooth things out?

BRM: Sorry, need a little help with the cross-hatching. What exactly does it look like?

AJP: I plan to do the valve guide seals, etc. I have not cleaned the valves up enough to inspect them for pitting.

Spike: Too late. Already turned it. Can you turn the engine over counterclockwise?

 

[inkpot]

Don't count on it. Those marks only line up at long intervals, depending on the ratio between the two sprockets.

Any reason he cant just rotate engine 180 degrees to see bottom of bore and the rotate it back to where it was?

 

[-Spike-]

Can you turn the engine over counterclockwise?

Yup.