Screw Head Imbeded In Piston

[imported_KEEPER]

Heard a tapping sound from my starboard eng on sat. Determined noise was from starboard head. Pulled head and found two pistons with 1/4 round brass imbeaded in pistons. Found the source of the brass was from two different carb throttle body butterfly screw heads that had sheered off. 1997 yamaha SSII. I need some advice.

I removed the screw heads which left an indentation. Should I put it back togeter or replace the pistons?

The threaded part of the screws are still in the throttle shafts and seam tight. Should I ping them in or try and remove them. There are two screws in each butterfly.

I will remove all the carbs and inspect the screws. This engine had the powerhead replace when it was a year old. I believe that someone check and over torqued them at that time.

Thanks,

 

[mflan77]

Re: Screw Head Imbeded In Piston

Since you already have it apart I would replace the pistons at a minimum. You also need to look for any scoring on the cylinder walls if it was actualy embeded in the piston I would think that there is some other damage inside but I would defenitly replace the pistons

 

[imported_KEEPER]

Re: Screw Head Imbeded In Piston

Thanks,

I found both screw head imbeded with no missing pieces. The cylinder walls look good. the cylinder heads only have a slight indentation. The screw head looks like they only hit once and embeded. The screw heads are 5mm wide by 2mm deep phillips. The engine has performed well and I would like to leave well enough alone if I could.

Has anyone ever seen this happen before?

Has anyone ever run an engine with slight piston dome damage?

The service manual does not reference this.

Whats the deal with the screw heads sheering off?

Thanks,

 

[mflan77]

Re: Screw Head Imbeded In Piston

Hey it probably will run fine for a while who knows it might run forever. If it were me I would replace the piston since it is apart. If money would not allow that I would smooth the indent out with a die grinder or better just wait till you have the money to get the piston.

The screw head could have come off just from a lot of use -open ,close ,open ,close vibrating ,ect. things happen to the best of us.

any changes in the pistons can change a lot of other things and you realy dont want to run with one piston the has been damaged if the piston gets under to much stress in there it could come apart. That does a lot of damage I have seen this in car engines. Pistons you want them all the same and in good shape they are the heart of your motor