87 Force 85 Cylinder Scoreing from Overheating

[gram404]

I recently overheated my engine from a failed thermostat. I noticed that I had a big drop in power and immediately got off the gas and shut down the engine as quick as I could. When I got home I did a cold compression test of all cylinders. The top two were at 115 and the bottom one was at 40… I took the head off and the upper two cylinders, pistons and head loom about on par for an 87 two stroke. The bottom one has scoring on the top of the cylinder and some residue on the exhaust ports (see attached photos).

-What are my options for fixes? I assume trying to hone out the cylinder is probably out of the question right?
-How involved is taking out the block and putting in a new one?
-Does anyone know of a good parts shop? I live in ct and I am willing to drive a fair distance if needed

I have just done a ton of work to my 87 bluefin, and would prefer not to scrap it…

 

[Jiggz]

Looks like the scoring is not that bad. You don't have to disassemble the block, instead remove the bottom carb and intake adapter and then access the rod and cap bolts with a 1/4" 12 point socket. Be very careful with the roller bearings. It will fall apart and make sure you have everything. Tilt the head so any bearing falling off will roll down the intake opening. Catch with a rag. Push out the rod and the piston out of the head. From here assess the scoring, as there may have been more that you cannot see when the piston is in.
I did mine the same way almost 7 yrs ago and still running. Get a honing kit if the scoring is not that bad, i.e. barely catching your finger nails. And then measure the bore and make sure you order the correct size piston and rings. I used the Wiseco piston but this requires a new wrist kit but it also makes it easier to put it back together. I think this is enough for starter. If the scoring is really bad, you have no choice but to disassemble the block and have it machined.

 

[gram404]

Looks like the scoring is not that bad. You don't have to disassemble the block, instead remove the bottom carb and intake adapter and then access the rod and cap bolts with a 1/4" 12 point socket. Be very careful with the roller bearings. It will fall apart and make sure you have everything. Tilt the head so any bearing falling off will roll down the intake opening. Catch with a rag. Push out the rod and the piston out of the head. From here assess the scoring, as there may have been more that you cannot see when the piston is in.
I did mine the same way almost 7 yrs ago and still running. Get a honing kit if the scoring is not that bad, i.e. barely catching your finger nails. And then measure the bore and make sure you order the correct size piston and rings. I used the Wiseco piston but this requires a new wrist kit but it also makes it easier to put it back together. I think this is enough for starter. If the scoring is really bad, you have no choice but to disassemble the block and have it machined.

Thank you for the info! Did you end up replacing just one or all of the pistons? Is it fine to have two stock pistons and one wiseco piston (I.e. could it cause balancing issues)

 

[Nordin]

Do as jiggz suggest and if you can catch the score with your nails you have to rebore the cylinder.
There are no problem to put a OD piston in one or two cylinder.
No balancing is needed.