Plan of attack on my rebuild project

"Hello again,

I pulled the

"Hello again,

I pulled the head off of my Force 70, and found two damaged pistons. The #2 has 3 ripples in it along the edge, and the #3 has 2 ripples in it. Looking straight at the damaged areas from the tops of the pistons, I can see the rings, but neither of them had any parts fall off. #1 looks fine. Luckily from what I can see, it did not hurt the cylinders, and the 45 degree honing marks are still there.

My question to the experts is, what would have caused this kind of damage to the two pistons? Could something have come through the ports that would have caused these ripples in the pistons, or could overheating, predetonation or lean gas have caused it? Before I start buying pistons, rings and gasket sets I want to get a good idea of what I should look for so I don't neglect a problem in an other area and have the same thing happen again.

Just another quick note, I would like to thank everyone for their input on this forum. I am learning a lot by just reading some of your feedback on other issues, and this board by far is the most informative one I have found. Keep up the good work!!!

Thanks,
James"

"One possible cause could be t

"One possible cause could be that the rings stuck, then pieces of the piston could start to break off due to heat, expansion, etc. Could also be caused by overheating or a lean carb mixture. There are many possible scenarios, the fact is that you will never know for sure.

Fix it, then make sure everything on the motor is as correct as you can make it, use good lubricant, and make sure that the water pump is working."

"I replaced the water pump imp

"I replaced the water pump impeller and thermostat right after I bought it. The impeller was shot, and I'm really thinking it had been shot for quite a while before I bought it, and I'm sure it was probably overheated, but like you said-I will probably never know the answer to that. The guy that owned it didn't seem that smart, and I'm sure that my current situation was a direct result of his lack of maintanence.

I will check over everything when I get it apart, and like you said, use a lot of lubricant during re-assembly.

Any things that you can think of to check kindof as an "As long as it's apart" type of thing?

Thanks a lot!!!

James"

"fuel pump diaphragm, clean an

"fuel pump diaphragm, clean and inspect carbs, lean mix definately could cause your problem, run on the rich side (somewhat) to be safe.

you can replace pistons without cracking the case on force, pull the carbs off, adapter plate and reeds and you can get to the bottom of the connectiong rods take off the rod base, make sure you get all the needle bearings then you can push the piston up and out the top of the block. Reinstall the new ones the same way, lots and lots of needle bearing install grease will hold the needle bearings in place while sliding the rod back on the crank. Yes it's a pain with those bearings trying to assemble it through the intake, but if you can get it, you don't have to crack the case open at all. Put some loctite on the connecting rod cap bolts. I have done both ways, full teardown and rebuild because the cylinder was scored (then you have to tear down) and also fishing the new piston in on a friends because there was no scoring.

Also, the wrist pins on a force piston are Pressed in , they are a pain to get out!! the new pistons have a wrist pin that floats in and is held there with circlips, much nicer. I was able to pound mine out with a 3/8 socket extension, fit perfect over the pin. place the piston on a form fit wood block with a hole to receive the pin and Carefully punch it out, you don't want to break that connecting rod, they are NLA and next to impossible to find, even on ebay. And after a while they mate with the crank, so a different one may wear differently"

"I didn't think that it wo

"I didn't think that it would be possible to put pistons in it without cracking the case open. Definately sounds a lot more inviting than tearing the whole thing down. But I have one question......I noticed that in your post, you said to take the "carbs" off, will this work being that it is a single carb Force motor?"

"I have 2 carbs that feed 4 cy

"I have 2 carbs that feed 4 cylinders. you have one that feeds 3, basically the same. pull the carb, behind that is the adapter plate, then the reeds, then you can get to the connecting rod ends and pull the pistons out the head.

If there is any damage to the cylinder, a tear down and re-bore is the only way.

Also, there are needle bearings around the crankshaft, you have to be sure not to drop any of them into the case, otherwise......teardown.

Teardown is not as bad as it sounds, very easy actually.

Any questions, just ask"

What year and model anyway? I

What year and model anyway? I would just like to pull up a schematic to look

Model year 1991.

Model year 1991.

"yep, should be able to get at

"yep, should be able to get at the rod end caps after taking the "carb" off then the adapter plate, then reeds."