Piston problems

BrandonG · Apr 9, 2013

I heard rattling in my 66cc 2 stroke so I took the top end apart. I found damage on top of the piston, matching damage on the head, and the damaged part of the piston scraped down the cylinder wall. The motor still ran fine. maybe a loss of power? but still up to 30. so not too much. I did sand the head to get a good seal but there is still a slight part of that ring on the head. I ran it with no head gasket but didnt like how high the compression was because it was hard to start. Since that I've put maybe 150 miles on it WITH the a new metal head gasket. Could the piston have hit the head randomly like that? btw I have about 600 miles on the engine runnin 32:1 since 200 miles.

How do I fix this? really dont have money for a new engine or top end. It still ran earlier, so should I just slap it back together? sand down the damaged parts?

2door · Apr 9, 2013

It appears that your engine has injested something. Possibly a broken pistin ring or wrist pin snap ring. Are you using an air filter?
Have you turned the engine upside down and checked for any thing to fall out? It might have gone out the exhaust. It might have been a piston ring alignment pin. There should be one in each ring groove.

If you can't afford a new top end then my advice would be to put it back together and run it. The damage is above the piston rings so it shouldn't cause any problems. Sand or grind the rough edges smooth and go for it.
I would seriously inspect the crankcase for any foreign object or material to make sure something isn't still in there.

Tom

maniac57 · Apr 9, 2013

Remove the damaged ring and clean the ring groove and replace the damaged ring. It should run but I'd be worried about whatever caused the original problem....
As long as it has enough compression to run, go for it.
Just don't be surprised if it doesn't last long.

BrandonG · Apr 9, 2013

Both wrist pin clips are in place, both piston rings and their alignment pins are there too. The top ring was pinched right under where the top of the piston was damaged so it won't jiggle around on one side

As I was removing the wrist pin clips to take the piston off so I can sand it (I just remove the clips, then slide out the wrist pin right?) I saw this slowly rolling down the oily crankshaft disc. The thing thats supposed to be counterbalanced. I quickly grabbed some needle nosed pliers and grabbed it before it rolled away. This fits right into the shape on the top of my piston.

So now I have a pinched piston ring, deformed piston, head, and cylinder wall, AND a piece that my engine pooped out from somewhere. The question is where did it come from???

boofbike · Apr 9, 2013

Hmmm, kind of looks like, maybe needle bearing bits. not sure though.

Norman · Apr 10, 2013

That is a piston ring retainer pin, could be they pressed in 2 in one retainer hole instead of one, it took a while for it to work loose. If you look inside of the piston's skirt you may see the hole it came out of. It would be at the same location as where there's already a ring locator pin.
could be the weren't very careful when building the engine, I've found cigarette butts, metal shaving, and just plain dirt in new engines.

I'd ride like it was stolen, until it drops dead.

BrandonG · Apr 10, 2013

Today I was riding and the engine studdenly stopped and was locked up. took the head off to find an Identical piece stuck to the head. And more damage to the head and cylinder.

BrandonG · Apr 10, 2013

Norm, There is 1 pin in each piston ring groove, even after removing 2 mystery metal pieces out of the engine. Here's a pic to make sure we're talkin about the same thing.

Also, I know there's only one piston ring. I broke the other yesterday when I had it apart. I should have a couple new ones by the weekend. It runs ok with just one. Low on power, but still can get to 30. And beats pedaling any day!

Starting to thing it is a needle bearing. Where would that be? I assume theres bearings at both ends of the connecting rod, and then maybe 2 (one on each side of the connecting rod) on the crank? Which are needle bearings?

Norman · Apr 10, 2013

you should have needle bearing on the rod only. one set at the bottom end of the crank and one set on the piston end on the wrist pin. The bearing on the crank are ball bearings.

That photo you had of the mystery metal looked to me just like a pin that's pressed into the piston to stop the ring from rotating. But it could be broken parts of a needle bearing. You probably have the wrist pin bearing coming apart if you have more loose small parts like the first that happened.

BrandonG · Apr 10, 2013

I still cant get the wrist pin out. I have both little clips out, and I put the biggest alen wrench that fits in the piston in and Im hammering it hard! It has moved about 1/8" out one side but one go farther. Theres no trick is there?

2door · Apr 10, 2013

BrandonG said:
I still cant get the wrist pin out. I have both little clips out, and I put the biggest alen wrench that fits in the piston in and Im hammering it hard! It has moved about 1/8" out one side but one go farther. Theres no trick is there?

The wrist pin should slide right out. The fact that you're having that problem tells me you've found the source of the little metal piece. Your wrist pin needle bearing has come apart and seized in the piston and on the wrist pin.

You might try heating the piston a little. The wrist pin and bearing cage are steel and the piston will expand, hopefully allowing the pin to be pressed/driven out.

I suspect you might find the piston is damaged as well so be prepared to replace it.

Tom

BrandonG · Apr 11, 2013

It was the needle bearing! Ordering a new whole top end.

Are there any suggestions for performance parts? MM head? high compression? or just 80cc slant and sand the head down again?

Also, tearing apart the crankcase to look for the rest of the bearing. So what tool(s) do I need for that? I know theres something for the drive sprocket and maybe more? Any gaskets that are a must to replace? Should I go stock or homemade?

Thanks for all the help!

crassius · Apr 11, 2013

absent a wrist pin extractor, you can use a heavy hose clamp around the piston with a couple holes in it where you put a nut between piston & clamp and run a bolt thru nut into wrist pin - the bolt will push out the pin without you having to hammer on it & screw up your rod or rod bearing on the crank

kinda old school, but in the 50s I didn't have much money for special tools : (

mark880088 · Apr 11, 2013

I have two used heads for sale. I have the straight plug head for $5 or angle head for $15 plus actual shipping. If your interested send me a pm with your zip and ill check shipping costs. shipping wont be much cause they are light 3 or 4 bucks probably. btw both heads are in very good condition.

headtrama · Apr 11, 2013

Looks like the bottom needle bearing in the rod is coming apart. I had a new engine do the same thing to me.

BrandonG · Apr 17, 2013

Replaced the needle bearing, piston, rings, head, and cylinder because it was all scratched and scraped up. I flushed out the crankcase to remove any remaining parts of the blown needle bearings. Put it all together and now its locked up.

I can clutch in and spin it free, so I know its not on the countershaft. The internal reduction gear is not jammed, and the magneto is now off and still jamming. It will spin about 3/4 of a turn and then jams. I can hit the connecting rod back down and it then can spin normally the other direction 3/4 of a turn before jamming again. The top end is off so it's something on the crankshaft. Any ideas what?

maniac57 · Apr 17, 2013

Sounds like the primary drive is boogered up. Pull the big sidecover and check the big gear on the clutch and the small primary drive gear.
If they are good, has to be bearings...
or a ring hanging in a port...
or something else...
Need to look and see.

BrandonG · Apr 17, 2013

Everythings off that I can get off without the clutch screw tool. So its not a ring on a port or either of the gears. Maybe a main bearing or something. I guess I'll wait till I get the tool and tear it apart

crassius · Apr 17, 2013

got no solution, but I feel your pain : (

biknut · Apr 17, 2013

I hate to be the bearer of bad news but I've been down this same road. Is this a BGF motor by any chance?

No matter, you might as well buy a new motor, because you're probably going to need a new rod. The rod is probably the cause of the problem in the first place. It's what caused my failure. At 600 miles the needle bearing in my BGF motor failed. I tried replacing it, only to have it fail again in about 200 more miles. Close inspection revealed a very slight imperfection in the small end of the rod, that was causing the needle bearing to go bad.

You could order a new crank assembly, but that's going to be tricky trying to get all the right parts. It's easier, and probably less expensive in the end to just order a new motor, and use your old motor for spares..

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