Trying to understand something basic

Hi guys, quick question. I ended up taking off my cylinder and cylinder head to my puch maxi to displace some water that got stuck in there from cleaning, and I for the first time got to see my piston and rings I believe (not mechanically inclined). Anyways, I thought If I pedaled my moped, that the piston would move back and forth, but it didn't, it just sat there, but I could pedal my moped forward and backward just fine. Is that normal? I thought if you pedal forward that your piston moves, even if your moped is off.

And I also thought when people say their engine won't turn over, that they just couldn't pedal their moped forward, because their piston was stuck. But in this case, I can pedal forward, and my piston doesn't move. I was able to move it by hand (I grabbed it and moved it in and out, didn't seem too hard physically).

Anyways, why won't my piston move when I pedal forward with the moped off?

Re: Trying to understand something basic

are you engaging the starter lever??

Just pedaling alone wont turn the motor over.

Re: Trying to understand something basic

What kind of a moped is it?

Re: Trying to understand something basic

It's a 1978 Puch Maxi, and I wasn't using my starter/clutch lever (the black little lever on the left handle bar), is that necessary for the piston to move?

Re: Trying to understand something basic

yes, that lever is what engages the pedals to the engine. Be careful though, I broke a piston skirt doing that once. When you pull in that lever while pedaling it that piston does not have the cylinder to keep it in a nice linear motion. Instead it's going to smack around violently and possibly break something. If you want to see the piston moving then I suggest you pull the chrome cover off the side of the engine and turn the flywheel by hand. This will move the piston but not violently. If the engine were "not turning over" it would mean that when you pulled the little black lever it would lock the back wheel and the pedals. What you should feel is a fairly heavy and pulsing resistance as the engine compresses air.

Re: Trying to understand something basic

yes. that little lever locks the chain from the right side(the pedal hain) to the chain on the left side (the drive chain) which in turn turns over the motor. and whala it starts up.

Re: Trying to understand something basic

DONT TOUCH THAT BIKE GET SOMEONE TO PUT IT BACK FOR YOU< THE RING PLACEMENT IS CRUICIAL AND LIKE THE DUDE ABOVE SAID< IF YOU ENGAGE THAT SHIT WHILE PEDDLING>>>BYE BYE MOPED!

I hope its not to late, hate to see a good moped die!

Re: Trying to understand something basic

A moped is hard enough to pedal when the engine is not turning, I'd sure hate to try and pedal one with the engine turning but not running. My Puch is very hard to start by pedaling, and pulling in the starter lever. It just locks up the back wheel. I have to put it on the stand, pull in the starter lever, and kick it over with all my weight to start it. Much more difficult than a Tomos, but then it also has more compression. Peace, Jerry.

Re: Trying to understand something basic

Oh crap, I guess this may turn into a repair then? So before I put it all back together, what should I know about the ring placement? I haven't touched the starter lever yet, and now I'm not planning on based on what people said above (thanks for that info) about possibly jacking up my ped. I can't just pop everything back on (like the cylinder head, and cylinder)? Or do I have specially orient the pistons and rings prior to putting it all back on (since I moved my piston by physically pushing the piston in and out just to see it move)?

Re: Trying to understand something basic

I meant piston, not pistons in the above post just to clarify

Re: Trying to understand something basic

Make sure the piston and cylinder are clean, put oil in the cylinder, and on the piston and rings, pull the piston out as far as it will go (TDC), stick the piston top in the sleeve on the bottom of the cylinder, and compress the rings by hand, while wiggling the piston into the cylinder. Remember that while doing this, you also have to fit the cylinder over the 4 studs. Don't forget thr base gasket. And use plenty of oil, you don't want to gouge the inside if the cylinder or the outside of the piston while putting them back together. Peace, Jerry.

Re: Trying to understand something basic

I did it to my '67 Allstate Sabre. I'm still trying to get a piston and I still have flashbacks of that dark day...it was the day I brought it home, 4speed manual shift...then I wake up in a cold sweat. luckily his is a great engine to learn on as parts are still cheap and plentiful.

Re: Trying to understand something basic

You need to orient the piston rings in their grooves before you try sliding the piston inside the cylinder. Ok, you know that the piston ring is not quite a complete circle, right? In the groove the piston ring sits in, there is a little pin. You need to get the ring turned in the groove so that the two ends come together right where that little pin is. As long as you do that, it should slide in fairly easily.

Re: Trying to understand something basic

Oh yeah, I forgot that part. It's done that way to prevent the rings from rotating on the piston while the engine is running, and possibly getting the ring gap caught in the ports. (thats for amodoko) Peace, Jerry.

Re: Trying to understand something basic

Ok sweet, thanks guys, tomorrow I'll just try to put it back together. I'll clean up the cylinder and cylinder head, I'll use lots of oil while putting the piston back into the cylinder. I'll make sure the grooves line up in the rings with the cylinder before sliding it in. Hopefully all will go smoothly, thanks for the info and the warnings. I appreciate it.

« Go to Topic — end of thread

Want to reply to this thread?

We'd love to have you join the discussion, but first you'll need to login (or create an account).