Hi :wave: just bought a new barrel/piston/head for my moped, its 20cc larger than standard, only problem is, is that the piston wont go in the barrel, well i can get both of the rings in the barrel but the piston wont move freely up and down when the rings are in, it's like it's stuck. i bought a ring compressor but it's too large but getting the rings in isn't the problem, could it be that it isn't going in straight?

thanks!! :worship:

someone must know

i will ask nige 2moro 4 u. he has put the 70 kit on his ped.

cool, thanks

put just a ring in the barel, push it level and then check with feeler gauge the gap in the ring is right

whats a feeler guage? lol

A selection of flat blades that are a measure of thickness, i.e. .05 mm. The same type of tool that you use to check your valve clearances.

It's possibly that the rings you have are too big, so that when you put them on the piston and then push into the barrel the ring end gap is too small. This won't allow the rings to compress enough (the ends are touching and won't allow the rings to compress further) and could be causing the piston/ rings to put too much force on the cylinder walls.

But bear in mind that a new piston and rings will often be quite stiff, especially if the barrel has been rebored and has yet to bed in. You could try putting some oil round the bores to piston gap and see if that helps?

hi, thanks for that! i tried using WD40 but it didnt seem to help, i might try vaseline but didn't think should be nescassery, it's a new kit, it come all together with piston, head, cylinder etc. i'm gonna take it to my local bike shop and see what they say, incase they've messed up somewhere giving me the wrong piston but i think you need a special ring compressor because it's a competetion high compression unit. thanks for your reply :worship:

hi again, tried with margarine in the cylinder and it still wont go in theres to bits underneath the ring like a little bit of metal on both bits of the piston but not directley next to each other, do they have to go in anyway special (if you know which bits i mean) or does the piston have to go in a certain way? (first time i've done this) thanks for your help!

they go on other side of barrel to exhaust port iirc, you dont want them near a port or they catch it and bust the rings

Couple of things. Which end of the barrel are you trying to fit the pistons into? I know my old Honda only took the pistons if they were fitted from underneath the barrel rather than the top.

Also, some pistons have a tiny little 'peg' in the ring groove that locates the end of the rings and stops them from rotating around the piston. If the ends of your rings have a tiny little cut out in them, make sure they are being located over the pegs as mentioned above. If they aren't the rings will be pushed out more by the pegs and this could be stopping them from compressing enough to fit in the bores properly.

You'll get there in the end, but DON'T force it. Piston rings are quite brittle and break easy, as I know from bitter experience :bang:

Alex-R said:

hi again, tried with margarine in the cylinder and it still wont go in theres to bits underneath the ring like a little bit of metal on both bits of the piston but not directley next to each other, do they have to go in anyway special (if you know which bits i mean) or does the piston have to go in a certain way? (first time i've done this) thanks for your help!

Click to expand...

Alex just to add to the last post which is very good, First did you mean 20 thou o/size??
2/ the pegs in the ring grooves stop the rings from turning in the groove.
3/ you need to gap the rings; measure the width of the peg in the groove add on 4 thou /inch of diameter of the cylinder,, note that number
4/put the ring in the cylinder push it down about 1 inch with the bottom of the piston this wiil keep it square in the cylinder.
5/ now measure the ring gap and compare it to the answer in no. 3
6/ remove the ring and file it until you arrive at the answer in no.3(and be careful they are brittle)
7/ clean the parts , assemble with the oil that you use in the motor ie. no margarine vaseline chewing gum etc.
8/you do not need a ring compressor on a single cylinder motor, only a little care, nothing has to be forced they go in easilly with your thumb nails,
have fun
Clive

thanks a lot you three for the detailed help (which is 1 what i need lol) i'm going to have another try using your advice later and i'll let you know how i get on

thanks alot! much appreciated :worship:

still trying lol :bang: :bang: i have to keep taking breaks or i'll need a new window after i throw it down the street lol

Alex
Just ask the question, it aint that difficult we all had to learn.
Clive

hi again, ermm i'm gonna sound a right idiot but... i overlooked the part about the rest pegs lol, when i closed the gap of the rings the piston went in first time no problems. So thanks you three! i couldn't have done it without you, and i now know how to do it properly :worship:

:bang: ok well i was putting the barrel and head on, tightened the bolts, on 2 of the long engine bolts the head of the bolts has snapped off, didn't even think of using new bolts! ahhh how can i get them off? thanks again :bang: :bang:

Remove the 2 good bolts, Can you get the head off??
If yes you now have enough old bolt showing to grip and turn dont force it ,it may be loctited into the crankcase carefully heat the area to break the loctite(do this away from all petrol)
If no ,can you lift the head and or cylinder high enough to get some grips in the space underneath if still no. I am afraid the engine will have to come out of the frame
.

rgds.
Clive

hi, thanks for the advice, i have more than enough room to fit grippers on but they just wont grip it, is there a special way to do it? i'll keep trying. thanks again

Depends on what you are using pliers are no good, footprints or stilsons get tighter as you turn them , molegrips are also good if you can get them tight enough onto the bolt.
rgds.

Clive