Jump to content

pap top 80 fit piston back into cylinder help required !!


markpulling
 Share

Recommended Posts

Hi all ,just in the process of fitting a new head gasket on my top 80 ,easy job I thought ,take off head fit new gasket then refit ...simples WRONG !!I have just spent 4 hours trying to get the piston back into the head ,you have to squeeze the piston ring with your fingers right down while simutaneously keeping piston and head all straight and level, there is zero percent room for error as the tollerance has to be so tight ,I called andy at skydragons to ask if I was doing anything wrong and he said I was doing it correctly but it is a long hard job,has anybody done this themselves and able to offer me any tips ,or if someone out there can do this in their sleep ill gladly pay you to do it for me if your local to me in dorset,many thanks in advance MARK

Link to comment
Share on other sites

try using some 2 stroke oil inside the cilinder to make the piston go into the cilinder easier. May be try using a friend to lower the cilinder down as you keep the rings in place.....

Are you sure you have the ring's seated correctly? some pistons have little bit to stop the ring spinning

Link to comment
Share on other sites

Mark,

I've refitted my piston, what I did to keep the rings in place was to use a large cable tie.

Pull it tight around the rings to keep them in their grooves, then push the piston down into the barrel and the cable tie will slide up and hey presto, job done.

If you're stuck finding a cable tie big enough I have a few, just ask and I will send you one,

cheers,

Alan

Link to comment
Share on other sites

Yes the ring is seated corretly ,its a spring loaded affair which you have to squeeze with your fingers with all your might to make it flush with the piston then try and get it into the cylinder ,will try again tommorrow when im a bit fresher !!post script thanks alan to do it your way do I have to remove the piston and put it in from the top rather than going up from the bottom ?

Link to comment
Share on other sites

Pistons always come up from the bottom of the barrel.

There should be a chamfer around the base of the bore to help 'guide' the rings into the bore.

I am not familiar with your current piston/ring setup but there are a few things that could be causing problems.

For starters, your comment of having to use a great deal of force just to get the rings sitting flush into the grooves does raise some concern.

A lot of the bike engines I re-build have two different types of rings fitted to the same piston. One is of the normal parrallel face construction, the other has a tapered edge(normally the top edge). The uses the combustion gases to help force the ring out onto the bore.

Where the rings locate on the pegs (in the piston) are some cutouts. Again, if the rings are fitted into the wrong groove, they will not sit totally flush into the piston.

Also important is a lot of rings have a top and bottom face. Normally, the top is marked/stamped on the ring.

If the piston is the original, does it have carbon/gumming binding the rings in the grooves?

As Mark pointed out, use LOTS of 2t oil on the rings/piston and bore.

You could try the cable tie or use a large jubillee clip(not too tight mind)! to compress the rings and slide the barrel DOWN over the piston.

OR....

Pop the lot up to Sussex and I'll get it sorted!! :wink:

Link to comment
Share on other sites

Just a thought but are you lining the pin up before compressing the ring and have you fitted the ring the correct way up so that the locating pin slots neatly into the recieving groove cut on the ring!!!

Isn't that what i already advised? Lol.

I dont think the ring compressor would reduce down small enough for these little pistons, could be wrong though?

Link to comment
Share on other sites

The locating pin in the ring slot on the Top 80 is tiny and you need to be really careful that the pin is between the ring gap, and keep twiddling it as the barrel rides over the ring and closes the gap up. The pin is also in an awkward position near the back of the frame. If you get that bit right the barrel will slide on easy without any tools. As mentioned, lots of oil on the barrel chamfer.

Link to comment
Share on other sites

Are you trying to do this with the piston still attached to the rod?

My personal preferance is to fit the top part of the piston into the barrel on the bench, where I can see what I'm doing and get my fingers to all sides of the piston. Once all the rings are in the bore, the assembly can be offered up to fit the gudgeon pin and the retaining clip or button replaced.

Good luck.

Pete.

P.S. reading through all the answers to Mark's question, I have a mental picture of Mark struggling in his shed while half a dozen of us stand around, pointing and offering advice.

May I extend this metaphor by offering Mark a virtual cuppa? :D

Link to comment
Share on other sites

Done it !! the drinks are on me .. :lol: it was exactly what neilzy and enzo said ,what had happened was when I took the cylinder off the piston the piston ring then springs out slightly and must have spun arround the piston somewhat ,I hadnt realised that there is a tiny locating pin in the groove you cant see it but I was able to feel its location with a needle ,I then marked its location spun the ring round until the slot was directly over the locating pin ,then with a good coating of oil gently squeezed the ring and the cylinder just slipped down like a glove ,it was so easy ,so just so others dont make the same frustrating mistake I made the ring had spun round and was ON TOP of the locating pin no wonder it wouldnt go in !! ,many thanks again guys hopefully flying this weekend :acro:

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share



  • Upcoming Events

    No upcoming events found
×
×
  • Create New...