Best way to install piston in a single?

[Simonpsmith]

I have to put the piston back in my barrel. Bit worried about breaking a ring.
Is it easier to install it first, from the top, then lower the whole shebang before fitting the gudgeon pin?
Or lower the barrel down onto the piston after attaching to the pin?

either way, what sort of compression tool is best?

[Roger Gwynn]

Fit piston to rod, place a couple of supports under the piston to stop it moving about. Lower cylinder onto piston, gently wobble it about so that the rings are compressed by the chamfer and push down, gently, making sure that the rings are not pushed downwards past their grooves. Have a medium screwdriver handy to push the rings in to the grooves.
Have a go with the piston on the bench first, wobble and gentle push or use a ring compressor if you like. I once did a 4G without compressors, traumatic but successful.

[Simonpsmith]

Thanks Roger, most helpful.
Good idea to try it off the bike first .

[ian williams]

hi simon ;
its all as roger etc says really , some guys do make up wooden blocks to sit between piston and top of crankcase so the piston is vertically straight .
you should be able to squeeze rings in with fingers and as you drop barrel down onto piston and it will sort of pop in place with just a little push or light tap with leather or plastic mallet ..
you can also use a piston ring compressor , or make one from some very thin sheet metal yourself by rolling some around piston and put 2 little 1/2" 90 deg bends in end so you can grip with pliers or grips to squeeze the rings into their grooves , then just place compressor over the rings and squeeze it up and then slide barrel down and you can gradually drop barrel over the rings as you bring it down and wiggle about with the ring compressor so it drops down at same time .
easiest way to get better idea is to search youtube and youll find someones done a video youll understand and can follow .
ian

[Simonpsmith]

Proper old school fabrication
https://youtu.be/aerdr95Bf4Y?si=3G3HU9fanEfBoq5u

[nevhunter]

There's no ONE way but Having the Piston in the barrel and inserting the Piston pin later with the Piston warmed to make the Pin go in easily is time tested. Have the far circlip in it's groove and keep the case covered with a clean rag to prevent anything dropping in there. Double check piston ring end gaps and groove depth. Having a Part of the Ring pop out of the groove while installing is the Main cause of ring breakage. IF you are not using a ring compressor you rely on the chamfer a great deal. Star the insertion by entering the portion of the ring opposite to the gap first. Staggering the Compression rings is advisable. IF you have to file a ring end to get the gap do it evenly from both ends and make sure they Match up to the other end. Try to avoid distorting the rings when putting them on the Piston. Nev

[Simonpsmith]

Thank you everyone for your suggestions.
In the end, as I managed to borrow a compression tool, I decided to put the piston in from the top of the barrel.
This went OK and with some generous amounts of heat to the exposed gudgeon pin area, the pin went in nice and smoothly too.
On to the rest of the rebuild