One giant leap forward for Ted not a giant leap for most sohc members!
This afternoon I started the task of fitting pistons into the bottom of my block cylinders after a couple of decades only fitting pistons on cars from the top end. This video was my homework the day before :-
https://www.youtube.com/watch?v=YfCwpDsP_5EFor the benefit of those who have yet to start this task I'm going to verbalise my process.
1) I checked that the piston ring gaps were suitably in a staggered position on each piston & that there was oil smeared on the cylinder insides. Gasket was in place with the two locating dowels
one on either side.
2) I put a long socket on the mainshaft as my clutch basket is not in place so I could easily rotate the crank slightly if needed to wiggle pistons a tad.
3) I found a suitable piece of wood to support the block at the centre where the camchain runs. I ensured that the wood was tall enough to hold the block just clear of the pistons when 2 & 3
pistons were close to the top of the stroke.
4) I carefully fitted the block over the studs lowering it until it touched the piece of wood. (see picture)
5) I fed the camchain through the block using a cable tie then secured it to the frame so the chain was reasonably taught. (used spare small dog collar on frame lol)
6) I rotated the crank so that pistons 2 & 3 were about an inch from maximum height - the idea was I would be able to pull the pistons up towards the cylinder liner/block if needed.
7) I carefully removed the block of wood - then put another block of wood that was about an inch thinner in place carefully feeding the pistons into liners 2 & 3 as I lowered the block ensuring
pistons 1 & 4 were not trapped as I did this. The cylinder liners have a great suitable taper start to them.
I then made sure the top ring of piston 2 was in position at the start of the taper to the liner. I then moved to piston 3 and fed the top ring into the taper. A combination of pulling up on the
pistons or allowing the block to move down made them go into place with no need for excessive force that could break a ring.
9) Once the first ring of pistons 2 & 3 were into the taper I squirted some thin oil onto the top of the pistons. I then repeated the above process until the second ring & finally the oil control rings
were inside the bores. I lost count of how many times I circled the bike ramp to check everything was in place. Now I was happy that pistons 2 & 3 were in place I rotated the crank to give me
some room / height to repeat the process for pistons 1 & 4.
10) I now had all four pistons in the liners so was able to just wobble the whole block down very carfully & evenly making sure the liners did not touch the crankcase sides as it finally engaged
the bottom dowels.
11) Tbh the whole process took about 40 minutes as I kept walking round to make sure each ring was in place. I found that I could not just use my fingers to fit the rings for the last two pistons
as the gap and angle was a bit tight even when I rotated the crank to raise the block a little. I used a 4" offcut of 25mm Speedfit pipe to assist my finger nails for the last two pistons.
I had no issues with the front down tube getting in the way - periodically the wooden block would fall out so I would move it to the other side.
..
block in position by
Macabe Thiele, on Flickr
pistons in place by
Macabe Thiele, on Flickr
