Re fitting cylinder block

[Phil Frost]

I’m just about ready to put the block back onto my Flyer. Nice simple job on a four stroke twin where both pistons rise and fall together. Easy on a single too. In fact I have a selection lengths of hard wood to slip under pistons to keep them steady while I fit barrels.
With a 180 crank the job becomes a little more intricate. I haven’t fitted the pistons yet so not sure if there is a gap between both pistons and the crankcase mouth at some point in 360 degrees, I doubt there is. I thought I’d ask the forum if there is a trick to this that everyone in the club knows, before I try to re invent the wheel. I bought the last set of 500cc +060 rings from Scott Spares so there isn’t much room for error.

Phil

[Jan Buchwald]

If you don’t have a tool to keep the rings in, you can make one from a piece of the steel strap, used to strap boxes

[Phil Frost]

Yes I’ve got ring compressors to suit. I’ve done the trick with a strip of tin can and a jubilee clip in the past. Works a treat.

Thanks
Phil

[dave bushell]

I use greased jubilee clips and start with the pistons level. The weight of the block is enough to slide the clips down if they are at the right tension. When the rings have just entered the block I support it while I undo the clips, remove them, and lower the block fully.

[Phil Frost]

The general method I’m familiar with. It’s supporting the pistons level while I slide the block into position. Is there a trick or is it just lock the crank with pistons level and proceed as normal. Albeit with wobbly pistons.

Phil

[Jan Buchwald]

As I remember it, I started with one piston up, and “leveled” the other in place

[BRIAN MARSHALL]

Hi,
It is easiest on cylinders that are not excessively rebored, because as standard, there is a considerable chamfer to the bottom edge of the bores that greatly helps getting the rings “started” into the bores. As the cylinders get rebored the chamfer is progressively lost, until by the time you get to +.050 or +.060″, there is nothing left of that helpful chamfer. It’s more of a problem with 600 engines than it is with 500’s as the latter seem to have a bigger chamfer.

It is a job that is MUCH easier if you use a pair of guide rods to make sure that the barrel goes down square on to the crankcase mouth. They are easy to make out of lengths of 3/8″ steel bar. Just cut about half an inch of 26TPI thread on one end, and screw them loosely into the holes that the cylinder holding-down bolts go into. In other words they are like a pair of those bolts with the hexagon heads cut off, but make them a bit longer for ease of use.

I hope that you don’t break any of those precious rings. Use plenty of oil !!
Brian

[Anonymous]

I used to use ring compressors but then realised that if you set one piston 2/3rds up (and the other therefore about 1/3rd up) you can hold the barrel with one hand whilst tipping the furthest up piston a little to feed the front of the ring in first then push the back of the ring in with your finger/nail whilst straightening up the piston. Repeat for bottom ring then do the same for the other piston. Most impotant thing is to make sure the piston ring pins are aligned with the ring gap before you start or you will break a ring.

Your rollers were posted today, you should have them tomorrow or Monday!

Best regards,
Richard

[pplatt]

An interesting question. I would like to know how one deals with the wobbly piston problem too. At the moment it sounds like a six handed job!

Does having to deal with barrel & head as one unit make things much harder?

I need to know these things ready for when my first decoke comes around!

-Pete P.

[dave bushell]

Two hands are more than adequate, any more and there wouldn’t be room to work! Having the head fitted on a detachable block I find helps as one can fit plugs and the compression slows the descent of the block into the crankcase. I also put a sheet of cardboard or hardboard between the frame and the cylinder block to protect paintwork as the block is slid into position. Before I started using jubilee clips to hold the rings in position, I used to use a piece of cord attached to the head and wrapped a couple of times around the handlebars to lower the block in a reasonably controlled manner but since using jubilee clips I don’t find a need for the cord.

[Author]

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