pistons first or cylinder?

[limeyrob]

I'll be fitting the pistons and cylinder block this week.  Bottom end is done and in the bike.  Normally I would fit the pistons to the rods, support them and using a pair of ring compressors push the block down.  Done this many times it seldom goes to plan without a few hick ups.
Recently saw a video of a guy fitting the pistons to the block then supporting the block and fitting the gudgeon pins.  Its looked like there was less to go wrong (so long as you didn't' drop a circlip).
Thoughts, advice, comment please.

[muskrat]

G'day Rob.
I've always dropped the barrels over the pistons, even on 4 & 6 cylinder bike motors. I had thought about the pin clip method but the risk of losing a clip or damaging a piston or worse (clip coming out on the run) warned me off.
The old poly pipe and hose clamps have worked for me for 50 years.
Cheers

[limeyrob]

Thanks, just been getting the cylinders ready. I've stoned a very small chamfer on the bottom of each bore.  Its +60 and I'm surprised how thin the skirts are. The bores are slightly off centre in the casting - a Friday afternoon special me thinks. Its an odd engine - its been honed and the rings are new, looks like it's not run since they were fitted but I've had to rebuild the bottom end.  No way was it usable.  Oil seals on the exhaust guides so they were worn to hell too.
I'll decide 5 mins before I fit it

[groily]

G'day Rob.
I've always dropped the barrels over the pistons

+1 for that, though have done it t'other way before now with engines on bench.

[CheeserBeezer]

I think it's much easier to fit barrels over pistons as 'jiggling' the gudgeon pin through a hot piston without the ability to 'jiggle' the piston square because it's so hot seems messy to me. You'd also have to line the con rod up blind. Use the best quality ring compressors you can get. Crap ones should be avoided as they'll cause more problems than they solve. I've made some out of clear plastic tube and they're brilliant because you can see through them and you know everything is going squarely into the barrels at the same time. I always make sure there is a slight chamfer on the skirts, as you have done.

[chaterlea25]

Hi All,
Adding a pair of parallels between the crankcase and piston holds them square while you attend to other matters lowering the cylinder down.
Even lengths of prepared wood lath will do if you don't have parallels

John

[limeyrob]

Well its done. Two dowels to steady pistons, decent chamfer on cylinder bases, ring compressors and plenty of oil and its gone together a treat.  Now waiting for the head to come back from machine shop.

[bikerboy]

Pistons on and barrels lowered to meet them I have found easiest what work are you having done to the cylinder head? Only asking cos it might be a good time to have the exhaust seats replaced to handle the ethanol fuel

[limeyrob]

Its an alloy head so I'm hoping the existing inserts are OK for now.  The guides were very bad and one had been moving in the head. The only oversize guides I could get needed turning and honing.  Its over at Classic and Modern in Bracknell.  They did a decent job on the crank and that's fitted nicely but they do seem to take their time, the head's been there a good few weeks now.

[bikerboy]

Its over at Classic and Modern in Bracknell.
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They did one of my alloy heads and changed the exhaust valve seats. Not cheap but they made a reasonable job of it. I tend to go to a place in Church Crookham now mainly because the guy owns old brits himself so I trust him to know what he is doing. Famous last words 

[coater87]

 I think this is a "other side of the world" thing.

  If you tried fitting the pistons in first, you would never go back to a god awful set of ring compressors, cuss words, pinched fingers and broken rings.

 I honestly think if your sight or sense of feel is so degraded that you doubt a circlip has seated, get a younger person to lend a hand. They may really enjoy helping with the project.

Lee

[berger]

i went to the pub nothing unusual about that then , so who holds the barrels with the pistons in while the pins are shoved in . i do it johns way wood across the mouth under the pistons --- solid -- and well lubed brass sheet with clips holding in the rings and bingo jobs a gudden

[berger]

er you did go to the pub what you on about now loon? it is copper sheet

[sean]

Well its done. Two dowels to steady pistons, decent chamfer on cylinder bases, ring compressors and plenty of oil and its gone together a treat.  Now waiting for the head to come back from machine shop.

this is when I prime the oil pump and make sure its working especially  if you replaced it with a blue one .....easy to turn the motor over with no compression .
as for your question I use parallel bars under the pistons and keep a rag in the crankcase hole until pistons are in the cylinder .