Getting pistons back into cylinders!

**cbfb** · 20th November 2010, 18:12

Oh dear, I've come unstuck a bit, took the cylinders off my GSF250, inspected the pistons, everything all good, now trying to get it back together again. Er, how do you get the pistons back into the cylinder?

As far as I can see, you should assemble all four pistons on the conrods then slide the cylinder block down over them. Sounds easy eh but it's a BASTARD to do

Is there an easier way or a tool I don't know about or something? Manual is f all use and google isn't helping for once.

Also am I ok leaving the original cylinder gasket on? It looks fine. Will be replacing the head gasket though.

Sorry if I'm monopolising this forum lately, appreciate all your help though.

**MotoKuzzi** · 20th November 2010, 19:00

There's a tool called a ring compressor that helps. Never done a 4 cyl m/cycle before, I imagine you would have to remove conrods from the crank and do one piston at a time?

**cbfb** · 20th November 2010, 19:08

Originally Posted by MotoKuzzi

There's a tool called a ring compressor that helps. Never done a 4 cyl m/cycle before, I imagine you would have to remove conrods from the crank and do one piston at a time?

I have heard about a ring compressor, but I can't figure out how it would work if I'm trying to slide the block over the assembled pistons?

No the conrods stay in place and the pistons go on the little ends, then the block goes on top. That's what it says in the manual anyway...

This is what it looks like at the moment:

Click image for larger version.

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**cs363** · 20th November 2010, 19:14

If you want to do it that way, use the cheats method - get four good quality hose clips slightly larger than the pistons and use them as ring compressors, once you've got the cylinder over the pistons you can just undo them completely and remove them. Make sure to use plenty of engine oil to lubricate the rings/pistons.
It is a hell of a lot easier to do individual pistons and rods though, rather than trying to do the whole four at once - you'll probably need an extra pair of hands to do it that way.
Personally I'd replace the base gasket as a matter of course, you don't want to get it all back together only to find that's leaking.....

**MotoKuzzi** · 20th November 2010, 19:15

Ok. I have only done car engines and in that case you do each piston into the bore individually with a ring compressor with conrod attached and then connect the bottom part of the rod to the crank.

To achieve what you want to do your'e gonna need 4 ring compressors and a lot of hands. Hopefully some one who knows will pop along soon.

Cheers.
Mark.

**Mental Trousers** · 20th November 2010, 19:17

A ring compressor tool

You can use some of these if you're careful

You'll still need at least one extra pair of these though

**FJRider** · 20th November 2010, 19:18

I found hose clamps (lightly fastened) on the pistons ... slide the cylinder block down ... but don't drop them into the crank area as you remove them from the con-rods ...

**MotoKuzzi** · 20th November 2010, 19:22

Good idea, i imagine you would run the risk of scoring the rings if they were clampe too tight.

**FJRider** · 20th November 2010, 20:30

Originally Posted by Mental Trousers

You can use some of these if you're careful

You'll still need at least one extra pair of these though

Place a block of wood above the bottom gasket to rest the cylinder block on as you undo the clamps ... sorted ...

I used them on the top end rebuild of a GS1000S by myself ... no worries ...

**jonbuoy** · 21st November 2010, 05:22

Car ring compressors are usually too big for wee bike pistons, nails and fingers and a helping hand will do it. Hose clamps can scratch the pistons.

**cbfb** · 21st November 2010, 11:29

As always, some very helpful replies there. That's given me plenty to go on.

Ring compressors x 4 = a bit pricey. So will have a go with hose clamps if I can find a suitable size.

Yep I can wedge some wood under to hold the block up, good idea.

Will enlist the girlfriend to help, might take a bit of persuasion!

Bugger about having to replace the gasket, I was thinking that because failure of the base gasket isn't as critical as the head gasket (i.e. just get an oil leak) I would leave it, but if you reckon it needs doing I won't argue.

**rwh** · 21st November 2010, 12:32

Wouldn't it be easier to turn the crank so you can do two at a time? Or does that cause confusion with setting up the timing chain etc?

Richard

**cbfb** · 21st November 2010, 12:58

Originally Posted by rwh

Wouldn't it be easier to turn the crank so you can do two at a time? Or does that cause confusion with setting up the timing chain etc?

Richard

It would be easier, but unfortunately there's just not enough room to work in there. You wouldn't be able to get the pistons in under the block and the pins in next to the other pistons

**rwh** · 21st November 2010, 14:06

Originally Posted by cbfb

It would be easier, but unfortunately there's just not enough room to work in there. You wouldn't be able to get the pistons in under the block and the pins in next to the other pistons

Oh - I was thinking of putting all the pistons on the conrods first, but just putting only 2 at a time into the cylinders.

Richard