How to remove a stuck piston

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Paul Gasson
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How to remove a stuck piston

Postby Paul Gasson » Mon Dec 21, 2015 8:41 pm

I have one obvious problem with my 1950 NH project and that is that the piston in rusted in the barrel. It has been soaked for some time with various products to try to move it but having lifted the barrel from the crankcase, I can feel rust under the piston as well as on the top area.

If anyone else has had this problem, I would appreciate details of how they solved this. I would like to use the barrel as it is in good condition apart from one small part of a fin missing and hopefully a rebore will be possible. I cannot see any oversize markings on the crown.

Thanks,

Paul
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PeterW
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Re: How to remove a stuck piston

Postby PeterW » Mon Dec 21, 2015 8:58 pm

I had a similar problem with a 600 a few years ago. The bike had been in a hedge for at least 25 years. I left it soaking in diesel for a month, carved a block of wood to the same diameter as the bore, warmed the barrel then "tapped" the wood with the biggest hammer I had to drive the piston out. Worked a treat.

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Re: How to remove a stuck piston

Postby paul.jameson » Mon Dec 21, 2015 9:49 pm

See my reply under your other topic. I didn't read far enough down the list before writing!
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: How to remove a stuck piston

Postby Simon.Gardiner » Mon Dec 21, 2015 11:28 pm

I've always used the soak/heat/bash approach (partly because the most rusted bores I've had to deal with have been the ones that haven't had any cylinder heads).
Your piston isn't flat-topped so a big piece of wood is fine, there's not a lot of point in turning it to the diameter of the bore. You can give it a lot of welly - the piston crown is the strongest part and anyway (ultimately) the piston is expendable.

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Re: How to remove a stuck piston

Postby nevhunter » Mon Dec 21, 2015 11:38 pm

I have gotten pistons out by putting the head back on and filling the space with old grease and pumping more grease in through an adapter in the plug hole to force it out . If it's heavily rusted below, this is not advised, as the piston will jamb firmly in the rusted section. If it's like that you have to dismantle the crankcase s and split the flywheels and carefully scrape the rust from the bore below the piston. Nev

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Re: How to remove a stuck piston

Postby Ian.Taylor » Tue Dec 22, 2015 5:43 am

Good advice Nev
Back in 77 when i first purchased my VHA it also had a stuck piston and like many i soaked it,heated the barrel and drove the piston down only to discover when I removed the cylinder I had broken the bottom of the skirt.
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Re: How to remove a stuck piston

Postby AndiRobinson » Tue Dec 22, 2015 8:02 am

4 strokes are much easier than two strokes in that there are no ports for the oil or diesel to leak out of. I found that filling the bore with oil and heating it with a blow torch has worked well in conjunction with the hit it method.

If the piston is a bit down the bore then I lift the barrel and put it on a couple of small bits of hard wood so the bashing does not effect the cases

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Re: How to remove a stuck piston

Postby Paul Gasson » Tue Dec 22, 2015 7:01 pm

Thanks for all of the suggestions, I have used a different release spray and will leave it for a little longer and try the block of wood approach whilst still assembled but not giving it too much abuse. If this does not work I will try adding a little heat, surely the piston will expand faster than the barrel so it will all need to get up to a good temperature before I potentially get the maximum clearance? I like the grease approach but I do not have a way to make a fitting for the spark plug hole.

What about making a plate to go over the barrel using the head mounting threads and a large screw in the centre. Any thoughts on this?

Thanks,

Paul

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Re: How to remove a stuck piston

Postby steve.clarke » Tue Dec 22, 2015 8:09 pm

You need the Heat Paul if you don't free it off you can collapse the piston crown.
Cheers Steve.
57VH 58VH 56HS IN A 58FH Frame, mortal remains of a 57NH 1999 FZS 600

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Re: How to remove a stuck piston

Postby Simon.Gardiner » Wed Dec 23, 2015 11:31 am

Paul:
If heat is going to be applied the barrel needs to be hotter than the piston; there are a couple of different ways of achieving this, eg. heat the barrel taking care not to also heat the piston (eg damp rag on top of it) or cool the piston (got any dry ice?) . Or both :)
I think Steve's pointing out that with enough heat you could just melt the top off the piston anyway!
That idea with the plate would work pretty well - as long as you can get a seal between the plate and the barrel.
(Putting some oil/diesel above the piston and heating it can help the fluid to penetrate. Also just heating up good and hot then allowing to cool a few times can help as the heating/cooling can break down some of the things causing the 'stiction')
Use something really heavy to hit the wood with - it's a lot easier to control and to get a good solid 'thump' against it, which is often the trick with something seized.

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)


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