RD250 cylinders seized... help required

[budgie]

Hi Guys

i am just stripping an RD250 A/C unit, for full on race tune and will be sending to Mr Abbeys emporium of speed for his careful attention, however my doner engine is putting up a fight as it's been sat in a damp garage for many years before I bought it... and on removal of the heads has shown its pistons are well seized in the bore...I have tried the tap of pistons with a lump of wood... no movement, and whilst it will be rebored and crank rebuilt so I am able to be more brutal, I am reluctant to belt ten bells out of it if anyone has any good tips that I can try,  all suggestions greatly received..

Gavin

[earthman]

Have you tried a good application of say penetrating oil and left over night? Apart from that, how about applying some gentle heat to the cylinders?

[Ozhammer]

+1 for soaking them in a good penetrating oil and applying heat (I had to go beyond gentle though to free one bore of my 400). It’s worth spraying the penetrating oil into the intake and exhaust ports too, as the more you can get in there the better tbh.

Keep applying each day and allow it a decent amount of time to do its work and hopefully you will be able to free them without having to resort to unnecessary brutality.

[docjones]

Try pouring some diesel in the bores and leaving it for few days, then tap lightly with wood, it's done the trick with several of my long forgotten engines over the years.

[budgie]

Thanks guys, I am soaking with penetrating fluid overnight, one piston is down so ports are open, so more difficult to get it to soak... if you were heating, where would you heat, cylinder or piston.? Or both...?

Cheers

Gav

[Jethro5]

You are trying to expand the cylinder so apply the heat evenly around the cylinder. You might even try a damp cloth on the piston to keep it as cool as possible.

[steve h]

Nov 2, 2017 22:38:12 GMT 1 Jethro5 said:

You are trying to expand the cylinder so apply the heat evenly around the cylinder. You might even try a damp cloth on the piston to keep it as cool as possible.

Or some of that plumbers freeze spray

[steven]

Hi,
I have a circa 1920,s Villiers engine that had sat in a shed for years, the piston was seized solid.
I got the piston out.... but it took me two years !
I soaked it in various mixes of various fluids, all the usual ones.
What got it out in the end was soaking it in a bucket of water for a few weeks, water was something that I found out about online, and it worked.
I still feel the fact that I soaked it in a bucket of diesel for approx two years before hand helped the water method to work !
Molases was about the only thing I didnt try, but that got mentioned too for freeing up stuck pistons.
steven.

[reedpete]

This is a common problem on those old engines...
The actual specific problem is that the rings are rusted to the bore , its generally not the piston itself stuck to the bore unless it hot seized.
Consequently heat actually dosent do as much as one might hope since the bore and rings just move together.

You need to use a 50mm core bit/hole saw and cut the soft Ali crown away accessing the top ring. Then you need to tap the ring directly with old flat screwdriver etc to loosen and remove the top ring . Then repeat going down to the second ring. Once that’s out the piston will respond much better to oil and heat, if not just fall away directly.

Little bit time consuming but will systematically get you where you want to be.

[earthman]

Nov 2, 2017 23:31:59 GMT 1 reedpete said:

This is a common problem on those old engines...
The actual specific problem is that the rings are rusted to the bore , its generally not the piston itself stuck to the bore unless it hot seized.
Consequently heat actually dosent do as much as one might hope since the bore and rings just move together.

You need to use a 50mm core bit/hole saw and cut the soft Ali crown away accessing the top ring. Then you need to tap the ring directly with old flat screwdriver etc to loosen and remove the top ring . Then repeat going down to the second ring. Once that’s out the piston will respond much better to oil and heat, if not just fall away directly.

Little bit time consuming but will systematically get you where you want to be.

Good point about the piston rings, never really thought about those being the main culprit,....drilling sounds extreme but I guess that's got to be the only way sometimes.

[budgie]

Cheers Guy's

as always lots of useful info, and as Reedpete says, as long as it gets me to where I want to be...thats fine.. I have all winter.!

I will let you know how it goes.... slow , I guess.....!

Gav

[budgie]

Well, soak in Diesel, wurth rost off, and a littel gentle heat.... and nothing... would not budge... so left overnight... decided that because full rebuild was following, I would use a nice piece of wood and use a little heavier force... ie move up a hammer size.... and bingo... bit more sweat and swearing and i am now in a position where I can move on.. so thanks for the suggestions and help guys...

Gavin

[yamark]

Gav, Reedpete's method is how I've removed "fused pistons" in the past.

After the crown of the piston is gone, I saw to the back of the piston rings in 2 places.

You can tap this section of piston and piston ring away. You then have a gap for the remaining piston to be broken into.

It's slow work, but it never fails.

Good luck with it    

[budgie]

Job done...! The cylinders can now be cleaned up and off to Mr Abbey for the tune... crank out tomorrow!!

Gav

[earthman]

Back in the nineties I remember using a product called Release made by a company called Chemaide if I remember correctly, it may have only been available via the commercial market, I'm not sure but it were probably the best fluid that I've ever used to free up parts.

Good to hear that you got it free in the end Gavin.

[steeley]

Some years ago saw a programme where a tiger moth bi plane was being restored. The engine on it was seized up and this old boy heated a saucepan of engine oil up and poured it on top of the pistons and freed it off. of course on a 2 stroke engine you would need to block the exhaust and inlet side off before applying the hot oil.

[earthman]

Nov 5, 2017 7:44:15 GMT 1 steeley said:

Some years ago saw a programme where a tiger moth bi plane was being restored. The engine on it was seized up and this old boy heated a saucepan of engine oil up and poured it on top of the pistons and freed it off. of course on a 2 stroke engine you would need to block the exhaust and inlet side off before applying the hot oil.

Oil & heat sounds like a good combination to get things moving.

[steeley]

Ah , and when I meant heat the oil this was on a camping stove and it looked like you wouldn't want it spilt over ya .