JCB Blue material piston /ram seals

[RedLiner]

Hello all, I've owned and operated my 1993 JCB 3CX Sitemaster for the last 12 years or so here in sunny Southern Spain.


I've replaced seals on quite a few of the rams without any major problems.
I have just removed the ram that operates the extending dipper. I replaced the gland seals to the threaded cap and it slid nicely onto the piston rod. I then removed and replaced the crumbling seal to the piston head with it's rubber base and fibre rings to either side.

However the trouble started when I tried to insert the piston into the ram. I applied plenty of hydraulic fluid to the inside of the ram and to the piston head and seal. It would not push into the ram and subsequent persuasion with a club hammer did nothing.
I then tried lining up the piston rod and ram casing perfectly and pushed it (very gently) with a dumper truck. The result was damaging the blue seal which I had to discard.
I have another seal kit but don't want to repeat damaging the blue seal again!
Carefully examining these blue seals the material resembles hard plastic and not the usual softer seal material.

Is there a trick to push the piston head back into the ram without damaging the blue piston seal? I did gently rub the sharp edge inside the ram with fine emery paper but the piston still won't enter the ram casing easily and I don't want to apply too much force and wreck another blue seal.

Usually piston bores have a slight taper to facilitate entry of seals or piston rings whereas this ram casing interior goes directly to bored diameter.

Any help or advice would be greatly appreciated,

James.

[AndrewMawson]

Perhaps warm the seal in hot water to soften it?

[RedLiner]

Perhaps warm the seal in hot water to soften it?

Thanks Andrew, to test the material I did try placing the seal I damaged into hot water but it didn't make any difference, it still felt hard and plastic like and didn't feel softer or stretchy.

I'm now thinking to line up the piston and ram cylinder and use a hydraulic car jack where I will have more control with pushing in the piston.
The part number for the seal kit I'm using is 991/00095 which is for a 40mm. rod and 70mm. cylinder. I've had these two seal kits in their original plastic packing bag for a couple of years, but I shouldn't think they would deteriorate i.e harden?

James.

[Muz]

I usually rotate the piston as if you are stirring some porridge, whilst pushing it in, and use vaseline rather than hydraulic oil .. but I expect that wont be so easy here given its size and length, hot water on seals usually works, but its got to be pretty hot to take effect.

[RedLiner]

I usually rotate the piston as if you are stirring some porridge, whilst pushing it in, and use vaseline rather than hydraulic oil .. but I expect that wont be so easy here given its size and length, hot water on seals usually works, but its got to be pretty hot to take effect.

Thanks Muz, I eventually succeeded to get the piston rod back into the cylinder

I spent ages with various grades of wet and dry emery paper to ensure that the entry point was absolutely smooth with no sharp edges.
I had thought to use a hydraulic jack to push the piston rod into the cylinder but it didn't work when inverted so I used a humble scissor jack.
Thinking on your lines I didn't use hydraulic oil but a light silicone grease to facilitate pushing in the piston rod.
I balanced and lined up the piston rod and ram cylinder on two metal trestles between the digger bucket and the dumper truck bucket. With constant checking and very careful use of the scissor jack the piston rod suddenly went into the ram cylinder.

It's now all back together and working perfectly with no leaks from the gland seal and holding the extending dipper arm without dropping.

Thanks again for the helpful replies, it's much appreciated. Oh! and doing all of this in 36ºC was none too pleasant and it's not really hot yet

James.

[v8druid]

Thanks Muz, I eventually succeeded to get the piston rod back into the cylinder

I spent ages with various grades of wet and dry emery paper to ensure that the entry point was absolutely smooth with no sharp edges.
I had thought to use a hydraulic jack to push the piston rod into the cylinder but it didn't work when inverted so I used a humble scissor jack.
Thinking on your lines I didn't use hydraulic oil but a light silicone grease to facilitate pushing in the piston rod.
I balanced and lined up the piston rod and ram cylinder on two metal trestles between the digger bucket and the dumper truck bucket. With constant checking and very careful use of the scissor jack the piston rod suddenly went into the ram cylinder.

It's now all back together and working perfectly with no leaks from the gland seal and holding the extending dipper arm without dropping.

Thanks again for the helpful replies, it's much appreciated. Oh! and doing all of this in 36ºC was none too pleasant and it's not really hot yet

James.

..... that's the downside of living the dream