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Old 07-10-2020, 07:49 PM
andyrob andyrob is offline
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Default JCB 802-4 mini-digger track idler tensioner problem


I've thrown a track and think I just need to release the grease valve on the idler unit and slide the idler/tensioner unit back so as to give me the required slack.

However, having done that I find the slider holding the idler wheel won't move at all and I don't want to use brute force, and a little ignorance, to move it back.

It could be that the grease-ram (whatever it's called) is seized - which is perhaps why when I've tried to take up the track slack in the past it's not moved - hence the thrown track.

Any suggestions please?

Last edited by andyrob; 12-10-2020 at 01:10 PM. Reason: SPAG
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Old 22-10-2020, 11:24 AM
andyrob andyrob is offline
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Default SOLVED: JCB 802-4 mini-digger track idler tensioner problem

Well, 255 views with no suggestions so far. It must be an unusual problem.

This (below) would also apply to the similar JCB 802, 802 Super and many other machines, I guess.

For the benefit of future readers it was the track adjuster/tensioner ram that had seized and so prevented the track form being tightened - which led to the track coming off its drive sprocket.

I ran lots of oil around the sliding parts that the ram is fitted to - in case they were seized into the main casing but that didn't solve it when I tried sledge hammers (on a wood block), ratchet straps around the track. (If doing this put the strap at 90 degrees to the run of the track, ie not round the track itself).

The simple solution was, first, to make sure the one-way (?) valve was removed (the part that the grease nipple which is used to tension the track is inserted).

Then, with the machine raised on one side, I ran the track very slowly and, as it turned, inserted a 1" round bar between the track and idler sprocket.
1" was big enough for me, I guess a bigger one might have been necessary if the track was slacker Also, perhaps I should have first used something like (softer) broom handle or similar - just in case the forces were hazardous using steel on steel.

This tightened the track as it rotated with the bar between the sprocket and the inside of the track. The ram 'gave' - and with such force that a large clump of grease shot from the ram, just like a paintball 'bullet'. It thought something like a bolt had hit me.

So, if/when you do this, make sure you're clear of the (removed) inspection cover where the valve/nipple has come from - or put the cover back on temporarily.

Last edited by andyrob; 22-10-2020 at 04:00 PM.
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Old 12-06-2022, 11:44 AM
andyrob andyrob is offline
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Default Re: JCB 802-4 mini-digger track idler tensioner problem

Further to getting the jammed idler wheel and adjuster off, the next problem was getting it all re-fitted and the track re-tensioned.

Trying to pump up the piston in the tensioner I couldn't get any grease through the grease nipple. Here - as often is the case - there were two problems. The non-return valve in the hex-bolt which has the grease nipple facing out was very 'sticky' and let only a little grease through before jamming shut.

And the small bore of the grease nipple didn't allow enough flow of grease to open it. So, I used a small punch through where the nipple is fitted to loosen the spring loaded NR valve, then drilled out a spare grease nipple and fitted that, then pumped away - 5 seconds later all done. I also slipped a 'cap' over the end of the piston as, with an old track, there was a lot of outward movement before the slack in the track was taken up. I wasn't sure if I'd run out of travel/adjustment and fitting the cap (which looks like a steel bottle top) gave me 1/2" of extra length to the piston.
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idler wheel, mini-digger, tensioner, track thrown

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