Army R85A1 piston sticking.

[basher]

I have an Army r85 and I fitted a new piston into it as the old one went bust. Now when I pull the trigger it'll fire a couple of times then sounds like the gears are just spinning. When I looked in the top of my split gearbox I saw the piston all the way cocked and as soon as I deprecated the two halfs the piston shoots forward again. Can somebody help. Cheers

[big red]

Re: Army R85A1 piston sticking.

Think sa80 pistons are different to standard length could be wrong, has it the new one the same number of teeth as the one you removed?

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[colinjallen]

Re: Army R85A1 piston sticking.

The Army R85 uses a longer piston than a normal AEG; if you want to run a standard length piston you need to fit a spacer between the piston head and the piston and replace the sector gear with a standard one.

[basher]

Re: Army R85A1 piston sticking.

Oh right the piston Iv fitted has the Sam among of teeth it after checking them along side each other the new one is slightly longer.

[big red]

Re: Army R85A1 piston sticking.

That will be the answer then I would think

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[basher]

Re: Army R85A1 piston sticking.

Ok cheers

[basher]

Re: Army R85A1 piston sticking.

So we're can I get an original piston for it?

[colinjallen]

Re: Army R85A1 piston sticking.

http://www.zerooneairsoft.com/produc...oducts_id=4231

That should fit; it is what I had in mine until I changed over to a standard length piston.

[big red]

Re: Army R85A1 piston sticking.

http://www.zerooneairsoft.com/produc...oducts_id=4231

That should fit; it is what I had in mine until I changed over to a standard length piston.

Changing to "standard piston and gear" that's how to stop the semi lock up isn't on g&g and a&a???

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[colinjallen]

Re: Army R85A1 piston sticking.

It helps, but does not entirely cure it.

[big red]

Re: Army R85A1 piston sticking.

May try it on my sons as he has that problem

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[Mearcat]

Re: Army R85A1 piston sticking.

You say the piston sticks after a few shots and you can hear the gears spinning? This sounds like the piston jamming inside the housing rather than the gears holding it back.
Also the piston releases itself when you release the top half of the gearbox from the lower half? This would mean the piston is jamming on a part of the gearbox rather than the gears.

Double check that the pistons groves fit over the rails on the black housing and that the piston seats on the rails correctly when you fit it together. I have encountered a few jammed gearboxes where the piston was not quite seated on the rails.

Another place to look is the cylinder, it must sit in the black housing correctly, with the outer surfaces flush with eachother. if its not it will alter the pistons path enough to jam it rearward.

The only other means of jamming the piston is if it moves to far rearward and wedges on the spring guide.

These are the only things I have encountered that cause what you have described.

With the semi lock up problem, there are no ways to "fully" cure the problem. You can minimize their occurance by firstly training your trigger finger, making full trigger pulls rather than half pulls. The lock up occurs when the switch contacts don't allow enough power through to spin the gears past the cutoff lever point, so the gearbox stops with the cutoff lever jamming the trigger switch.

After I had improved my trigger control, I had to do the following to futher reduce the occurance with my old 8.4V 4600Mah battery:

1. Replace the cutoff lever with a G&G one, they are better machined and made of a tougher material than the Army one.
2. Replace the wiring with 16awg (standard is 18awg which carries less current). This is thicker than the standard so careful positioning was needed.
3. Fit a NanoASR Mosfet. If you fit one it must be one without Active braking as the R85 already has hard wired active braking.
4. Replace the battery terminals with Deans connectors.

Once I did this trigger lockups only occurred when the Nimh battery was running low, so you knew when it was time to recharge/Swap.

That setup has ran for the past 9 years until a surge from the battery spectacually dying (with smokey bright sparks) blowing the fuse and Mosfet. I have since replaced the battery with Lipos and a new NanoASR and no longer get lockups.

Damn it just seen the age of the post, oh well Knowledge shared is always best.

[Sitting Duck]

Re: Army R85A1 piston sticking.

piston sticking is the lame pre-cocking feature on lower juice batteries

I "think" but don't quote me the sector gear might be able to be swapped out for a sr25 19 tooth sector
BUT don't quote me on that coz the gears inside are of the v6/7 type used not the more regular gears like v2/3's
however I "think" the sector is the same or compatible with regular sectors & the sr25 has 19 teeth instead of 16
so the sector is std type sector & the bevel might be a std bevel too

it is just the spur gear than comes from a v7 set I think

You can use a spacer 9mm or 10mm on a regular piston (3 teeth less x 3mm = 9mm less teeth)
BUT you should change the sector or remove the unwanted teeth or it may catch on piston release
also with the 510mm barrel it would be struggling for volume though the r85 cylinder is ported
& your fps may drop a little from short stroking with a regular piston installed.

If one of the experienced l85/r85 tech's out there could confirm for 101% certain the sector is compatible with regular/sr25 sectors
then you might be able to grab a cheap shs sr25 set just for the sector gear to stop this possible pre cocking gremlin