Short stroking

[MistroJoe]

Hey guys/girls,

I've just performed what I must say is a perfect angle of engagement, however now I'm concerned with premature engagement.

My piston has the second tooth removed which is great, but until now I've had no need of a dremel etc. I've removed the bearings from my piston head so that will help a bit, but I can also remove the last tooth on the piston which is the metal one (it just slides off) I have no doubt this would eliminate any risk of pre-engagment but is that ok to do? This would been my last tooth is plastic.

Is the answer really to remove the first tooth on the sector gear and if so which is the best way to do this?

Thanks

Joe

[BikerEddd]

Re: Short stroking

You CANNOT short stroke a piston when it only has one metal release tooth. If you took a tooth off of the sector gear then your final tooth would still effectively be plastic. If your release tooth is plastic then the piston will be ruined within a few shots.

Unless you are running a pretty serious rate of fire setup I wouldn't worry about PME.

[MistroJoe]

Re: Short stroking

It would be either or but thank you

So no need to worry about pre engagement at all really? I'd be running it on a 7.2 lipo i guess

Cheers

[BikerEddd]

Re: Short stroking

You must do both when short stroking Well I guess you could leave extra teeth on the piston but that wouldn't be very professional logic would suggest that you have to have the same number of teeth on each 'gear' be it the sector gear or the piston rack. If you have extra on the sector gear then the piston will 'bounce' off the last one and if you have too many on the piston then it simply wont get used and add a bit of extra weight.

If you manage to get pre engagement running a 7.2v lipo then myself and the rest of the teching community would all be extreamly excited to know how on earth you manage that (other than replacing your spring with many some sort of super weak elastic band system)

At 350fps you would need to be running 11.1V, mosfet, high speed motor and almost certainly high speed gears. Again it would change gun to gun but you get my point in that in order to get pre engagement you have to be pushing a very high rate of fire. Much higher than anything a 7.2V will deliver with a 350fps spring

[laurence]

Re: Short stroking

If you really want to, its a pretty easy job. You just need to get yourself a piston with as many metal teeth as you wanna short stroke, +1...minimum (eg, if you wanna short stroke your sector gear 2 teeth, you need a piston with at least 3 metal teeth as you'll need to take 2 off, and then be left with a metal 'release tooth'. These can be remove with a hacksaw and file fairly easily.
Also if i were you, id replace the bearings on your piston head, it wont affect pre-engagement that much/if at all and will do more good being fitted. Another note, when you short-stroke because the piston is being released earlier the spring doesn't receive as much compression, = slightly lower fps. Removing the bearings will again reduce your fps further as the spring, again, isn't being compressed as much.

So in short:
-Take the same amount of teeth off your piston as you do your sector gear (dremel no necessary, i never used one)
-Always make sure the last tooth on the piston is metal (or you'll strip it in no time)
-Keep your bearings on your piston head (or get a bearing spring guide instead, as you have the piston head bearings though, you might as well use them)

Happy tinkering!

[sj_asc]

Re: Short stroking

It's essential that the teeth are removed from the initial pickup side of the sector gear to avoid running into tappet timing issues. Removal of piston release teeth are only essential if your sector gear has an enlarged release tooth (Marui, Gaurder, Gen 1+2 SC), however it's as said tidier practice. As also said, the tooth being released from must be steel.

If you are only removing one tooth, then bare in mind that if you are also planning to do AoE corrections then the piston will be spaced back approximately the lost distance of the short stroke - so spring tension should remain roughly same at peak compression.

Regarding the need for short stroking in this particular setup, you are very unlikely to run into PME issues with a 2 cell lipo with any relatively pedestrian gear ratio or motor, so it's not essential.