Piston tooth keeps tearing off.

[Buds and Suds]

This is in my CA m15a4 SPC

In the mechbox is,

Metal bushings
Metal spring guide with bearing
Piston head with bearing
Polycarb piston
Stock cylinder and cylinder head
Stock gears and shimming

Problem is after reasembling my gun after putting in my new metal spring guide, my gear broke off the "main" tooth on the piston after about 50-100rnds. This was with a m120 spring. I put it back together with a prometheus M110 and a new polycarb piston and new pistonhead with bearing. After about 30-40 shots, bam same tooth tore off my piston. Im unsure what is causing the problem.

[CDN_Stalker]

9.6V battery by any chance? Or maybe the piston head + piston body is longer than the stock ones, causing the shearing off (seen it, measureed it, even 1mm or 2mm longer to the rear will fuck a piston bad like yours did).

[Buds and Suds]

well, the first time it happened was with a m120 spring. The only thing different from stock was the metal spring guide, the piston was stock polycarb. Im useing an 8.4v batt as well.

[CDN_Stalker]

Sounds like you bought a shitty brand of piston. What make?

[K-D0G]

Im pretty sure that the first tooth should be made of metal for this reason. Must be the brand of piston as stated above.

[lord_sid]

Which Tooth are you talking about? The first engaged one tooth or the metal one at the end?

Usually the gears will eat the first 2-3 piston teeth if it does not engage the first tooth at the right spot.

Check this link: http://www.airsoftmechanics.com/home...nt/view/21/29/. I had this happen to me with the same bloody piston.

[Buds and Suds]

The first engaged one was the one that broke on both, not the metal tooth, #1 I believe its called. It was a deep fire full tooth polycarb. And a stock CA polycarb. Both broke, the stock one broke first.

[Darklen]

Sounds really odd. Try putting one of the pistons back in without the spring and see if it moves relitively freely. Also check to make sure the piston rails are not damaged cusing the piston to twist in the cylinder housing. Make sure to tighten it up as if the spring were in it as well.

[ILLusion]

Check the engagement of the sector gear's first tooth against the piston's first tooth. Make sure it's grabbing in the slot and not striking the face of the tooth.

Do it with the spring out and gearbox closed. Manually turn the gears with your fingers - there should be ZERO resistance between initial engagement and movement of the piston. If it pauses for a moment, then it's not engaging properly. Testing must be done with the gearbox closed, because with it open, the piston is not aligned properly, and thus, fooling you in to thinking it's engaging properly.

What brand piston head are you using? And this is a stock mechbox?

Also, what battery are you using?

[m102404]

If you can compare the over all lengths of stock TM piston to the overall length of the piston+piston head combo you're using, you might find that your combo length is anywhere from 0.5-1.5mm too short. If that was the case, tooth #1 (from the back, open end of the piston) would sit too far forward and the sector gear would come up and mash it, teeth #2 and #3 (etc) would be out of whack as well.

That happened on a couple of pistons I had, I used a washer to build up the space.

From face of piston head to base of piston, measured with a micrometer:
Stock TM - 73.95mm
Stock CA - 73.15mm
Stock JG (v2 I think) 74.72mm

The deepfire piston and modify piston head combo that I use is in a rifle at the moment. First setup "normally", I shredded a piston almost immediately. Second setup (new but same parts) I compared to the TM piston. I remember that it was shorted than the CA one (but not the exact ammount, sorry). One washer, about 1mm I think?, was enough to bring it up to the stock TM length. It's had about 1000 rounds through it now...zero wear, running with a 9.6v, EG1000 motor, 300fps spring.

The other deepfire piston I used was attached systema silent piston/cylinder head combo. Because of the shape of the piston head, it couldn't get a measurement of it's OAL. So I indexed off the back of the piston when the piston is at rest (like Illusion describes) and compared it to the stock TM piston. I think that it was a hair shorter than the stock TM. It's had over 4000 rounds through it, 9.6v battery, Systema magnum motor, deepfire mosfet and 300fps spring (crazy ROF...just for fun). I took it apart 3 days ago to take the mosfet out and there's just the slightest wear on the first tooth (just a rub on the edge where the sector gear hits it).

I hope that helps, I probably butchered the description (no morning coffee yet).

Tys

[Buds and Suds]

makes sense. Problem is why would my first piston break since it was all stock except a m120 and metal spring guide. I have a 3rd piston im going to try taking special care to make sure the gear will engage it properly. I think this is the reason why the other ones broke. I rechecked my piston, and even though its hard to tell, I think it was struck on top of the tooth. Also the 2nd tooth in was also stripped. Also seemed like it was struck on top. I checked the measurements and the piston head + piston combos all line up size wise. So is there any additional things I should pay attention to, to find the issue?

[Buds and Suds]

Originally Posted by m102404

From face of piston head to base of piston, measured with a micrometer:
Stock TM - 73.95mm
Stock CA - 73.15mm
Stock JG (v2 I think) 74.72mm

So a stock JG v2 piston will not fit a stock CA? I dont have my stock CA piston anymore, but my deepfire piston/head combo matches the length of my stock JG piston/head perfectly.

[CDN_Stalker]

Originally Posted by Buds and Suds

makes sense. Problem is why would my first piston break since it was all stock except a m120 and metal spring guide. I have a 3rd piston im going to try taking special care to make sure the gear will engage it properly. I think this is the reason why the other ones broke. I rechecked my piston, and even though its hard to tell, I think it was struck on top of the tooth. Also the 2nd tooth in was also stripped. Also seemed like it was struck on top. I checked the measurements and the piston head + piston combos all line up size wise. So is there any additional things I should pay attention to, to find the issue?

Because the spring puts more resistance on the pulling back of the piston. Gear pulls piston back vs. spring pushing piston forward.

[SHaKaL]

You should assemble your mechbox without the piston and check if your gears moves freely. I changed my bushing in my CA25 (they put bearing bushings in a 400fps+ and one broke) and the gear were pressed to tight (not the same clearance as my old bushing); had to reshimed the gears.

[mateba]

Is there any chance that the piston was slightly off track? You can file, round and polish the tips of the rails to prevent this. I would remove the 2nd to last tooth too once you fix this issue. It'll help your gear engagement with the piston.