P90 metal gear issues

Hi there, i have recently been trying to install metal gears into my p90, they seem to fit well ad seem shimmed ok but once the motor with pinion gear is added the gears refuse to go back and let the plunger go back in. with the motor removed it all seems to run smooth. I’m not sure what the cause is.

What is the gear ratio
AOE correct (angle of engagement)
Tappet plate or spring rooted
or motor height

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i’m using 16:1 mainly as i cant get hold of 18:1 atm but was assured by seller they would be similar in installation. AOE i’m not sure of this term so cant confirm or deny, it all seems flush. tappet plate ans spring seem fine. motor height maybe could be a factor, i tried a few different heights but not really any difference. All runs smooth and all teeth line up well on rail but once the motor gets put in its like its impossible to spin the gears and push the rail again.

Is your cylinder seated correctly? I’ve had an issue when mine moved every so slightly and the box bound up.

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here is a picture on aoe

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looking at the image i think aoe is ok. i’ll strip it down again clean it up, re shim then i’ll upload some images if still being an issue.

I think i might know the issue now, one i’m an idiot and 2 thanks for the AOE suggestion it led to me possibly finding the issue. I thought when the spring pushes the plunger down it reverses all the gears and the motor pinion, i see now the sector gear loses connection and that sends the piston back, whoops.
i did think 16:1 would be a lot of torque to send in reverse back. i think i might have to remove the final tooth on the sector gear now. I just really did not want to as its a set of $40 gears. oh well i just spent more than that on bits last week. will keep you guys posted how it goes , thanks all

Don’t take a tooth off the gears, take a tooth off the piston!

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oh ok. the seller of the gear told me to remove a gear tooth. is the advantage over one or the other

You can put gear sets in many different blasters, and as they are a set you don’t want to customise them for a particular blaster.
Piston tends to stay in a blaster.

The main reason however:
Good gears are usually balanced so that when they spin their weight doesn’t shift (which will destroy your bearings.) It’s like when you get your tyres balanced on your car and they put the lead weight on them so they don’t wobble.

If you start taking off gear teeth then the centre of gravity of the gear won’t be in the centre. The gear will wobble. That won’t end up good for your gearbox over time.

Personally, whoever said take the tooth off the gear doesn’t know what they are talking about. That’s a red flag right there. I’d be cautious of any advice they told you after that…


thanks a lot for the info. I would rather remove the piston tooth even just for it being a cheaper part. what you just said makes lots of sense though. glad I joined this forum it’s been loads of help

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I don’t understand why you have to remove any teeth ? Please explain why you are doing this ?

I also don’t understand why you say not to remove a tooth off the sector gear ?
This is quite ok and is very common practice in short stroking and causes no issues at all :thinking:

Thought it would unbalance the gear?
I stand corrected then…

once the spring is in the gear can’t spin back enough to disengage the plunger rail to it gets stuck. the guy who sold me the gears reckons he removes the tooth of all his sector gears to compensate

It actually does the opposite, If you hold the gear in your hand and spin it quickly you can feel it is out if balance, so removing some of the sector teeth makes it more balanced, but it doesn’t matter :+1:

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So your saying the gear moves the piston too far and it hits the back of the gear box ?

no it’s more once the spring is in the plunger won’t go back any more. I even put a weaker spring in to re test

Well in that case I would think the motor is not powerful enough or the anti reverse latch has an issue , did you rewire anything ?

I bought one of those $25 upgrade over standard motors for my acr j10 early on and it would do the same thing on a 1.3mm spring. Pull spring to the back but not quite far enough to release. Put standard motor back in and it ran fine.