Took my specna apart and found no compression.

[Caj109]

Hello,

I'm taking my specna arms edge SA-E03 apart to change the gear set and shim, while it's apart I thought to check the compression but seems to be none existent.

When pressing together it just sounds like it's passing the piston or the cylinder to me. And the cylinder head has all sort of marks over it from the piston smashing into it. See below.

Would it be best to rebuy it all or just the piston  & cylinder head etc?

Seems the nozzle does have an o seal in it and two o seals on the cylinder head.

Did use it on Sunday and was firing 0.9 j with 0.28 unless it's me

Thanks

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[Pseudotectonic]

You need to narrow down where your leak is

For example you just compress the piston with cylinder with your palm, and then add the cylinder head and try again, and then add the nozzle and try again

Then you will know which part is leaking more or less

 

[Caj109]

You need to narrow down where your leak is

For example you just compress the piston with cylinder with your palm, and then add the cylinder head and try again, and then add the nozzle and try again

Then you will know which part is leaking more or less

Thanks! Good shout. I'll give this a go and see. Just a bit weird as was running 0.9 joules on Sunday unless it's me not doing it right

 

[ak2m4]

there's a few video's on YT which explain how to check the compression.  Those parts look ok.  The cylinder head pad has taken a little beating but should still working ok.  Also check your bucking and hop chamber.

 

[Caj109]

there's a few video's on YT which explain how to check the compression.  Those parts look ok.  The cylinder head pad has taken a little beating but should still working ok.  Also check your bucking and hop chamber.

Good to hear piston head marks are fine, I'm assuming the bucking and hop are fine as ran the gun on Sunday 0.9 joules with 0.28.

What's the reason for the damaged head? If you have seen it before

Plus its reasonably new 60 maple leaf bucking.

It could just me not doing it right but I'll recheck tomorrow for sure as working fine Sunday nothings changed since.

Thanks

 

[ak2m4]

Looks to me like the aeg was left for a few weeks / months with the spring in a fully compressed state - imprinting onto the cylinder head pad.  

 

[Caj109]

Looks to me like the aeg was left for a few weeks / months with the spring in a fully compressed state - imprinting onto the cylinder head pad.  

That would make sense as been left a few years in the loft haha! Should of thought about removing the spring at the time. 

Least it shouldn't affect it much now I'm running it. Hopefully compression is fine once I recheck thanks

 

[Rogerborg]

Yup, @Pseudotectonic has it right, test each component in isolation by adding them one at a time. And when checking the nozzle seal, check it with the nozzle forwards, not just mashed back against the cylinder head (it helps to use your third hand for this part).  A sparing amount of silicon oil or grease can do a great job of improving the seal.

This is a wild guess from just looking, but I prefer my piston rings to be slacker than that. You can take the ring off, then stretch it over the cylinder to slacken it up, or replace it with something a little bigger (and stretch that too if you like) - I use 19mm x 2.5mm nitrile. 

 

[Caj109]

Yup, @Pseudotectonic has it right, test each component in isolation by adding them one at a time. And when checking the nozzle seal, check it with the nozzle forwards, not just mashed back against the cylinder head (it helps to use your third hand for this part).  A sparing amount of silicon oil or grease can do a great job of improving the seal.

This is a wild guess from just looking, but I prefer my piston rings to be slacker than that. You can take the ring off, then stretch it over the cylinder to slacken it up, or replace it with something a little bigger (and stretch that too if you like) - I use 19mm x 2.5mm nitrile. 

Thanks mate, yeah I'll give it a try in isolation and see if I can pin point the leak or just me being an idiot!

The piston head o ring was a bit slack but will see tomorrow when I test if I need to play with it. Thanks for the idea of stretching it though I'll keep in mind

 

[Sewdhull]

Looks to me like the aeg was left for a few weeks / months with the spring in a fully compressed state - imprinting onto the cylinder head pad.  

Surely in an uncompressed state, but with the preload of installation?

Leading to the same thing. Rubber is soft and that alloy looks sharp.

 

[ak2m4]

yes sorry, that's what I meant. 

also could have been someone used some non-silicone grease and it's degraded the rubber on the pad, even with no load on the spring will create a nice pretty pattern on the pad ?

 

[Caj109]

Got the compression sorted now lads, holding air with thumb over nozzle and pushing piston in.

I just put all the o seals over the cylinder to stretch them a bit and all new silicone grease on them.

Gearbox back together finally yet to try it out to make sure shimming was all good haha.

Is it worth plugging a battery to just the gearbox first before putting back into reciever? To test it runs cleanly.

Cheers

 

[Sewdhull]

Yes indeed it is.

 

[Caj109]

Yes indeed it is.

Alright mate does this sound fine to you? I can't really tell haha!

I've changed the gears to 13:1 SHS, Shimmed good enough hopefully! SHS high torque motor and 7.4 fully charged lipo  






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[Shamal]

Sounds ok to me?