Canadian Airgun Forum

I have a crosman optimus (sub 500) which I bought from Canadian tire. After some time, I received my PAL. So I decided to upgrade my gun. I bought the B18-00-4D PISTON SPRING from crosman's website and changed the spring. Now, the gun shoots at an average speed of 860 FPS. The only issue I have is that after every shot, there is a little smoke coming out of the barrel. Very little, but I can see and smell it.

What could be burning. I have stopped using the gun just in case this is something dangerous.

Can anyone help?

nothing wrong just some oil or grease in the piston tube, that's what we call dieseling
that's what happens when you increases your FPS it creates more heat, if its just a little your ok
unless the smell bothers you, if it was a lot you could potentially burn your piston seal
you should have cleaned the piston tube before installing the new spring
also what did you lube the spring with ? was the new spring oily ?

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"A candle loses nothing by lighting another candle"

What Ace said! Also, I do love the smell of burnt oil out the barrel - it takes me back to childhood and conjures up fond memories of shooting in my back yard. Mmmmmmm - better than doughnuts.
The dieseling could be giving some extra fps but it should burn off and settle down pretty soon with regular shooting (100 pellets or so should do it, since it's only smoking a little).

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Iacio, ergo sum

It's not a lot. And I dont mind the smell. I used white lithium grease to lube the spring with. Is that Ok?

according to the data sheet white lithium grease is flammable so no its not ok
use moly lube something like this...https://www.airgunsource.ca/us/air-vent ... paste.html

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"A candle loses nothing by lighting another candle"

The cheap Princess Auto ".177 Grizzly" diesels all the time ..but then again, one needs hydraulic oil on the pellets ..so they don't get stuck in the barrel

Thank you. The one from Aor venturi is out of stock. Will something like this do?

Liqui Moly 2003 Mos2 Long-Life Grease, 100 ml https://a.co/d/4cWdfd0

Anything that shoots 600 and more fps will make smoke due to heat and pressure in the chamber

And fuel

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VE7SHM//VE7ZJ

Moderator

Crosman uses a number of ways to detune a gun to less than 500 fps.
Your gun may (probably) have one or more of the following:
Longer piston (shorter stroke makes less swept volume)
Compression ratio relief hole drilled into the front of the piston
Bleeder hole in the front of the piston (usually through the aforementioned compression relief hole)
A weak spring.

The holes can be filled with JB weld.
Swap the spring (you already did this)
The full power piston is 150mm long. I have seen 170 and 190mm pistons. The longer pistons can be cut down to 150mm, but a lathe should be used. You can buy a 150mm piston from Crosman and just drop it in. Then you don't have to plug the holes mentioned above.

My experience with Optimus' detuning is a 170mm piston with a weak spring and no holes in the piston. If your gun is detuned like this, you would need to replace the 170mm piston with a 150mm piston to get full power. Some shooters find the longer 170 mm piston gives a shorter, snappy recoil and a more pleasant shot cycle when paired with a full power spring. Member TCooper has an Optimus detuned to mid-600 fps with a weaker spring, reduced preload and the 170mm piston. It's a beautiful shooter and not pellet picky.

I have a Fire NP that I uptuned. I installed a stronger strut from a sub-500 Crosman F11 in .22, and plugged the holes in the front of the piston. It shoots in the high 600's with the 170mm piston and the mid-power strut. It's not pellet picky, has low recoil, and is a joy to shoot. Too bad it still has the firing sound like pulling a toilet plunger off a linoleum floor... It's my only gasser. All my other boingers are just that, springers.

Edit: After saying all that, in your case I would shoot it as you have it tuned and enjoy the aromatherapy.

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Theory is when you know how something works, but it doesn't.
Practice is when something works, but you don't know why.
In my shop, Theory and Practice are combined!
Nothing works and I don't know why.

Two lathes and too many projects

Hey mm. Sounds like you’re having fun with the Optimus. I had one when I started, a few years ago. I really liked it. It’s the first rifle I started having some consistency with.

What weight of pellet are you using to get 860 FPS? It looks like you may have the medium-length piston. That’s the piston my rifle had.

The Optimus isn’t very heavy, it can be a little jumpy with the strong spring you got. I did ok with that spring but I preferred one of the lighter ones. My Optimus was maybe a little pellet picky, and hold sensitive. More or less shoulder made a difference. Have fun.

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Stephen
low- / mid-level springers

.177 Cometa Fusion, Vantage 3-9x40
.177 Cometa Fenix LT, Endurance 4-16x50
.22 Cometa Fenix, Airmax 3-9x40

As Lauchlin noted above, there is no smoke without fuel. A combustible oil or grease is necessary.

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Best Wishes
Daryl

Thank you so much for the information. Mine does not have a relief hole.

I was wondering if anyone knows the part number for the full power piston (150 mm long)?

I really appreciate your help.

Inhaling cigarette smoke is bad for health (at least the Government say so), I am sure the smoke from the muzzle is not good for health neither.

I place a little fan/blower right next to the muzzle to blow the smoke away so as to minimize the amount of smoke inhaled. Other reason for doing so is I personally do not like the smell of it.

WOW - just WOW!

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Best Wishes
Daryl