mkII Tx running warm

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Phils_wicked
Posts: 14
Joined: Sat Nov 05, 2016 9:43 pm

mkII Tx running warm

Sun Nov 06, 2016 7:18 pm

Hi all, any idea what can cause a MK2 to run hot? It currently has a standard air arms spring/guide and piston weight. No power washers are fitted. I'm leaving it cocked in a safe place for 24hrs, not that I find this helps usually. I will also retest tomorrow to make sure my readings from the combo were accurate.

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FPoole
Posts: 339
Joined: Mon Feb 16, 2015 2:37 am

Re: mkII Tx running warm

Sun Nov 06, 2016 7:41 pm

That means the gun is an efficient one. It should be a good thing because you can get full power without as much spring or preload. A custom delrin tophat, in place of the steel weight, might slow it down a bit and smooth the shot cycle.

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Phils_wicked
Posts: 14
Joined: Sat Nov 05, 2016 9:43 pm

Re: mkII Tx running warm

Sun Nov 06, 2016 8:35 pm

Thanks. After I have retested tomorrow, I may try running it without the piston weight and retesting. I've just moved house and am under strict no spending instructions until the dust settles lol

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TenMetrePeter
Posts: 1043
Joined: Wed Jun 29, 2016 5:40 pm
Location: Luton Beds UK

Re: mkII Tx running warm

Sun Nov 06, 2016 9:01 pm

Isn't it just physics? Compress a gas and the temp goes up. All the energy you put in at the lever is stored in the spring but then on release will be converted partly in kinetic energy of the pellet plus some heat as the air compresses ahead of the piston. The heat is conducted through the cylinder wall as an inefficiency but I dont see how you can avoid it.
Same as pcp cylinder heats up when filling from a tank.

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Phils_wicked
Posts: 14
Joined: Sat Nov 05, 2016 9:43 pm

Re: mkII Tx running warm

Sun Nov 06, 2016 9:54 pm

TenMetrePeter wrote:Isn't it just physics? Compress a gas and the temp goes up. All the energy you put in at the lever is stored in the spring but then on release will be converted partly in kinetic energy of the pellet plus some heat as the air compresses ahead of the piston. The heat is conducted through the cylinder wall as an inefficiency but I dont see how you can avoid it.
Same as pcp cylinder heats up when filling from a tank.


Absolutely agree mate, my use of the term 'warm/hot' refers to the guns power output rather than the temp.

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TenMetrePeter
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Joined: Wed Jun 29, 2016 5:40 pm
Location: Luton Beds UK

Re: mkII Tx running warm

Sun Nov 06, 2016 10:17 pm

D'OH!

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FPoole
Posts: 339
Joined: Mon Feb 16, 2015 2:37 am

Re: mkII Tx running warm

Mon Nov 07, 2016 3:31 am

Those springs are funny about how they gain and lose power. I used to do a lot of chrono strings and I can load and fire fairly quickly. If I shot at a normal pace, say load and shoot in 15 seconds, I would get a steady string. If I waited for 1 min. after loading to fire, the shot was always around 5-10 fps faster. I've heard many accounts of a gun being left cocked loosing power, only to have it climb back to pretty much the same spot it was after a day or so.

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Phils_wicked
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Joined: Sat Nov 05, 2016 9:43 pm

Re: mkII Tx running warm

Mon Nov 07, 2016 10:01 am

Well... here goes.

I retested the gun this morning and unsurprisingly there was no change to power output.
Then I removed the piston weight from the end of the spring and retried. Initially I got 11.96ftlbs. That's with no preload washers or piston weight using Eley wasps 5.5mm at 14.5grn.

I then tested some AA Fields and got 10.4flb average...

Just out of interest i then refitted the piston weight and an extra preload washer and got exactly the same output with the wasps. I'm wondering if there is duff seal or something going on. For now I've just dismantled the action until I can diagnosis.

Any thoughts folks?

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juanpablo
Posts: 9
Joined: Mon Mar 23, 2015 6:41 pm

Re: mkII Tx running warm

Mon Nov 07, 2016 6:43 pm

I had a similar problem with my mk2 and started a thread some time ago.
At the time I had owned the rifle for 20 years but had just started using it regularly again.
I think the main problem was that the piston seal had gone hard and allowed lube to get in front of itself.
I say I think because I did the usual polish job and replaced the spring with a AA one at the same time and had all sorts of problems with it binding in the piston therefore producing inconsistent results.

I now use a Titan no.3 after having found that the recommended No.9 would simply not fit into the piston and, without any weight and only 5mm of preload I get 11.2 with most pellets including Fields but Hobbys are the ones to watch at 11.8.

After reading your post I tested the rifle with Wasps which I had bought to try through my Mk1 airsporter
they gave about 11 in the TX but were very inconsistent certainly not what they were 40 years ago.
Looking at the wasps I would question the stated weight and therefore your power reading but, as I dont have scales I cannot advise fully and wonder if anyone reading this can be more specific.

I have recently replaced the seal again with the Australian one and so far am very pleased with it.

Good luck - I spent ages trying to tame mine but it is my favourite springer of all time so well worth it

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Phils_wicked
Posts: 14
Joined: Sat Nov 05, 2016 9:43 pm

Re: mkII Tx running warm

Mon Nov 07, 2016 8:42 pm

That's interesting to know mate. Thanks. I'm trying to think of a plan of attack to work out exactly what the issue is, as cash is tight.

Come payday I may invest in a Tinbum kit and new breach/piston seals.

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