Vmach kit and hw77 power adjustment

[hungryb]

Hi,

I just bought a little chrono to see test my HW77K that I recently fitted with a Vmach kit. The output was quite inconsistent going from 10.3 to 11.4 with 3 of the supplied washers fitted.

I started to see what difference adding / removing washers would have.

After my tinkering the power with 3 washers was down to 10.5 and adding more washers didn't add power with any consistency.
I've now added all the washers and the plastic spacer and I'm running at 11.5.

I'm surprised that I had to add so many washers and the spacer to get there.

The only variable I see that may tinkering may have is wiping grease from the spring.

Any idea what may be causing slight inconsistency?

What power difference have you found one washer to make?

Thanks

[Vonnegut]

did you size the piston seal?

An overlarge piston seal will cause friction and this could lead to unexpected low power as the spring has to overcome this friction.

[hungryb]

No, I didn't see the need. It is the Venom seal and a pretty good fit. I think I may have been too heavy with the grease on the spring. I'll clean it up and try again.

[John2]

You will need to run this kit in 500 - 1000 pellets

As my HW97 did, now steady at 780 FPS with 8.4

[Swiss Tony]

My kit took 2000 pellets before it settled down. Beware the power creeping up too.

[hungryb]

My kit took 2000 pellets before it settled down. Beware the power creeping up too.

Blimey, that's going to take me some time. I only make a few shots a week. A tin lasts for ever! I better make some time to use it a lot more to get the bedding in done.

I just mopped up all the excess grease popped in two washers and it's at a fairly steady 11.2 with 8.8 grain F&T specials. I'll keep an eye on the creeping power.

[Gwylan]

Is it dieselling? Is the breech seal OK?

Gus

[Silent Sniper]

as you have said to much grease and gwylan is right its probably dieseling the other thing with these kits that none of the makers tell you (hint hint)it is better by far to put the brass or metal washers in the piston as they act as a weight and the delrin spacers in the spring guide end,, the delrin if put in the piston end can actually absorb power by acting as a cusion i have seen a few like this and they are often inconsistant

[hungryb]

Thanks guys,

Interesting point about the delrin absorbing power. Makes sense.

The seals are all new and fine. I think I've sorted this now. I'll test some more tomorrow, but it seems that the problem was too much grease on the spring and inside the piston. There is a piston sleeve so the grease was probably having more impact in the smaller gap. Quite amazing the impact the grease had, and there wasn't that much of it really.

[Peter Dunkley]

I would look for something wrong myself. I put a V-mach tune in my 97 "same gun" and had to reduce the main seal as it was much too tight. I am sure the instructions said not to put the delrin washer in the piston.
Mine was consistant pretty much from the word go after the tune but as they say the gun just gets smoother with time and the power will rise, but it's easy to just pop one washer out. One steel washer in mine equated to almost
.5 ft/lb.
I don't know how much grease you have in yours but I spread some of the supplied grease in the comp chamber, rubbed it well in.THEN CLEANED IT ALL OUT WITH A DRY CLOTH! Just the faintest smear on the seal and assembled it with some grease on the rear of the piston.
I dont see that there is enough grease supplied to over grease the spring.
Do hope this helps. My gun is super smooth.

[Lumberjack]

Blimey, that's going to take me some time. I only make a few shots a week. A tin lasts for ever!

By the sounds of it a lack of "bedding in" could be the cause of the apparent inconsistancy.

Leave it with a couple of washers and don't be tempted to tinker any more.
Check the power regularly and unless it goes over leave it be.

After you've put 200-300 pellets through it the power should be fairly steady. Only then should you start to "tweak" it. If it's any help; in my 25mm version, one washer is around 0.25ftlb.