HW80 tight spot in comp tube

[accused]

I have an old HW80 that struggles with power, after changing seals, spring and guides and eve the piston I have found the issue.
The last 10mm or so of the tube near the tp is much tighter if you push the piston down the tube.
I tried wet and dry on a dowel then lots of metal polish but it's still there
Is there a solution or do I need a new tube?
Thanks.

[bighit]

You could have it honed but it may cost more than a new one. A gunsmith may have hones but not sure if they would have 30mm ones. They would normally only have ones to fit shotguns barrels.

You have the danger of making it worse though if you do not know what your doing. You could inadvertently make the correct bore diameter part wider if you do it wrong.

It took me a while to learn how to hone engine bores so they were the same size from top to bottom with a dedicated honing machine

[evert]

I had a similar problem on one of my 80's.
My solution was a brass lap made from a thick walled brass tube turned down to fit the cylinder precisely.
Mounted the tube on an aluminium bushing that had a center hole threaded m10 so the lap cloud be run on a cordless drill.
A lap like this mainly removes high spots, so you dont run the same risk of ruining the tube like you do with other honing tools available to hobbyists.

[accused]

Excellent thank you, probably beyond my abilities but I may investigate further. New tubes are around £159 worse case!

[Shed tuner]

just buy a secondhand cylinder from on here or . £50-£80 depending on condition.

But the method evert described would work fine - you have nothing to lose !

[TonyL]

I do hope you can get this sorted. One would hope that a specialist engineering firm might be able to sort this for you if you can't do the work yourself.

I wonder if another idea might be to (once the work has been done) have the cylinder then sleeved down and go for a reduced cylinder conversion using precision seamless hydraulic tube and go for a 24 or 25mm piston. Although this would work out to be a pricier solution, at 12 ft.lbs you would end up with a much nicer firing cycle and reduced propensity for the 80 trying to go over the limit. In fact, this situation probably presents the ideal opportunity / excuse to go for such a conversion if funds allow.

I'm sure our very own NickG would be able to undertake the work for you on a postal basis if travelling is not an option and he has successfully sleeved cylinders down to as little as 20mm.

Hope this helps.

[accused]

Thank you for the replies, for now I think I will post a wanted ad!

[T 20]

I had a similar problem on one of my 80's.
My solution was a brass lap made from a thick walled brass tube turned down to fit the cylinder precisely.
Mounted the tube on an aluminium bushing that had a center hole threaded m10 so the lap cloud be run on a cordless drill.
A lap like this mainly removes high spots, so you dont run the same risk of ruining the tube like you do with other honing tools available to hobbyists.

Hi Evert

That's how I do them, this method was described by Mike Wade in his book "Power Without Powder" on tuning the HW80 --- there's actually two different versions of the book (Blue cover and Orange cover).
Mike sold his hones under his "Viper Tuning" brand name along with his PTFE piston seals, hand wound springs and Delrin guides, apparently he also supplied springs to John Bowkett.

Mike's hones were adjustable so you could open them up slightly as needed, I just make a second hone if working on a really bad cylinder --- another trick when using just one hone is to use fine lapping paste for the first lapping, then coarse lapping paste for the second lapping.






All the best Mick

[accused]

Very interesting, I met Mike a few times must be 30 plus years ago and bought bits from him including one of those adjustable hones! Long since lost sadly.

[Murphy]

Would this work? CLICKY

[accused]

I think I'll buy another comp tube then risk playing with this one, spent quite a bit getting the gun sorted with a .25 barrel ect

[T 20]

Would this work? CLICKY

I wouldn't recommend it, if your cylinder has an oval bore it will end up with an oval bore with honing marks.

If you use a perfectly round hone you end up with a round cylinder bore with honing marks.




All the best Mick

[BC312]

Sounds like the tube has had a bad knock like a shallow dent, did this suddenly happen or occurred over time. Have you eyed the tube upto a light like checking a bend in a barrel. If someone has cramped the tube up in a vice and over done it, you could easily get a tight spot.

[accused]

The gun was bought some months ago, its a Mark 1, it was only putting out about 9 ftlbs in .22. Inside I found a horrible lightened piston and all seals were very tired.
I bought a new piston and seals, put a new spring in and bought a .25 barrel.
The tube is in excellent condition so I doubt a dent, nothing visibly wrong.
It takes a spring to give 11.5 that would normally give 20!. I was hoping to use a nice lazy spring for easy cocking...thats when I realised something isn't right and discovered the very tight last 10mm.

[bighit]

Would this work? CLICKY

Not really.

The stones are on a pivot so they can move so only the tips will be touching . So in the OP's case it could pivot on the narrow section due to limited contact (10mm) and then start making a groove where the stones tips contact the wider part. Plus they catch in the cocking slotting you not careful.

Fixed stones would be better or the methods Mick and others have said.