GTA
General Discussion To Gateway To Airguns => Gamo Gate => : October 06, 2006, 03:36:03 AM
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I'm getting everything together for my first DIY tune on my Shadow supreme and was curious about compression chamber honing. I've read an article from CDT's site (Tuning B18-19 and Gamos) and it mentioned using a 3 point brake hone.
1) Are there certain sizes of hones that should be used, or would any that fit the inside diameter of the cylinder be ok for the task?
2) If a hone is not used, are there effective alternative methods to break the glaze from inside the the compression chamber, such as light sanding, that could be used as well?
Thanks
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Mark
I have watched CDT use the hone on my chambers. It looks like the shoes are about an 1 1/2" X 3/8" long. there are three of them. I do not know what number abrassive stones they are but CDT will know. The way I understand it is that you want to get a lite cross hatch in the cylinder in order to capture a small amout of lubricant for seal.
Hope CDT will chime in on this. It is a critical proceedure and you need to do it correctly..:)
Sorry I can not help
Gene
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Thanks Gene. It was one of Charlies articles that I had gotten the info off of. I just wasn't sure if there was a specific size.....I've seen various sized ones, and they should all fit. I was just wondering if there was an "optimal" size for the task....or it there was an alternative method. It's funny, I used to rebuild the top ends on my MX motorcycles several years ago, and know exactly what you mean about the cross hatch pattern; and that there are actually similarities between an engine top end rebuild and an air gun....who would've thought. :D
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I believe that CDT suggests a 320 grit stone. As for the specific type of brake cylinder hone, it shouldn't really matter all that much - 2 leg or 3 leg.
BTW, in my (automotive) experience honing tends to go better when a cleaner or solvent is used to keep everything wet.
In lieu of a hone, it is possible to get decent results using a sandpaper flapper (320 grit) in a slotted rod, and spinning it in a drill. This will dress the surface and provide light deburring, but a hone will be more effective at addressing more serious problems. But if the chamber is in fair shape, this might work OK.
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The three leg hone is the better one to use, the thing to rember when buying a cylinder hone is that some are to large to get into the cylinder.
It's only a one inch bore and some have large ends on them so take a ruller with you when you buy a hone.
The one I have is an older one from years ago and I had to modify it before it would go into the cylinder.
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Thank you very much guys. I've never done any honing myself, for engines, I used to take it to the MC shop for things like boring, honing, etc.. However, I had used scotch brite pads to break the glaze in the bore, so long as the surface was decent and that seemed to work pretty well. Thats why I was curious if another method would work with these. I'm in the last stages of getting my spring compressor completed....hopefully tomorrow. Once I get the spring out, I'll check the inner surface. I'm hopeful that it will be pretty good since I haven't shot that rifle that much....maybe 500 shots or so. As you'll probably have guessed by now, once I get this apart, you'll be seeing a couple (of dozen :D ) more questions from me. Thanks so much, again. 8)
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Peterdraggin is right about the three point hone. It is better to use than a 2 point and even better yet is a Flex-Hone. However, when using a Flex-Hone, you must be careful as it is very easy to over do it. Also, if using a Flex-Hone, use the 320 grit. It can be used for the synthetic seals as well as for the leather seals. If used for the leather seals, follow it up with some 400 wet/dry paper and do not cross hatch.
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Thanks for your help Bob, I really appreciate it.
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dunno about the gamos,but I've never seen a decent bore in a chinese cylinder (after tuning a few dozen) The b-40 may be the exception.Every one has had low spots and scoring(artifacts of how they are chucked?) Anyhow,I use a 3 leg hone with the longest stones I can get,special order thru the local autopart store,just over 2" long .This setup will keep the bore a little truer than a flexhone.Pick up a cheap dentist mirror and re-bend the neck to get a good look at the bore.A smoooth,round cylinder will do wonders for consistency,power,and seal life.
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...isn't it really a good idea to make sure you use a "bottoming" hone? Otherwise, is seems that a ridge might be left in the chamber wall right at the end of the seal's travel... something that could catch and possibly wear the seal.
I say this because there are some brake cylinder hones out there that are meant for wheel cylinders - which are bored straight through - that would leave the last bit of the chamber untouched, because the body of the tool extends beyond the honing stones.
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A cylinder hone whether it's a two point or three point will do no more than follow the contour and imperfections of the cylinder simply because there is not a 360 degree total and even contact. For all intent and purposes, a cylinder hone is not designed to true cylinders but rather resurface them. It will not help much in truing it up at all but will remove and break the surface as well ok for cross hatching.
On the other hand, a true flex hone will actually true the cylinder with it's hundreds of beads and equal pressure applied throughout the 360 degree radius as it is being honed and cross hatched, or if need be, turned until it is pretty close to perfect if it's not to far out and/or too much metal needs to be removed. About the only thing any better than a true flex hone is to stick it in a lathe and rebore it.
That's why they use boring bars on engine cylinder walls and not a cylinder hone. They use a cylinder hone after the cylinder is round to finish the process. Make sense??? :) :) :)
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You are right Vince...but most brake cylinder hones now have the edge of the stone recessed on the mount. In fact, I haven't seen one without being recessed in years. Up until about thirty years ago, they used to bake them on in an oven. That being said though, you can carefully grind the edge of the stone mount down to the edge of the stone itself. Be careful not to get it hot though as it will destroy the adhesive that they use now to mount it with and the stone will not stay on.
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I believe the "flex hone" would have a similar problem. If its the one with the little balls, I don't think this would quite get to the botton, either. Since the actual cutting is done by the very tip of the balls, I think there's gonna be an untouched portion at the very front end of the chamber. The uncut section would be almost 1/2 a ball diameter in width.
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You are right about that Vince, but it would be much closer than if using a standard brake cylinder hone. Cross hatching that close to the very bottom, (say within 30-40 K) has no real value and in fact, might possibly be better if it were not as it would seal better. However, with normal honing, the little surface taken off the wall would not be significant and leave very little edge and tapered at that. We are only talking about a thousandth or less (per side wall) in most cases (unless the tube had a severe problem). Because of the taper on the leading edge of a parachute seal such as Gamo, RWS's, Beemans GS guns, Maccari seals and most Chinese seals, it would have no affect on it or at least very little. If it were a straight cut seal like those used in an FWB and some of the other upper end European guns, especially German made, it might be an issue but even then I would doubt it. Synthetic seals with the tapered edge are somewhat forgiving and is one of the reasons that mass produced gun manufactures use them. They are less susceptible to severe damage due to the rough stamping during installation. So we know that that is not the total solution too...lol... :o :o :o
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I decided to puchase a flex hone for cylinder honing.....my measurements for the ID are .985 for the Gamo shadow chamber...does that sound about right???
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Yup. 25mm=.9842"
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Thanks Vince
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Yes, cylinder’s ID is .985"(25mm), but so far I was able to find Flex Hones sized to: BC15/16" - .937(23.8mm) and BC1" - 1.000(25.4mm). One is small, the other one is a little bit larger to fit in a cylinder.Those who used it, please advise.
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The one inch flexhone is to big to use in the Shadow tube.
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You cannot use the 1 inch in the Gamo without causing some damage but the 15/16 will work however you must be very careful when using a FlexHone. It is very easy to over do it and to create more problems than you solve. It only takes a few slow revolutions to hone and cross hatch it. A FlexHone has a tendency to take a whole lot off very quickly. Do not hone at high speed and I would suggest a 220 grit hone...no more than 400 at the very most. Quite often, after FlexHoning, I will use a three point cylinder hone to lightly resurface it so as not to cause premature seal wear. A few hundred shots and the seal is wasted, lube leaking past it causing detonation and spring damage can occur. I seldom recommend a FlexHone because of the care that must be taken when using.
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Thanks again guys, I appreciate your input.
Now, Charlie, you scared me for good. I’ll wait until I’m in your area to entrust you with my gun :). However, I did a simple “tune-upâ€: deburred the cylinder, changed the piston seal (Apex small seal, which was very tight at first) and put Maccari’s heavy tar on spring. It already feels differently.
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No need to be scared, just be cautious. :D