Moderators/Professional Tuners, help!!

[microsalmo]

Thank you both. 

I looked up the grit on the stone, and it is 220.  Was that to harsh?  If it was, I have had no such effects on seals in the other two guns.  They are both smooth and void of any cuts.  As for fit, the hone could be easily spun with my fingers in the tube.  I did modify it with a dremel so that the tops of the stones made it to the end of the compression tube, rather than the metal plates the stones are glued to. 

These are great suggestions.  I will use the soapy water sink method going forward.  As for the stone... at 220 grit is it ok, or do I need to search for something finer?  Also, can I hone this tube again, or is it junk now?  I cant imagine I removed to much metal if any?

[WHITEFANG]

IMO I'd say a combo of issues. TOO much LUBE, to harsh of grit on hone. The 220 grit will remove much material if you are not carefull. Debur is what it is and only remove what just has to be removed, no more. I am thinking that I used 400 grit on the ones I have honed. The consistant marks indicate a rough surface on contaminated surface. Brass barrel washers will help the barrel lock up. A hand held hammer impact will tighten up the  barrel bolt much better than a plain screwdiver. Just hope you have not removed so much material that you have a lot of slop.

[microsalmo]

Thank you. 

On the material removal... I hope not too.  It sure fits tight enough.  It's by far the tightest of my guns in that department.  By the looks of the seal pictures, it seems real snug, no?

So are we sure on the 400 grit hone versus the 220?  Do I need to go shopping?

[WHITEFANG]

OTHERS know more about these guns than me. I used hones forever on other things and to me the 220 is to harsh. 400 may be a little light for some. It also depends what and how you keep the stones lubed while honing. You can not get the tube perfect with the brake hones and you could get the tube out of round with high and lows if you don't keep the hone centered in the tube. You done need a rough surface for the seal to seat.

[thekid]

This is what I do,

Take gun apart, clean gun with brake cleaner ( well ventillated needed) Piston, spring, guides, inside compression tube.

Set everything a side on towel (old),
Start with compression tube (action), debur the cocking slot and sharp edges where trigger  block is held and end of the action.

Clean with brake fluid again, use soapy water and hone to crosshatch( checked my hone 220 grit), rinse. Use dry cloth to rub out inside of the compression tube spinning the whole time. Use light and inspect, hit with brake cleaner again and let dry.

I would change seals now, and if still as tight resize and make sure the compression tube is spotless before reassbling.

Then move onto the rest cleaning everything over and over, debris will destroy.

Seeing you built cars, you know that anyways.
Rob

[microsalmo]

Wow, lots of good information... and a few contradicting answers.

How many revolutions with the hone guys?
Should I hone again with the 220?
Should I hone over it with the 400?
Soapy water or oil?
Do you apply moly with brush or finger?

Thanks, Steve

[thekid]

Myself, no need to hone again.
Inspect and clean may be needed. Looks like it could be debris causing those marks on the seal.
Does the piston have marks as well, as that would indicate grit in the tube.
If you have another seal I would use it.
Lightly use moly on the outside of seal lip and on piston, if compression tube is spotless, then re-assemble and shoot.
That is what I would do.
Rob

[microsalmo]

Thank you Rob.

[microsalmo]

... found a 400 grit hone at Napa this afternoon. $18 

[john]

m, i'm looking at my spare unused piston (same part as yours). It is ~1inch diam. The cocking slot in this piston is ~4in long. This tells you the compression chamber is ~1in diam by ~4in long. A TRUE crosshatch would therefore be a one inch square X. The compression chamber is four(4) of those side-by-side X's in length.

Even IF you spun your drill slowly AND moved it in-and-out quickly, you still did not get crosshatching. What you got is a bunch of circular scratches perpendicular to the compression tube axis. Luckily, since 220 is not very coarse and since you did not run the hone stones dry, you did little or no damage. Unluckily, if you believe crosshatching is necessary (which i don't even tho i did it also), you're really not getting the (fabled?) benefit of crosshatching.

Let's review the history of crosshatching. It all started as a way to get lube into the compression chamber in order to ON PURPOSE cause combustion for more power. It took a while for people to figure out that was a bad idea for several reasons but mainly because the gun is not designed to take advantage of more power...it (piston mass, chamber volume, port diam, bore length, spring constant or ram strength, etc.) is not tuned for more power. Then the airgun community decided crosshatching was still a good idea, not for combustion, but instead to keep the piston seal lubricated. We really wouldn't want those piston seals (can you say 'synthetic', not 'leather') to dry out, would we? Do you really think any of our present day piston seals suffer from lack of lubrication?

Forget doing any more hatching of any kind at all. I submit that the piston seal skirt scratches are due to the seal being too tight a fit. Instead, put a new Crosman piston seal in OR a much looser fitting JM seal. The purpose of a JM seal is not to get more power. It is to get one that holds up better than the stock seal TO the stock amount of power and holds up with a reduced amount of lube...teflon, low coefficient of friction, slippery stuff, slipperER than the nylon(?) i believe the Crosman seal is made of. .

I submit that the damage to the piston seal face at the location of the tranfer port tells you that dieseling or just plain too much power for some reason or other happened and blew piece(s) of seal out your bore behind a pellet or two. It is possible that the stock gasram is too much more powerful than the spring these guns were originally designed for.

Look, once the pellet exits the far side of that treerat's head, you've proven you don't need more power. What are you trying to do, richochet the pellet off the tree trunk and hit him again with it?

Plan on removing and examining the replacement seal after a few hundred rounds of having fun practicing & plinking. There should be no scratches on the piston seal skirt. There should be no missing seal material from the face of the seal.

Now, here's more bad and opinionated news. I submit that none of the above is what's causing your inaccuracy. I submit that seals as mildly damaged as yours don't cause inaccuracy and pristine seals don't guarantee accuracy. Look elsewhere for the source(s) of schizophrenic grouping. As I've posted elsewhere, the stock lock pin (like every other part on the gun) may have been loose (or too tight causing other problems). Is your action ever contacting the stock in inappropriate ways? Is your cocking linkage rattling around during firing? Is your trigger group touching the stock or trigger guard? Is your shroud loose? Are pellets hitting the shroud? Intermittent scope problems? When was the last time you minimized parallax? Why have you not popped for a chrony? Have you moisture-proofed your stock? If your cocking process is anything but silky smooth, there's a problem somewhere. I could go on but...thanks for posting your progress and for listening to my rant.

[Mark 611]

John has made some very good points here, but seein's how you've already done the hone IMO a little rough yes run the 400grt stones lightly to clean up the heavy scratches you've put into the tube and make sure it good and clean before you re assemble it with the proper amounts of lube in the right places JMHO

[cell]

I would run a cotton ball in and out of the tube...everywhere a stone and file touched it. If you see snags then maybe it might shed some light? Then again you might not see any snags. Just a thought.

Patrick

[shadow]

As Gene mentioned the scratchs are from burs in the tube or it could be from the hone job. Ed

[uncle paulie]

Hones have sharp edges when new, after they are used a bit, the edges become rounded as they conform to the shape of the tube. If your initial honing was just 6-7 passes, you only scuffed the surface of the tube with the sharp edges of the stones and got a less than optimum surface on the tube. If your home is set for too light pressure,  you will not necessarily get a true honing as the stones may chatter. I would hone again, use the finer stones(you can also just purchase the replacement stones at auto zone) and I would run the drill at a bit higher rpm(2-300)  and give it 8-10 strokes up and down. When done, the stones should have a rounded edge and you should be good to go. The idea is not necessarily to have a true 45* angle on the cross hatching, the opposing strokes are to create a more uniform surface. When you first run some coarse sandpaper in one direction, it leaves a highly scratched surface in one direction, as you change directions, it scratches more of the surface in a different direction. As you continue sanding and changing directions, the surface becomes more UNIFORMLY scratched. That uniformly scratched surface is what you are seeking. Should it take off a bit too much, you can always go to a slightly larger seal to easily solve that issue. Also, if you are going to get into this stuff(self-tune), you really need a chrony to check your efforts and it's the best way to know how your guns are performing over time.

pv

[WHITEFANG]

Some say to use the micro scuff pads. The honing is to make the tube uniform in ID. and what I call deglaze the walls so the seal can seat. One thing I am wondering is why is it when you brake down a new gun you see no cross hatching? Most I have looked at were shiny and smooth. I have not put a magnifier on any of them so there could be some and I never saw it. I agree with on the stones, they have to conform to the ID. of the tube. You will notice on hones that they will after use have a more curve look that flat. Many factors in using a hone on any thing. Amount of load on the stones,RPM, grit, timing of the strokes, lube, keeping the hone parallel to the tube not to mention the after cleaning and prepping. Not cleaning the object after the honing is as important as the proper honing.

[microsalmo]

Thank you all so much. I've read all your reponses multiple times.

What's everybody doing on moly application to the piston & seal skirt. I've got a jar of JM paste now. Is it best to apply a transparent coat with a hoby brush, or a little thicker uniform coat with your finger?

[ivanpros]

I replaced a seal on my hunter sport that was over-sized and saw the same marks on the seal like on your picture. Replaced with the correct size and no marks. Same accuracy issues with the over-sized seal that went away with the new seal.

[tjk]

Instead of investing in a bunch of seals that may or may not vary in size for a correct fit, why not size the seal. Everyone here seems to pop out the suggestion to simply replace the seal, when they (larger seals) can be sized down to be custom fitted better than an 'out of the bin' batch seal.

[WHITEFANG]

I have re sized, let me correct myself, tried to re size some seals. Some have worked and some did not work out. One thing I did not do is get a measurement of the ID. of the tube to compare the correct sizing. I had the mic for the ID. BUT FAILED TO USE THEM. Without the proper tools to size the seal I always wonder how true the OD of the seal is in circumference. I conducted mine with a bolt/nut and washer set up chucked to a drill. I used a mic and measured the old seal and made my adjustments from there. Finally gave up and bought replacement sized seals. Most of my trail and error was trying to make a seal from another make of gun fit another one due to not having a replacement on hand.

[microsalmo]

What's everybody doing on moly application to the piston & seal skirt. I've got a jar of JM paste now. Is it best to apply a transparent coat with a hoby brush, or a little thicker uniform coat with your finger?