Author Topic: Moderators/Professional Tuners, help!! (Read 1725 times)

microsalmo · « **on:** January 24, 2012, 01:27:20 PM »

Gentleman, would you please look at the skirts on these piston seals and diagnose them... if that's possible? They came out of my Benjamin Trail NP. I can't keep this gun shooting straight, and I have had it apart three times, and checked all the obvious stuff many times over (barrel clean, lockup, stock screws, crown, shroud, scope, mounts, etc..)

I bought the gun new, and after 100 rounds through it, it was shooting 1" groups at 25 yards consistently with most any quality pellet. I took it apart and did a debur, chamber hone, brass barrel pivot washers, clean, grease, and added Charlie's trigger. After the tune, it again shot 1" groups for 100 rounds. Then with a lot of pellet experimentation, it started one-holing JSB Exacts at 25 yards. Over the next 250 hundred rounds, it would alternate between one holing and spraying, until it finally just sprayed all the time.... by spray, I mean 2" groups at 25 yards, and by one holing, I mean .30" or less at 25 yards for 5 shot groups. After this one started consistently spraying for 100 rounds, I gave up. The power seems good, but I do not have a chrony. The time to impact seems about the same as my other guns.

This one has me totally stumped, so I'm asking for help.. I've got two very successful tunes under my belt... one with a Remington NPSS that consistently shoots .30" groups at 25 yards, and the other with a Ruger Air Hawk that consistently shoots .50" groups at 25 yards.

I've noticed two obvious potential culprits with this Macarri seal. One, the cuts across the skirt, and two the burn mark on face of the seal where is smacks the transfer port. I've had my other guns apart a few times and their seals are perfectly smooth even after a few hundred rounds. All of the stamped slots & holes of this compression tube have been debured. What could there be up in the compression chamber that would cause these cuts? How can they be so uniform too all around the seal? And could they be the culprit of my accuracy issues?

Thanks, Steve

gene_sc · « **Reply #1 on:** January 24, 2012, 01:34:56 PM »

First off the blue JM seal shows signs of dragging accross sharp edges when it was installed. If you deburred it then it is not good enough...

Second thing is on inside of seal those should not hurt anything unless they have rased edges. If you show burn marks on face or edg of seal then that is caused by detination. To much Lube in front of seal. Make sure seal was not to tight in bore.

Detination can cause spraying of shots like you discribe. Use a chrony to determine what a 20 shot string give you.

microsalmo · « **Reply #2 on:** January 24, 2012, 01:48:38 PM »

Thank you Gene. So the cuts most likely came from installation? I guess I do need to debur agiain (will do). How could they be so uniform around the piston seal... there are no stamped pieces on the top of the receiver tube??

Detonation, hugh? Perhaps I am lubing wrong?? I've done all 3 guns like this, and the other two came out fabulous;

After a thorough clean...

1) pea-sized dot of Superlube Grease spread over an entire shotgun bore mop. Then, I run this mop through the entire compression tube on a cordless drill until there is the lightest appearance of a thin coat spread evenly throughout... so thin you cant feel but just see.

2) Honda Moly 60 Paste brushed over piston, covering 1" behind seal, sides of seal, and 1" at the end of the piston. This coat is also very thin and uniform... it's translucent.

That's it. It has worked great on the other 2 guns. Would this method of lube cause detonation?

Thanks, Steve

kmiJ · « **Reply #3 on:** January 24, 2012, 02:08:50 PM »

My Trail NP .22 seems to be doing something similar. I've asked for opinions in a different post. Pretty much checked everything but not tearing apart because of warranty. I can shoot two dime size 5 shot groups from 3o ft. and then miss the trap.

Still checking things out . Love the gun tho.... Good luck and hope you get it figured out.

KmiJ

Mark 611 · « **Reply #4 on:** January 24, 2012, 02:40:54 PM »

theirs 2 other things that could be causing POI shift a bad fitting breech seal and your pellets, in consistant head sizes on your pellets will cause different POI! I know everybody thinks pellets out of the same tin should shoot in the same place but not so! pellets in the same tin can vary as much as 5 thousands of an inch and if the breech seal isn't fitted correctly will give the same POI shift,

Kailua · « **Reply #5 on:** January 24, 2012, 03:05:42 PM »

Airgun Toys which you can find in the GTA mall has replacement barrel block brass washers. Might ask if replacement washers help accuracy. It is an upgrade which a lot of owners do.

microsalmo · « **Reply #6 on:** January 24, 2012, 03:08:55 PM »

Thanks for the feedback guys. I'll re-debur this thing first, and go from there. It would be nice to know form one of the professional tuners first; if my method of lubing is proper to minimize dieseling.

I'll check the breech seal too. I've already tried the kleenex thing, and it didn't budge... maybe it's blowing out the bottom??

Anyone have issue with the lube method? Would it cause dieseling? There is no smoke in the bore like during the first 20 shots after a rebuild, but I do get a VERY little at the breech when I crack it open still... and I have about 400 shots through this one now.

Thanks,

Steve

microsalmo · « **Reply #7 on:** January 24, 2012, 03:09:33 PM »

Quote from: Kailua on January 24, 2012, 03:05:42 PM

Airgun Toys which you can find in the GTA mall has replacement barrel block brass washers. Might ask if replacement washers help accuracy. It is an upgrade which a lot of owners do.

done, made my own - thanks

Calmark · « **Reply #8 on:** January 24, 2012, 03:18:03 PM »

I don't know if you've checked it already but you could have a scope issue. Since it started shooting inconsistently at first and only later lost all accuracy it could have been a gradual then eventual total failure of the scope. You might try shooting with a known good scope to see if that returns accuracy. Lastly, don't give up. You'll find a cure if you keep at it. Good luck!

thekid · « **Reply #9 on:** January 24, 2012, 03:43:09 PM »

I am no pro, but I have tuned all my airguns to crazy accuracy.
I like my piston seals to fit nice meaning it doesn't take a lot of force to move in the compression tube.

Why would you use super lube in the compression tube, I would use Molly on a rag before that.
To be honest I don't use anything in the compression tube, just on the piston which will make it onto the compression tube.

With those seals being that tight you would scrape of all the lube, when cocking the gun, building it up on the backside of the piston seal.
When you shoot the sudden stop of the piston would force the lube (super lube + Molly) into the crosshatching, behind the seal in the uncocked position. When you cock the gun again, there will always be more lube then wanted until the gun burned it all off.

Done this stuff before, best to put just Molly on the edge of seal and 2 spots on the piston.. behind seal and bottom of piston.
It will work up onto the compression tube anyways. TOO MUCH LUBE.

The ding on the face of the JM seal is from the transfer port as the seal semi covers it.

Just my opinions.
Rob

microsalmo · « **Reply #10 on:** January 24, 2012, 04:16:25 PM »

Rob, thank you!!!

That all made good sense. I've got some Maccari Moly Paste too try too, and I think I will on this one. What are your thoughts on Honda's Moly 60?

The reason I used the Superlube is because I found an old document published by Charlie Da Tuna about lubes. It read;

"SuperLube can be a good lubricant. It has a silicone base with PTFE to help fill microscopic imperfections in compression chambers in synthetic seal guns and tubes but must be used sparingly as it will cause detonation."

And I have been using the Honda Moly 60 on all my guns because the same document read;

"Used as a lube for piston walls, spring guides, pivots, spring ends and many other applications. It is also used in home brews. There are not a lot of known sources for a good Moly lube in small quantities with a 60% ratio (preferably 65%) or higher. Don’t use the cheap low grade stuff from Wally World or part stores. Maccari of course has it and Honda does have one with 60%, although they may have to order it.

Honda part number…..Moly 60 Paste…….Part Number 08734-0001"

Is this document dated, and could it be part of the problem? Thanks again!

Muppit · « **Reply #11 on:** January 24, 2012, 04:21:07 PM »

i had all the same issues with my g1 extreme after i converted to a np gun and i have so may parts here i was able to mix and match and try differant items and pellets, i did as some of you have done lube just the piston on both ends very lightly stress very lightly. one gun shot great and still does the other not so great. i have checked and changed everything except the compression tube and the gas ram. to no avail. i check the gas ram in the titan and the g1 extreme with the bathroom scale and one piston was consistant at 135 lbs give or take a couple lbs and the g1 extreme that was doing as your is would spray 2-3 inch groups, that ram was taking 105 to 130 lbs to compress in the scale. it varied almost every time i put pressure on the piston i got a differant ratting on the compression of the piston. is this the problem. i'm still not sure i have not needed anything from crosman so i have not ordered another ram yet but if you have a spare try it. as for the supper lube in the tube i don't put anything in the tube just a little moly on the piston.......dave

Smackey54 · « **Reply #12 on:** January 24, 2012, 04:25:27 PM »

I suspect the uniform "scratches" on the side of your piston seal comes from, as Gene says, burrs....and the reason they are uniform may be that you pushed the piston straight into the chamber. Perhaps you could try gently turning it when you put it back in after deburring?

thekid · « **Reply #13 on:** January 24, 2012, 04:29:25 PM »

Even charlie recommends JM's moly...before the honda 60. It can be a substitute but JM'S is better.
The thinner the moly (viscosity) the easier it will migrate into the compression tube, when in a bind you can use moly 60 but less is always better. Same goes for JM's moly a little goes a long way.
Rob

microsalmo · « **Reply #14 on:** January 24, 2012, 04:35:14 PM »

Thanks guys. Do you put on JM's moly with a brush or with your finger?

I spent a long time deburing this tube... I guess not long enough. I just cant figure how it got cuts around the entire circumference when the cocking slot is only on the bottom of the tube? I will tear it apart and check again.

tjk · « **Reply #15 on:** January 24, 2012, 04:47:05 PM »

I sure would like to know your " honing " method. From the looks of the outer face of that seal, it is either too tight, a rough job attempting to cross-hatch the compression tube, or a mixture of both. Not talking down to you by any means, but one can really do more harm than good with a break hone and a drill. Those don't look like scratches from installation upon installation of the piston. Some folks are for lubing the pipe, and some folks are not. Me, it's a borderline kind of thing and rifle dependent with seal fit. If you feel you need to lube the tube before installing the piston, burnishing the comp tube with moly will aid the process. Just go easy and really work it in. Then buff it with a dry mop. You might not see any, but it is there;) "a little dab'll do ya"

microsalmo · « **Reply #16 on:** January 24, 2012, 04:56:45 PM »

I used the standard $20 brake hone from Harbor Freight Tool. The stone looks pretty darn fine but was without a grit label. I shot the tube with RemOil to get it good & wet, and made 6-7 passes with it at slow/medium speed? I tried to match the drill speed/pass speed to stay at the ideal 45 degree angle. I say ideal... that from my car building days of course. I did all the guns in this fashion - bad?

I'm thinking same as you... something is buggered up in the tube where I can see or feel. How else could there be cuts around the whole perimeter of the seal, right?

I'm open to any suggestion at this point. Thanks fellas.

... oh, and it is significantly tighter fitting than my other two guns. But so is the OEM seal from Crosman. I have both at the house, and they are the same diameter - the Maccari and the Crosman.

thekid · « **Reply #17 on:** January 24, 2012, 05:33:03 PM »

My guess the cuts are from the cross hatching.
My brake hone uses 280 grit stones. Used soapy water as cutting agent.
Too deep of cuts (less grit stone) the more damage will occur to the seal, don't want to polish it, just scratch it for the lube to cling to.

I suspect a low grit stone was used causing deep score lines in the tube, causing the damage to the seal when being cocked.
The worn area's on the seal lip are from the compression stroke and they are worn.
Maybe a finer stone is in order, to take the sharp edges off the compression tube.
Rob

tjk · « **Reply #18 on:** January 24, 2012, 05:45:17 PM »

Try this when cross-hatching. Draw a sink of warm water and add some dish soap to it. Place a wash cloth in the sink and allow the forks of the comp tune to rest on this on the bottom of the sink. Holding the hone chucked in the drili in one hand, and the comp tube at a 45 degree angle with the open side up. Make sure the soapy water is deep enough to allow a steady supply of fresh soapy water to enter the cocking slot while performing the work.
Another thing to keep in mind is not to have he tension on the home too tight within the comp tube. If you cant turn it with your thumb and first two fingers, then it is to tight. Be careful when pressing the hone to the bottoming out depth. Depending on the hone you have, you want nothing but the hone elements hitting the end of the comp tube. Spin the hone as low as you can go and work the honing from the end to the slot area. Cros-hatching as you would in the process at a medium speed. Too fast and you will remove too much material, and to slow may result in gauging the inner comp tube walls them selves.
Sizing the seal can be performed with a piece of all-thread, two nuts, two washers, a cordless drill and a fine file. A lathe would be ideal, but not everyone has a lathe or has access to a lathe. Hth's

uncle paulie · « **Reply #19 on:** January 24, 2012, 06:14:29 PM »

Just a note about hones. Many of the hones have stones which are shorter than the metal carriers they are attached to. If the carriers are not shortened, you will scrape them on the back of the breach and the stones will not reach the bottom of the compression tube. The seal will eventually fail because each time it is fires it will run into the chamfer at the bottom. Additionally, it will also over time take the shape of the smaller diameter at the bottom and become too small to function properly in the rest of the tube.

pv