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Another Gamo repair/upgrade

PostPosted: Sat Nov 14, 2015 4:09 am
by Scotchmo
One problem with Gamos was that the clips and then the pins which attach the linkage would sometimes come apart during a match.

I replaced all of the pins with 8-32 screws and nylock nuts. No more targets falling apart during matches. But the screw threads develop slop faster than the pins might have. The ctr-to-ctr distance on the linkage affect the over-center function of the target.Too far over center and the target is hard to knock down. A coin, washer , or shim, under the foot will correct the over-center, but the amount of shimming can vary depending on the target. And it does not prevent more slop from developing in the linkage.

I did some checks on one of our worst targets.

Far over center:
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Shimmed with coin:
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The red and green lines that I show need to intersect the base in front of the paddle pivot in order to retain the over-center latching. The closer the line comes to intersecting the pivot bolt, the easier the target trips.

I found some spherical bearings that bolt up easily and remove all slop from the linkage. They are also adjustable for length. Much better than using a loose threaded screw as a bearing surface.

Original linkage on left. Spherical bearings in middle and right:
Image

The ctr-to-ctr spacing on the stock linkage is about 1.68". As the distance increases the mechanism becomes less and less over center and easier to trip (even though the faceplate is resting farther forward). The ctr-to-ctr spacing can be increased to about 2" before losing the over-center latching. At which point the target may not want to stay up. I went with a compromise spacing of about 1.8" on the new adjustable linkage.

Linkage adjusted shortest possible for maximum over-center (trips at 2fpe):
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Linkage adjusted to 1.8" ctr-to-ctr (trips at 1fpe):
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18fpe hits on the tale did not rattle down in either case.

The 1fpe test was with a 14.3gr@140fps as my only multi-pump is a .22 caliber. I retested with a SSP pistol using 7.33gr@400fps (2.7fpe) and it was able to take it down every time.

A property of the Gamo spring loaded target is that it wants to fall back even when angled forward a significant amount. Leveling is still important though not an absolute as far as function.

Image

I retested it at a 10 degree incline:
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The 2.7fpe still took it down however the 1fpe would not.

I'll be retrofitting 4 of the targets right away for testing during matches, and probably the rest in the near future.

Edit: I changed to a 1.68" linkage spacing on the spherical bearings. That's what the original Gamo linkage used and it seems to be the better compromise. At least when the target is mounted level.

Re: Another Gamo repair/upgrade

PostPosted: Thu Nov 19, 2015 7:36 am
by rws45user
very nice work . I just looked at my new gamo target and there is a lot of lateral movement in the linkage. I can see how if left the way it is ,over time the lateral force on the clips would force them off. There is enough room to add one more washer . I added a 19mm dia washer with a 1.5 mm thickness I placed it in the upper one and lower pins . I put the big washer between the target bar and the linkage bar on the clip side . I put it there because the 19mm washer acts as a stabilizer and stays in contact with the targets bars metal around its hole where the pin goes through all the way to the end of it shape where the washer ended up ending at the same place . There is very little lateral movement now . I measured the lateral movement at the center of the round target at the top and there is only about 1.5 mm movement just enough to allow not restricted movement . before it was a good 8mm movement. How did you add photos I'll take a photo when you tell me how so you can see it . I think stopping all that lateral movement it had is going to stop any problems taking place in the future and would be a lot cheaper and less time consuming than what you did for the "home shooter" ,but for match use I don't think you will ever need to fix that target again for sure .

Re: Another Gamo repair/upgrade

PostPosted: Fri Nov 20, 2015 6:06 am
by Scotchmo
Upload photos to the net, and then use the Img tag to bracket the link location . I use Photobucket for photo hosting.

We had problems with clips popping off of Gamo targets. I replaced the pins with screws and they never fail, but after two years, slop in the mechanism has made them either subject to easy rattle downs or problems with low FPE hits.

Here is a link to those mods and others:
http://www.slsba.org/airgun/misc/Gamo-fixes.htm

More tests with the spherical bearings is showing some additional benefits. I readjusted the linkage length to match the original Gamo spacing and the targets still seem to go down consistently and resist rattle downs fairly well. A Gamo squirrel target with the spherical bearings is resisting rattle downs better than a Gamo target using a heavy aftermarket faceplace and the original link plates.

The spherical bearing linkage does not offer any lateral support to the paddle. So the paddle has even more lateral movement than before. But it does not bind when the paddle is pushed sideways. I'll tighten up the paddle pivot some and maybe come up with a better paddle bushing or maybe stabilizing washers as you did.