TF99/QB36-1 conversion to Gas Ram (Photo's added)

[mtbdrew]

Finally got the gas ram from Crosman and have done the conversion. These are the Crosman Titan parts I ordered:

Gas Spring                    BT9M22-00-5  - $ 26.00
Plain Plate                    BT9M22-00-7  - $ 1.15 times three
Back Spring Guide        BT9M22-00-2   - $ 2.31

In addition also used several washers I had on hand with one of the above plain plates to make a guide to hold the gas ram shaft in the center of the piston. This was done by welding the plain plate to several washers that had center holes larger enough for the gas ram shaft to slide in freely. The homemade part was then inserted into the TF99 piston. Decided on this mod so I could use the same setup direction for the gas ram as Crosman does in the Titan GP. Used a wood bore bit to drill out the existing plastic spring base to accommodate the Titan's Back Spring Guide (first cutting off the spring guide from the TF99 part). Once enough material was removed to allow the Fixed Pin holes to line up, inserted the Back Spring guide of the Titan into the TF99 part and installed two of the plain plates into the Back Spring Guide to give pre-load on the gas ram to match level in my Titan. Re-assembled gun and put about twenty rounds through just to confirm everything was working. It was too dark by then so didn't get any chrony results yet, hope to tonight. Will say that the cocking is much smoother than before although a little more effort is required. The biggest difference so far is that the horrendous spring twang this gun had before is gone.
One major word of cation for anyone planning on trying this conversion. Be careful once you have the gun out of the stock. There are several pins used in the trigger mechanism as well as the cocking assembly. These are all very loose and will easily fall out. Lost one that I had to replace with part of an old drill bit that I cut and filed to the right length.
Need to work on the safety mechanism that is supposed to lock the cocking arm open while inserting pellets as it doesn't always latch. I believe it would benefit from some sanding as well as a stronger spring.
Chrony results below.

Here are the photo's:


Shows all the parts used in the conversion

Homemade GP guide to keep arm centered - several washers and one Crosman plate welded together.

Back Spring Guide inserted in the bored out TF99 part.

Finished Gun with Leaper/UTG Scope

[Donny]

ill be watching this thread closely

[mikeiniowa]

look for numbers around 1000 fps with normal pellets, may want to use 10.5 for best results...done a few of these...

[mtbdrew]

Wow Mike you must be using a beefier gas piston than the Crosman Titan's. Either that are putting a little more pre-load on the piston than my setup?

Here are the results so far:

JSB 8.44           CPHP              RWS SD 8.3       Cros Destr        Air Arms 10.3

806.0               913.6              914.4                 888.5                783.5
802.1               897.2              896.4                 898.7                771.2
806.5               906.8              915.6                 891.1                784.7
804.7               893.3              899.7                 891.7                796.4
813.5               925.5              912.3                 891.0                781.6

Here are the original spring results:

JSB 8.44gr                CPHP                    Cros Destroy                AirArms Diablo Field 10.3
830.9                        934.8                    903.4                              782.8
838.2                        933.7                    958.2                              791.2
811.3                        934.8                    921.9                              781.7
818.1                        924.8                    947.3                              791.7
809.9                        890.1                    907.0                              778.3

So far I'm very happy with the results, the gun is very smooth to cock and no longer has the tooth rattling spring twang that made the gun just about unusable before. For those looking to increase the FPS I'd suggest getting one of Mike's or if doing the conversion yourself going with the XL 1100 or 1500 gas ram from Crosman. Not sure of the size of the XL1100 or 1500 tube but if they are larger than the Titan then the fits might be more comparable to the larger TF99 diameter? At least in regards to the Back Spring Guide.

[mikeiniowa]

I don't have a 99 here to measure but one thing to look at is length of stroke, the ram has approx. 4 1/4 inch so if it's over 4 inches spacing will need  to be done. You only need about 1/4 inch over to hold the ram tight, as long as it doesn't come loose when released then you are good ...also transfer port is important, smooth and polished with a tight seal, don't increase diameter. Could try a liner to reduce and see what happens.....

[mtbdrew]

Thanks for the suggestions Mike but I'm very happy with the gun as it is right now. The little loss in speed is more than compensated for in removal of spring twang. I did some plinking last night and this gun doesn't seem to be as hold sensitive as my Titan using the same ram setup so that is an added plus. Screaming speed is not a factor for me with this gun, I'm more interested in accuracy, easy of shooting and no twang.

Only other mod I see is the latch spring for the cocking arm safety. I still need to polish the workings and would like to add a stronger spring to ensure engagement every time. As of now it is a hit or miss thing. Any suggestions on were a replacement spring can be purchased?

[Kailua]

 If you like to experiment with different springs.  Spring wire in a variety of thickness can be bought at gun stores like Midway USA or other stores.  Can also stretch out a existing coil and rewind it to a different diameter using a rod, drill bit shank, or even a allen wrench.

[mtbdrew]

Good to know, thanks for the info.

[mtbdrew]

Added the photo's promised into above posting.

BTW, didn't need to change the latch spring out after all. Turned out that the stock was rubbing on the mechanism causing it to stick sometimes. Little work with a Dremel and the issue was correct. 

[z28rod]

excellent info.

[mtbdrew]

Thanks. The more I shoot this gun the more I appreciate it, it is rapidly becoming my favorite non-pcp gun. And by far the best plinker I have.