Taiyo Juki Bobcat repair

[Mark D]

Looks like about 6.7ft lbs on average, I would say that's a bit low, compared to say a Cr 167 or 187. As I don't have either that's a guess based on my Cr160 which from my old records was around 11ftlbs at around the same temp.

More tinkering required

[ratbuster2240]

Another great project and another air rifle I've never heard.

[jirushi]

Thank you gents.

@Mark, I think you're right. The Taiyo is still wasting too much CO2. The massive hammer makes it a bit difficult to tune. I have shortened the hammer spring, but I might have to remove another coil.

Crosman 160 is .22; the .177 Taiyo Juki Bobcat will be less efficient anyway? But I have done a shot string with my Crosman 187 this morning, and I got 42 very consistent shots, most were at 178 m/s (584 ft/s), using the same pellets as in the Bobcat: 8.44 gr 4.53 mm. The highest reading was 604 ft/s, lowest and also last tested shot was 558 ft/s. Will have to test outdoors, but I think this will be fine for 20 meter plinking on a nice day?

Almost twice as many shots from the wee 187. Barrel length is approximately the same. The Taiyo tube has more dead space (2 capsules, of which only one is pierced). This could lead to quicker pressure drop.
But I still think the hammer is the main issue. Another option is to try a stronger valve return spring. The one I'm using is already very stiff. But I must compensate for that big fat hammer!

Any other suggestions?

The 187:
Better in a few ways: lighter, better trigger (actually, really good trigger), two power cocking, plus power adjuster hex screw which is accessible from the outside.
Only downside is the lack of a scope rail. This Crosman mount is ok, but it doesn't feel very solid and only accomodates a slim type scope.

[AllanM]

Very nice looking 187 Louis.

I see what you mean about the scope sight. Could you not remove the fixed rear sight and fit another Crosman sight (as well as the first one - so you have two) to make the whole mounting more secure -- just a thought!

Apart from having a custom scope mount made, there's not much you can do about the slim scope -- for what it's worth I think these dinky little guns look better with the slim type scopes.

[jirushi]

Looks like about 6.7ft lbs on average, I would say that's a bit low, compared to say a Cr 167 or 187. As I don't have either that's a guess based on my Cr160 which from my old records was around 11ftlbs at around the same temp.

More tinkering required

Hi Mark I checked my 160 this morning and indeed: 10.8 ft/lbs.
It makes a big bang!
Nice to shoot, but I do prefer the smaller, shorter 180/187.

[jirushi]

Very nice looking 187 Louis.

I see what you mean about the scope sight. Could you not remove the fixed rear sight and fit another Crosman sight (as well as the first one - so you have two) to make the whole mounting more secure -- just a thought!

Apart from having a custom scope mount made, there's not much you can do about the slim scope -- for what it's worth I think these dinky little guns look better with the slim type scopes.

Thank you Allan. I am in doubt about this 187's looks. The stock was in bad shape. I nowadays try not to refinish stocks, as I often regret the loss of originality / patina / history, but this one needed to be sanded down. The sort of ebony forend tip was something I wanted to try, but I'm not sure if it suits the gun. 100% blonde would probably be nicer? 100% stained a bit boring? Hmmm, choices.

Yes I agree, slim scopes look good on these vintage guns. The Haweka sight on the 187 is nice and clear. Many of those old slim scopes aren't.

[AllanM]

I would go for the 100% blonde (they always have more fun!) just like your great looking J C Higgins 180.

[jirushi]

A Taiyo update:

I have finished tinkering, and now I have three power options, depending on the number and type of o-rings in the hammer tube, to restrict the hammer and, I think, reduce hammer bounce. These o-rings can be installed/removed by unscrewing the trigger mech (2 screws) and using a dentist hook, accessing the hammer tube via the hole for the trigger sear. I have glued a piece of leather, which is the basis against which the o-rings rest. These results are using one CO2 cartridge and 4.53 mm 8.44 gr JSB Exact.



(Reminder: starting point was 8 very loud shots per CO2 capsule at 196 m/s; 643 ft/s; 7.8 ft/lbs, before power went down).

Option 1
One nbr 90 o-ring
20 shots at 190 m/s; 620 ft/s: 7.2 ft/lbs

Option 2

One nbr 90 o-ring and one silicone (red) o-ring
30 shots at 180 m/s; 590 ft/s; 6.5 ft/lbs

Option 3
Two nbr 90 o-rings
50 shots at 160 m/s; 525 ft/s; 5.2 ft/lbs.

This is probably not the best way of tuning. But quite practical?
I have by the way also done some more or less proper tuning work:
- valve: much stronger valve return spring. O-ring around Crosman 160 valve stem in the valve to reduce CO2 loss via the stem which is thinner than the original Taiyo stem. You can see this o-ring on the photo, through the transfer port of the valve.
- tighter transfer port
- shortened Crosman 180 hammer spring. I tried 4 lengths of hammer springs, and this seems to be the best one. Relatively stiff (thicker wire), and shorter than the original spring.
- I trired to use a converted - thank you frakor - lighter, two power Crosman hammer - this failed: the diameter of this hammer is a fraction too small, and the Taiyo sear can't grip this Crosman hammer.

Next plan is to test accuracy. I must wait for a warmer day!

[jirushi]

Ps. For comparison:
my Crosman 187 does 35-40 shots at 178 m/s; 584 ft/s; 6.4 ft/lbs on 2 clicks (full power) with one CO2 capsule, using the same pellets (8.44 gr 4.53 mm JSB Exact).