Taiyo Juki Bobcat repair

[jirushi]

I am tinkering with the Taiyo's.

They are the worst gas hogs I have.
I got 10 shots out of the .177 until velocity started to decrease rapidly. That's on 1 "powerlet".
De second powerlet isn't pierced, but serves as a spare (?).

Mods so far:

- shortened hammer spring (I used a spare Crosman 180 hammer spring)
- stronger valve return spring
- beer can rolled up to sleeve the inside of the valve.



- o-ring around the valve stem inside the valve, to reduce/prevent CO2 leakage via the stem.
I am using a Crosman 160 valve, which has a thinner stem. The o-ring seems to be working well as I don't feel any CO2 blowback from the action during the shot.



- narrower tp > haven't finished this project yet. I've modded a delrin QB78 tp, not sure if it will work in the Taiyo.
- two o-rings in the hammer tube to reduce hammer bounce:



- thumb tack glued on inside of tube cap; it worked, so the gun can use its two CO2 capsules now

[jirushi]

The mods above, minus the thumb tack, improved shot count from 10 to 30 (on 1 CO2 powerlet).
Using 8.44 gr JSB 4.53 mm.
With velocities ranging from 175 to 193 meter per second (192 to 212 ft/s).

Velocities before the mods were around 210 ft/s, so I think the gun is still at its max.
This probably means that I still have CO2 waste, but less than before.

One factor is the huge hammer. 62 grams.
Frakor is going to modify a two power Crosman 180 hammer, which weighs 51 grams.
Otherwise I could drill a hole in the Taiyo hammer, but I'd rather keep that original.

Tinkering with CO2 guns - more fun than any other type, imo.

[jirushi]

An update.

The two-power, lighter Crosman hammer idea doesn't work. Maybe there is a way to make it work, but for now the Taiyo trigger sear cannot grip the Crosman hammer well.
However, frakor did a great job at drilling the hammer pin hole at the right place in the hardened steel:



I should probably concentrate on the hammer spring and valve return spring to improve consistency, although I am already quite happy with the 30 shots at an average of 590 ft/s (8.44 gr JSB), per CO2 capsule.

Miroku scope: from the same manufacturer as the Taiyo. Too big for the gun and awkward pellet loading; too low. But really clear and surprisingly light.





Simple 4x20 Kassnar scope, pretty bright. Ugly on the high mounts, but the only way for comfortable .177 pellet loading. Plus I can still use the opens with these see through mounts.

[Geezer]

Brilliant stuff.

I’m assuming that Miroku scopes were just a regular Japanese scope branded for them, rather than them owning a scope factory too?

[jirushi]

Brilliant stuff.

I’m assuming that Miroku scopes were just a regular Japanese scope branded for them, rather than them owning a scope factory too?

Hi Geezer, yes it must be rebranded.
It's a good quality scope. Probably made for firearms. I must check the parallax.

I've finished finetuning this Bobcat.

This morning's shotstring, at 15.5 degrees Celcius. 8.44 gr 4.53 mm JSB's.
About 10 seconds between shots.

In meters per second:


That's about 23 useable shots between 604 and 571 ft/s. On 1 CO2 capsule. Not sure whether this is good or not, shot count wise for that kind of power.
Useable for plinking, up to 25 meters? Will test soon.

The "exploded view diagram" above wasn't 100% correct btw. One part is behind instead of in front of the hammer.

This is what's in the gun now, plus an o-ring inside the valve, around the valve stem.

[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]

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.