Muskin Cat for the kids

7

724wd

New Member
#1
#1
I was given two mini bikes this summer from a friend who had a stroke. There's a thread in off topics if you're interested, but let's get to the meat of the discussion.

Winter is deep here in the inland northwest so I thought I'd get to work! My daughter and I removed the little Briggs from the Muskin frame and pulled the wheels to check bearing and tubes and such. Also yanked the throttle as it's cracked. The other day I bought a Predator 212 for it. I've got a pile of Briggs 5 horse motors in the garage now, but I want this one to progress a little faster than if I needed to rebuild an engine, too.

Someone welded a bike sprocket next to the original, so we'll grind that off and get it out of the way. Also thinking of going to a larger front wheel/tire (has a 4.10-3.5-4 now). Thinking of a 6" steel wheel up front to match the rear.

I see there's not bushings in the fork head tube, so I'll pull the fork and grease it up good. Maybe mount a small headlight on the triple tree.

Been looking a lot at what parts to get and haven't figured out what kind of gearing to go for. The original sprocket is nearly the size of the rear wheel, which surprises me! seems it might not be built for speed, which would be ok. I'm planning more of an offroad, gravel road rig for the kids. Anyone have any recommendations as to what gear ratio would be appropriate? Also looking at tires... WHOA! Too many choices! 4.10-3.5-6 Carlisle knobbies seem to be a favorite, but then I happened upon snow blower tires! Maybe too aggressive? And not speed rated, of course. been perusing the forum here and I see Snow Hogs are also well thought of. For dirt/gravel, what's the favorite tire?

Quite interested in a brake kit, as well. I'm thinking a scrub brake might not be ideal for the kids. It's been recommended to look into the clutch band brake, so that's on the list.

The Plan, so far...
Muskin Cat frame & fork
Harbor Freight Predator 6.5 horse
Predator throttle kit
Throttle for 7/8” bars
Clutch 5/8” bore
Clutch Band Brake Kit
Tires Carlisle stud 4.10x3.5x6
Kenda X-Trac
Snow Hog
6" front wheel
Extreme Gold chain #35 & master link
Yamaha seat foam
clutch cover
 
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7

724wd

New Member
#5
#5
I ordered a 6" steel front wheel & bearings today (to replace the harbor freight 4"er), and got a PAIR of 4.10x3.5-6 Kenda Snow Hogs for $21 (+$10 to ship)! That seemed too good a price for 2 to pass up, even if they end up softer than expected and wear quickly. Next up is the clutch, brake kit, throttle, and chain! Should be good to go by spring!
 
danford1

danford1

#6
#6
I don't think that is a #35 chain sprocket. I counted 45 teeth. If that is on a 6" wheel then my guess is that is a #40/41/420 sprocket.
Measure the distance between two point of the teeth. If it measures 1/2" between teeth then you need a clutch with for a bigger chain. If it measure about 3/8" between teeth then it is for a #35 chain.
Now... the #40/41 clutches come with a 10 tooth sprocket. With your 45 tooth rear and 10 tooth front your ratio is 4.5:1
That is a speed ratio, not a low gear power ratio. That bike will have a lot of top end speed and slow acceleration.
Most minibikes with a #35 chain and 6" tires will have a 72 tooth rear and a 12 tooth clutch for a ratio of 6:1.
Gear ratio and rear tire size/diameter go hand in hand for figuring top speed.

6.5hp on a small minibike with a child on it is going to be fast. I don't know what size your children are, If they are small and light...
think about their safety.
OK now for the brakes. A clutch brake works Great. It has really good stopping power and will lock the rear tire with a gentle squeeze BUT when the chain falls off or breaks, you don't have any brakes other than feet/shoes. My suggestion would be a drum or disc brake on the rear rim for safety. NOW I have also had a minibike with both a clutch band brake And a rear scrub brake for emergency's. That is a decent option but you really have to train them and constantly remind them about the scrub brake being there in case they need it. It is quite easy to forget it is even there while riding with a good band brake. Make sure they know it is there and to use it if needed. Scrub brakes don't stop well but they will stop. (provided the rear tire isn't flat or wet)
I'm just voicing my opinions on your present set up, other opinions may vary.

Danford1

EDIT: I just looked at your picture again. I see the other sprocket now :) It looks like an 80 tooth #35 chain sprocket.
Having the sprocket the same diameter as the rear tire is NOT a good idea. The chain/sprocket will dig into the ground on left turns and could easily slide out on concrete resulting in a crash.
A 66 tooth or 72 tooth #35 sprocket would be much better in my opinion. That would be a 5.5:1 or 6:1 ratio with a 12 tooth clutch.
 
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7

724wd

New Member
#7
#7
Thanks danford1! Good ideas, and yeah, the bicycle sprocket definitely shows up better than the 'real' sprocket! :laugh: I was counting teeth last night and got 72, but math isn't my strong suit. My hope is that me new tires are smidge larger diameter and will help with the size discrepancy between sprocket and tire.

On brakes, I'm not sure there's enough room for a separate disc or drum on the rear. I'll have to measure some more, but the frame isn't very wide, even with the 4.10/3.5-6. I was thinking of leaving the scrub brake like you mentioned, and making sure my daughter (9yo) knows how it works. My 5yo son is likely too small to straddle the cat (he was a premie and doesn't grow very fast), but I was offered and accepted a Suzuki JR50 for $100. It needs a carb kit or new carb and rear brake shoes, but shoot, hard to pass for that price! I think it will be a better ride for him, with suspension to make it easier to keep his balance (he's a terror on his balance bike!).

With 6.5 horse on tap, that should give my daughter room to grow. She's a very cautious sort and I don't image she'll be pegging the revs any time soon :laugh: :thumbsup:
 
7

724wd

New Member
#9
#9
Well, got quite a bit done this weekend! Pics to come, but of note are I unpacked the Predator engine to find a Hemi :thumbsup:, and that is wouldn't fit in the Muskin frame with the fuel cap on :frown:. But then I took the tank off and if I use the right stud in the left hole and fabricate a simple offset bracket, it should work! :shifty: Anyone run into this problem before? That 212 REALLY fills the frame! :blink: But it looked pretty good on the M&S bike I have!

Bought a couple of locking collars for the axles so I can ditch the multitude of washers acting as spacers. Got my new front wheel, and the new Snow Hogs are on the truck for delivery tomorrow :rockon:

I do need to look into different air filter and exhaust for the 212. Anyone have favorites?
 
7

724wd

New Member
#10
#10
I've got my parts ordered for the Muskin from OldMiniBikes! The $21 pair of Snow Hogs are great! Still not sure about offsetting the fuel tank or finding a replacement of some sort.
 
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