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Reviving an atk 406 mx 2 stroke from abandoned

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I'm reviving a 91 Atk 406 mx that was left for dead, in the snow of Colorado. So I have found a few repairs that save this bike from scrap as parts are super pricey. This is not a restoration, this is intended as a bike to be ridden and 100% functional with not spending tons.

 

1st the kickstart knuckle is not hardened steel, and strips easily. I searched for this part and only found them in the $400 range. Easy permanent fix, that maintains serviceability of the clutch. Simply drill the Kickstart knuckle 5/16ths bit see pictures attached, and tap with a 3/8-16 tap, the use a 3/8" x 3/8" Allen set screws for less that a dollar. The only hard part is, now drill a 3/8" in the Kickstart shaft 1/4 inch deep, any deeper and you will hit the gear shift shaft. Pictures attached. This works exceptionally well as the setscrews are hardened, so is the shaft so it does not cause damage. And can be removed very easily. 

2, the viewing window on the master cylinder was cracked and I could not find, new factory part was $180 the $3 fix on this is to take out all of the plastic and clean it exceptionally well, cover the hole from inside of the cylinder with single piece of duct tape, stuff the master cylinder with paper towel to support the tape. make some one minute epoxy, and fill the hole with a little bit over full to cause a bubble see the attached pictures, I have used this trick over gluing a nickel or dime in its spot, when this dries it's clear enough that you can see the brake fluid level and will not corrode. I have done this for years never had a leak.

Fyi I was a ASE auto mechanic with over 20yrs experience, but not a bike tech, so take the advice or not. I just hate seeing vintage bikes go to the dump cuz the rider can't afford or find parts.

 

I hope this helps at least one person that cannot find parts.

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Edited by Patrockyj
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53 minutes ago, motoxvet said:

Store it inside - out of the weather!

Agreed that's how it was when I got it

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So have you actually finished that kick repair and does it work?  That's the trouble with bikes that kick over hard.  It's hard on all the related components.

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6 minutes ago, motoxvet said:

So have you actually finished that kick repair and does it work?  That's the trouble with bikes that kick over hard.  It's hard on all the related components.

Yes the repair is complete and extremely strong, and I've kicked it over quite a bit and no issue. The set screw is tight and I still tightened the knuckle with the factory Bolt. 

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Nice work.  That's what's nice about the repair experience you already have even though it wasn't bikes specifically.  I always thought bikes were more of a "destructive testing" type of repair vs. automotive.  You almost always find something BROKE but with auto's, not as much.

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That takes me back.  I had a 1990 ATK 406 Cross Country (six speed) years ago.   Biggest gripe I had with it was the flat slide Mikuni that didnt have a pilot circuit.  Dunno if that was the OEM carb or not.  Spent too much time jetting and tuning it.  Was just a crappy carb for tight slow speed trails and such.

 

Anywho, I replaced that carb with an oval slide Keihin carb (IIRC, from a 1986-1988ish CR250 or CR500).  Once I jetted it correctly, it was a 100% improvement over the Mikuni. Great response, and no more tendancy to stall.

 

It also had a habit of cracking the pipe, and the inlet tube of the silencer.  The weird airbox/tube that live behind the carb and reached up to the AF on the left side of the fuel tank was a bit fiddley and a PITA to keep sealed.  Power delivery and character was perfect.  Suspension was good for the time period.  Brakes were pretty good.  Was a TALL bike too. 

 

The American Dirt Bike folks still had tons of parts in the early 2000's.  Probably not anymore.  I bought an NOS kickstand assy for $60ish.  Bolted to those two threaded holes below the lower shock mount on the swingarm.  That 399cc Rotax engine (and the 248cc versions) shared many parts with the older Rotax powered CanAm and CCM machines.  I bet they used the same kicker knuckles.   Another area to search....

Edited by Eccentric
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Ahhh, ATK memories!! I had an '89 406 back in the day. Clutch pull was a bear but she was a torque monster.

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2 minutes ago, DrX_950 said:

Ahhh, ATK memories!! I had an '89 406 back in the day. Clutch pull was a bear but she was a torque monster.

Yessir.  Mine was able to keep up with a CR500 on a loose uphill, yet was still very responsive and controlable on tight, slow trails.  Top speed was pretty good with the 6 speed trans too.  I'd heard/read that the 6 speed was fragile (compared to the 5 speed), but I never had problems with mine.  IIRC, CanAm had a 500 class version of the 5 speed engine in an early '80s MX bike.

 

I'd forgotten the stiff clutch pull.  I replaced the lever assy with an aftermarket one with multiple cable barrel holes for leverage ratio choices.  Helped.

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35 minutes ago, Eccentric said:

That takes me back.  I had a 1990 ATK 406 Cross Country (six speed) years ago.   Biggest gripe I had with it was the flat slide Mikuni that didnt have a pilot circuit.  Dunno if that was the OEM carb or not.  Spent too much time jetting and tuning it.  Was just a crappy carb for tight slow speed trails and such.

 

Anywho, I replaced that carb with an oval slide Keihin carb (IIRC, from a 1986-1988ish CR250 or CR500).  Once I jetted it correctly, it was a 100% improvement over the Mikuni. Great response, and no more tendancy to stall.

 

It also had a habit of cracking the pipe, and the inlet tube of the silencer.  The weird airbox/tube that live behind the carb and reached up to the AF on the left side of the fuel tank was a bit fiddley and a PITA to keep sealed.  Power delivery and character was perfect.  Suspension was good for the time period.  Brakes were pretty good.  Was a TALL bike too. 

 

The American Dirt Bike folks still had tons of parts in the early 2000's.  Probably not anymore.  I bought an NOS kickstand assy for $60ish.  Bolted to those two threaded holes below the lower shock mount on the swingarm.  That 399cc Rotax engine (and the 248cc versions) shared many parts with the older Rotax powered CanAm and CCM machines.  I bet they used the same kicker knuckles.   Another area to search....

Yeah the rotax part under any brand name was unavailable except for one guy in Europe and he wanted 350 euros

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it seems like everybody has the part and then when I go to buy it then they don't have them or they're's 200 or $300

Edited by Patrockyj
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5 hours ago, DrX_950 said:

Ahhh, ATK memories!! I had an '89 406 back in the day. Clutch pull was a bear but she was a torque monster.

Yes she is with that clutch pull, I just ordered a set of cnc machined aluminum adjustable levers, Ebay 35 bucks, but I don't intend this to be a Factory restoration I want it comfortable to ride so, new 2019 engineered adjustable levers were a no brainer for 35 bucks. I just wish they had prime 2-hour delivery on those, but remember in 91 you'd use the Yellow Pages to find a cycle shop, pick up the phone and have human interaction, to find parts? Was Amazon even up bookstore then? By the way I neverbgh owned one of these bikes in the nineties anything else you can suggest, to make it a better beast?

Edited by Patrockyj

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Just the usual freshening up of an older bike.  New brake fluid.  Go through the wheel bearings and headset bearings.  EBC probably still catalogs brake pads for these.  I imagine that the forks and shock could use a rebuild.  They're standard WP pieces from the period.  Any good suspension shop could rebuild 'em with new seals and fluid, and if needed could respring/revalve things for your weight.

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Update so far, fork seals are great, kickstarter repair is solid and shows no wear to 3/8" port drilled, top end is now to spec. Air intake bgh thru carb, Flushed front and rear brake fluid. Rear shock is amazing. Exhaust manifold has a minor leak so I'm going to pull the pipe and make a new gasket, because I'm sure 8 factory exhaust gasket is $150. And if I already have the pipe off I may as well repack the silencer because cuz it looks old as hell, and put some high temp paint on the inside bend. The clutch, bottom end and transmission, are all adjusted to factory spec with no parts needed. ATK has been amazing, they have published The Factory owners manual, parts catalog and full service manuals for free download. I cannot wait to put some videos of her, fully functional and 100% done maintenance. I'm actually thinking I may even run a dyno to see what kind of power is that actually makes.

Edited by Patrockyj
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12 minutes ago, Eccentric said:

Just the usual freshening up of an older bike.  New brake fluid.  Go through the wheel bearings and headset bearings.  EBC probably still catalogs brake pads for these.  I imagine that the forks and shock could use a rebuild.  They're standard WP pieces from the period.  Any good suspension shop could rebuild 'em with new seals and fluid, and if needed could respring/revalve things for your weight.

Great advice thank you very much, the fork seals are actually brand new so I know the last one to work on her started

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48 minutes ago, Eccentric said:

Just the usual freshening up of an older bike.  New brake fluid.  Go through the wheel bearings and headset bearings.  EBC probably still catalogs brake pads for these.  I imagine that the forks and shock could use a rebuild.  They're standard WP pieces from the period.  Any good suspension shop could rebuild 'em with new seals and fluid, and if needed could respring/revalve things for your weight.

Thank you, like I said I normally do cars but this bike is cool and solid... now. Remarkably all of the bearings are not showing any bad wear, of course I pushed all the old grease out with new synthetic grease, (if you want to know how to flush bearing grease, it's an oldschool trick, but ask). I found the pads easily. I am thinking the tank decals are not worth crazy money they're charging for them. But I have had amazing luck in the automotive world and on watercraft plastic, using CSI Ceram-X Polish, to restore the plastic to bright. I'd love some feedback on a how important the factory decals really are? I'm asking more from an ego perspective. I am considering getting this bike to amazing condition and put her up for sale or keeping her I'm not sure yet.  The full decals are almost 200, they add 0 performance and have no effect on ride ability at all. How big of a deal is this?

Edited by Patrockyj

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That's a personal thing.  The vintage/evo/retro dirt bike thing is really taking off.  Don't know enough about that MX racing scene to know if your bike is eligible or desirable for any classes as it has upside-down forks and F/R disc brakes.  I'm not crazy about the decals (they were all absent from my  bike when I got it).

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12 minutes ago, Eccentric said:

That's a personal thing.  The vintage/evo/retro dirt bike thing is really taking off.  Don't know enough about that MX racing scene to know if your bike is eligible or desirable for any classes as it has upside-down forks and F/R disc brakes.  I'm not crazy about the decals (they were all absent from my  bike when I got it).

Thank you for that insight. I just revived a 90 RM250l, and the guy that purchased it, was involved with a vintage MX race series in Colorado, he was indicating 20 years old or older with Factory Forks. I messaged him earlier for a link to the details and I will post if he provides it.

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Edited by Patrockyj
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13 minutes ago, Eccentric said:

That's a personal thing.  The vintage/evo/retro dirt bike thing is really taking off.  Don't know enough about that MX racing scene to know if your bike is eligible or desirable for any classes as it has upside-down forks and F/R disc brakes.  I'm not crazy about the decals (they were all absent from my  bike when I got it).

Also my personal opinion is I would much rather have that 200 dollars spent on reliability and comfort upgrades, than a decal set, I am just looking to see if my opinion is unique? 

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