Ducati Monster Forum

The power of orange indeed...

My boy will be 6 soon, so I decided I'd take on this little restoration project.

An early 70's Montesa Cota 123

He can ride it around the yard if I ever get it running again... The motor is seized, every bit of rubber except the silicone exhaust connector is toast. The exhaust has been cobbed together, which is probably what caused it to stick in the first place.


(http://farm6.staticflickr.com/5039/6928601026_868c157d48_b.jpg) (http://www.flickr.com/photos/26408631@N02/6928601026/)
Z's Cota 001 (http://www.flickr.com/photos/26408631@N02/6928601026/) by nh_painter (http://www.flickr.com/people/26408631@N02/), on Flickr

Needs a little appearance work too.

The seat isn't stock, easily undone from the looks, and the rims are pretty rusty.

Still, not bad for a 40 year old dirt bike.

Maybe a set of Akront aluminum rims, a blast and paint on the frame, new piston/rings, tires and tubes...

and whatever else crumbles when I touch it.

Should be fun.

Mmmm - Montesa!

When I was growing up we idolized those bikes! Good to see that you are bringing it back to life.

Great little find there.  [thumbsup]

/like

not enough o's in cool [thumbsup]

Neato.  [thumbsup]

Good luck with that! To state the obvious, you can't run ethanol in that tank.  ;) Some old guy had some bits because I had to find some tank tie downs before I could sell my Rathmell Replica. They're supposed to look a bit like this. Got mine running for my kid but he was already too big!  ;D http://www.wmsbrg.com/ebay/history/77montesacota348/ (http://www.wmsbrg.com/ebay/history/77montesacota348/)

Somebody bought a ton of parts from Cosmopolitan Motors when they closed. Maybe you can run that down too.

I started my Observed Trials "career" in the early 80's on a Montesa 123 Cota and progressed to a Montesa 348 after that.  The little Montesa 123 was the most reliable competition bike I ever owned, it just ran for ever.  I frequently drowned it in rivers and then just removed the spark plug, turned it upside down, pulled the kick starter a few times,
turned it back on its wheels, replaced the plug and start it up to do the next stage.  First modification on my competition 123 was to lengthen the clutch lever on the motor side to give more control on the bar lever.  Second was to remove the speedo on the rhs fork.  Those where destroyed in the first obstacle.
Very good starter bike for observed trials, just replace the seat.

 [thumbsup]
so what's his favorite color?

He told me flat black.  :D

bacon of course!

 [thumbsup]

DP that is one sweet looking Wallet-hole if I ever saw one!!   ;D

[laugh]
A bacon themed bike must be done!

Actually, I'll coat the tank and run the lowest grade that doesn't cause pinging.  ;D

On that bike you'll know quick too!  ;) 'Seem to recall that I used to run Golden Spectro 50:1 and had jetted accordingly. The old Champion plug worked best. The period Bosch equivalent was OK too; used those because I could grab them in the shop for free since some older Benz used them.  8)

The "maniac" with the pretty bikes in NC should be able to fill in the details since he used to compete on a 123. Must get down to NC sometime to check those out!

I used to run Spectro in the pump injection on my Kawasaki. I had good luck with it.

I liked the golden gear too.

No idea how this one's jetted.

The first order of business will be to get the motor out and the head off to see what the bore looks like.

I already pulled the plug, and it doesn't look like it was hot when it stopped running...it's pretty black.   :-\

I've done a little poking around on the web and pieces are available whether Used-NOS-repro

This project will not happen all that quickly with all the other stuff that's going on around here.

Give me a kick in the butt reminding me when I have a ton of time/money invested in it and it still isn't done.  ;)

In our competition bikes we used:

NGK BP6ES Spark plugs (the genuine Japanese made NGK's)
Castrol R two stroke oil
NEVER leaner than 30:1 in cold weather and 25:1 in warm weather.  This is critical for these bike.  Many motors were destroyed by running leaner than 30:1!
In South Africa we only used 97 octane pump fuel and never had ethanol blends.  In Africa they use corn to feed the hungry.

This bike had a 7 in it and it was kind of black...

I spent yesterday afternoon tearing the bike down a little...

removed the tank...there was no petcock.

I pulled the plug and sprayed a little weasel piss in the hole and gently rocked the bike...

nothing.

I decided to not pull the motor yet, so I pulled the head.

I've had a lot of 2 smokers apart, and the inside of this thing didn't look anything like a bike that stuck while it was running.

The bore was glazed, but had no scoring at all and not rusty...yet the piston was stuck solid.

So I pulled the air filter...an aftermarket Unifilter which crumbled in my hands...and behold the mung in the bellmouth. It was definitely dried up fuel and oil mix. I figure the lack of a petcock and the basic properties of the Amal carb allowed the contents of the tank into the crankcase.

So I proceeded to heat the cylinder with a heat gun and kept the bore full of penetrating oil and used a bar to pry up on the cylinder...gently...it budged...so I kept prying and tapping and heating...and finally got the cylinder off.

The top ring was pretty much free in it's groove, but the bottom ring was stuck. A little penetrating oil and some working it with my fingers and I got it out.

The small end bearing was stuck. The piston wouldn't pivot on it's pin. The connecting rod was the same way at the big end, and the crank wouldn't turn.

So...I filled the cases with Dexron and started spraying penetrating oil on the small end needles.

I started examining the bottom of the cylinder and the liner and it was caked with dried up fuel and oil. A little Dexron and scrape with a paint stick and it came right off.

I also pulled the left case cover so I could access the flywheel nut to turn the crank.

To make a long story short...the bottom end is completely freed up, I got the piston off, and I think I managed to capture all the loose needle bearings...I'll install them in the rod and make sure. If not a caged needle is available. I ran a hone through the bore and cleaned up the majority of the glazing and the mung ridges from the rings.

I'll disassemble the carb and take it to my buddies shop and put it in his ultrasonic cleaner along with the piston.

I'll measure things up and as long as clearances are within reason I'll bolt it back together and check for spark, adjust things as necessary, and see if it runs using a remote fuel tank. I'm not looking to make this a new bike.

If I get it going I'll continue with the project. If it doesn't run I'll have decisions to make.

I'm thinking it will run.

Very impressive!  [thumbsup] The ultrasonic sounds like a good idea if the carb has a metal float. All might be good. The one time I let my carb varnish, I just ran down to Cosmo and picked up some jets. Ran fine with the new ones.

The original petcock was conventional but may have had some plastic bits inside the tank. My 348 used to starve occasionally so I fitted a Montesa MX "peanut" which was rubber. Of course they don't last more than a few years. There must be other dirt bike petcocks which will screw in there but what do I know.  ;)

Moto Motivo might be onto something with the Castrol R. It's messy and carbons up but my 348 used to stick occasionally when it was very hot. Would start right back up though. Never had much luck with the NGKs. The Champions were always a nice tan at the tip.

Nice project and goodluck with it. I am always looking for barn finds. In march of 2011 i picked up a 1974 Yamaha RD 250 thats been parked since 1976. Got the bike home a little premix gas as i did not trust the oil pump and a quick carb clean it started on the third kick. Have fun and stick with it these old bikes are getting hard to find.

I'll probably run R in it....I love the smell of bean oil.

There are repro petcocks available that will screw into the tank bung.

Biggest hurdle right now is the fact that there doesn't seem to be any 20" trials tires...anywhere. I can find the 17" rear, and I can find a 20" rim.

If I get it going it looks like I'll have to lace up a 21" front and an 18" rear to match. That will also require new spokes.

Buchanan's has a budget bare steel rim that would be perfect for painting, or maybe I'll try and find some used alloy rims that I can make work.

All this is contingent on the thing running and being basically sound.

Time will tell.

Make sure that big end bearing is clean as a whistle, one of the rollers skids at speed and it's all over.

Can you get a new rod and big end bearing and pin?

Yes.

I'm not going to split the cases just to clean though.

  Coker has 20'' tires,you may be able to find something useable.No link ;D

:-*

 [laugh]

I checked Coker. I didn't see any trials type moto tires.

I'll look again.

Update...

I've located a set of used rims.

Reasonable price. I'm going to buy them as they are located at the same place I'll buy a caged needle for the piston pin and some other small items.

Maybe he has the missing airbox too. I'll get back with him early next week.