Topic: C70 madness

[andrewk]

Well, I may officially be off my rocker.    Sometimes I don't know what the hell I'm thinking.

I picked this up a couple a weeks ago for dirt cheap.  1981 C70 Passport.  Has a Chinese pitbike engine in that makes some terrible noises from the bottom end.  However, despite the noise, it runs good and pulls hard.

I guess the short way to say it is that right now, this thing is a real piece of sh*t.  But, it's got some good things going for it.  The best part of the bike are the tires.  They're trials type tread, brand spankin new.  Huge too- perfect for what I want to do with it.  It's also got a brand new seat pan and foam that came with, just gotta find a nice cover, or make one.

The idea for this thing is to have something cheap to bomb around town on.  I've got some friends that all ride these small bikes, and riding my 750 with them is pretty lame, haha. We've got several gravel/off-road areas around here that are out of the way- perfect place to goof off responsibly.  Since this thing is already so thrashed, I can pretty much do anything I want to it and not feel too bad.  There's no "restoring" this thing, and no real need to keep it stock, especially when I can get more displacement for pennies on the dollar.

The first order of business is to get the final drive sorted out.  The swingarm is fooked, and I need to rebuild it.  The chain tensioner fork on the end has been broken and welded before (like sh*t) which doesn't allow the chain tensioner to operate properly.  I think I'm just going to cut off the junk and re-fabricate it with new tabs.  I had to shorten the chain (  ) to ride it today, so a new chain and sprockets will be in order too.

The front fork on the cubs is a leading link design.  Kind of novel at first, but not having any front suspension while braking can be sketchy at times.  Something to get used to, and the front fork works pretty well still.  Might add some preload to the springs if I can.

The engine will be the big deal I think.  It's either a transmission or crank bearing that's squealing like hell.  The neat thing about all these Honda Cub variants is that any of the Chinese clone engines will bolt in, and they're a dime a dozen.  Now, I certainly understand that the quality can be lacking on these, especially compared to Honda quality, but this is something I can live with.  It's looking like I can pick up a used pit bike in some sort of "needs work" condition for around 150. So long as the bottom end bearing aren't #$%*, I can mix and match parts and build this thing super cheap.

Well, am I nuts or what?    I'll update this like a project thread, maybe even keep a dollar total to show you just how cheap a cheap bastard can be.    Any comments, criticisms welcome!

Purchase Price: $50
Gas for test ride (fill tank): $2.62

Total to Date: $52.62

[joesmotos]

50$ bikes are the best...its just a 70..Beatrice ATV parts has tons of parts cheap for those things..
Costs me almost 100$ a pop to fill my dually,,lol

[toytuff]

Gotta love them.

tt

[andrewk]

Here's a better pic of where its at.  Winter be damned, snowing here today.

I rode it a bit today and that new engine will probably have to come soon.

[Old Scrambler]

If you know anything about motor work...........you can likely repair that motor for the cost of a washer or two in the clutch or tranny.  If you do replace the motor............look at a 90 or 110 Lifan. 

[andrewk]

Thanks for the reply.

I've considered fixing the engine that's in it, as I am comfortable enough/ know enough to get it repaired, but in considering the cost of likely needed parts (at least one bearing in the trans and a gasket set) I think I might be money ahead to pick up another engine.  Around here, I can pickup a 110 or 120 cc pit bike in "needs work" condition for about 100.  So long as the bottom end is good, I can put the top end I've got on it.

There are a couple of other considerations, too.  First is that the drain plug is completely goobered.  It's got a failed helicoil in it already, too.  Yuck.  Looks like the alloy the case is made out of doesn't like to be worked very well.

Also, at one point, someone broke off an intake manifold bolt.  They drilled it out, but the bit drifted and came off the screw, so they just drilled it off to the side and helicoiled that.  Intake is mis-matched to the head "considerably."  Probably 2 mm or so, just enough so that the thing still seals

So between these three things, I don't think I should waste too much time with this engine.  I could fix the drain plug, replace the head, and fix the transmission, but I don't see myself saving any money.

[andrewk]

Been a few weeks here, but I've been messing around with this thing still.

Finally got a flywheel puller in the mail, along with some other goodies from Dr. ATV.  Enough stuff to rebuild the swingarm and rear wheel.

I decided to dive into the engine, after it finally locked up on me.   At first I didn't see what was wrong, has a bent shift shaft, but the gears are otherwise great.  When I took the crank out, I finally inspected the rod closer.  Never seen one fail quite like this.



Looks like water damage is the culprit, but what the picture doesn't show is the PLAY in this rod.  Bearing clearances are wide enough to through a cat through (50 thousandths conservative?) and the side play is almost a half inch.  Holy crow.  It's a wonder it ran- when you spin it over the bearing it's good and crunchy.

So, I am on the lookout for another pit bike I think.  I've found replacement crankshafts, but with everything else this thing needs, this is probably the nail in the coffin.