CB125 shakedown

The CB125 seems to be up and running well. There were a couple mishaps but those got sorted out quickly.
I took the bike out for a spin to test everything out and make sure all is well.

Rest stops make good places to  put a bike through it's paces.

I think I might go up a size in the main jet. It's a 110 now but I think it could stand to be a little richer at full throttle. The pilot jet got bumped up from a 38 to a 40 and that seems to be doing nicely. That's it for now hopefully with this little guy out of the way I'll start getting some other bikes knocked out.

She purrs like a machine gun

I figured out the reason the CB125 wouldn't start. After many attempts the best I could do was to get it to backfire through the carb. This told me that it had to be a problem with the ignition timing but no matter what I did I couldn't get it to time correctly.

That is until I decided to take a closer look at the points advancer.

[Left] Timing advance unit from a parts CL125
[Right] Timing advance unit from my CB125
Can you spot the difference?

Looks like the advance shaft was on backwards, so off it came.

Much better.

MUCH better.

CB125 Head Work

So I buttoned up the motor with the new piston and leakdown tested it. I gained about 4% - putting it well into the 'acceptable' range. However it's still not quite where I want it and I can hear a definite hiss coming from the head. So off came the head and out came the exhaust valve since it was the most proximate to where the hiss was loudest.

The best way to prevent the loss of ferrous parts is to keep them bundled together with a magnet. In this case a rare earth magnet out of a harddrive.

After pulling the valve I checked for burrs, carbon buildup and any obvious damage.

The valve seats looked good and I didn't see any damage to the valve. There was a bit of carbon buildup though. The valve itself also had a bit too much play in the guide. It rocked back and forth about half a millimeter, which is WELL over the limit according to the FSM spec. A new valve will be taking its place soon.

I cleaned the carbon buildup from the exhaust ports. I'm debating on whether or not to port the intake and exhaust tunnels. 

On a very serious side note, it is always good practice to wear safety gear when working on bikes; gloves, protective glasses, etc...
Little did I know that in this case the requisite safety gear for valve spring removal includes a cup. Yes, a cup, like the ones baseball catchers and football players wear. I had the valve spring fly off and nail me straight in the barracks. That put an end to my night. Recovery beer and a good night's sleep and I should be good to go at it tomorrow.

.25 over the line - new CB125 piston installed.

I found a spare hour to drop the new piston into the freshly bored CB125 engine.

I'm bored

Well that was fast. So much for the 6 week turn around time I was quoted. RB Designs had that cylinder bored out and shipped back to my door in under a week! That's exceptional by itself, and absolutely stunning when you consider that they're all the way on the west coast and I'm in VA. They must have had it bored and shipped out the same day they received it.

It looks good! I can't wait to try it out.

I owe  RB Designs  a huge thank you for knocking that out so quickly (and affordably). Also, bonus points for the fantastic packing job on everything. I feel downright embarrassed about my packing/shipping skills after seeing that.

CB125 Cylinder Leak

So even after finding a replacement dowel for the CB125 motor, it still is not up to par. In fact it seems worse now. I pulled and inspected the rings, reassembled and measured and they seemed fine and within specs but the cylinder is now showing a 12% (best reading) loss. That's about 3% worse than before. I can hear the hiss coming from the crankcase as the cylinder bleeds air. The only logical explanation is the piston and/or rings. Rather than screw around with it any longer I'm just going to have it bored .25mm over and go from there. I'm not even going reassemble it fully to do a compression test. On the upside the head seems fine and I guess I won't be needing those new valves I bought :-/

CB125 parts motor

I pulled the motor out of the CB125 parts bike yesterday. It wasn't pretty.

Those of you with weak constitutions might want to skip this post.

Yes it's as dirty and rusty as it looks.
And yes the floor is covered in PB Blaster.

A sign on things to come. The carb is filled with mud.

The bolts came off and motor dropped out without issue.

She's dirty but seems to be in fair shape.

A bit of Simple Green a scrub brush and a hose can work wonders. 

This used to be oil.

That sure is some corrosion. The piston was rusted in place.

The valves had seen better days too.

Lots of scraping, cleaning, PB, heating, and hammering
with a socket freed the piston from it's cylindrical prison.

Think it might just need a hone?

Yeah...

The dowel came out easily and has found a new home in the good CB125 motor. Funny thing though, this motor was also missing a dowel; just a different one than the good motor.

Finding the source of the CB125 compression issue

Well I knew I wouldn't be able to sleep a wink without knowing why the hell the CB125 motor won't hold compression. Seeing as how I can use all the beauty rest I can get (I am not a pretty man) I cracked into the motor as soon as I got home this afternoon.

It took about 20 minutes to get the motor off the bike, partly because I was slacking, and partly because I got distracted a bit. Once the motor was off, the hunt was on...

It took about another 20 minutes to get the motor apart because I completely forgot that I needed to remove the rear axle to pull the rotor again.

Axle / makeshift rotor puller removed.

5 minutes later this is how she looked.

Things seem good so fa-oh wait a minute...

One... Two... Shit.

Well I somehow missed that there are supposed to be dowels around three of the cylinder studs. Probably because that one was missing to begin with.
Do I think this is the cause of my problem? Probably not, at least not entirely. I'm gonna replace it though and see how that affects things before I start boring out cylinders and cutting valve seats.

Now here's the kicker... I don't really feel like waiting 2+ weeks to get a 10x14mm dowel from Honda, and I don't have to. However, solving this issue ASAP requires me to deal with this:

Freshly hosed off, this baby is about to get torn to pieces.

Don't get me wrong, I am TOTALLY appreciative that this bike is here for the picking (props again to Bill Becker for hooking me up with this bike.) Unfortunately, the motor is completely seized and there isn't a single thing on this bike that isn't rusty, muddy, bent out of shape or all of the above. Also the lack of a center stand should make things interesting.
Given my lack of frustration so far, it's all I can do to not hang the bike by a noose around it's head and chop the motor out with a sawsall and a mechanical laugh. Before that happens though, I'm going to float the bike in some PB Blaster and call it a night. Maybe tomorrow will hold some good luck for me.

Well now I'm just confused...

I'm taking another stab at working the CB125's issues out.
Since I couldn't keep the cylinder at TDC for a leakdown test, I removed the tappet adjusters so the valves wouldn't engage at any point during the stroke. With the cylinder at BDC of both compression and exhaust stroke I got this:

85 out of 90psi is about a 10% loss

I'm showing less than 10% loss. I know this is totally acceptable in larger bikes, but I'm not so sure if this is good for this particular bike. I'm going to remove the carburetor and exhaust entirely and re-do the compression test. We shall see how it goes from there. If that turns out okay I'm completely stumped and I suppose I should re-check my timing? It was spot on when I last looked, maybe all that kick-starting changed something though...

The CB125

I'd been looking for a good bike to use teach the girlfriend how to ride when I acquired a CB125 for a cheap sum:

Obviously it didn't run but the previous owner explained that it "had a new piston and should be an easy fix." In rebuilding the engine he had dropped a bolt down into the motor. Apparently that was the last straw and he was just looking to get rid of it, title and all.

She was in fairly good shape but still needed a fair amount of work. Since I've had other projects on my hands she sat there just like that for a while. That was until recently when I got a wild hair to take a motorcycle with me to Nomadic Roots Festival this year. With only about 2 weeks to go until the festy started, I jumped in with both feet.

The goal: 2 weeks to take a basket case and make it run like the dickens, so I can ride it around this festival!
Full album of all the pictures can be seen here: http://imgur.com/a/VZ5OQ#0

The engine got tossed up on the work bench for a quick goin' over, and locating of the fugitive bolt.

The whole thing broke down extremely easily. the whole process took about an hours worth of work and another hour's worth of beer drinking and research.

I ran into a bit of a snag when I hit the rotor though. I realized very quickly that I didn't have a rotor puller and didn't want to risk damaging the rotor by prying it out with screwdrivers. So, I thought to myself, "alright, a rotor puller is just a bolt right? What bolt do I have that will fit this?" After a number of attempts and failures I had an epiphany; I knew exactly where to find an M14x1.5 bolt.

HA! It fits perfectly.

Where did this spectacular specimen of a rotor puller come from, you ask?

Boom.

Yup. That's the rear axle of the very bike this engine belongs to. 

Damn, Honda engineers are brilliant.

With that out of the way the rotor popped off without fuss 
and the offending bolt was located.

I continued to break-down the motor with obsessive fervor. 

I didn't split the cases but I checked everything else; piston width, piston rings, oil pump, cylinder width, etc... The cylinder could use a good hone, possibly even a bore+hone but with only about two weeks till the festival, this wasn't in the cards. I decided to button it up and hope for the best.

I managed to find some allen-head bolts to replace the JIS sidecover bolts in a box of random hardware I had lying around. That worked out surprisingly well.

After fixing the flipped clutch mechanism 
I buttoned up the right side and moved onto the left. 

Whoops! I forgot the tensioner. Start over.

Much better.

While I was down there I cleaned out the oil filter.

A little assembly lube on the cylinders...

and it slid on without a fuss.

Then the head popped on.

Don't forget to lube the 'shaft.

Now, the left side proved to be a bit trickier because the endless cam-chain was very difficult to get over the camshaft sprocket. It took a couple of tries before I realized I should put the cam chain over the sprocket before it goes on the camshaft. Then I should mount the cam chain over the crank shaft sprocket.

Second assembly attempt done right.
Note: cam chain guide @ crank not yet installed

Be sure the crankshaft and camshaft are properly aligned when installing.
The cylinder should be at TDC.
The cam gear bolts and the timing  marks should align like so.

Timing advancer and points plate installed.

Take a moment to adjust the valve lash.

Piston should be at TDC of compression stroke.
Compression stroke can be found by checking rocker arms for free play.

Then set points gap.

.020~.040mm is about the right gap. 
.030mm  should be perfect.

With all the assembly out of the way, the motor was ready to be mounted. 

A bit of wiggling and stretching and it slid right in.
(yeah yeah, that's what she said)

About a week ago I acquired a FREE 1973 CL125 from a very kind gentleman who is into old Yamaha enduros.

Sorry, I didn't even have a chance to take a picture
before I started harvesting parts.
Handlebars and tank were already removed to be used.

Little did I know that this bike would come in very handy during this frantically paced speed-build.

My CB125 gas tank had been JB welded all to hell; a pipe fitting had been stuck onto the tank to accept a 1/2" thread petcock, also the pinch welds were coated in JB weld. Since the "new" petcock was leaking like crazy I decided to check out what parts I could salvage off the CL125. 

The tank was pretty beat up but not leaking.
However it was also FILLED with rust and crud. 

A bath in the ultrasonic cleaner cleared the petcock and carb parts well.

I blew this power supply immediately. A battery charger was used instead.

Electrodes hooked up.

Sodium carbonate and water.

Flip the switch and watch the rust fly.

Like magic.

The black stuff is converted rust (aka black oxide)

Meanwhile back on the bike...

The poor little 6v battery needed to be kept charging...

so I bought a Genius charger from Manassas Honda
I have to say this thing is awesome so far.

A previous owner had bypassed the killswitch on the controls.
I have no idea why, because the switch tested fine.

So I whipped out my trusty soldering station...

and spliced the switch back in the circuit.

Controls are all wired up and working fine.
I also installed Posh natural gum rubber grips.

With the majority of the repairs done, it was time to prep her to run. I made a static timing light with a 12v light bulb, some gator clamps and some wire. You should always have one of these handy, even if you don't have a points based ignition system. They work well for timing induction based systems as well as testing hot circuits for continuity. 

Timing light all wired up.

Light kicked off right at the firing mark. Perfect.

Light comes back on about 40° later. I guess that's right?
I may advance the timing later depending on how she runs.

Just a few more things and this bike should be ready for her first test run. I ordered a new 428 standard DID chain and 14t front and 35t rear JT sprockets from Manassas Honda. They mounted up fine, although the painted sprocket was difficult to get on the rear wheel. I wire wheeled the paint off the inside of the sprocket where it meets the hub and it slid on without an issue. I let the chain sit in a 50/50 mix of gear oil and 10w40 for 24 hours prior to mounting. I plan on oiling the chain with heavy weight gear lube from here on out.

Sprockets on, chain mounted and tightened to the proper slack.

After I finished the major tasks I decided to spruce the bike up a bit more. I pulled the scrambler side pipe off the CL125, and performed electrolytic rust removal similar to the gas tank. This didn't remove as much rust as I'd had hoped so I nailed it with some Prep-N-Etch to get the rest. Unfortunately there was still an unacceptable amount of rust under the freshly converted black oxide, so I took a wire wheel to the whole thing. A couple hours later the pipe was cleaned but very obviously pitted and rough looking. To remedy this, I stole some of Elrich's header wrap, and wrapped it up nice and tight. The heat shield cleaned up pretty well and, despite being bent to shit, went back on easily. Although if I ever wrap another pipe I'll be sure to wear long sleeves. Some of the fiberglass (okay a lot of fiberglass) made it's way from the wrap to my skin and left me itching like I was buried in a hill of fire ants.

Yeah, I stole your pipe wrap Elrich. It wasn't enough anyway.

SO ITCHY

From here on out I thought it would be smooth sailing. The exhaust went on without a fuss. A little bit of bending and hammering of the mount brackets was necessary to accommodate the increased thickness of the wrapped pipe, but all-in-all not too much effort was involved.

By now I was completely stoked. I was just moments away from firing up the bike, but it was late so I decided to hold off until the morning. Unfortunately I was a bit TOO excited to sleep so I stayed up all night packing for Nomadic Roots and preparing my gear. I also did a few little tasks to keep me busy; lube all the cables, pump up the tires, install sprocket cover, replace fuel lines, prepare a toolbox, wipe up any dirt and oil still on the bike, etc...

Six A.M. rolls around and I think that's late enough to start the bike and not piss off any neighbors, so I give it a go annnnnnd... nothing. Kicking for about 20 minutes and all I got was one measly backfire. So I checked the timing; it was fine, checked the valve lash; also fine. The spark plug could stand to be replaced, but it was sparking and properly gaped so that should at least get her running right? I checked the carbs and fuel was running to them. The spark plug was wet from gas so I know there's fuel getting to the cylinder. 

The three things a motor needs to run are: fuel, spark, and compression. I know I've got fuel and I know I've got spark, so I decide to face my worst fears and check compression.
I used a pressure gauge with check valve to monitor the max compression while I kicked the bike over a few times. The highest it ever got was 60psi. Sixty psi isn't too bad right? It's a fairly small bike, maybe it's not a very high compression motor. Let's see what the manual has to say about this...

Fuck.

I tried to do a leakdown test but the pressure from the compressor kicks the motor over from TDC (compression stroke) and starts blowing air out of the exhaust. I tried to hold the motor by putting a wrench on the rotor bolt, but all that did was loosen the rotor bolt. I'm going to attempt to pressurize the cylinder while turning the rotor to see if the pressure drops anywhere throughout the whole range of the stroke. This will at least help eliminate piston rings as a problem.

So that's how it ends. Anticlimactic, I know. I'm not going to have the bike finished by my deadline of tonight, and I'll be forced to WALK to the lake with the rest of the pedestrian plebes. I'm still itchy from all that fiberglass, and I'm very disappointed in my oversight of the compression problem, but I'm determined not to let that ruin my long weekend.

Hopefully I'll have better news for you all next week.