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...

Launch cancelled: motor paint a no go.

After months of indecision, much hemming and hawing, and more flip-flopping than a a politician in sandals, I've decided NOT to paint Elrich's F2 motor. Instead we decided that the raw aluminum will best match the rest of the bike so we're sticking to that.
The rough sanding marks made in preparation for paint are going to be tough to overcome, but I think it'll be fine. Here's everything laid out for your viewing pleasure:

This little guy might still see some paint,
just to make it easier to clean off when we have to change the chain.
Also it will be a lot easier than having to remove all that stock paint.

I took the liberty of sanding and polishing the faces of the
shifter and rotor cover. They had some bad pitting on them.

I also removed and checked the cyl studs.
Some weren't properly torqued, and this can cause leaks at the gaskets.

Don't forget to use thread locker when re-installing them.
Just a dab'll do ya!

Voila! Studs are stud-ly once more.

Stay tuned. I have a feeling that this project will go much faster than the last one.

More painting - CB750 tank and XS650 teaser shots

I came back from Texas to find the weather here in VA had warmed up significantly.

Last couple days were perfect temperatures for painting so I decided to take advantage of the nice weather.

I started (re)painting Joey's K3 CB750 tank and finished up Tommy's XS650 motor. Here's a couple teaser shots:

First coat of metallic cast iron went on really thick (and kind of runny).
I'll be sanding it all even before the second coat.

The paint area as it sits currently.
That's the XS650 left engine cover in the way back there.

Decals for the fuel tank and sidecovers.
I'm still considering something else instead.

Oh yeah, they're REFLECTIVE vinyl. Pretty cool right?

Custom mixed a gold/bronze-ish metallic
engine enamel for the YAMAHA inlay.

It's really hard to properly photograph the metallic paint.
So here's some more pics.

It looks slightly more gold in person. 

This is the side engine cover before.
It's funny how just a slight difference can really make the motor  pop.

There's more to come very soon. I'll be posting the other side of the XS motor as well as the final product of the K3's gas tank and matching sidecovers in the near future.