One 'not careful owner'. Project CB 125F

[Dan Norse]

Been away from bikes for a few years and decided to ease back in gently with a little runabout, ideal for our low speed local roads.

I’d long admired the looks of the various retro looking bikes, but was put off by the relative lack of reliability and quality issues of the Chinese bikes I'd read about and the better ones are out of my 'allowed' price range...

So I set out to try and recreate a little of those rugged, basic bike looks using a tried and trusted base bike from one of the main Japanese manufacturers.

After looking for a while I found a 2020 Honda CB125F which had been gently thrown down the road at some point and also been neglected in the oil department. i.e. it had been run dry, que lots of smoke and drama followed by six months parked in the garage and one very p*ssed off mamma.

I paid a measly sum and am setting about creating the bike I’d always wanted. I'm collecting 'goodies' in readiness and have removed most of the largely broken plastic.

Looks like the previous owner wasn't bullsh*tting when she said it ran out of oil... Have to say that otherwise it all looked pretty good in there. The oil screen was spotless (only 5880kms on the engine) and the centrifugal oil thingy was also spotless.

I was expecting to find metal everywhere. There was even compression when I undid the screws on the spinner...

Next up is to pull the head and cylinder to have a squint at the piston/rings/bore and give the con rod a good 'wiggle' etc. I'm sure the piston and cylinder will be toast. Maybe some seals or even the clutch too, will have to see.

Cheers for having us

p.s. if anyone knows how these little engines typically 'fail' when run dry, I'd love to learn from your experience. I'm imagining that the piston will expand and seize first, maybe before the crank etc. is damaged (wishful thinking maybe??)

[stinkwheel]

I'd be having a very close look at the cam and follower surfaces and journals. Also the oil pump and oil pump drive gears.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[A100man]

Did someone just pour half a cup of treacle into an ice cream tub?

I wouldn't spend too long trying to fix the motor if the crank and/or head has given out. Usually quicker/cheaper to replace the whole unit from a crashed one.
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Dan Norse]

[Dan Norse]

[Zen Dog]

[ThunderGuts]

A lot of Wemoto stuff is pattern parts too, so you won't necessarily be getting the quality either of the original components.

An engine out of a crashed bike would be my preference too. Not sure if you have to have the exact bike or if you can fit one from an FI CBF125 though?
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TG.

[Dan Norse]

[stinkwheel]

[stinkwheel]

[A100man]

[Dan Norse]

Took the head and cylinder off at the weekend and it seems the bike is running a special fuel saving piston...

What worries me is I can't find the 'bit's. I've flushed out the cases with tons of diesel and swished it all around but still nothing when I strain the flushed diesel into a tub.

The crank bearings feel 100%, no 'grittiness' etc. There is no detectable radial play in the big end and .2mm side play (bang in the middle of the specs range of .1 to .35).

The little end is troubling, I had to heat up the pin to draw it out and there is some damage to the pin. I won't know for sure about the little end until I get a new pin.

If the little end is toast, that's annoying because it doesn't look like you can buy con rods separately, it's a part of the crank assy.

The cylinder is borderline hone-able, but I've decided to grab a .25 oversize piston and re-bore the cylinder, it's less work and cheaper than buying a new cylinder and then you know its good.

It's all exciting stuff and I forgotten just how much I like the smell of oily diesel lol!
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If you want to meet interesting people, do interesting things...

[Dan Norse]

[stinkwheel]

I've melted a few holes in pistons in my time and that's not what it looked like. That looks like it's been smashed in (or out). Is there corresponding damage on the head?

I'd definitely be splitting it and having a good poke around in case whatever it was is still there. I always split engines unless all the bits were 100% accounted for and always found stuff. Those bikes have an oil strainer and centrefugal filter. I bet both are full of shiny sludge.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Dan Norse]

[Dan Norse]

[Easy-X]