Sunday, 10 November 2019

CB250 rebuild part 8


If you've been following this then you're most probably wondering what I did about the alternator because I haven't mentioned it yet. Fact is I thought I'd be clever and that hopefully it wouldn't need to come off, I really hoped the cam chain would slip past the middle bearing carrier thing on the crank and I could slip on a new one while leaving most of the left case in situ. This didn't work out.
There is no room around the carrier and the stud for the nut at the top of it is always going to be in the way. This was a bit of a downer. So now I had to wrestle with the flywheel bolt and taper while the crank can freely rotate because I can't use a penny in the primary gears to stop it.. First remove the alternator cover:
The chain is driven by the start motor (yuck), here is the sprocket that sits on the end of the motor:
Refitting this to the motor would have been impossible with the alternator cover in place anyway so this all turned out to be not so much of a loss as I thought. So, oil filter chain wrench doodad:
Special clacker at the ready again..
Turn the chain wrench thing around so you can tighten and start with the special flywheel puller tool (bolt).
You might need a little extra help to stop the crank turning. These pistons are dead anyway because I'll be buying new barrels and probably pistons so I had no qualms about this.
After what seemed like sheer brutality (tighten the bolt, hammer, tighten, hammer, tighten, hammer) there was success!
Everything should be easy now. I don't know why the steel plate spacer thing is so rusty though.
The rollers for the starter clutch promptly fell out, except for one which was stuck in place. These will no doubt be a very good game of fun-ness to put back. Also red rust!
Thankfully the flywheel is magnetic so can serve its true purpose of a way to not lose things.
Since I apparently have to remove the crank from the case to fit a new cam chain I had to remove the other piston so that the con rod would fit between the studs. I didn't lose any circlips this time!
Another look at the carrier. Them bob weights are massive ain't they? I actually had to use the clacker to undo the bolts around it, using a normal wrench proved too difficult because I couldn't get the case to stay still.
Remove the bolts (and one nut for some reason) and let Thor do his work..
Thor actually causes me a problem later on from this, it turns out the middle bearing can move around in the carrier and this moves it so that the old chain won't come off. That takes me a while to figure out. Anyway, store the crank somewhere clean. If you can.
And admire the now emptier crank case!
There is a main bearing, a seal and some kind of gasket behind that plate. I don't want to see them if I can help it.


I really wanted to replace the cam chain because "people in the know" know that the chain will be super slack by the time 93K is up. Here's how my original chain (bottom) compares to a brand new chain (top):
Hardly worth bothering with. Perhaps it's the 2000 mile oil changes I religiously do, or perhaps it's because the motor is so mild that the cam merely caresses the valves but this doesn't seem in dire need of replacement to me. Anyway, the trouble I had with the bearing carrier - it was because the stud that the tensioner sits on didn't seem to be far enough away from the crank weight:
But it turned out the carrier with the stud on it actually quite freely moves side to side and must've been dislodged by Thor. Oh how I laughed.

Wednesday, 6 November 2019

CB250 rebuild part 7


Before going any further I decided the next thing should be to try and extract what was left of the bolt that was supposed to be helping to clamp the head and barrels down but had instead been broken for a long time. Armed with nothing more than a cheap Am-Tech Dremel rip off to make a small dent in the top of the bolt (the supplied drill bits being made of cheese) and then a small Black & Decker drill with a proper bit in it I did actually manage to make a dish in the top of the steel! I was surprised, most convinced that the drill would just slide off and ruin all the aluminium threads surrounding the hard steel..
And maybe it's a better picture with some flash?
The next step was to try and get some extractors to grab the bolt and turn it out, Dad had a cheap set that looked the business:
But they proved to be completely ineffective, nowhere near sharp enough to get a hold of the steel. Plan B!
Torx bits are great. A few taps with the hammer to make it bite and..
Very little effort was needed to unscrew the remains, it was never tight. Again I wonder if the bolt had a manufacturing fault in it right from the start? Anyway, one empty hole!
Is the thread okay though??
It is! Success!! I done did some proper engineering like.


With everything going so well it's time to try and split the cases. I had a go at cleaning them to stop too much gunge getting inside the motor, I think you'll find my efforts were more than acceptable (?)..
I had a go at pulling on the bolts that used to hold the clutch cover on but that just wasn't doing the business.
The bolts go back in this sequence, lest I forget.
That is some spare washing line, part of a plan. This day was windy, which nearly blew the cover off the awaiting frame.. Cor look arrit!
Must fix must fix must fix.. Time to employ the plan. Remove the plunger gubbins from the old scrap clutch cover, thread the washing line through the clutch plunger arm hole and the dipstick hole, bolt the cover back on the engine and then use the washing line to suspend the engine from an engine crane or whatever. Boom, all the weight on one side. Good Lord I'm so clever.
I used a bit of wooden stick and a mallet and set about separating the cases. This took a lot of effort, I don't know how else you would ever do it. I don't need to tell you why you shouldn't jab a screwdriver in between the halves, right?
The starter motor hole also took a good malleting.
At this point the cases seemed to stop separating any further, had I missed something??
It turned out it was just the countershaft bearing being tight in the case, nothing a few choice mallet whacks couldn't sort out.
At this point I realised I had to remove a piston because the big studs in the cases won't go past it, and it's easier (and safer) to unclip a piston than remove those studs.
Annoyingly the circlip pinged away never to be seen again but no time to mourn that now, things are just getting exciting!
One last pull and..
A quick squizz shows the gearbox is probably not falling to bits, no missing teeth or any obvious smashiness to report. Excellent.
Remember where this goes. It comes off the shaft very easily so I'll probably get it wrong later on.
Welcome to the weird bearing carrier thing in the middle of the crank, and the strangest cam chain tensioner I ever done saw.
And also the upper front mount, sporting serious ovality. However it does also show that the dowel pin has not been worn right through, which means that particular bit of housing is still round and the cases will go back together straight if I ever get that far.
Maybe this can all be saved after all, the only truly dead bits found were the heavily scarred bore and the detent arm. In case you even thought to ask, the crank and all of its bearings are perfectly tight. Hmmm.

Monday, 28 October 2019

CB250 rebuild part 6


I don't know what this picture was for but I took it so here it is.
The next step to total engine disassembly is to remove the clutch cover. Simply remove the bolts and off it comes, not even stuck in place because clutch plate replacements are a frequent milestone in CB250 ownership.
This clutch cover is completely knackered as the locating boss/hole for the tacho cable is ovalled beyond hope and the driving pin for cable broke somewhere in Spain, so its last job is to act as a bucket for engine parts. Next up is to remove the oil pump because it is in the way of getting the clutch basket off, spot the difference!
Easy enough again, just take the bolts out.
Next up is the clutch, first remove the radial bearing and springs from the centre of the clutch by, you guessed it, removing the bolts!
Then stop because the days in November are ludicrously short and it's dark and cold. Also you need a special tool for the clutch centre nut and, even though you know (you know!) you have one somewhere you just can't find it. You also know that the CBX250RS has a traditional hex nut and that no one has died from its application. So then go order a cheap one from Hong Kong which takes an age to arrive.


Bloody Honda mutter mutter, special nut for no reason mumble grumble.. With the right tool to hand it's time to attack the centre nut. This is quite difficult when the crank can spin freely, I decided to use an electronic wheel nut remover/impact tool to clack it off. This worked a treat but remember to bend the staked bit of the nut off the countershaft first.
Into the clutch cover/bucket it goes..
The plates put up a real fight before finally coming out, I think this is because there are small but definite notches worn into the fingers of the basket. Never mind.
Next up is removing the primary drive gears, this is quite easy as long as you have an early copper penny handy - don't use a later steel one as it could damage the gear teeth. I think the year of changeover was 1994? You might want to check that.
And let loose the impact driver of war! After this everything just kind of falls out.
Remove the rest of the oil pump body using the correct screwdriver bit, everything in here will be JIS. If you use a screwdriver you'll never get proper angle/torque on it, those who know will use a ratchet and a bit like so:
Looking quite good now innit? Next up is to remove all the gear selector gubbins, and here we may well have found why the gearbox was getting so sloppy - why is the disc on the end of the detent arm so far from central?
Hmm, massive wear is why.

That disc in the centre is supposed to be a circle, with all this wear the gear change shaft will be able to move further than it is supposed to which would explain the increasing frequency of missed changes. Hopefully this means the rest of the gearbox is still okay, that would be nice.

Next up remove the detent star (remove the bolt, durrr) and then remove the gear change shaft. This is kind of interesting because it slides inwards..
This may or may not have ruined the seal around it, I dunno. Chuck it all in the bucket.
A good day's work, I say!