Honda loving. CD125 benly twin rebuild.

[manbearpig]

This little thing is my Honda Benly 125 twin. It's a wicked little bike, and has prooved to be ultra reliable. i bought it about a year and a half ago to get to a from work when I only had a CBT, and it's been dragging my ass around in all weather ever since. i have done nothing with this, apart from treating it to a new battery when I first got it. The only love it recives is fuel, and in the past couple of months, an increasing amount of oil. It used to go off the clock which is about 72/73 mph, but now if you take it over 50, you get clouds of wibblepoo bellowing out the back, and it's a bit sluggish. The tyres are worn as well, so I thought I should give it the love it deserves and give it a full pimp. I've been a bit lack lustre on the photo taking, but you get the idea.





These were a right pain in the bum to put on. They are supposed to take tube type tyres, but I wanted a wider more modern tyre, so these tubeless beads had to be prized over my tight spoked rims. A few red nuckles later and they were on.









This is the first time I ever removed the plugs. I'm suprised it even ran, let alone reliably in all weather at the first nudge of the button! You can't see the filament very well in this photo, but I couldn't even see it in real life! It was caked in tar and wibblepoo.



Mmmm. Cruchy



Now, booboo numero uno. I dropped a circlip down inside the cranck case when I was removing the pistons. Bad times. It's a wet sump contain ing the gearbox, so what strated off as an afternoon job became a lot more in depth. Spent frickin ages flushing it out with a mix of old engine oil and fuel, but nothing came out. Miserable, got oil all over me and the garage floor, and all my prize rags are all oil soaked . Anyway, got bored of that and thought 'sod ya, I'll ride ot about regardless and hope for the best', and carried on with the other stuff.

My new honeing tool



But first made this..



50 metre extension cable to run power to the garage, to run this..



Then I got out the trusty new polisher wheels again (yes I know this is a brush, the polish bit came later after a wet and dry)







But I can't find any photos of the finished result - more on that later.



Anyone for coke?



Anyway, all cleaned back up, buffed and polished, pistons all clean, valves and head cleaned up, and pistons dressed with the new rings. Apart from one of my new sets of rings was missing a ring, so I had to recyle one of the old ones - not ideal. Right, full of beans, I started putting it back together again.

Dropped another circlip in the crank.

Fu@&$£"^&* Cu&**%$£"&*

Down tools, push the engine to the side of the garage, go in and have a cup of tea.

It's still there now, about two weeks on. Really don't want to have to split the casings, and the crancks are too close to get a magnet probe down in there. Boo.

[bomberman]

magnet stuck on a steel coathanger??

[jrevillug]

Would a pickup tool go in through the oil drain? And would the circlip come out through it?

[manbearpig]

As far as a coat hanger goes, if it gets stuck to the flywheel or cranck and comes off the coat hanger, I'd be a bit stuck, and no, unfortunately it doesn't come out through the darin hole. however, by removing the outer casing and the oil pump mech, it would come out through there no worries, but unfortunately after several hours of flushing, it didn't

[waveman1500]

I know how you feel mate, my hands seem to be cursed to drop every small part I ever hold as deeply as possible into the corresponding mechanism.
The last time I changed a set of points led to about a 90 minute hunt for the two screws, one inside the bowels of the distributor and the other one somewhere in the front suspension of the car!

Best of luck with it. If in doubt, just buy new circlips and put the motor back together. If they're stuck enough that you can't find them, then they hopefully shouldn't cause too much trouble.

[10mpg]

why not just split the casings and remove the circlips? hardly a big job on something like this, and at least you stand a chance of the engine not crapping itself as the circlips find there way around the engine..

you've already got the barrels off you're halfway there..

i always stuff rag down the crankcase holes when I'm building up something like this, as you always drop the little fekkers

[ben1]

Just seen this on Retrobikes , doing good with your rebuild i see , glad i found this thread as it is more upto date than the bike forum.

[manbearpig]

Yeah, the only design floor actually that I can see on the engine is the crank case splits virtically down the middle axis if the bike, and not horizontaly down the sides so you can just pop it off like a bonnet. If I split it, all the gears and their shafts will fall about all over the place, and I'm not up for a gearbox rebuild. Having said that, it is a Honda, and it should be designed pretty inteligently. I'm just dreading the worst.

Oh yeah, these turned up yesterday....



new rings to replace the recycled oil scrape ring out of my odd set, and stem seals for the Z.

[93fxdl]

if the twin is like any of the other j engines i have pulled apart they usually leave everything in one side, just lay over and lift the uppermost half off and all the bits should stay in the "bottom" but which side should be top i don't know
a suggestion for getting bits out of the bottom of a crankcase is to smear grease over the bits of crank you can get to then rotate the crank so the greasy bit is down then turn the engine upside down and give it a shake so hopefully the bits will fall onto the grease and stick then you turn the crank and pick them off
the trouble with leaving the bits in there is they can end up in the gearbox as the engine and box share oil, so in my view leaving and hoping isnt an option
ttfn glenn

[manbearpig]

Yeah, I need to get them out. I'm not so frustrated with it now, so I reckon I'll get down there and do something with it soon. I need to get an impact screwdriver from somewhere to take the oil pump off so I can split the lump. The good thing is it just passed the mot a couple months ago, so if I can get it done, I can ride it about instantly.

[10mpg]

I've never stripped any split case engine and found that the bits just ping apart everywhere
they are designed to come apart you know, just get a good work area, a nice clean bench not you garage floor, take it steady and work out which side will be best to remove, it should become obvious when you get it a cm or so apart, though it's been a while since i messed with bikes i seem to remember it's normally the clutch side that you lift of on Hondas,

[manbearpig]

Nice one, ok. In that case I don't need to take off the oil pump, as it's on the 'wet side'. makes sense actually, being that the spindle and final drive poke out the bit you put on last. I'm back on night shifts again now for the next few days, so I'll negotiate with the misses and see if I can get some time on it after then.

In other news, the 70's Cb250 I was looking at may become available again in a couple weeks, so If I can get it all pimp fresh by then, I might be selling it to fund that.

[manbearpig]

Hhhhmmmmmmmm.

Oh dear.


Well, the mojo returned in full force the past couple of days - i managed to fish one of the circlips out with a bit of bent wire but sadly the other one was no where to be found. I thought I would split the casings and get it out - but I got most of the way there and couldn't take the oil pump off (haven't got an inpact screwdriver) - so I thought i would leave it to the gods (it's only a tiny wire one anyway )

So, spent the last couple days slowly and methodically putting it all back together again. ground the valve seats, cleaned all the ports with the dremmel brush, fitted new stem seals and rebuilt. got the bores back on with my new rings etc, new gasket seals and dowels, new gaskets all round - good. Putting the rocker retainers back on now and guess what happened - dropped a big thick washer down the middle

Not very pleased I pressed on and tried flushing it out by taking off the oil pump pick up and flushing around with fuel and having a bit of a fish with my bit of wire and a magnetic strip - nothing doing. Bo11ocks I thought - it's going back together......

The moment of truth arrived and I got the engine back in the bike. the engine would turn over on the button quite well but every now and agin would just sort of get stuck. Scrached my head a bit and though it ws just getting stuck in TDC or something - anyway, cracked on. Engine wouldn't start. Usually a reliable little thing so I thought to myself the carb might be gunked up after kicking around on the garage floor for the past month or so. Took that to bits and cleaned - nothing doing.

Took the plugs out and realised the clunking was the piston coming up and hitting the open inlet valve

Oh dear. Something seriously wrong with my suck squeeze bang blow and I've probably bent the valves.

So, it's got to come to bits again. I'm going to arm myself with an impact screwdriver so I can split the casings and get out that bloody circlip and washer, then rebuild the curse word again.

My questions to you retro chaps are these:-

a. can a I just reuse the new rings or does the act of fitting them in the barrels take the edge off and is a one-time sort of deal?

b. How the hell can I figure out my valve timings now? I'm searching the haynes and coming up with nothing. i may as well disregard all of my markings as they are clearly out, so how can I determine where the cam should be in relation to TDC?

Luckily I have a spare head with good valves (but I'll have to rebuild it anyway) but I don't want to go through all of that again only to put it back together and smash the valves again with the pistons. Also, I want it run well, so how can I accurately do this??

thanks in adavance and thanks for reading.

[10mpg]

you can reuse the ings as many times as you want providing you do not damage them on removal or refitting, I would strongly advise against swapping them engine to engine but putting them back in the same bores they came from is no problem at all.

I think it's very odd there are no timing marks on the crankcase and the head but if you really can't find anything, (usually just a scribed line in the flywheel and cam drive sproket that line up with lines or lumps in the crankcase/head, or sometimes with the edge of the head itself.

Take photo's of your flyweel and cam sprocket (both sides) and show us..

Remeber to time on the firing stroke...

[manbearpig]

Yeah, I mean't my marking which I made - The trouble is becasue the cam spins around as you try and undo the bolts, the markings spin around and you have to make some more - I now know what to do so i won't make the same mistake again!

Yeah, there has to be some kind of markings right? I just can't find anything in the manual (yet). So you say they should be a marking that I can allign my flywheel with the cam?

[chopnpop]

I know its very slightly different, but the cb lump has a few marks on the fly wheel.
Take out the spark plug, then if you use a socket & ratchet on the fly wheel (rotate it anti clockwise), take the piston closest to the fly wheel (makes life easier) up to TDC on firing stroke, look through the inspection hole (thats where the writing will be) and then make a note of what it says (there should be a little line in the flywheel, with TL or something. and then a small line on the casing.)
then, up top, while the piston is at tdc on firing stroke, ensure that the cam loves are 'flat' (equal distances away from the rockers) sounds to me like you've got the cam timing advanced by a couple of teeth. so the exhaust lobe will be closer to the rocker than the inlet one.

easy fix:
loosen cam chain tensioner; then if you pick the chain up at the back of the engine, and kind of feed it over the cam sprocket (i think it'll only be one tooth or 2 max) once you've done one, you'll have to spin it back to TDC on firing stroke. to see how the lobes are doing. should only take an hour or so if you keep your cool

as for the valve. I doubt you've bent it mate. I had mine doing the same. and sorted it out. now running fine..

goodluck. and keep us posted
-Liam

[manbearpig]

Nice one dude!

Ha ha! I've just found the page in the manual - page 85, chapter 1, section 38. easy money.

the question is, do I just line it up and ride it and hope fot the best, or should I take it all to bits again and split the casings and fish out the circlip and washer?

My better instinct is telling me to take it all to bits again, but it's just sooooooooooooo time consuming.

[joethefish]

Take it to bits.. it sucks but will definately suck less than feeling great having it running only for one of your lost bits to end up somewhere making a big crunchy I'm about to cost you lots of money noise.

[chopnpop]

^^ agreed. i managed not to drop anything where i couldnt retrieve it. but i'd definitely say split it.
as the old saying goes.. "better to be safe, than sorry.." when you do get to removing the oil pump.. it takes a bit of welly, so don't give up straight away

[manbearpig]

Yeah, I know. such a drag - I need to do a full brake overhaul and re-build on the viva along with the balljoints, the Z still needs some attention and I'm a bit worried about what daily commuting will do to the CB. the CB is the oldest bike out of the lot and although there is nothing wrong with it, it still feels like an old bike (the CD when running well would see it off) - coupled with other time restrictions it's all mouting up.

the thing is you need to be able to trust the machine you drive/ride. What's the point in being intrested in engineering/mechanics and spending so much time rebuilding something when you are going to set it up to fail anyway? It's coming to bits - it just suck and money is low in the Mitchell household at the mo. I think the plan is to get the CD back on the road and use it as a winter hack, and have the Z for sunny days. Cheers for the input guys - much appriciated. I'll stick an update up soon