Author Topic: YB100 Restoration.  (Read 1842 times)

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Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #15 on: October 23, 2018, 09:50:21 PM »
I am a little disappointed with the performance, especially when my wife came past me on our CB100N!! But a guess there is some tuning potential with a two stroke.

I don't know what's more upsetting about that statement, the fact that it was your wife, or that it was a Honda.....
RD250 E, on the road.

YB100, restoration/customisation under way.

Offline tractorman

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Re: YB100 Restoration.
« Reply #16 on: October 25, 2018, 09:57:08 AM »
I think the fact it was a Honda. Although the Yam is standard, I reduced the main jet size slightly, which seems to have improved the performance. I have a test of a 75 YB100,and they reckon it will do 70mph, mine struggles to 60mph, so maybe the later ones are strangled by noise and emission regs.

Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #17 on: November 01, 2018, 07:22:35 PM »
Crankcase screws all out bar one, and that's on the upper kickstart boss, so about the easiest to get to, I'll settle for that 8)

Most of the others just gave in to the impact driver pretty swiftly, from the heads its never been apart before. Reluctant one, I cut a slot in it with hacksaw, them it broke out one side so I sawed the other half off. The cases will come apart and I can thread the broken stud and use two nuts, or have nut welded on etc. A way will be found!


Head and barrel off, the head is good, the piston shows evidence of a seize, but the barrel is not scored. Its on std bore, but done near 14000 miles so going out to first O/S seems appropriate, I have pattern barrel so will compare them.


TM, you might want to check your gearing, the earlier YB's have different No. teeth sprockets to later ones, not always apparent on replacement part listings which you are getting. I should think these are good for 65mph, there's not much of me to carry, so hopefully!
RD250 E, on the road.

YB100, restoration/customisation under way.

Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #18 on: December 12, 2018, 04:35:37 PM »
Probably about half way with this now. Just the forks and wiring loom left on the frame. Everything else has come off and been cleaned up and painted, or given a polish or replaced in the case of rusty nuts and bolts.

Rattle can paint job, stick on pin stripes.


Polish up and plastic back to black.


Swing arm and shock absorber bushes replaced. These are the rubber type sandwiched between two steel tubes. Don't try to drift out, just saw through in a couple of places and punch out the the sections. Put the new bushes in the freezer over night, heat the arm with a paint stripper gun. A bit of copper slip in the hole and press in with a vice and socket.


Aluminium paint finish stripped off of wheel hubs and polished up, a time consuming, but strangely satisfying job. New wheel bearings fitted. Used the paint stripper gun to heat the hubs to get the bearings out. New bearings left in freezer over night, hub heated again and drift in with a large socket and block of wood. Only the sprocket carrier bearing was really gone. New bearings and seals from Simply Bearings uk online, easy to order if you can measure a bearing and seal. Sadly the weather and time has got the better of the rims and spokes, would be nice to replace, but not this time round. Polished as best I can and painted spokes black, I think it will look alright.



Next up is to get the crank and gearbox out of the cases.

RD250 E, on the road.

YB100, restoration/customisation under way.

Offline kawazonkey

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Re: YB100 Restoration.
« Reply #19 on: December 30, 2018, 10:08:49 PM »
You've been busy! Tank looks great. Doubt the bike had any restrictions in it, was after all designed as a little commuter but yes, good for a bonkers 70mph lol.

Offline Motty

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Re: YB100 Restoration.
« Reply #20 on: December 31, 2018, 08:46:03 AM »
The rebuild is coming along nicely although that poor old piston looks like it has seen better days



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Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #21 on: December 31, 2018, 09:25:47 AM »
Yes, it's obviously nipped up at some point in the past. Quite scored on the skirt, but the barrel is clean so lucky there. It is on standard bore, I've got a 1st o/s piston for it so can have it bored out, but I also bought a pattern barrel and piston - not sure which way I'll go as yet? Still need to get the crank and gearbox out,  hopefully after the holidays are finished I can get on with it! Only the forks and wiring left on the frame now. I need to get this back together so that I can start on the stuff I want to do on the 250 during the closed season, I don't have the space to have both apart at the same time...
RD250 E, on the road.

YB100, restoration/customisation under way.

Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #22 on: January 17, 2019, 09:57:34 AM »
Crank and barrel at the engineers. Hit my first hurdle though, front forks are ruined  :(

Water has been trapped under the dust caps and corrosion has severely pitted the chrome legs and made a right mess of the sliders which appear to be some kind of steel, and dissolved the cir-clips holding the seal in. I don't see either section being salvageable in any cost effective way.

I can see secondhand ones coming up on ebay, but not that cheap and may well have similar issues. As I'm not restoring this to standard, I'm thinking of Frankensteining on another front end, possibly a YBR 125? Any other suggestions, thoughts? 
RD250 E, on the road.

YB100, restoration/customisation under way.

Offline mech73

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Re: YB100 Restoration.
« Reply #23 on: January 17, 2019, 10:43:16 AM »
YBR rear wheel will fit in a YB100 swinging arm, but a custom spacer has to be made and also a little machined off the sprocket face in order for the wheel to be centred and lined up with the chain. I managed to fit the front wheel using some hybrid forks made out of a mixture of FS1E and YB100 parts. This is my sons bike. It's a fizzy frame but the main part of the frame is identical to a YB100.



However that wasn't your question which was will YBR125 forks fit. Someone did this early last year this so they will, but they needed to use different yokes. I think they were RS or RXS 100/125 yokes. From memory (so don't take this as definite) the YBR yoke stem was too short although the bearing dimensions were the same. Fortunately RS or RSX stachion diameter matched the YBR ones. I don't know whether the stanchion spacing stayed exactly the same or whether some spacer changes were required.

Here's a picture. It belongs to Alan who's not on this forum but uses the name Kingtut on several others.



Any FS1E forks will fit but they're for 17" wheels. RD50M or MX forks will also fit and the matching cast wheels fit straight in a YB/fizzy frame, but they're highly sought after and usually expensive. If you wanted to retain the original drum braked spoked wheels then a whole set of RS/RSX forks should do the job, but check the stem dimensions will match before spending too much.

This is mine with RD50M forks and RD50MX wheels.



Oh and a true 60mph is a fairly good top speed for a YB100 in neutral conditions. Tall gearing means they will sometimes go a bit more down hill. I think the standard exhaust especially on the later models is quite restrictive as they really do seem to go better with any sort of expansion chamber. Annoyingly my sons YB is a a couple of MPH faster than mine and both motors were built the same. His just has a very battered ex fizzy micron.
« Last Edit: January 17, 2019, 11:03:18 AM by mech73 »
1973 RD200
Basingstoke Hampshire

Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #24 on: January 17, 2019, 11:39:05 AM »
Mech73,

brilliant post  :-*

What a gold mine of inspiration and info, very helpful!

Couple of very nice bikes you've put together there, well done.

So, the YBR stanchions won't fit in the YB yolk? different spacing between the legs? I'll keep a look out for the other yolks you mentioned on ebay. I'm wondering if it would be possible to weld a longer stem onto a YBR yolk, I've not got the yolk off yet, so not seen how its machined. Just thinking, YBR stuff much cheaper/available than RS or RSX parts.

Regarding the speed. In the Haynes, it shows earlier YB's with a different compression ratio and gearing. The early ones, 2UO had a different air filter box too, larger. I don't think it fits the 18N as they have a different engine side cover - all this assuming that the earlier ones were quicker??

Thanks again, great post :)
RD250 E, on the road.

YB100, restoration/customisation under way.

Offline tractorman

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Re: YB100 Restoration.
« Reply #25 on: January 17, 2019, 12:58:29 PM »
Thank you for confirming the top speed. I have a 1975ish test of a YB100(a proper test where the guy,used it for more than a few hours, think he actually bought it for his wife) any way, he said top speed was 70mph. Mine will pull about 60mph on a good day, with a tail wind. I think the older model had a shorter exhaust, and yes a different air filter. Mine will be up for sale this year and may be at Popham, my wife prefers the CB100 and her DT125E, so the sale will fund another project.

Offline mech73

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Re: YB100 Restoration.
« Reply #26 on: January 17, 2019, 04:36:40 PM »

So, the YBR stanchions won't fit in the YB yolk? different spacing between the legs? I'll keep a look out for the other yolks you mentioned on ebay. I'm wondering if it would be possible to weld a longer stem onto a YBR yolk,


Not sure about how the spacing compares, but the YBR stanchions are a bigger diameter than YB100. I think YBR are 30 mm and YB100 27 mm.

A fizzy or YB100 stem in the YBR bottom yoke may work. It would depend on how the top yoke interfaces with the stem as well. It may need a custom stem making. or the top yoke machining.
1973 RD200
Basingstoke Hampshire

Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #27 on: January 24, 2019, 08:04:45 PM »
Down the rabbit hole I go.

YBR 125 Custom: Front wheel w/Disc, Caliper and master cylinder, spindle, speedo drive. Rear wheel, sprocket hub, brake plate, spindle. RS100 top and bottom yoke on the way.



YB wheel assembled in the swing arm.



The YB sprocket hub fits in the YBR cush drive. The YBR sprocket drive hub is about 10mm taller.

Brake plate doesn't fit, the YBR has a wider dia drum.

Torque bar is near enough to work.

The YB has a 12mm dia spindle, the YBR is 15mm and only fits through one side of the YB swing arm. Could machine that out, but I would then have to change the chain tensioning arrangement  as well.

Assembling the YBR wheel in the YB swing arm using the existing YB spacers and the YB sprocket hub on the loose YB spindle.

Hard to tell exactly due to the play on the spindle and measuring on the tyre center line, but it looks like I am off center with the wheel towards the sprocket side by 5-10mm, as was told above. As I'm using the YB spacers, the sprocket should currently be in line with the gearbox one, so now I can see how taking some off of the face of the sprocket carrier would help, along with redistribution of the spacer sizes..possibly.

My thinking at this stage is to knock out the existing YBR bearings and fit ones with a 12mm dia center to hold the smaller spindle firm, then I can get a better measure of the wheel position with the tyre off too to find the true center.

Knock on effects of this is: I'll need to bush the YBR brake plate hole as it will be a 15mm hole on a 12mm spindle. The sprocket axle spacer needs a packer to contact the bearing. I'll also need to make a wheel bearing spacer of the right dia.

Worst thing is machining off the sprocket carrier on the sprocket face side. It isn't a flat face, but has four raised bosses, so it can't just be milled off in one - smells expensive?

So, anyone like to chip in with thoughts or suggestions, happy to kick it around.

On the brighter side, I made some new aluminium trims for the clocks as the originals were scuffed and rusted. I'll make a custom dashboard later on to take a more traditional round clock, but its easier to use the existing tidied up for the moment.

 



RD250 E, on the road.

YB100, restoration/customisation under way.

Offline mech73

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Re: YB100 Restoration.
« Reply #28 on: January 24, 2019, 08:59:16 PM »


Assembling the YBR wheel in the YB swing arm using the existing YB spacers and the YB sprocket hub on the loose YB spindle.

Hard to tell exactly due to the play on the spindle and measuring on the tyre center line, but it looks like I am off center with the wheel towards the sprocket side by 5-10mm, as was told above. As I'm using the YB spacers, the sprocket should currently be in line with the gearbox one, so now I can see how taking some off of the face of the sprocket carrier would help, along with redistribution of the spacer sizes..possibly.

Worst thing is machining off the sprocket carrier on the sprocket face side. It isn't a flat face, but has four raised bosses, so it can't just be milled off in one - smells expensive?

So, anyone like to chip in with thoughts or suggestions, happy to kick it around.


I machined the sprocket carrier on a lathe, I can't see exactly how I mounted it, but I did use a 4 jaw chuck and some sort of mandrel.








Sprocket fitted but another surface (the bit just inside the sprocket) of the cush drive had to be machined down a little to clear the inner edge of the tab washer.



I'll have a look through some more pictures and sketches to see what I did with the spindle. I think I used the original one with some spacers and bushes.

edit - looking through some old posts I used 15mm o.d. 12mm i.d. stainless steel tube around the original YB spindle with custom spacers on both sides. The YB spindle is quite long as it passes through the threaded spacer on the sprocket side with a big nut on the outside of the swinging arm. It looks like I didn't use the YB threaded spacer, so that required a spacer on the outside that from memory I think was top hat shaped so it fitted partially into the inner spacer.



Thinking about it some more, it may have been easier to use the 15mm YBR spindle and widen the RH slot. That's assuming the YBR spindle is a suitable length and it may not have been.

Update: I found a sketch of the LH outer bush. But not the LH inner or RH one.

Looks like although the YB spindle I used was 12 mm the thread on the end was M10.


« Last Edit: January 25, 2019, 03:29:30 PM by mech73 »
1973 RD200
Basingstoke Hampshire

Offline Reving Kevin

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Re: YB100 Restoration.
« Reply #29 on: January 25, 2019, 06:35:52 PM »
Very helpful, thanks  :)

 ''looking through some old posts I used 15mm o.d. 12mm i.d. stainless steel tube around the original YB spindle with custom spacers on both sides.''

That is a good idea! With that I can use the YB spindle and get away without making a bush for the brake plate, changing the bearings and making a bearing spacer too. I'll look on ebay for a supplier.

Thanks for the lathe pics too, I can see how it could be done now and can provide the engineers with a sketch.

Got the tyres off today and cleaned up the wheels and sundries. When I get the packing tubing I'll be able to measure for the spacers and how much to trim off of the sprocket carrier more accurately. I'll also need to figure what to do about the 'top hat' spacer that goes between the outer wheel bearing and the inner of the sprocket carrier bearing, as it is too short, maybe another bit of packing tube...

If you had used the YBR spindle on yours, you'd have needed to change the chain tensioners to suit, or got some YBR type ones which would have meant grinding off the lugs on the end of the swing arm that the bolts pass through and the nuts bear on.

Still waiting on the RS fork yokes. I'f the stem fits the YB frame, and the spacing between the legs is right for the wheel, it should be a lot more straight forward that end.

Thanks for the help.   
RD250 E, on the road.

YB100, restoration/customisation under way.