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Suzuki B100
Topic Started: Mar 31 2018, 01:51 PM (854 Views)
Othen
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Baron
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I thought subscribers might be interested in this one. I bought a 1976 Suzuki B100 (120cc) as a barn find from a breakers yard 2 years ago. It was in a bit of a state: pretty rusty, non-running engine and someone had (probably 30 years ago) tried to hot wire the bike and so ruined the ignition lock (which was a pity as the bike would have been trivially easy to hot wire without damaging anything). It was cheap (from a breaker's yard) and although not really my sort of thing, it was too good to let die.

The bike came with the original bill of sale and the white type log book, but had never been scrapped. The story was it was bought by the first owner in 76, he rode it for 10 years and did 15,000 miles then suddenly stopped using it is 86 (the last tax disc is still on the bike), pushed it to the back of the shed and bought another bike for his commute to the shoe factory.

I thought I might just get it running and riding as a winter project (remember, that was 2 years ago). A bit of welding saved the rusty swing arm, I found a new switch and key (brand new, amazingly exactly the same item is still fitted to some bike or another that is still in manufacture) and re-wired the bike one afternoon. The engine would turn over by hand, but to be safe I thought I'd better strip it down to find out why the bike had stopped working in 1986. As I did I found the right (drive) side main bearing had disintegrated completely...

Posted Image

... the engine/gearbox strip down was not too difficult and all the bits I needed (mainly bearings and gaskets) were surprisingly still available and quite cheap. Having got everything back together the first time, I found the kick starter pawl still in my box of bits - and so had to take most of it apart again to put it back in the right place!

The engine turned over nicely now (and the top end was fine), but I thought I'd better work out why it had suddenly stopped in 1986. I found the answer whilst inspecting the auto-lubrication system. Someone had replaced the check valve that injects oil into the crankcase with an ordinary hydraulic union, as you may see from the nail inserted into it, this item has no one-way valve to stop the crankcase pressure forcing oil back against the pump:

Posted Image

So, that is why it failed. The new check valve was still available (new) and has sorted that problem. The rest was just getting rid of the worst effects of 30 years unused in a shed: most of the chrome had peeled off and so I painted over with some mat black to stop any more corrosion, the frame got a quick rub down and a coat of lacquer and the exhaust was roughly repaired (with plates, rivets and exhaust paste). A new set of points and a plug had the thing running, and to my surprise the cycle parts were more or less okay (with a bit of grease and fettling). I had no intention of a full restoration, but the bike had been saved so I sent off to DVLA and got a new V5. The 'sort of' finished bike is here:

Posted Image

That takes up to this time last year, where the running and riding project got pushed to the back of the garage and my Triumph Scrambler moved to the front for the summer season (I'm a fair weather rider). There the bike stayed until last week when I noticed it whilst working on my recent acquisition (CCM CXR230 - see my other thread). Once the CCM was through the MoT I ran out of things to do, and so tried to start the Suzuki. The battery (a tiny 6v affair) had died some time in the last year. A replacement arrived in the mail this week, I charged and fitted it this morn, gave the plug a clean and the B100 started after about 4 kicks. I smokes like a 40 a day man of course (like all 2 strokes from the 70s - but I also run this one on a weak 2T mixture just to be sure), but it runs okay and rides (as far as the end of the cul-de-sac and back), the gearbox changes, the brakes stop and the clutch clutches.

I noticed the lights are a bit dim (there is not much of an error budget with a 40 year old 6v system) so I'll pick up a tin of contact cleaner this week and have them gleaming (well, perhaps glimmering) pretty soon.

I don't think I'll do any more to the bike than that. I've achieved my aim and I'm not interested in a full restoration. The bike will become tax and MoT free next month (I think it would pass an MoT once I've sorted out the earth returns with the tin of contact cleaner, but there is no point as it will be MoT free in a month or so). At that point I think I'll look for a good home for the bike.
Edited by Othen, Mar 31 2018, 04:21 PM.
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Monty
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Charlie Big Banana's
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I had a B120 engine in a go kart I built many moons ago, bought the whole bike for 35, ripped rear wheel apart and used the brake hub on the rear axle of the kart.
If it aint sharp I can play with it
My Utube Channel, lots of bike vids here. Subscribe if you likehttp://www.youtube.com/user/choppermark?feature=watch

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Lardmarc
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Jester
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Monty
Mar 31 2018, 06:00 PM
Ripped rear wheel apart and used the brake hub on the rear axle of the kart.
Snap.........I did the same same with an old RD200. My engineering skills weren't up to much back then, the way I fixed the hub to the axle broke occasionally leading to some hilarious/ hairy moments.
Just a flunky along for the ride.
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Othen
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Baron
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B120 in a kart - marvellous!
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Othen
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Baron
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I don't know whether this link to the B120 running will work:

https://1drv.ms/v/s!Ask6E_1jz4xIskb-lEyqgdOTrHLE

... if someone would try it and let me know whether it works over the 'net I'd appreciate it.
Edited by Othen, Apr 1 2018, 06:12 AM.
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Monty
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Charlie Big Banana's
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Worked for me, nice one
If it aint sharp I can play with it
My Utube Channel, lots of bike vids here. Subscribe if you likehttp://www.youtube.com/user/choppermark?feature=watch

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Othen
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Baron
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Monty
Apr 1 2018, 06:58 AM
Worked for me, nice one
Many thanks, that is good.
Alan
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Lardmarc
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Jester
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Nice. I like an 'oily rag' finish.

Well done.
Just a flunky along for the ride.
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Othen
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Baron
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Lardmarc
Apr 1 2018, 10:37 AM
Nice. I like an 'oily rag' finish.

Well done.
Thank you.

I was just talking about it with my 13 year old son, and mentioned that perhaps we would sell the Suzuki on to a good home after 20 May (when it becomes tax and MoT free, so ownership will be even less onerous). To my surprise Dan said he really liked the bike, and asked if we could keep it. Well, it is really cool having a 42 year old bike - particularly one with a 42 year patina, and I have a soft spot for it so perhaps we will keep it after all.

I agree with you about the oily rag finish (a good description), the only thing the bike really needs is a new header pipe, which is still available from the USA at about 70 delivered (or perhaps I just do a much neater patching job on the original, which might be more in keeping with the rest of the bike than shiny new chrome and a good excuse to buy a MIG welder).

Alan
Edited by Othen, Apr 12 2018, 06:51 AM.
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Lardmarc
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Jester
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'Oily rag' is my favourite build, you don't spend much time cleaning it after a ride.

Posted Image
Just a flunky along for the ride.
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Othen
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Baron
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I ran the B120 up the other day only to find it leaking heavy oil from the exhaust. Obviously the crankcase seal on the drive side has failed in the year it has been standing. A new 47mm seal arrived in the mail yesterday (cost about a fiver) and I'll put it on in the next week or so. I think I recall it is not too hard a job: just remove the oil pump and clutch, take off the pinion bolt and pull out the spacer from the middle of the seal, then drive the new one in and re-assemble.

Something always goes wrong when working on 40 year old machines though - so I'll allow myself half a day :-)
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Monty
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Charlie Big Banana's
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You will also probably need a new gasket
If it aint sharp I can play with it
My Utube Channel, lots of bike vids here. Subscribe if you likehttp://www.youtube.com/user/choppermark?feature=watch

Posted Image
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Fallsoffalot
Commoner
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My first 'proper bike' was a brand new b100p. Loved it. Road from Norfolk to Somerset & back. Before that I had a Raliegh runnabout.
And yes the lights were crap.
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Othen
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Baron
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I got round to changing the drive side crankcase seal last week. Everything came apart and went together pretty easily, and I suppose it only took an hour or so. I was a bit worried that nothing needed gorilla-ing back into place - but it seems okay.

I still have a problem - the bike starts but will only run for a few seconds before the plug oils and it cuts out. I think what has happened is that in the past year that the bike has been standing some gearbox oil has seeped past the leaky seal and is sitting in the bottom of the crankcase. Every time I kick it over some gets sucked up into the combustion chamber and oils the plug before it can get going. Somehow I have to get the oil out - probably the easiest way would be to run the bike for long enough for the oil to get pumped out of the exhaust port (luckily it is clean oil - changed just before the bike was put away a year ago). To that end I'll fit a new plug and fresh fuel (the stuff in it is a year old and a 2T mix - which is probably not helping matters). If it will start (and smoke like a 40 a day man) it should clear the gear oil in a few minutes. If that doesn't work the next easiest solution will be to pull the head and barrel, then mop out the bottom end with some petrol - so I've ordered a spare gasket set just in case (only 9).

I think I'm on the home straight with this one now,

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Monty
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Charlie Big Banana's
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wont it be just as easy to strip the engine and replace the crank seals, you may only have to remove the covers and rotor to get to the seals with out having to split the casings, if they are sucking in gearbox oil then they wont be be giving you good vacuum to suck in the fuel
If it aint sharp I can play with it
My Utube Channel, lots of bike vids here. Subscribe if you likehttp://www.youtube.com/user/choppermark?feature=watch

Posted Image
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Othen
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Baron
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Monty
May 20 2018, 09:37 AM
wont it be just as easy to strip the engine and replace the crank seals, you may only have to remove the covers and rotor to get to the seals with out having to split the casings, if they are sucking in gearbox oil then they wont be be giving you good vacuum to suck in the fuel
Hi Monty,

Perhaps I didn't explain very well: I've just replaced the drive side seal (as you say, a pretty easy job) because it had failed in the last year the bike had been standing. The crankcase seals are fine now. The issue I have is that the plug keeps oiling - I think because there is some oil trapped at the bottom of the case. My first theory had been that this was some residual gear oil from when the seal was leaking that must have found its way into the middle of the engine - and that may still be the case.

I have another theory that it might be excessive 2T oil from the positive oiling system. I noticed the oil pump had not been set up properly and was always at least half open - which would allow more than double the normal amount of oil to be injected - perhaps too much for the engine to burn. I've corrected that fault now, and as this is the much easier one to fix I'll try it again with a fresh plug and fuel first.

If that doesn't work I think I'm back to mopping out gearbox oil from the bottom of the crankcase. The good news is that taking the head off an air cooled 2 stroke single will just take a few minutes.

I'll let you know how I get on.
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Othen
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Baron
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... I took the head and barrel off the B120 today (which took about 15 minutes including removing the seat, tank and carburettor). The bottom of the crankcase was fairly dry, which was good news as it means the cases themselves are not leaking. I found the problem at the bottom of the right hand transfer port: the little hole that runs down to the outside of the drive side bearing (between it and the seal) to promote lubrication was choked was full of heavy oil - which can only hand come from the gearbox before I changed the leaky seal the other day.

I've cleared out the passage and will leave it a day or two to make sure everything is dry before putting it back together...
Edited by Othen, May 22 2018, 05:48 PM.
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Othen
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Baron
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The B120 is back together and running pretty well:

https://1drv.ms/v/s!Ask6E_1jz4xItQrqyzp2EOs5FtHD

I'll sort out the poor lights (just a bad connection somewhere I should think) - and then it is finished.
Edited by Othen, May 28 2018, 04:58 AM.
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Othen
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Baron
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... After running pretty well for a while, the B120 started sipping gear oil again. I think I've worked out the issue:

Posted Image

I had fitted a 26x47x10 oil seal, as specified in the ancient B105 parts manual I have. When I stripped the right side of the motor to reveal the crank seal I noticed the hole (mentioned above) that leads up to the right side transfer port and promotes oily airflow through the drive side bearing would clearly be blocked by that depth of seal. Once sealed off my theory is that the vacuum in the top part of the tube eventually sucks oil in through the outside of the seal (where it seats on the crankcase web).

The solution: the original Suzuki seals don't seem to be available now (and anyway they would just be ordinary nitride seals but cost 5 times as much), so I've got some 26x47x7 seals, which should leave a 3mm gap outside the bearing to allow for the oily airflow. I'll put one in later this week and see if my idea works. I don't normally use any sealant (apart from a bit of silicon grease) to seat oil seals, but in this case I'm thinking I might use a smear of Loctite 603 to make sure it stays in place on the crankcase web and maintains the 3mm gap.

... I'll let you know if it works :-)
Edited by Othen, Jun 4 2018, 07:27 PM.
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Othen
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Baron
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... As an aside: I registered the B120 as an historic vehicle at the Post Office yesterday (a really simple process). So now it is tax and MoT exempt. I can't really think of any reason not to keep the bike now: I'll add it to my multi-bike policy next time it comes up for renewal and I might even take it out on the road every now and then.
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