Monday, May 31, 2010

engine overhaul

The 5speed SS50 engine that was under the motorcycle was leaking some oil from the cylinder base and behind the generator cover, so it needed to be taken apart, even though it has only done about 500km.
The problem at the cylinder base turned out to be a cylinder that wasn't flat, so it was turned on the lathe to get a flat surface for the gasket to sit against.
I thought it would also have a leaky cranckshaft oil-seal, but it was dry in the center of the generator. Next guess was the O-ring around the stator plate, when I took it off the plate, it was so dried out, that it broke instead of stretching.
So hardened it doesn't even lose its shape when broken:

when the head was off, I took some pictures of it, next to my "old-school tuned engine" this has an older type head with even bigger fins:

and more importantly, nicer ports:

Both are cylinderheads from the 5speed models, with extra and bigger fins then the 3 and 4speed models, but even then there are differences.

The other head has since been flowed to look more like the "old-school" one

Wednesday, May 26, 2010


Tuesday I took the moped to work, but when driving home, it began to vibrate at high revs and it made some funny noises. 5KM later I was at the workshop, had a quick look if the flywheel nut might have come loose, but it didn't, so I thought it should be a clutch problem. After all these years of abuse, I finaly managed to break the engine.

Today I started disassembly by taking of the exhaust to have a look at the clutch, but to my surprise, it turned out to be as simple as a broken motormount bolt.

I had a new bolt, put it in, put the exhaust back on, started the bike, and the vibrations were gone, engine still in working order, dispite years of abuse.
This motor has almost no compression, you can hear the piston ratteling in the cylinderwall, it never gets new oil, at best the old stuff out of a race-engine, it gets overrevved, overheated with burnouts..... but I still can't get it to really break. Real Honda quality, no chinese parts.

Jet problems

The SS50 motorcycle engine is now pretty much run in, but the carb settings are a litlle of. So I thought I would try a different main jet but to my surprise the keihin SS50A carb is so old that it doesn't have the standardized jets still used today. Now available are jets with 4mm and 5mm treads, as far as I know M4 and M5, but mine has a coarser thread M5x1 ???
In any case it has the same threads as the jets used in the CB72 PW22hov carbs I have, the powerjet type.

some measurements:
5mm threads

6mm head

8mm long

and a view of the coarse threads

If anyone knows where to get these old jets, please let me know, I need something like a 75 or 78

Saturday, May 22, 2010

BMW test

I've been riding my R90/6 for a little while now, and I am starting to get used to it, but at first I thought it was a real heavy beast that didn't want to go round corners. Making it into a caferacer would then only make that worse, with narrow clip-on bars and such.

When I was young (about 15 years ago?) my dad built a BMW caferacer together with Jan Hoogstraten who stil ownes the bike. We asked him if we could borrow it for me to experience what a BMW caferacer would feel like. Here it is next to my R90/6

I've only ridden it for a few kilometers now, but it isn't disappointing, I want to ride it some more, to get a good feel of the bike, but I think I'll keep my R90/6 to turn it into the JBT-interceptor styled caferacer I had planned.

The M10s on the back is the name of the bike, being compiled of the enginetype; R90s and my dad's name; Martien ("tien" means "10" in dutch)
Note the single sided paralever swingarm from a later type.


The SS50 motorcycle had some problems with the clutch slipping through at high speeds when asking full power. As this weekend I want to ride it in a night time honda-run, I wanted this fixed, so I opened up the engine, even though it has not even run more than 500km yet.

I found that the clutchsprings I had put in, where probably new as there was still yellow paint on them, but they were weak compared to the new springs I had with partnumber: 22401-036-000.
when measured at compression to 15mm the yellow springs had 5kg while the 036-springs had 8kg.
So new springs were mounted with new plates, as you don't know if they might have been warped from slipping, although I saw no blue spots on them.
First testrun it seems okay, lets see if it will hold.

Friday, May 7, 2010

engine building

The building of the racing engine has really begun.

I've fitted the altered 4speed gearbox with 3-4 made a little closer.
Fitted the best cranck I have with new bearings, oil-pump cleaned and fitted with new gaskets.

Gear shift drum turned out to be a bit different from the one that was in this engine originally.
That one had a circular plate on it as I know off the SS50 engines, but it couldn't be fitted to this gear shift drum, as it is a bit longer and then the clover shaped plate on the end wouln't fall onto its guidepin. So no extra plate here, should be no problem.

Next was the shift shaft, both shafts I had were bent, I bought a new one, but that didn't fit. The shaft was 0.5mm thicker where it shoulf fit into the right cranckcase and it had no bushing for the spring to fit over.

Now the shaft is turned down on the lathe, and a loose bush is made to fit over it, just as in the newer engines. so it fits in my old cases without altering them.

Shopping at the local Honda store

This evening I went shopping, the CB100 needed a new throttle slide for the handlebars, as the old one was pretty well worn. And then I allways think of other things I might need.
Like I want to put blinkers on my ss50 motorcycle, but don't have a switch for it. I have CB type switches on the bike, because of the normal throttle in combination with the clip-on bars. When browsing thru the CB50 parts at the shop I found an english style CB50 switch in new condition.

Although I don't really want to take it appart to use only the top half, I bought it anyway, maybe someone I know would be happy with it to use on their german CB50 as they don't have high/low switches.
Also in the CB50 bin, this nice SS50Zk1? switch with the separate on/off switch and (p-L-H) on top instead of (off-L-H), I know these were used on general export SS50Zk1's with the racing style seat. I just couldn't leave it, with this I can also have a parking light on one of my SS50's. Not because I need it, but just because it is possible.

Sunday, May 2, 2010

First event of the year

Last friday was the first event of this year, in Nieuw Vennep there was a section of industrial area where they created a track. In the morning we had some rain in training, but in the afternoon for the first heat the sun began to shine, with the second heat the track had almost completely dried up. I had to get used to the CB50 again, as this was the first ride since last season, but I've got the hang of it again. Some pictures with thanks to Lea Langezaal.

Me (75) chasing Cor on his sachs (57)

more pictures of this event found on the CRT website

Saturday, May 1, 2010

computer crash

Sadly I had a slight computer crash lately, so that was the reason there have been no updates. I have lost some of my files and some links to interesting pages. Now I am starting to get things up and running again, and updates are on the way, as the bikes haven't been sitting still. But if anyone has nice links, please send them so I can get my favorites filled up again.