SOHC.co.uk Forums > CB500/550
Partially Restored 74 CB550
davidcumbria:
Have done this now and thought I’d record a few comments based on my experience and forum research.
I used a bulb in series with the points with a loose battery to determine the opening point since the loom is not in place yet, as seen in Millyard video. Problem was my test bub was too high a wattage and I ended up partially melting the insulation washer at the contact feed. Good job I had bought some nos FEW brand breakers on eBay. These are Japanese made and seem well constructed - better than the ones I took out. They seem to be used as oem by Suzuki and Kawasaki. Anyway lesson learned and I used a 2W bulb after that with no problem.
When I set the points gap to 0.35mm with new points ( ie middle of the 0.3 to 0.4MM, 12 to 16 thou range ) I ran out of timing adjustment. Have since learned this was probably due to the base plate having some slop in its mountings which can be eliminated by shimming the mount with a piece of sacrificial feeler gauge or by lightly tapping the mounting flanges inward. Otherwise as I found getting the timing and gap in range is a hit and miss affair as the back plate moves when tightened down. There is also some sideways slop in the 2/3 mini backplate. Good maxim is points gap affects timing - timing doesn’t affect points gap. I got there in the end by sufficient random efforts but not happy that my points gap ended up at the top end of the range.
Points gap sets dwell ( the angular duration that the points are closed to charge the primary coil) and so ideally gap is as small as possible. It’s arguably not so critical on sohc points set up because the dwell is already very generous compared with say a V8. I have now bought a Gunson auto ranger analogue dwell meter which are reckoned to be better than the newer digital ones. . The theoretical correct setting is 23- 24 degrees on 8 cylinder meter setting ( wasted spark issue ) but because of tolerances between points/ back plates / cams it is more important is get the dwell on both sets of points the same, and to dynamically check timing at the same time. Once set with new points you can just keep readjusting back to this point on the meter as the contacts and cam heel wear. Full advance is when the ll mark lines up and should be at 2500 rpm.
This a very good read.
https://motorcycleproject.com/text/sohcign.html
I’ll report back on the dynamic set up when I get the bike running which shouldn’t be too long now. Wrestled the headers on for my 4into one yesterday - why weren’t we born with 3 hands !
Oddjob:
Many many moons ago I bought a Gunson Dwell meter for a car I was tuning. Like Mike Nixon I decided the best way to setup the Dwell on my 500 was to fit a new set of points, gap them as good as I could, using TEC points, then see what the Dwell read on the meter. As it turned out it was 48 iirc, not wanting to forget this I scribed it onto the meters face plate, I have since found out that the official Dwell angle listed by Honda was 50 degrees for the 500, so I was very close.
In hindsight what I should have done was retest the setting using the Honda equipment when I had access to it in the trade but tbh the bike ran great at 48 degrees and was the same engine that would tick over at 5-600 rpm. Interesting to read Mike saying no more than 1100 rpm for timing when some members are advising setting the tick over at 1200 rpm, I always followed the Honda setting of 1000 rpm as the optimum setting. Faster tick overs just disguise engine faults in my experience, not saying you shouldn’t do this btw, better to have the engine ticking over smoothly than banging it’s nuts off, just as long as you are aware of the faults like a slack primary chain and get round to fixing it before it really becomes a problem.
McCabe-Thiele (Ted):
Interesting read Dave - only thing I would mention is a higher idle speed will increase flow to the camshaft.
Seabeowner:
Just to add the owners manual for the 500s and 550K3 both specify setting for points gap at 0.3-0.4mm. I wonder what the dwell variation is between 0.3 and 0.4.
And the two cam assemblies numbers for Hitachi and Toyo are the same for 500 and 550K3, so you would think the dwell is the same.
It's on page 181 of my manual and Honda are capable of making one or two or three mistakes.
Oddjob:
500k3 or all 500s though Seabeowner? The coils are the same as well I'd imagine, in fact there are a great deal of the same parts fitted to both the K3 and the 550F2, however the intake system was completely different, the fuel air ratio was different, the K3 was made to fit into environmental policies in force at the time, the 500 and 550Fs weren't. I tend to ignore the 500K3 as it's like a unicorn, if you see one you are lucky.
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