Honda CB750 Clutch Slipping | Detailed Clutch Rebuild Guide | Cafe Racer Build | 34
After I finally got to ride my project cafe racer CB750 I found a few issues and what I thought was a misfire actually developed into very obvious clutch slip.
Things that I used:
Westway 10-40w Motorcycle specific oil: ebay.us/EIXt9U
EBC CB750 SOHC F2 Uprated Clutch Springs: ebay.us/gVrrFi
CB750 Type B Clutch Plate: www.ebay.co.uk/itm/265610210131
At first I noticed a change in engine note when riding a little faster, I did think it might be clutch slip but it was so inconsistent I wasn't sure. After I had put a few more miles on the bike, the fact that it was clutch slip became more and more obvious. To the point that the slip was so bad I could hardly set off. :) I knew that there may be a number of different issues, but the one thing I realised was that I hadn't adjusted the clutch at all, I had just accepted that it wasn't dragging.
Although the cable was adjusted correctly I hadn't adjust the release mechanism under the cover on the right hand side of the engine. This is where the cable pulls on a lever which then moves a mechanism that releases pressure on the clutch basket. The adjustment is quite simple, in that you have to back off a screw half a turn from fully home, and hold it there with a lock nut.
I suspected that the adjustment was too tight and this was causing the slip, but when I adjusted it, expecting to be able to go for a ride, it made no difference, so I knew I would have to inspect the clutch plates. The other faults there might be are mechanical failure of the releasemechanism that seemed unlikely, or worn or damaged clutch plates. Oh and there was another possibility, the oil I had used was not motorecyle specific. It was very simple car oil. One of the problems with using car oil in a motorcycle is that it can contaminate the wet clutch plates.
I have used mineral car oil in lots of similar bikes in the past, the wisdom being that the cheaper oils didn't have the adatives that affected the plates. I have never been caught out with this before, so I didn't expect to be now.
When I stripped the clutch I did find that the lift plate did have some damage, but nothing that would stop it working OK. I will replace it some time in the future, but new ones are very expensive for what they are, so I will wait until I find one at a swap meet. Apart from the lock washer not being properly fitted everything else seemed in good condition, in fact could almost be new.
The clutch springs where probably fine, but where longer than what I belive is standard, but this seems to be quite common. To ensure they weren't the problem I replaced the with heavier EBC springs, they are quite cheap so it seemed a sensible move, and I could be sure that they were the right ones for this engine.
I also noticed that the last clutch plate which should be B type with longer tangs on the outside was actuall just a standard plate. I bought a correct one to fit, but I do believe that the standard plate should just work fine, there doesn't seem to be any good information on the internet about what the outer plate does, just a lot of conflicting forum posts.
I cleaned all of the clutch plates with brake cleaner. They aren't like the old cork ones, so they don't really soak up a lot of oil. I had a bit of a scare when I removed the engine oil, as I could see lots of sparkles in the oil pan. But I checked some oil straight out of the oil filter and there wasn't any in that, so I realised it was probably the stuff that had come of the clutch plates when I cleaned them in the same oil pan, not emptying it before draining the oil. I am pretty sure about this but I will look at the next oil change.
I removed all of the oil, and have not used the correct 10-40 motorcycle specific oil, which mentions for use with wet clutches. I suspect that it is possible that they have started to add more of the clutch damaging addatives to the cheaper car oils now, and this has caught me out.
Having put it all back totether it now does seem to be working alright, but I won't be able to really tell until I ride the bike. Typically the weather has become very wet, so that wont be for a week or two.
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