Re: I need a new clutch
Posted by shinyribs on Jul 04, 2012; 4:35am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/I-need-a-new-clutch-tp4023610p4024323.html
RE: a clutch on a '76F others models may apply.I'm not sure which.
These are not my words,but info kindly given to me by someone else:
That clutch consists of 6 "square-cut" fiber plates, one "slant-cut" slip plate, 5 steel plates and a double-stacked spring steel plate to allow the whole pack to slip, using the "slipper plate", if you launch too hard. The reason: the first gear is quite tall, and the dogs on gears 1 and 2 (gear # C5 in particular) tend to chip off under heavy clutch action, causing loss of the L shift fork and the C5-C2 gears. This is long history of rhte post-1975 engines.
The fixes:
1. Get the gearset back-cut by APE. This resolves the tendency of the gears to push each other apart and damage things when under heavy throttle.
2. Lose the double-spring plate in the clutch, and the slanted-cork plate. Add one more steel plate in its place, and install all square-cut cork plates. Although Honda's are pricey, they are also the longest-lasting under all conditions, including racing, in my experience - with one caveat: use Barnett springs on those plates. And be sure to EVENLY tighten the retainer plate (each bolt 1 turn at a time - seriously) when installing/loosening, or you'll be buying another one...
3. DON'T use 10w[something] oils, and DON'T use high-detergent oils. Both will make the plates slip and burn the cork. Use at least 15w40 diesel oils (dragracing) or 20w50 motorcycle or Racing oils (longer races) for good results, as these all have lower detergent. Consider using a zinc additive, too, as this raises oil pressure, increases cam lobe lubrication, and makes the clutch plates break friction quickly and grab evenly when engaged. Most oils after 2002 have almost no zinc in them (thanks to the EPA and a crooked politician, but I digress...).
That "slipper plate" is the one where the cork looks like a pinwheel. The longer groove between the corks causes the oil to take a longer time to exit the plate surface after you "drop the hammer" all the way, so it gives a fraction of a second of slip before final engagement. This was thought to be a 'shock absorber' of sorts (and it really is such) that would help with the fast wear of the 1 & 2 gears on the post-1975 bikes (F0 and later) with the close-ratio gearboxes. It only helped a little, though: today we see many, many more of these later bikes with the C2-C5 (2nd gear) dogs and slots badly worn, as compared to the earlier bikes. It was probably just a little bit too tall...
In the later years, Honda added sometimes whole clutches made of these plates (and some modern sportbikes are like this), for more cushion. It makes a noticeable lack of snap when dropping the clutch quickly. Some magazines of the 1970s era complained about how sudden the Honda 750 clutch engaged: this also played a part in the change. The hub could not fit more than 7 plates without changing the engine cases, which then would protrude into the rider's foot, so adding the squishy dual-spring steel plate(s) and the slip plate became their solution.
On the CB500, almost all the bikes came with ALL slanted "slipper" plates. These bikes frustrated their owners (I was one of those, as was my brother) when racing on production tracks, because you could never get a good, hard shift. We swapped to the square-cut plates, while some folks tried the Barnetts: this was where we discovered the Honda square-cut plates with Barnett springs were king.
If you get plates from your local Honda shop (pricey, but good quality), be sure to pay for them AFTER they show up, if they have to order them. Their parts system got mixed up in California for a while, and Honda was shipping slant-cut slipper plates as stock plates. I got 2 expensive sets of these, and it took me 5 years to use them up, one at a time... :-\
BTW: I just discovered today that the so-called "Barnett springs" from APE are much too long to fit the CB750 clutch. Looks like a misapplication: don't get them there...
Yes, I think the slipper ones are slightly bigger OD. They came from the CX500 design (NR500, really). But, you can just drop a standard plate in its place. I would suggest inspecting the dual-steel spring plate closely to make sure none of the little rivets have worked loose. Sometimes they do, and this can make a noisy clutch rattle sound, especially in neutral. If loose, try tapping them tighter on their crimped side with a small hammer and rounded-end punch, or ground off large nail (round off the point) to set the rivet(s) a little tighter. Or, if you can locate one of the GL1000 (1978-79) replacement clutch plate for this one, which was an unsprung, thicker steel plate (one piece), it will also stop the noise and will also add a solid lockup to the clutch. The tiny springs in that dual plate are part of the delayed-grab design.
You might also find an old trick will work to add an extra friction plate overall: reverse the order of the first plate into the stack, making it steel instead of cork. Then, install the cork/steel/cork...stack, using only single-steel plates, losing the squishy one altogether. This can allow room for one extra cork plate overall. Not all of the hubs will fit this: the late K3 thru K5 hubs did, and the F2/3 hubs did, IIRC. I haven't done this in a long time..