Topic: New clutch is slipping hard?

[Aceon]

Hey all, after my winter rebuild my bike (1977 CB750) was making a lot more power and finally starting to slip the clutch on WOT. The clutch likely had 40k+ miles on it so I decided it was time to install new friction plates, steel plates, and springs using this kit here:https://4into1.com/clutch-rebuild-set-honda-cb750f-1975-1978-cb750k-1976-1978/

I let the plates sit in new 10w-50 Valvoline conventional motorcycle oil for about 2 hours, then installed them in the bike, changed the oil and went for a test ride. The clutch lever is definitely harder to pull with the new springs, and the new clutch seemed to grip well, though slightly grabby in first. I drove around for a good 10 minutes with up to half-throttle acceleration that wasn't slipping the clutch. Everything was good, break in period has begun!

Then, the bike sat for a week and I took it out for a 30 minute drive today. The clutch was slipping HORRIBLY above 1/4 throttle and could barely do more than get me up to speed. Clutch performance improved as the bike warmed up, but still wouldn't take 1/2 throttle acceleration. I triple checked the clutch adjustment at the handle and at the adjustment nut and that made no improvement. In lower gears it would slip for a moment, then engage properly, then slip for another moment, then engage again - it was pretty weird.

I would really appreciate any input or suggestions you guys have on this situation. My only guess is that the plate stack is slightly thinner than before causing weak engagement. I also picked a very cheap clutch kit, I may just swap to the CycleX kit if this one doesn't work out.

[scottly]

Were your old parts worn out? Measure the thickness of the friction plates. 40K miles isn't that much for these bikes, unless they were all drag-strip launches. If the parts are in spec, you can try the 4-1 springs if they are stiffer, or shim the stock springs.

[HondaMan]

Switch to Bel-Ray EXL 4T Mineral oil, in 20w50 weight.
I had similar problems when I used Valvoline's "motorcycle" oil, 'twas quite the mess. It took about 100 miles for the Bel-Ray to wash out the Valvoline and make it grip right again. And, this clutch had nearly 58k miles on it when I did this, it's fine now at about 80k miles on it.

[M 750K6]

BelRay isn't as widely available in the UK. But an oil with JASO MA02 rating should be good for motorbike wet clutches.

[Jerry Rxman Griffin aka MuthaF'er]

Was a 2 hour soak long enough? Wet the surface only? Any real penetration? The rule of thumb I've always heard is overnight.

[Aceon]

I'v heard that newer clutches only need a few hours to penetrate, but I guess this isn't technically a new clutch at all. Do you think if I re-soak them, they could improve? I'll measure the old plates and try those with the new springs if they're in spec, the bike was pretty beat on when I bought it so I figured a new clutch wouldn't hurt.

Mark, I was previously using this Valvoline oil with the previous clutch and didn't experience slippage until the extra power was added so I would assume the new clutch should achieve equivalent performance, if not better with the same oil.

[scottly]

Check the adjustment down on the clutch cover. I adjust it so that there is 1-2mm freeplay when I push on the end of the lever with my finger, rather than tighten until resistance is felt, then back out a certain amount.
Also, I've used Valvoline motorcycle oil with no clutch issues in my 836cc motor that makes 70HP at the rear wheel.

[Don R]

 What he said ^.

[HondaMan]

Someone here has said Valvoline has a motorcycle oil that DOES work, but it isn't here in the local town where I live. I've loved Valvoline oil in my vehicles my whole life (still in my cars), but in the bikes it never has performed like the Castrols or the Bel-Rays I've used.

[Aceon]

Hey all, found the issue and I'm slowly learning to measure BEFORE installing things!

The new clutch pack is severely undersized and my old clutch pack is under spec as well.
If I remember correctly, correct early pack thickness is 1.460" and late model thickness is 1.560" (I have a late model K7)

My NEW clutch pack measures:
Total plate thickness: 0.961"
Total steel thickness: 0.473"
Total pack thickness: 1.434" (0.126" off spec, missing a steel)

My OLD clutch pack measured:
Total plate thickness: 0.946"
Total steel thickness: 0.581"
Total pack thickness: 1.527" (.033" off spec)

So that certainly explains the slipping! My question is this: the NEW plates seem a little undersized, they're about .137" each compared to the ideal .141" spec - do I need new plates? I can combine the new friction plates with the old steels to get up to 1.542" total thickness but that is still 0.018" below spec. Should I get a thicker clutch or go with the combination of plates I have? Thanks!

[Tracksnblades1]

Sorry to read about your 4 into 1 debacle…
That’s why Frank the Dragracer and most everyone runs OEM clutches…

[scottly]

The K7 clutch has a double steel plate, which accounts for the pack thickness discrepancy, and a deeper clutch basket to match. The new plate pack is only .015 thicker than the old pack, so that's not the issue. Try reusing the double steel plate. Also, the springs are different: IIRC the K7 springs are stiffer but shorter than the earlier springs.

[Aceon]

Now with the new plates combined with the old steels, I measure to almost exactly to spec at 1.55” but the bike won’t move when I pull the clutch in?? Even if I fully tighten the adjuster screw and pull the lever all the way in, I can barely move the bike. It seems too thick now, unless I installed something wrong. What gives??

Also, Scottly that seems reasonable. I’ll swap one of the steels for a double and report back in 30.

[scottly]

but the bike won’t move when I pull the clutch in?? Even if I fully tighten the adjuster screw and pull the lever all the way in, I can barely move the bike.

Did the kit come with new springs? If so, are they longer than the old ones? Use the old springs.

[Aceon]

In my wisdom, I threw out the original springs a while ago 

It’s getting late so I may not be thinking exactly straight but I’m stumped.
- The new clutch pack barely engaged with the new steels, plates, and springs (.093” thinner pack compared to the old one) and would not hold any sort of power.
- Reusing the old steels, the “new” clutch pack is only .015” larger than the old, original clutch pack, but now it won’t disengage?

I have no idea

[HondaMan]

When the total height is less than OEM height by 1mm (0.040") it is considered 'worn'. (In the different 750s the total height number varied 4 times, for the K0-K3, the (K4-6+F0-F1), the F2/3 and the K7/8. There was even a [largely non-documented] 'dual-spring-wire' clutch (like the one I had in my K2 with K1 engine when i got it new), and it only had 6 cork plates with a shorter basket.)
Whew...
The key to understanding which thickness is appropriate is the dual-steel 'slipper' plate, normally found as the 1st steel plate behind the top cork plate - which, BTW, has wider tabs on its outer fingers than do the other cork plates in all clutches with a dual-steel slipper plate.

If the dual-steel-sprung plate is removed in favor of a new clutch, the best way to make up stack height is to add another steel at the bottom of the stack, most of the time. This won't rattle. The best way in the 'spring-plate clutch' is to replace the first steel one with the 1979 GL1000 extra-thick back steel plate, if you can still get one. Then the rest of the clutch becomes like the K1-K3 version (7 corks), simpler overall.

The thing that concerns me a little here is: your new steel ones appear to be thinner than the OEM steel ones? Do they have the tiny divots on the plates that help hold oil in place, or are they simply smooth plates?

And, does the new clutch have 7 cork plates?

[Aceon]

Thanks for all the helpful info! To answer your questions, the new steel is the same height as the old ones, just without the extra thick plate - sorry if that was confusing. My new clutch pack included 7 friction discs and 6 steels. And no, unfortunately the new ones don’t have the dimples in them. If I’m understanding your solution correctly, I should be able to use the old steel plates but swap a new “normal” plate instead of the double-thick plate? That should result in about a .030” thinner stack than I just tested if my math is correct.

[scottly]

I did the opposite, where I robbed parts from a K7 clutch to rebuild a K1 clutch. I had to re-use 1 K1 friction disc, as the K7 outer disc had wider tabs that wouldn't fit into the K1 clutch basket, and I left out the K7 double steel disc. I used the shorter K7 springs, but I had to use .200" thick shims to make them work with the early clutch. I suspect that the longer springs from your early kit are getting compressed to the point of coil bind, which is why the clutch won't fully disengage.
EDIT: The shims were .075" thick, not .200".

[Aceon]

That could definitely be possible, I guess the thicker pack could exacerbate that issue. Do you know what the spring size is supposed to be on the K7? And do you guys have any recommendations on where to purchase a kit that might actually fit?

[scottly]

I've posted the specs on the springs somewhere here before, but it's been a long time. Here's a pic that shows the difference in height, with the early spring on the left. Since you don't have the original springs, maybe try using the most the most worn parts (which don't sound like were worn out of spec) with the new springs?

[Deltarider]

Switch to Bel-Ray EXL 4T Mineral oil, in 20w50 weight.

Bel-Ray must blend good oils. I remember a test carried out by a Dutch motor magazine. They tested several brands of the popular 10W-40 motorcyce oils in a standard and quite simple test of which I forgot the name. A lubed shaft was spinning in something adjustable and more and more pressure was exercised until the shaft seized. A gauge informed at what pressure a particular oil gave up. There was one oil that they did not succeed to make the shaft seize at all: the Bel-Ray EXP 10W-40. Would any of you know what the name of that test is? The test was done over 30 years ago.

[Aceon]

New Barnett spring are on order, I'll update once I try them out. In the meantime, any other insights to why a slightly undersized clutch pack won't disengage would be greatly appreciated!

[bryanj]

From what i read you assembled it with different parts to what you took out i.e. no thick steel plate.
You simply cant do that with Honda clutches and expect it to work

[HondaMan]

Switch to Bel-Ray EXL 4T Mineral oil, in 20w50 weight.

Bel-Ray must blend good oils. I remember a test carried out by a Dutch motor magazine. They tested several brands of the popular 10W-40 motorcyce oils in a standard and quite simple test of which I forgot the name. A lubed shaft was spinning in something adjustable and more and more pressure was exercised until the shaft seized. A gauge informed at what pressure a particular oil gave up. There was one oil that they did not succeed to make the shaft seize at all: the Bel-Ray EXP 10W-40. Would any of you know what the name of that test is? The test was done over 30 years ago.

There was a similar test that went 'on tour' here in the USA around the late 1980s: I worked in the oilfield then and we were looking for superior oils for the heavy-duty trucks we used. It showed any oil you wanted to try, and then showed oils with heavy amounts of ZDDP (which included the sponsor's oil brand). You could alter the force on the lever to increase/decrease the loading. This showed (then) that the Valvoline, the then-new Mobil 1 Synthetic, and the [old] Castrol XLR were superior. All those oils are gone now, though, except for one that beat all the others: AMSOIL. The funny part of this test was: it wasn't sponsored by AMSOIL!

I still have to say that the CB750 with the least amount of engine wear I've ever seen at 50k+ miles was one the owner had always run with AMSOIL. If I could get that same oil here, I'd use it: so far I've only found it in Wyoming.

[HondaMan]

New Barnett spring are on order, I'll update once I try them out. In the meantime, any other insights to why a slightly undersized clutch pack won't disengage would be greatly appreciated!

Disengagement depends largely on the whole clutch pack height. The lifter in the clutch cover only has a +/-2mm reach (4mm total range).