Topic: Ross’s 1975 CB750 K5

[BenelliSEI]

I took it out this morning.  Clutch seems fine now.

Great! “Don’t fix what isn’t broke”.

[Galactica]

Ok.  So I’ve ridden the bike about 300 miles.  Today my grandson had a baseball game that I attended.  When I left my garage, cold engine, I noticed a slight shudder as I engaged the clutch.  Hmmm.  I stopped and started again. No issue, so I went to the game.  All seemed fine until I approached the parking lot.  Leaving a stop sign, a pretty significant shudder upon clutch engagement.  Damn.  On the way home it occurred again with an accompanying significant rattle, which could have been the engine complaining about it.  I’ve not felt this kind of shudder anytime in the past. 

Should I just go ahead and replace the plates, discs, and springs?  Are the parts at Vintage CB750 good quality?  I guess I’ll need the special tool as well. 

Please chime in.

Cheers,
Ross

[newday777]

Ross
Before you jump and order parts, get a definitive diagnosis. Wait for answers.
I don't remember how deep you went into the motor on this project.
Did you get into the bottom end at all? Did you have the transmission cover off and inspect the shifter pivots, ie the allenhead screw on the end of the shift drum, it is a flat head screw, conical back into the big washer to be sure it is tight?
Did you adjust the clutch at the clutch cover as per the manual?
What oil do you have in it?

[newday777]

I had the pleasure of having The Lone Builder, Sean, stop over on his trip last week and he was having trouble with his K4 with clutch (he thought), had to adjust it a lot in the past 1500 miles. We put it on the lift, pulled the clutch and inspected it, totally within spec.
Andy750 piped up of having had similar issues on his going up a mountain over in Austria. Ended up the Allenhead screw kept coming loose. The screw was staked by the factory. Andy said to put locktite on the threads and tighten it was the fix.
Pull your transmission cover off and inspect the screw that it is tight. If you have had the cover off, the gasket should be OK to use again, if it doesn't tear apart.

[Galactica]

Ya, thanks Stu.  Absolutely right about jumping to a conclusion without proper diagnosis. 

It’s a little after 4:00am now.  Couldn’t sleep.  It happens when things are bubbling in the back of my brain.  I woke up about 3:00.  Thinking about it.  The more I think about it, I don’t think it’s the clutch. 

Stu, I didn’t get into the motor/transmission at all.  It feels more like it’s jumping out of gear.  Nine or 10 years ago I did up a KZ1000 LTD.  Did a rebore and head rebuild.  Put it all together assuming the transmission was good.  Not so.  As soon as I applied throttle on in second gear, it chattered and chunked.  Can’t remember which gears, but the dogs were worn where 1st & 4th gears meshed.  Managed to find some better gears and reassembled.  Then it was jumping out of third gear.  Fixed that and had a fantastic bike.

It’s hard to remember exactly what that chatter felt like.  It was 9 or 10 years ago.  And in 2016 I had a near fatal motorcycle crash and have lost much of my memory.  At least I’m still on the green side of the grass.

But to answer your questions.  The previous owner said all was good, and I had no reason to disbelieve him, so I didn’t get into the motor/transmission at all.  I’m running 15W40 Shell Rotella oil. I’ve done the clutch adjustment, screw all way in and back out 1/4 turn (with some more fine adjustments). 

I think it’s unlikely I’d get the transmission cover off without tearing the gasket.  This motor has never been touched.

[Galactica]

Also, I’m wondering if what you call the transmission cover gasket, is also called the shift cover gasket?

For the price of a gasket, it’s worth checking.

[newday777]

Get a Trans cover gasket and inspect it.
Sean's was hard shifting on him and hard to find neutral.
Do you hear noises in the transmission cover when on the centerstand, running, and shifting the gears? Hondaman says he has found a few of the K4 motors he's worked on with that screw loose, it could be in the K5s also as it is also staked the same way on my K5 836 motor I have on the motor stand.

[newday777]

Also, I’m wondering if what you call the transmission cover gasket, is also called the shift cover gasket?

It is where the shift lever is, but it is called the transmission cover. Here's the part number.

[Galactica]

No untoward sounds or running issues until this.  Just what is, I believe, the normal rattle that goes away when you pull in the clutch lever.

[newday777]

On the parts fiche with the Starter Motor

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750KA_(76)_750_FOUR%2c_JPN%2c_VIN%23_CB750-2540001_TO_CB750-2575894/STARTER_MOTOR/b3d05c73-22e7-4620-b018-132301d96b6e/b0bdb415-e315-4116-b18a-1391dc15b076/y

[Galactica]

I’ll order a gasket from somewhere and check it out. 

[newday777]

No untoward sounds or running issues until this.  Just what is, I believe, the normal rattle that goes away when you pull in the clutch lever.

You need to get close to hear any noises, even a screwdriver held to your ear or mechanic's stethoscope.

[Galactica]

Cover gasket ordered from Honda.  We’ve a long weekend coming up so it likely won’t arrive until end of next week.  In the next while, I’ll put the bike on the lift and give it a good listen. 

[Galactica]

So having the gasket on order, I decided to open up the transmission cover.  Mine is a #3 cross head.  Tight as can be.  Dang.  Now I’m thinking the worst.  Splitting cases and sourcing transmissions/parts. 

[newday777]

So having the gasket on order, I decided to open up the transmission cover.  Mine is a #3 cross head.  Tight as can be.  Dang.  Now I’m thinking the worst.  Splitting cases and sourcing transmissions/parts.

🤔

[Galactica]

So I got parts today from VINTAGECB750 in Ontario.  I had to wait for the special tool to remove the centre nut. 

I dismantled the clutch and measured the discs and plates.  They were all right on original spec.   The inexpensive (cheap Chinese crap) friction discs are barely within spec thickness and the friction material is much narrower than the original.  So I cleaned and sanded the plates with 600 grit paper, cleaned and oiled the friction discs, and reassembled it all.  The I measured the springs, they were well within spec, but the new ones were a bit taller, so I put them in.  Only 300 miles on the oil but I changed it as well. 

I ran the bike up and down the lane and all seems well.  We’ll see how it goes over time.  I’m confident that the clutch is fine.

[RAFster122s]

Sounds like you need to put better clutch disc friction plates in the bike, as it is a matter of short period of time before you will have to do the clutch again...

As far as the cross point screws go....
You are using JIS screwdrivers and driver bits, right? Amazon has inexpensive Vessel set of screwdrivers for $20. Won't help your needs for impact but but Motion Pro sells pairs of replacement bits for 1/4" hex drives that are affordable. #3, #2, and #1.
If you have the hammer impact driver then pick up a set of Vessel impact driver bits that fit the larger hex off eBay.
You can sometimes get away with #3 Philips on a JIS#3 but if you slip it is gonna bugger up the head...

[newday777]

So I got parts today from VINTAGECB750 in Ontario.  I had to wait for the special tool to remove the centre nut. 

I dismantled the clutch and measured the discs and plates.  They were all right on original spec.   The inexpensive (cheap Chinese crap) friction discs are barely within spec thickness and the friction material is much narrower than the original.  So I cleaned and sanded the plates with 600 grit paper, cleaned and oiled the friction discs, and reassembled it all.  The I measured the springs, they were well within spec, but the new ones were a bit taller, so I put them in.  Only 300 miles on the oil but I changed it as well. 

I ran the bike up and down the lane and all seems well.  We’ll see how it goes over time.  I’m confident that the clutch is fine.

So the friction discs from Vintage750 were different dimensions from the original?

When you pulled the clutch apart to inspect it were the friction discs wet with oil or dry?
My thought reading through your thread again this morning was that they may have been dry from inactivity that caused the shudders you were experiencing?

[Galactica]

Yes, the friction discs from Vintage aren’t near the quality of the originals.  The friction material is narrower (less surface contact area).  The channels in the friction material are directly opposite each other, not staggered like the originals.  And although the thickness is within spec, they’re thinner than the originals. 

The springs seem ok.  I used the new ones.  Had the bike out for the regular Wednesday BCCMC (British Columbia Classic Motorcycle Club) coffee.  Everything seemed fine, but it was pretty cold (9C) and wet, although it had stopped raining.  We’ll see how it goes when the weather gets hotter. 

Ya, personally I’d only use those particular friction discs if I had no other option.  I’m sure they’d work well enough, but I think the originals are much better.  There may well be other aftermarket options out there, but I didn’t look for them.  I think maybe EBC does some.

The discs did seem wet with oil when I dismantled them.

[Galactica]

Here’s an update.  The bike is running really, really well.  I get plenty of thumbs up as I ride along.  Doesn’t seem to be consuming any oil.

I’ve finally gotten around to getting a match for modern paint.  The closest I could see, bearing in mind that I ordered my paint from VMR, is Ford B3, Atlas Blue. 

Cheers,
Ross

[newday777]

Here’s an update.  The bike is running really, really well.  I get plenty of thumbs up as I ride along.  Doesn’t seem to be consuming any oil.

I’ve finally gotten around to getting a match for modern paint.  The closest I could see, bearing in mind that I ordered my paint from VMR, is Ford B3, Atlas Blue. 

Cheers,
Ross

Is that Ford blue the Planet Blue match?

[Galactica]

Ya, that’s the match. 

[Galactica]

So, at coffee last Wednesday we were talking charging systems.  A friend of mine is having issues with the charging on her ‘81 CB650C.  It brought to mind the system on my CB750. 

The system on my CB750 has a separate rectifier and regulator.  What I’ve found on the interweb is that my bike charges at 12.4v@2,000rpm, 13.2v@3,000rpm, and 14.5v@4,000rpm.  That jives with my own checks.  So essentially it’s not charging at idle.  Given that it’s charging as it should from the factory, and I’ve had zero starting issues, is there any advantage to installing a new integrated reg/rec unit?  ie, would it charge better at lower rpm?

[scottly]

is there any advantage to installing a new integrated reg/rec unit?  ie, would it charge better at lower rpm?

No, it will not charge better at lower RPM.

[Galactica]

Awesome, good to know, thanks.  Electrickery is something I simply cannot grasp.  When working on wiring, I try to always have a can of electrical wire smoke on hand to refill the system.