Topic: Clutch Hub modification posts

[HondaMan]

Several of you asked me for pix of "how to modify the clutch for smoother action and longer life". I'll attempt to show something here (I haven't posted pix here before, hope this works)...   

Below is a picture of the oiling holes in the "recessed" area of the hub splines, like the ones you want to add to your hub. These are the original "inner" holes, as Honda called them. Please note, this hub has not been modified yet.

Modified 2/6/06: can't seem to get the pictures to show, so here's a link to it at Snapfish.

http://www.snapfish.com/slideshow/AlbumID=36832905/PictureID=1068037281/a=44049126_44049126/t_=44049126

This next image showed both an "inner" and an "outer" hole set: don't add "outers" to your hub, at the "top" of the teeth. This weakens the hub a bit where the plates engage the center.

[-- This link did not work. If I find somewhere else or some other way to post these, I'll try them again.]

The hub you see here is from a 135 HP CB750, so the marks from the clutch plates are quite pronounced. It ran a stock Honda clutch with stock oil holes, which gave short life.

If you look around your hub, you will see "sets" of oiling holes, alternating 1-hole and 2-hole patterns. They also alternate "inner" and "outer" around the hub. Again, don't add "outer" holes, as this weakens the tooth in the hub. Estimate an "in-between position" from the existing hole locations, then drill 1/8" holes. Add as Honda did, 2-after1 and 1-after2. I typically add about 50% more holes than the stock hub had: different year models varied these holes, with the K8 having the most. (My K2 had 12 holes stock, now has 18 holes.) Also, bevel (some call it "countersink") the holes, all of them, on the inside of the hub. This improves oil flow and is the only "official" modification that Honda would approve, because they were so afraid of warranty issues with heavy-handed American riders.

[Sam Green Racing]

Nice red crosses HondaMan,    only taking the piss, I cant post pics as well 

Sam.

[jaknight]

   I want to thank you for the time and efforts you have put into this HondaMan, but sadly, I can't get any photos to pull up in your posting.

   I do appreciate your efforts; I hope you will hang tight (or is it hang loose?) and keep giving it the old college try............

   ~ ~ ~ jaknight ~ ~ ~

[supersport_CB400F]

pic  here # 2 is an incomplete addy

http://www.snapfish.com/slideshow/AlbumID=36832905/PictureID=1068037281/a=44049126_44049126/t_=44049126

http://www.snapfish.com/slideshow/AlbumID=36832905/PictureID=1068037283/t_=44049126/a=44049126

[newcbguy]

did anyone ever find out how to post that other picture? I am curious as to a fix for the quick clutch engagement. I dont however see any holes in the part that is shown in the first pic. Were those holes factory after '71?

[HondaMan]

Let me try again. I have a different pix program, now.
The first one is the stock upper and lower hole picture, the second shows one of the added holes, right in the center of the picture: there's 3 holes, left-to-right, hidden in the gunk.

[HondaMan]

Are the extra holes added along the whole length of the inner hub ? Would that equalize the oiling to all the plates or weaken the basket?
 DG

The general idea is to add 2 more oil holes, somewhere in between each pair of factory oil holes. You want to put these new holes down in the grooves, like in the picture#2 above, so it doesn't weaken the hub where it holds against the plate teeth. One easy method is to find those stock holes, down in the grooves, where there is only 1 hole, and it is off to one side or the other, then add a new hole in that same groove, opposite the first one (after K2, all of the groove holes were already paired this way, you'll have to use another groove...). Then, you'll have 2 holes in that groove. Overall, add 6-8 holes (8 for stock engines, 6 if you've hopped it up with cam, big-bore, etc.). Remember to bevel the new hole (and all the others, while you're at it) on the inside of the hub. Some of the stock hubs came this way, as it was a Service Bulletin for all the Fours at one point, around the introduction of the 750K2, but it had already stopped happening by the time the K3 came out. The K3 made considerably less HP than the K0/K1, so I guess Honda thought the cost savings of not beveling the holes was justified. It's not an easy thing to do: it requires a small countersink or shortened 1/4" drill bit and some patience, but it's worth every second you'll spend on it! 

[newcbguy]

Where would you start if your clutch does not have any of these holes?

[HondaMan]

Where would you start if your clutch does not have any of these holes?

Your clutch does have holes in the hub: that's how the plates get oiled. The holes are pretty small in stock hubs, and sometimes get blocked up with crud. Boy, is that hard on clutch plates!

[newcbguy]

Here is the hub that I am referencing because the one I'm using is on the bike. This one is off a KO bike. but I dont see any holes? I also scratched in the grooves with a brass needle to be sure. 

[newcbguy]

so whats the deal, do I have a super special rare, one off clutch hub made for the first sandcast or something?

[HondaMan]

so whats the deal, do I have a super special rare, one off clutch hub made for the first sandcast or something?

  Well, I have to say this: I've never seen one of those on a K0 before... 
Maybe we should get 754 or one of those others who has rebuilt a number of early K0s and see what they say about it? I've worked inside some K0s, but they were mostly from the non-sandcast era, as they were too hard to get, for most of us, until the K1 era.

Is/was your clutch "sudden" and "grabby", especially when hot? This whole business of adding oil holes was borne of Honda Racing techs to me, 'way back when...and, it fixed a LOT of 750s in those days.

[754]

I will try to get some Part # info for tommorow nite..

What is the engine # that the hub came out of?/

interesting..

[newcbguy]

I havent ever used this part it was pullled from a motor that I believed to be a k0 because it had the cable pull carbs on it. The motor number is 1010513. I pulled the clutch to get that backer plate with the 4 little bolts because I stripped mine. So I just happen to have had a clutch pulled when I came across this post. I cant remember if the one I'm using now has them or not. I dont remember them when I inspected the clutch, but I wasnt looking for them then.  I do have a clutch that releases late and quickly, and wanted to make it smoother, more gradual. I dont have a problem with it slipping though.

thanks for the help! I might just wait till the next oil change and take the clutch out and have a look.

[KRONUS0100]

hey guys.  what size are these holes supposed to be?  I installed a oem type clutch from our local parts store in my 76F.  it is adjusted properly according to the book, but still seems to be a touch grabby when the bike is hot, to the point it wants to lurch and squeal unless i find nuetral quick. (this is when sitting at stops). I do not remember seeing these holes when i instaled the clutch.....the basket is out of my original 76F and fitted to the new K2 motor...that was an interesting whoops....baskets vary slightly. Thanks...Matt

[HondaMan]

In American sizes, a 3/32" is about right. Don't forget the bevel.

[754]

Checked the book, they list a number ending in 010, then superseded by 020.. but do not show the serial # for when the change occured.

So we do know this they still ran the undrilled type at ser # 10,500..which should be a Oct or Nov 69 bike as far as I can tell.

[newcbguy]

So there is no harm to be done by drilling these holes if they aren't there I assume. Does it matter as far as placement on the inward spline? I see that I should alternate between 1 and 2 holes and end up with about 12-18 total correct? I dont mind breaking out the drill press, but dont want mine to blow apart or anything.

[Bodi]

Well, if you're adding 6 holes with one hole between each pair in the original, that's either 12 or 18 holes total (depending on whether there are 6 separate pairs or if you go between each of 6 existing holes). So if you have zero holes, make 12 or 18 new ones - I would tend towards 12 personally. Try to space them evenly, the tiny holes shouldn't affect balance much but trying to balance them won't hurt. I don't have a hub here but I would count the grooves and try to make a pattern to match the available spaces.
The point about bevelling is vital. When you drill from the outside you will get a clean hole on the outside but a raised sharp edged hole on the inside. Assuming your drill bit is sahrp, that is... a dull one will leave a mess on both sides. For really nice clean holes use a small bit first (1/16?) and then drill it again with the final size drill. Regardless, you will have a burr on the inside. Use a larger drill or countersink tool as HM says to make a beveled "funnel" on the inside end of the hole. When the clutch is spinning the oil coming from the shaft is flung out and flows around the inside of the inner hub, the layer is quite thin and any burr will prevent it from going into your hole. The countersink funnel catches much more oil than the plain hole would and improves oiling a lot.

[754]

I would not drill that early one...if it were mine

Get a later one and fly at it, someone will insist on an early one down the line & they are not going to make more of them..

Bet they are less than 25 for a drilled one on ebay, or get a whole clutch including the center part that always breaks.

[newcbguy]

yeah thats what I'm thinking 754. I will wait till next oil change and take the one I'm running out to take a look.  Wish I had thought of this post before I changed the oil last week 

[754]

Shoudnt matter about the oil change..

I bet if you started watching whole clutches on ebay, you may luck out and get one with Barnett plates in it.. at any rate dont hurt to have a spare..

[crazypj]

I have been adding oil holes since early 70's.
 I started adding holes because I thought it would improve cooling, only added them next to the internal ribs so oil would collect and be centrifuged through hub (all new sport bikes come from factory like this)
 I think its most important in the 'center' of clutch as thats where the plates run hotter
I've seen hundreds of CB750 hubs without any holes at all in them (and almost all the smaller engined street bikes)
 I'll see if I can get some pics
PJ

[newcbguy]

well I finally got into the clutch in my bike and it does have the oil holes, 12 to be exact. I went ahead and counter sunk the ones I could get to but didn't add any more. Clutch seems to work the same if not a little better.

[DWS]

Does drilling of the clutch work for the CB 78F3?
just got back from a 205 mile run and half way though the ride my 4th gear popped out a couple of times and it is now harder to get in neutral.
Will this help my problem?