Topic: DIY Rocker Arm Shafts

[rosewood]

I thought I would share this as someone may find it helpful....

I'm in the final stages of putting my CB550 back together and found that my rocker arm shafts have a fair bit of scouring on them and also there is some play in the cover as holes have obviously worn due to the shafts rotating. This is the early version with 2 piece shaft in stead of the single pinned 1 piece found on later models.

The diameter of these shafts appeared to be nominal 12mm. I sourced some 150mm long 12mm ejector pins used in tool making. These are ground finished, Nitrided case hardened and designed for a running fit so slightly undersize of 12mm. At less than $20NZ ($22 USD) I thought I would take the gamble and see if I could replace the worn shafts with these ejector pins.

They fitted the rockers very nicely, slide on with a hardly any play. Instead of the 2 piece shaft design I decided to replace them with one long one as in the latter design. This would help keep everything aligned and hopefully reduce further wear of the rocker cover.

This is a hard material so I had to cut the to the approximate length (leaving a little extra) with a cut off wheel on an angle grinder. Then mount in the lathe and drill and tap the ends with an M6. Now that I could remove the shafts once assembled in the cover I faced them to get the correct length by test fitting. I've allowed for an extra O-ring to be installed on the end of the shaft to help with the shafts rotating.

Any way thought this may be useful for anyone with worn covers needing a quick fix.

Cheers
rosewood



 

[RAFster122s]

This may address the shaft issue and the wear on one shaft may reduce the ability for the longer shaft to tilt and further wear in the same manner, it would not be supported in the worn shaft area. This would transfer the load to the inboard shaft hole. The pressure from both rockers would
Still have the issue within the cover wear...just transfering the load.  The length of cutters to do two rocker shaft holes is still the limiting factor for bushing those holes.

That said, this is a nice solution for replacing the shafts...thanks for solving this part of the equation.

[754]

I think he means after they have been bushed.
Have not been able to inspect the housing but I suspect the following requirements,
The cover be positioned  straight up and down in relation to cam bores.
Then the spindle is moved over and centered accurately over  known GOOD rocker hole.
Then reverse cover and it may be the same distance, if not clock in, and note your coordinates, to get back to your former setting.
Then flip the cover and clamp, then go to other side of cam center, same amount as hole one and two.

 To add support between the holes , you may need guide bushings...this keeps things straight when entering egged holes.

 For tooling iI would use a end cutting reamer... Chucking reamer, morse taper may increase accuracy.
You can probably cut a good 32 nd of inch or more, if it does not clean up hole to 90%, may need another reamer run thru.
 Then you make your bushings.

 Thats all I got... Which wears more inner or outer holes.. ? The first one or two may be able to cut with an end mill.

[rosewood]

Gentlemen I haven't modified my cover at all to bush them. Mine weren't too bad only one outer hole there was a bit of play. These pins fitted the covers a bit more snug compared to the original pins. I'm not sure what the spec is for pins, covers, rockers in terms of diameters (not stated in the manual). If the outer holes wear the most/first I think you could get away with just bushing this one easily, that would more than likely sort my situation out I feel.

RAF I agree with you 100% about the inner holes taking more load. Since mine isn't too bad and not wanting to take the gamble and modify my cover in case in ends in the garbage I'm going to leave as is. I still feel this will overall help the situation for now.

[Smudgemo]

There is a really neat article in the Oct/Nov 2015 issue of Machinist's Workshop where the author installed bushings in the rockers of his '74 TR6.  There were not originally bushed and apparently wear because of it.  He also created a jig to resurface the shoes following the correct shape.  Another neat story was one in the Sept/Oct Issue of The Home Shop Machinist where the author made push rod ends for a 1929 Humbler motorcycle.  I found both articles to be fascinating. 

I still think the covers could be bushed to accept a one piece shaft using rosewood's ejector pins or something similar.  I sourced some '77 parts so I don't care right now, but I'm keeping my old one and may one day play around with it.  I've got a mill and lathe, and a guy ought to be able to build just about anything with them.

[754]

You need room on the mill, rocker box must be around 14 inches long, probably has to hang over side of table. Then you need room to slipba 9 inch reamer into a tool holder, and probably 6 inches of quill travel....if you have less room , way harder to get three shaft bores cut in one setup..
Can be tricky...your results may vary...

[70CB750]

Ha, ejector pins, that brings back memories.

Good job, sir;)

[rosewood]

I also think bushing these covers is an option...maybe with a specialized cutting tool if a standard end mill/reamer is not long enough.

I picked up a spare old head the other week that I'm reconditioning. I skimmed it on a manual mill at my work last week. You can see in the picture of the mill there is an additional horizontal head (plugged with a cloth). If the cover is fixed to the bed face down I think this head could be used to machine horizontally which makes setup a lot easier.

We also have a 5 axis CNC mill available. (I've just laid the cover on the vice as an example) but if the cover is mounted to the bed directly face down again the table could then be rotated 90deg and there should be ample room to machine these holes from a head travel perspective.

In terms of setup I am thinking a longer ejector pin could be inserted and this used to locate the centre of the holes, this would make clocking especially probing on the CNC a piece of cake.

Not something I plan to do anytime soon but this would be my approach.

rosewood...

[RAFster122s]

From what I understand the cutters are not long enough to reach the end of the 2nd rocker shaft from the end if you are cutting it from both ends in four holes. Having a cutter made that could is very expensive.

[craz1]

Its an old topic but I thought I would add the following.
Hi Rosewood, I enjoyed reading your post from 2016 about making you own rocker shafts. Im in the same boat with the restoration of my 74 CB550. I started to look at my 8 shafts closely and did find play. I located 3 long shafts but plan on making the 4th if I can't find another long shaft. I was looking at a Honda Civic shaft which I can cut down if its 12mm, looks to be. The intake holes had the most play ranging from .0015 to .004. the exhaust holes were pretty good with .0005 to .001 play. While replacing the short shafts would help I still was concerned that the shafts would be subject to some flexing without addressing that wear. I started to think about shimming the worn spots using shim material cut to size. I cut the material to slide past the edge and a bit before hitting the wear mark. Looks like the wear was typically on the top of the bores with little to no wear at the bottom. The length was cut to about a third of the circumference of the hole. While inserting the short shaft with the taper and positioning the shim I was able to slide the shaft all the way in and recheck play until I found to right shim. I was surprised that the shim stock stayed put and did not slid out while inserting the shaft, however when removing the shafts the shims popped up. Once I corrected each of the 8 holes I decided to try and glue them in place. I started with Loctite 680 retaining compound. Although this may have worked it would have taken to long to set so I tried just a dab of superglue. To my surprise the shims were held in place and did not spring back, even the .004 shim which is pretty stiff. I think the .004 shim would be about the thickest shim you could use and have it held in place.
Now the shaft slide in with a bit of resistance and the shims are captive in the bores. I don't think the shims will move but you never know. I also plan on using some set screws to keep the shaft from turning and will post this once I get the cover back from the Vapor blaster