W/NG rocker box - clearence?

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david.anderson
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Re: W/NG rocker box - clearence?

Postby david.anderson » Tue Nov 17, 2015 8:35 am

Knud
If you remove the adjustment screw and tighten the acorn nut, the shaft will lock the rocker arms solid. The adjustment screw is there to stop the shaft from being pulled through and locking the rocker arms, and to set the end clearance for the rocker arms. When the end clearance is set and the acorn nut is tightened it holds the shaft in place. The shaft could also be made with a large boss on the end to replace the screw. The acorn nut could then be used to pull the shaft up against the rocker box, but there would be no way to adjust the end clearance of the rocker arms (except for possibly shims between the boss and the rocker box).
Have a look at the last photo posted by Alan. He has set the shaft to provide the correct end clearance on the rocker arms. The shaft is recessed into the box in the photo. If the screw were set to pull the shaft closer to the end of the rocker box, the end clearance on the rocker arm would be excessive.

When it comes to oiling, the rocker shaft is not drilled through from one end to the other. The oil way drilling stops at about half the length of the shaft. The only oil to come out would be minimal seepage around the outer circumference of the shaft.
David

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alan.moore
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Re: W/NG rocker box - clearence?

Postby alan.moore » Tue Nov 17, 2015 5:49 pm

David....well in the nicest way I respectfully disagree ;) that tightening the acorn nuts first locks the rocker arm solid. Or should I say that in my case I fully tightened the acorn nuts without the 'adjustment screw' being in place, and I still had 6 thou clearance on both shafts. This is the method described in the owners manual which states the cap (your adjustment screw) is only there to seal the end of the shaft.

It appears to me that the assembly is designed so that the shoulder on the end of the centre section of the spindle (the machined part the rocker arm rotates on) is pulled up tight against the distance washer when you fully tighten the acorn nut. This clamps the washer between the shaft and the casting boss. The manufacturing tolerances of the shaft, rocker arm and distance washer provide the necessary clearance and the shaft is then rigidly located laterally.

If you pull the spindle across / locate it by screwing in the end cap first you create a gap between the spindle and the distance washer but the shaft and washer are no longer clamped in position against the casting boss. Whilst it is true that this will provide clearance it means that the spindle is now secured and located laterally by the end cap which itself clamps against a less than solid fibre washer. I would have thought in engineering terms this is less than desirable compared with the very rigid assembly when you fully tighten the acorn nuts first and clamp the spindle against the boss.

There will of course be cases where the tolerances result in the rocker arm binding (although with the later setup there appears to be so much clearance that it is hard to see that setup causing the rocker arm to bind.) With the earlier setup, as Nev says, you can then take a thou or so off the ends of the rocker arm to get the required clearance.

The introduction of the altered spindle and spring suggests that there were problems with the earlier setup..although it had been deemed OK for the previous 10 years. Manufacturers do not normally alter components without a reason. Was the tooling for machining the faces of the bosses in the boxes getting worn? who knows. Whatever the issue a simple fix was to shorten spindle shoulder and add the spring which would allow for greater tolerances in the components.

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Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
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Re: W/NG rocker box - clearence?

Postby nevhunter » Wed Nov 18, 2015 12:09 am

The length of ground spindle section that the rocker pivots on will determine the end float where that is the method used. All rockers appear to be the same size. The actual thickness of the washer would only position the adjuster on the valve hardened cap, where I would not recommend anything but on centre. If you want to spin valves there are better ways of doing it. I suggest always tighten the acorn nut (with a spacer for convenience) to check end float as it may pull up a bit more than you expect. Solid washers are always better than a spring as a spring has more friction and is not a positive stop anyhow. It's probably used to quieten the mechanism the easy way. Unless you are racing, or fussy it's not critical anyhow. I have been running fixed washers and have no detectable noises from that area, on all bikes I have run Nev

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Re: W/NG rocker box - clearence?

Postby david.anderson » Wed Nov 18, 2015 7:51 am

Alan
One of my earliest experiences with a VH was to tighten the acorn nut before I tightened the screw at the other end. I then kicked the engine over and had no compression. After removing the rocker box inspection cap the exhaust valve did not appear to be opening. Then after some fiddling I realised the valve was held open. There was inadequate end clearance for the rocker arms. The cam had forced the arm to open the valve but the valve spring was not strong enough to close the valve against the shaft binding.
So after your experience of .006” end clearance I decided to do some measuring up. Clearly there are differences due to manufacturing tolerances or wear. Depending on the shaft and rocker arm that are mated the end clearance could be satisfactory or could bind.
David
IMG_0469.JPG

IMG_0474.JPG

IMG_0475.JPG

so you can see there is .010 difference in these 3 shafts

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Re: W/NG rocker box - clearence?

Postby david.anderson » Wed Nov 18, 2015 7:57 am

IMG_0478.JPG

IMG_0476.JPG

there is only .002" between these 2 rocker arms. But they will both only operate without binding with one shaft above.
David

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Re: W/NG rocker box - clearence?

Postby alan.moore » Wed Nov 18, 2015 5:28 pm

Maybe someone has access to the origional drawings and knows what the original machining dimensions / tolerances were. I read that most of the singles drawings were saved the day before that part of the factory was pulled down...they must be out there somewhere.
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
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