Can I bend my rockers?

This "out of centre" issue is due to machine error, just a fraction of a degree from the correct machine postion[valve guide bore] will be enough to place the rocker/valve off alignment by 1-2 mm.
Side valve engines use out out centre alignment to impart a rotation effect on the follower,but the valve's dont turn, to get this to happen the valve spring would need to "slip" around, which is not possible due to frictional resittance. Norton rocker wear pattern on the valve end suggest's the valve is held in one position .

Diablouph said:

Re: Can I bend my rockers?

by splatt » Sat Apr 14, 2012 9:17 pm



concours wrote:Rockers (all engines, not just Norts) are purposely arranged off center to rotate the valves.

Good ole internet,full of bullshit

Click to expand...

I too thought that all valves were turned by the rocker (or whatever was hitting it). I learned it in auto shop. Of course, I also learned that soon there would be a way to start a car by just pushing a button. I was told that the valves had to move to keep the seat clean and mated to the valve.

I'm still waiting for that button on my '73.

Click to expand...

well here we have video of the valves rotating on a BMW S1000r which incidently have rockers bearing on the valves.

http://youtu.be/vcyT18qk8ls


http://youtu.be/nsa6kq-qqIE

fredful said:

Diablouph said:

Re: Can I bend my rockers?

by splatt » Sat Apr 14, 2012 9:17 pm



concours wrote:Rockers (all engines, not just Norts) are purposely arranged off center to rotate the valves.

Good ole internet,full of bullshit

Click to expand...

I too thought that all valves were turned by the rocker (or whatever was hitting it). I learned it in auto shop. Of course, I also learned that soon there would be a way to start a car by just pushing a button. I was told that the valves had to move to keep the seat clean and mated to the valve.

I'm still waiting for that button on my '73.

Click to expand...

well here we have video of the valves rotating on a BMW S1000r which incidently have rockers bearing on the valves.

http://youtu.be/vcyT18qk8ls


http://youtu.be/nsa6kq-qqIE

Click to expand...

BMW uses positive rotating valves with offset rockers. They use specially hardened collets which butt together before they clamp the valve stem leaving the valve free to turn. The two piece welded valve is also hardened to cut down on wear at the collet groove.

If the valves on that bike are replaced with one piece valves with non-hardened collet grooves [IE Black Diamond] then the collets need to be ground so they no longer butt together. Then they clamp the valve stem and mostly stop the valve from rotating. Jim

MFB said:

Rebuild reaching final stages now. Am on to the cylinder head, and wanting to centre the rockers on the valve tips. Some are a long way off centre. Not too happy with the spring washer thingies, thinking of making spacers instead, as per NOC notes. Said notes also talk of bending the rocker slightly. If this is possible it would simplify the arrangement of the spacers. But it sounds drastic. Has anyone done this?
Cheers
Martin

Click to expand...

Attempting to bend the cast rockers can be fraught with risk of premant damaging the rockers. :!:
They will have to be firstly annealed, then bent, then re-hardened as to what they were before.

Personally if I was you I would leave well alone and try and use the other method advised here, that is remove metal from the side face if necessary.

The rockers are a high grade tempered EN# steel that will tend to break rather than bend. I'd think some meat could be milled off one side of the rocker to allow it to center on stem then use spacers &/or thacker spring to keep it there. Would be educational if we learned what feature is wrong to cause this instant issue here. It they weren't so pretty and nice to ride they'd have a bounty on these Nortons.

I spoke with a friend and qualified engineer ~

The rockers arms themselves are made from EN25 and are heat treated so I would avoid trying to bend them or they will break or crack.

Click to expand...

An update to my rocker problem: the rockers are now centred over the valves. Of the four rockers, three were a long way off centre. The right hand inlet needed about 2mm ground from the boss to allow it to move outward, while the other two only needed to move inward, into the space vacated by the thackery washers. I provided location of the rockers with spacers, and set the cold clearances at zero (or very close to zero). That's rocker to head clearance, not rocker to valve.
My knowledge of this bike goes back to 1973, and I'm pretty sure the rockers had not been touched since it left the factory.

Regarding the material used in the rockers, silly me, my manual tells me they're made from EN33. I should have looked. This is a hardenable alloy steel similar to EN25 but without the corrosion resistant qualities of EN25, which the rockers obviously don't need.

While the rocker spindles were out, I noticed witness marks near the ends which indicated that the oilways from the head were partially blocked to varying degrees due to the fact that the slots at the ends of the spindles don't align with the oilways. The spindles can't be turned very much for improved alignment as the keeper plates won't allow it, so I ground a relief on each spindle where indicated to let the oil flow more freely. These reliefs also helped to positively identify which way the flat in the middle of the spindle was facing after it disappeared into the rocker during the installation process.
I would like to include photos. I have a hard copy of the instructions in front of me, and an album in photobucket, but I still struggle with any post - 1970s technology. Ha Ha.

Cheers
Martin