Eye Candy Rocker Arms

Dances with Shrapnel said:

Anyone have first hand experience with (or know of someone) breaking/bending a rocker?

Pulled the head on the 500 Norton a few weeks back to find the two exhaust valves hit the pistons due to a sheared timing pinion key; valves were bent but pistons fine. Rockers were lightened (not insanely) and no damage. Interesting thing (in a strange way) is that the rocker spindles actually bent. These are the older scrolled type rocker spindles with a necked down center diameter.

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I've had broken rocker arms on a Rotax and on a Yamaha, but never on a Norton. To be fair, they ran at 8500 to 9000 rpm, and I don't normally rev the Nortons anywhere near that. I suspect the Norton rockers are plenty sturdy if not lightened excessively.

Ken

We've taken whittled down rockers to 10,500 with the 500 Norton and they regularly see 9,500 with extra heavy race springs and aggresive cam. Never broke a Norton rocker.

We did break a custom aluminum rocker with roller tips. Slick little set ups and will likely revist the roller tip concept when time permits.

I believe the dural nuts and allen key tappet adjuster is the cats pajamas if you want to drop critical mass where it counts.

Judicious use of a grinder in and around the ends and not getting the piece too hot should be the key guidance for do it yourselfers.

Below are two pictures showing aluminum rockers we initially used in the 500 Norton ultra short stroke. All work was by Herb Becker. The rockers are from billet with needle roller bearings on the spindles. Adjustment for valve lash is through eccentric rocker spindles.





These were run up to 10,000 rpm regularly with racing springs and MegaCycle D Grind cam. Ultimately one of them broke after a few race weekends.

Lessons learned:

Great for reduction of friction and loading of the valve stems.
Very springy as we tested it for stiffness compared to a lightened Norton cast steel rocker. I suspect our valve timing really lagged at high RPM.

Still viable but needs more design work. Maybe use steel rockers with roller tips.

Thanks for sharing the pics, John. Those really qualify as eye candy.

Ken

Yes, I agree.
eccentric spindles - cool!

Son of a Glockenspiel!! Those are beautiful, I'm not up on the race stuf can you explain to me how the eccentric spindles work??

If you look closely, the main length of the rocker spindle is ground eccentric to the ends. When in place, you rotate the rocker spindle through the slotted end which will raise or lower the rocker. This is how you get the adjustment.

Thanks, I thought that's how that worked. What locks them in place so they don't turn?

The head of the rocker spindle with the slot shoulders up against the head. The end plates are rather beefy aluminum with a circular recess bored in them which is a tad shallower than the thickness of the of the spindle head. You loosley snug the end plate bolts, make the final adjustment to the rocker spindle for valve clearance and then torque down the end plate bolts in order to clamp the head of the spindle. May not be the best mechanical way but I don't recall any problems with it. The HDXR750's us 7/16" and 1/2" spidle lock nuts but I am not intimately knowledgeable about how they work.

Note the groove beneath the head of the rocker spindle. This groove receives an o-ring which fits into the stock rocker spindle bore and creates the seal. The diameter of the spindle beneath the head is near stock. The far end of the spindle is reduced. Not shown are small bronze bushings which fit over the ends and have an OD near that of stock rocker spindles.

hobot said:

The real danger of grinding on sides is there is an oil passage near the surface, if broken into new rockers are like $80-90 each, so the ebay seller lost out a lot on that sale.

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I saw today that Andover's price is about $90, and Nutty Norvil is a lot more.

You are probably right Hobot about the guy on Ebay losing out. If new rockers are going for say $360 a set, then used ones ought to be worth half that. So if that guy spent an 8 hour work day @ $20/hr grinding, filing and polishing those rockers he should have at least got what a new set cost, but at $165 for his parts and labor he worked for nothing, which is probably why I have not seen another set of them pop up on Ebay for sale.

If someone did as nice job on a set of good used rockers as the ones at the start of the thread, they would have to be worth $400, which judging from the Ebay sale no one is willing to pay at this point in time, so for now the only people with lightened and polished or shot-peened rocker arms are going to be those who do the work themselves......

Aw shucks guys and gals, grinding the rockers is about the most high tech real hot rod builder feeling task ya can do to make the push rod puzzle a thing of the past, just don't take much off the very sides [I don't know which sides the oil passage goes down but in one sides exhaust rocker : ( ] All's ya need is bench grinder and sand paper and buffer wheel and steady hand for about useless rpm benefit covered up eye candy. I spend some more time after photo to take out the rest of the surface impressions seen here, just for show. Btw every time a stone point was resharpened - napped, they got a bit thinner till they just broke, but don't ya know there were ooh and ahh's around campfire oggleing each others lightness risking to bring home a meal or not.

hobot said:

useless rpm benefit covered up eye candy.

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Yep, really not necessary with a stock stroke Norton, even race prepped. This is based on what we "got away with" in terms of shorter stroke Norton rpm's

lcrken said:

I had the head off my 750 AHRMA racer, and the rocker arms are so pretty I thought I'd post some pictures. These were lightened and shot peened by Bob Gorsuch, now retired, at Excello Plating, long since closed. I suspect you get the same funtionality out of just lightening the lumps at the ends, but these are so good looking that I'd probably have more of them done if Bob was still around.

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I found a 1975 price list from Reg Pridmore showing a nice photo of the lightened rocker arms he was selling then, they look similar to the job done on yours. They were lightened, polished, shot peened and had a little logo of his on them. He sold them for $139.00 a set then, and according to inflation calculated from the Consumer Price index that amount of 1975 dollars is equivalent to $614.00 dollars today.

Pashaw why bother if that's all they take off and not even where it even matters at all, off the very ends - but nicer looking than factory - so yep appropriate to the subject line, covered up decoration appearance issue.