Topic: Rocker arm theory discussion

[754]

For CB750, was thinking..
 If they could investment cast from Ti, and the rocker pads get hardfaced.. There would be a substantial weight reduction.. And there may even be a market for them..
 Any thoughts ?

[kmb69]

Great idea if you can figure out how to do it. You get it figured out and it is probably patentable.

Couple of serious technical issues to solve.
1. Investment cast Ti will not be strong enough. Got to use machined billet bar or plate. Expensive.
2. Not easy welding non-Ti material to Ti. Probably require Electron Beam welding if possible at all.
3. I don't think you can apply a hard coating thick enough to wear any length of time.
    There are some special slippery coatings for Ti but I don't think they would stand up to the cam pressure.
4. Titanium is a very complex material regarding its grain structure and is not very notch resistant.

We machine a lot of Beta-C Ti and it requires a lubricant be applied just to check hardness.
Other wise it will stick to the diamond tip in the hardness tester and break the diamond.
Other Ti grades are not that fussy but they all have there idiosyncrasies.

Like I said, great idea, but you better put a serious engineering cap on to figure this out.

[Retro Rocket]

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[754]

How about forged? Maybe roller rocker?

[Retro Rocket]

How about forged? Maybe roller rocker?

Didn't someone make roller rockers for these in the  70's..? I'm sure I heard something like that..?  Billet Ti roller rockers........Mmmmmmmmmm

[turboguzzi]

if ducati stick to steel + DLC rockers in their mega $ GP racers, i 'd say its not worth doing....
Ti's fretting resistance is really bad.
rollers will require totally different cam geometries too
nice discussion but are you sure rocker mass is what limits rpm in a 750?

[johno]

While the chat is on rocker arms, my experience is the single biggest restriction I found to a major jump in HP was the rocker arm ratio, standard 1: 1  and you just cant physically fit in more cam , say .500 lift to take advantage of decent improved heads, It will take a ratio of 1.2 or something to get the big lift and open doors.

I didnt spend a lot of time on it but I started looking at different models, later models etc but with out success.
My conclusion was after the salt bikes finished I am planning to machine up rockers , with rollers , use a custom ducati based cam, custom cam bearings and mount from billet, change the valve angle in the guide only by couple degrees and shoot for .500 lift.    That would open the door for big cams like my raised port and mikes hi rise floor to take advantage of the big flows at 500.

Thats a winter project , right now I am struggling with the heat at 45c  or 118F every single day this week, tough in the shed,        time for a beer

[70CB750]

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[MRieck]

Like johno said...I'd look at the ratio first (like car rocker arms)

[kmb69]

Frank, et.al.,

This is actually something I have spent quite a bit of time thinking about. The best solution I could come up with was a roller system and like Turboguzzi says, would require completely different cam geometry. By the time you hang a roller of sufficient diameter on the end, I don't know if there would be any weight reduction but likely would have less friction. Maybe if the ratios were changed as mentioned previously, the spring would have more levereage to return the roller weight. The rocker would have to be longer on the spring side. That also gets the higher lift ratio that Johno wants. Might require a valve stem cap or a larger diameter adjusting screw to stay on top of the valve with the extra motion. Haven't laid that out to know for sure.

Pretty sure the roller rockers from some years back just had roller bearings for the pivot shaft. Not a true roller rocker as we are discussing here.

The ideal trick, I think, would be to figure out how to weld a hardface on Ti. Generally the Ti base will develop stress cracks when a dissimilar material is welded to it because the thermal conductivity, expansion, and contraction rates are significantly different between Ti and hardface materials. Like I said before, Ti is funny stuff and easily galls as well. It would definitely require a bearing/bushing for the pivot shaft.

[754]

Tis complex for sure,be easy if you could reliably spray or electroplated the hard surface.
 For perspective though, I think the rocker set in Ti would cost  800-1200 bux
Now if that meant special cam and cam/rockerarm cradles the billet blocks start looking cheap..

[Don R]

 Comp cams sells a chevy rocker that has a smaller moment of inertia than an aluminum rocker and it's made of chrome moly, I had them in my 383 dragster engine. Isky has fancy new lifters that use an axle for a roller pivot rather than a needle bearing. I took out stud rockers after a series of failures and installed T&D rockers on a shaft with the adjusters on the end of the valve.
 It's funny how the newest latest and best car rocker designs seem to resemble stock CB750 parts!

[754]

The following pic is of a roller rocker made in the 70, and 80,s.....pre CNC days. (for Big Twin H-D)
The company's name was Strocieck, I think they're in Illinois probably Chicago . I think he was a toolmaker..

Now I believe he offered them for CB 750,s,but that does not mean they were actually produced in numbers,  but I do believe some one did make some.

 They are roller tip and needle bearing pivots on shaft, I assume that would be a full roller rocker.

[Don R]

 Could a person cnc some new cam holders and relocate the pivot point? Would moving the contact point on the cam  end of the lifter change the ratio? Creative hardwelding?


 Johno has apparently given this some thought.

[scottly]

The stock Honda rocker is a variable ratio, due to the way the cam lobe sweeps across the rocker face with an asymmetrical lobe; it's not the same as a push-rod rocker with a fixed contact point.

[Don R]

The stock Honda rocker is a variable ratio, due to the way the cam lobe sweeps across the rocker face with an asymmetrical lobe; it's not the same as a push-rod rocker with a fixed contact point.

True, when I was  rotating my Kenny Harmon F cam to degree it I noticed there are spots where the cam turns but the valve  lift stays in one place.

[Old Scrambler]

Very interesting discussion......................I think the target has to be defined: something near standard motor size would benefit from higher RPM at standard arm ratios for the shortest movement. My plan is to reduce the combined weight of each combined arm, adjuster, retainer, spring, and valve by a total of 23 to 27 grams (just short of an ounce).

When going for a big-bore, I like the idea of changing the angle of the valve by moving the smaller exhaust valve away from the intake to avoid clearance issues for oversized units. This would require a slight angle to the seat. If the arms were welded and re-tapped at a very slight bias to the cam-side, as well as at a very slight angle, the adjuster contact to the valve stem could possibly be better aligned to avoid lash-caps. I believer the slight angle could be polished level on the contact pad to the cam. 

The following is a 1919 Midwest Engine as installed in our family tractor, a 1925 Allis-Chalmers 15-25. The suspended rockers are a 2 to 1 bias. That's my brother, Roger, in Ackworth, Ga.     

 https://www.youtube.com/watch?v=gZy2LH4fbb0&feature=plcp