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Myles Raymond
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#304143 03/21/10 12:57 am
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I was looking in on another thread that strayed slightly from the topic , went from cams to offset rocker buttons and wanting to hear more on this topic while attempting to prevent a total hijack of that thread I figured I'd post here .

Soo anyway , does anyone with practical experience with these have any info/tips/tricks they might like to pass on ? I have to admit that I dont have much of a head for cams and angles and things so I would appreciate if you could break it down to rookie level.From what I sorta "gather" the idea of these things is to change the rocker geometry in order to change the powerband in the engine?? I seem to recall seeing thios done with car engines and H-D's , had no idea anything like this was available for a Britbike. What are the advantages and disadvantagews of this mod? I would have to "assume" you would be giving up some reliability due to wear with the added stress? Would this be advisable as a mod for a daily rider ?

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Offset buttons were for moving the pushrod in/out from the rocker shaft. A quick fix rather than grinding a new cam. Moving it in gives more duration and lift. The change is usually small.
If you want more power, displacement is easiest, then porting, compression, valve sizes, timing port lengths, et cetera.

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Bonzo, I understand the offset buttons will give you about .025" more lift, everything else being equal, this should equate to a bit better midrange without detracting elsewhere. I would guess the leverage ratio change would put a little more load on pushrods, followers and cam but I don't think significantly. I've never tried them, just went to bigger cams but they are expensive now and take splitting the cases...offset buttons are easy to change and change back...Mark

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I've used offset rocker buttons in conjunction with stock Triumph 3134 profile cams with no problems and with moderate increase in performance.

As others have already said, the effect is to increase the lift slightly.

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I have them in my 883 A65 I have big valves and ports, with std cam profile obviously it was lacking in lift, because fitting them moved the power peak up about 1000RPM and gave 7-10 extra HP. It could probably benifit from more lift but is reliable like this, though it rarely sees more than 7,000 because of the 89mm stroke. It is recommended that you don't use heavy racing type valve springs with them. In a high reving shorter stroke engine I'd have a preference to do it with a higher lift cam and better than std springs.


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This is getting interesting . I have a "project" in the works with a SRM big bore kit and a H&C roadracing cam and have been told the cam might be a bit more than I wanna deal with on a streetbike so the thought of these offsets was appealing but if I am reading this correctly Mark is saying the cam would be the way to go ona a standard stroke A-65?Probably should look into something more streetable? The project engine is all disassembled at the moment and it would suck to split the cases again if the cam doesn't work out .

Thanks , this is something to thionk about -BONZO

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Sorry guys.. but to change the rocker ratio.. well you need to change the rockers to ones with more ratio. Moving the pivot point may be desirable to correct rocker geometry and reduce valve guide wear.. but moving the rocker inboard just moves the tip of the rocker tip (or adjusting bolt) towards the inside of the valve stem. Any gain in lift is hardly worth it.. maybe a few thou but no where near 0.025"

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Don't know alot about buttons but do know in the near future im going to play with a set,Guys have been using them for years but I hear they do load the rocker arms a bit more.%00 tri always had that nice feture to remove the cams with out slitting the cases. Makes me wonder why im not running it:)


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Ron, the rocker buttons move the point where the pushrods contact the rocker closer to the pivot, thereby increasing rocker ratio...and lift. The stock BSA sport cam for unit twins has .347" and .341 lift for intake and exhaust. The stock rocker ratio is 1.1:1 (I don't have the exact numbers on hand, but I believe the offsets were about 1.25" and 1.375"), giving .381" of lift at the valve for inlet and .375 for exhaust. If you install MAP offset rocker buttons, it moves the pushrod .060" closer to the rocker shaft and the rocker ratio changes to 1.16:1, giving you about .401" lift for inlet and .395" for exhaust. Not huge, but I can see it making a fair amount of difference. The added benefit is that you don't have to clearance the cases or the tappet block for a higher lift cam.


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Alex, if those buttons go in to the rocker box, then it changes very little. I suggest you get out your dial indicator and measure it... moving the rocker most likely just robs Peter to pay Paul... the contact point on the valve gets moved the same amount.. and the only thing it will accomplish for sure is faster wearing guides.. Making new rockers is the correct way to get ratio...

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Still don't think you got the picture yet Ron. The button is the ball end that the pushrod fits onto that is pressed into the rocker arm. Offset ones press into the same hole in the arm but the ball is offset from the hole centre so can be possitioned to be closer to the pivot giving a little more lift. With them mine now has .410" valve lift. It would be interesting to see what more lift again did to HP as it made quite a difference with just that little bit, so another .020" or .040" may liberate more power, though it doesn't really need it, and the guides would need to be shorter only by .040" I guess? Maybe next time I get a cam done, I do want to build a new 750 engine I can just swap over at some stage with a ballancemaster ring in the flywheel.


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Ya I didn't commment much on it because I didn't have concete numbers but alex's numbers sound spot on,It works Ron but yes it can put a load on some other parts.


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And yes they can be installed the other way round and change what might be a motor with little torque to one that would pull harder at a lower rpm.

Great to have three sets of rocker boxes, with buttons in the three positions, when trying to get a bike to hook up on the dirt.

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Howed you know im biulding a dirt tracker:)


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OK, I thought they went some how on to the rocker shaft... sorry.. my mistake... (I guess they should be more descriptively called off set push rod buttons...). yes then they do indeed change the rocker ratio... and yes they will need a bit more valve spring to offset the accelleration of the valve. I suspect what you want, is a SMALLER cam with the ratio and you should get more power everywhere... well almost your valve lift is still puny...Hmmm... need to see what they look like... wonder if I can make them (or something like them) to fit a Goldie... heh.. any pictures..??

Cheers..!

Ron

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Yes, thanks for the tip John... makes sense. Hope to have my 500 dirttracker motor finished soon too. If I could just break away from the vintage singles for a while! Too much fun!!


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I used the buttons years and years ago when our bikes were almost new.

It was an easy way to get extra valve lift without splitting the cases, actual hp increase unknown as I sure didn't have access to a dyno then. "seemed" to be good.

If one has access to the cams of your choice and the patience to install them, then IMO the buttons have no use. Adding lift to a race cam, you better know what you're doing.
Buttons and stock cam no problem.

The buttons looked just a bit fragile to me, there is no need for heavy valve springs with the buttons and stock cams. Heavy springs will be dysfunctional in that case.
Don't install them backwards as they will fit that way and have the reverse effect. The button goes toward the rocker shaft.

They were manufactured by Alloy-Tech of Tuscola, Illinois.
They haven't had them available for many years. Are they actually available anyplace?

>>steve

Last edited by SBoyd; 03/25/10 2:49 am.

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I got some from Ed V.
Hey Ron what lift do the valves have in the gold star? And what Dia valves? I'm using 44.5 and 39mm in the twin, and theory would suggest they would work better with more lift.


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I have them on the intake in my old racer. Always made getting the pushrods and rocker box in place a little harder. They worked okay, that little more lift is worth a little more flow at full lift. I have couple of sets I could spare if some wants to try them.

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Kieth, I'd like to try those out on a 750 kitted Bonnie I'm building with a 5-speed.

PM sent.


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Originally Posted by Mark Parker
I got some from Ed V.
Hey Ron what lift do the valves have in the gold star? And what Dia valves? I'm using 44.5 and 39mm in the twin, and theory would suggest they would work better with more lift.


Hi Mark.. A stock Goldie has 0.442" intake lift and 0.400" exhaust lift. Valve sizes in inches are 1.775" inake and 1.560" exhaust. If you look at today's NASCAR or many car engines you could almost say there is no such thing as too much lift. Lots of race car engines are now running up well over an inch lift... If you can increase lift without duration, then you will most likely find more power everywhere...

Cheers..!!

Ron

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Thanks Ron, 1.775" is about 45mm so if I could manage an extra .030" lift when ever I do another cam it may be a worth while thing. A cam giving .050" extra over std at the valve with std buttons would probably be best and is still not that radical on valve gear and guides.


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Be aware, though, Mark, that an extra .050" of lift also requires you to clearance the cases on an A65. Once done, though, it makes a BIG difference, particularly in concert with a flowed head...at least that was my experience.


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Isn't .060" the minimum clearance piston to valve, so isn't extra clearance to the pistons what you mean? (or maybe the pushrods would contact now?) That could be a problem on high compression pistons. Clay, reassembly, etc.

Just bunging in the offset buttons on a nonstock motor could be costly.
I would think a good trade off wear wise would be to also invest in the R &D springs and lighter collars, and lighter valves if available and reliable. How much lighter, titanium or aluminum is up to your finances :>

Does MAP make these offset rocker buttons now currently, and how much?

Also the mushroom rocker adjusters?


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Think that they are still listed in their catalogue. I bought some from them but was about 6 years ago....

MAP recommends them in only combination with standard cams and says that they should not be used with high lift (racing) cams.

HTH

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