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Author Topic: Roller rockers  (Read 46313 times)

Doug

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Re: Roller rockers
« Reply #15 on: July 27, 2006, 03:41:07 AM »
On the other hand the Alloy block BS motors goble up guides and bores....
Obviously it the material that counts as much as machining....

Doug

europachris

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Re: Roller rockers
« Reply #16 on: July 27, 2006, 12:21:29 PM »
I just restored a 1959 Gravely tractor with a proprietary Briggs side valve gas engine.   Plain iron guides and they were like new with no wear to speak of.  No lube but they're in enclosed tubes to keep out the dirt.

I thought Gravely made their own engines back then, before they switched to Kohlers?

They have that funny chain drive cooling fan and the oil system is shared with the transmission, right?

Great tractors.  I think they still make one model of the walk-behind, but they are fading fast.  No demand in today's throw-away society for a useful, multi-purpose, long lasting tool that you could will to your grandkids.

My father-in-law has a Simplicity walk-behind tractor that he purchased new back in the early 50's.  It's been through an engine and a lot of parts, but it still gets used every year for tilling the (large) garden.

Today we have the $800 Murray lawn tractor that might make 5 years before it hits the scrap-heap.......

Chris

Firebrick

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Re: Roller rockers
« Reply #17 on: July 27, 2006, 02:23:13 PM »
Not to rain on anyones parade but a roller rocker probably would be less durable here.  The pins on the rollers wear very fast if not made out of the right material and have excellent lubrication(the listers don't).  Once there is some wear the pins become a different radius(unless a brass pin is used but I would have reservations on using a brass pin that small)  than the roller and wear is accelerated.

Putting bearings on the shaft might not be a bad idea if they are packed with grease often.  Pads made of a high quality steel or coated as hotater mentioned would be the cats meow. An elephants foot type pad even better. 

Cujet, yes roller rockers/lifters reduce friction and stress in highly stressed application, ie large rocker ratios and steep/high lift cams or cams with a high face loading(stiff spring, small cam lobe).  In less stressed situations such as our listers the benefits are very negliable and they are in fact less reliable that the standard lifter/rocker arm.  Durability of rollers is much lower.
« Last Edit: July 27, 2006, 02:48:13 PM by Firebrick »

Andre Blanchard

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Re: Roller rockers
« Reply #18 on: July 27, 2006, 02:28:45 PM »
Has anyone fit a drip oiler for the rocker arms?
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cujet

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Re: Roller rockers
« Reply #19 on: July 27, 2006, 08:06:40 PM »
Well, I had been thinking about the huge valve lift numbers a listeroid has. Just that fact alone leads to geometric problems. I thing a well designed bearing at the tip would reduce valve and guide wear. I never considered a pin and roller tip, but rather a large surface area bearing. Lube should not be an issue with a sealed bearing. The skateboard bearing suggestion is interesting.

Chris
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snail

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Re: Roller rockers
« Reply #20 on: July 28, 2006, 10:58:24 AM »
Question from someone who hasn't got a clue... :D
   I was looking at a Lister A today ( that's a small version of a listerL, sidevalve petrol motor) and immediately noticed that the valves are deliberately offset from the lifters.On the L they're pretty much concentric (well, within 20 thou at a glance). What's the aim of the offset? Does it make the valves rotate? I presume there must be some advantage, because I can see the disadvantage of increased lifter wear and it must be worth the trade.Would the randomly offset rockers on my listeroid have the same effect?
   Come on guys (and Guy!) I need to be educated :)

Cheers,

Brian

BruceM

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Re: Roller rockers
« Reply #21 on: July 28, 2006, 02:38:56 PM »
Both my rocker pads initially contact the valve lash cap a 1/16" past the mid line, and then contact moves out further from center from there as the rocker pushed down on the valve cap.  If they are supposed to bear down directly on the valve lash caps, wiping through the center, I'm WAY off the right wiping pad profile/angle.  How does the DIY'er correct this??? Can I hand shape and polish the proper curve?

As crated, my rockers were way off center- so badly that based on George's CD I even ground down one rocker arm casting to move it closer to center, and put two washers inside the other to move it outboard.  I'm talking more than 3/16" off center. It's now "close" but not perfect.

So what is the straight scoop?  Was this huge offset an intentional way of getting valves to rotate? Or just another example of "de-value engineering" by Metro?

« Last Edit: July 28, 2006, 02:41:51 PM by BruceM »

GuyFawkes

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Re: Roller rockers
« Reply #22 on: July 28, 2006, 02:54:38 PM »
valves are held in place with collects and springs, the spring pressure is ALWAYS on the collet, and maximised when the rocker is compressing the spring, trying to rotate a valve with the rocker would mean trying to rotate the entire valve / spring assembly.

it is the compression and expansion of the springs that creates a very gradual rotation, more like creep than rotation, but it is there.
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cujet

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Re: Roller rockers
« Reply #23 on: July 28, 2006, 03:50:44 PM »
Bruce, Guy answered your question in a roundabout way. But the fact remains that the rocker should be centered on the valve in every way.

This is one of the goals of my roller rocker project. To make it hit the valve on center. I suppose I should make it adjustable to compensate for machining issues with diffrerent cylinder heads.

I like Hotaters idea of a stable rocker shaft mount. Couple that with roller tiped rockers and the valve guides may have a chance at long life.

In my mind, it is far easier to change roller tips on the rocker than valve guides.

So, what do you think guys, Billet aluminum?

Chris
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kyradawg

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Re: Roller rockers
« Reply #24 on: July 28, 2006, 04:47:20 PM »


Peace&Love :D, Darren
« Last Edit: August 03, 2006, 01:24:34 AM by kyradawg »

GuyFawkes

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Re: Roller rockers
« Reply #25 on: July 28, 2006, 05:59:05 PM »
The rocker pad should ONLY be centered on the valve tip at 50% lift.


err, no, unless you *want* to promote valve <> guide wear, and thus valve <> collet wear and eventually maybe drop a valve, the force, and therefore contact, should always be as near as possible to axial on the valve.

that's why the valve end of the rockers is a compound radius

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Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.

kyradawg

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Re: Roller rockers
« Reply #26 on: July 28, 2006, 06:55:17 PM »


Peace&Love :D, Darren
« Last Edit: August 03, 2006, 01:25:09 AM by kyradawg »

mobile_bob

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Re: Roller rockers
« Reply #27 on: July 28, 2006, 06:57:26 PM »
i myself would probably not use aluminum , because aluminum has a finite work life.

of course it may take years to fail, but aluminum will eventually fail. depending on proper engineering the piece will have a direct impact on how long it will last.

i like the idea of improving mounting of the rocker shaft, it needs to be rock solid, any wiggling means failure sooner than later.

i don't know whether or not i like the roller tip rocker idea, not sure it is really necessary.

Guy is correct in that the tip needs to have a compound curve, to get it to stay close to center of the valve stem. it also needs to be very well polished as it will have a wiping element as well as a rolling element to its action.

in practice tho most folks settle for the center at 50% lift with the rocker traversing from just outside center to just inside center, the goal is to get dead nuts on center thru the stroke.

there are many factors as i have posted before, valve stem height, rocker stand height and position, pushrod length, and cam lobe lift.
it is a series of comprimises to say the least.  probably best to actually lay it all out on a drafting table to arrive at the correct dimensions and placement of all components, or to trial fit and cycle thru the stroke taking incremental observations and plotting the results to any single change.

remember change only one thing at a time, and recheck, changeing two or more at once is asking for alot of mind numbing rethinking, rework, replotting and repeated steps with the same repeated results or worse results, and not knowing which change either helped or hindered the effort.

if you are intent upon using roller tips, be sure to use the proper brgs made for cam use, they have thicker outer races, which will be needed because of the valve clearance. the standard thin wall outer races that are meant to be supported will quickly fail (shatter) and cut up your valve caps.

i think before i would go to all the work designing a new valve rocker train i would learn from the original lister rocker end profile and try to duplicate what they engineered.

likely it could be done and the result would probably outlive anythng most of us are going to accomplish trying to reinvent the wheel.

bob g
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kyradawg

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Re: Roller rockers
« Reply #28 on: July 28, 2006, 07:26:18 PM »


Peace&Love :D, Darren
« Last Edit: August 03, 2006, 01:25:50 AM by kyradawg »

Andre Blanchard

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Re: Roller rockers
« Reply #29 on: July 28, 2006, 07:40:28 PM »
You guys do remember that these engines are running at 650RPM and have valve springs you can compress with your fingers.  :)
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