About time for the spintron
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Nater_Potater
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toppy said:
Thus, the drive towards beehive springs. Since they taper across their entire length (or close to), there's very little amount of windings that can resonate together, so most of the crazy shockwaves running back and forth are dampened.
As for the stem flex; damn! How do they not snap off at the retainer grooves? You can really see it at 23 seconds just as the rocker unloads.
Jim, you state this is a stock cam with oversized valves; at 6:05, they look very close to crashing during overlap. Is this just the angle of the view, or are they really that close? If the latter, how would you be able to run a "hotter" cam without interference? It would seem that increasing either duration or lift would use up the tiny bit of space there.
Thanks for all your time invested in this! And on an antique Apple computer, no less.
Nathan
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toppy said:In the footage of the valves from above it is clear to see the stem appears to bend as it moves and not simply travel up and down. It seems visible but less pronounced when viewed from the combustion chamber.
Is this due to value guide clearance allowing the valve to rock or is it flexing due to the loading and geometry of the rocker arm?
If the rocker arm is the main cause then what could be done to improve things and so take stress off the valve?
Great footage i have never seen valve spring coils flexing before even at full lift which surprised me. I aalways thought that under full load the tension in the spring would not allow this to happen. Thanks for teaching me something new and something i will be sure to remember next time am giving my bike a good fistful of revs
It is definitely flex of the valve stem. The valve guide clearance was held to .001.
I would like to see some type of roller tip on the rocker.
The elephants foot adjuster didn't pan out to well the last time I tried them. Jim
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Nater_Potater said:
Actually the beehive spring has similar sized coils over 80% of it's length. It is only the top few turns that reduce in diameter. Since they have no damper, coil resonance has caused spring manufacturers to turn to a conical spring for high rpm use and are now recommending beehives for low rpm applications.
http://www.superchevy.com/how-to/engine ... the-coils/
You definitely have to consider valve overlap clearance when timing the intake and exhaust lobes. As the cam gets bigger you either need to increase the lobe to lobe separation angle or find a way to increase the intake to exhaust valve distance.
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Oh, The antique Apple monitor is only there because it happened to have a composite video input that worked to monitor the camera when getting it pointed in the right direction.
The big box is row after row of memory chips to record the camera's output. You could put all that memory in a micro sd chip today -but them it probably wouldn't still be around in 20 years. Jim
The big box is row after row of memory chips to record the camera's output. You could put all that memory in a micro sd chip today -but them it probably wouldn't still be around in 20 years. Jim
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Nice to see the factory valve train behaving as good as seen on way more modern engines which ALL also show stem flex - often more than this Norton. D/t my early P!! foolishness=fondness of bullet proof hi rpm - I unexpected found pre-peel Combat valve float onset trying to pass a semi in time, somewhere toward end of red zone - so grit your teeth and spintron closer to 8grand where the aggressive cams really pay off. My sense is the normal upgrade K/W springs & black diamond 7mm stock size valves is good for 10grand.
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What are you achieving when you raise the power band of a commando motor to get more power ? If you are building a race bike, it is the way the whole package works together that is important. The commando engine has an inbuilt rev limitation which is not associated with the valve train. So surely the answer to going faster lies in the torque profile and gearing, which must suit the handling characteristics of the bike ? It is easy to build something which is mentally exhausting and even painful to race. I spent most of my early racing life with a short stroke (63mm) 500cc Triumph engine in a featherbed frame. To get the high revs, the cams were extremely long duration, slow lift rate, moderate max. lift. The bike was interesting to race, however I'm still carrying injuries from it. I suggest that the commando motor is probably as good as a big vertical twin will ever be. The Laverda 750 motor has a better bottom end, however is too heavy.
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acotrel said:
The two engines I am working on right now are an ultra-short stroke 500cc twin built for a land speed trial and an ultra-short stroke 750 for roadracing on larger circuits.
The 500 owner hopes to be able to rev to 10,500 and I am hoping the 750 will make power up to 8500 or so. To make good power at those speeds the valve control needs to be good. Valves that bounce on the seat are not only damaging themselves but they are also wasting power. Jim
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Jim
a valve that visually bounces will be in serious trouble if running persists at that rpm. Obviously you intend to add instrumentation to your spintron so these things can be measured. I look forward to seeing and hearing of the spintron development, it's some undertaking thats for sure.
The issue of the bending valve stems is unfortunately one that cannot be completely eliminated when rocker actuation is used. A centered rocker end pad will centralise the rocker contact on the end of the valve stem, but there will still be a small side loading component present.
The conical valve spring is not new, but is now perhaps better understood for the benefits it brings to an installation. Progressive winding of the coils combined with wire of ovate cross section makes for a really remarkable spring.
Your development work on the short stroke engines is probably of great interest to many members. I suggest it warrants a thread to itself instead of being added to this present.
a valve that visually bounces will be in serious trouble if running persists at that rpm. Obviously you intend to add instrumentation to your spintron so these things can be measured. I look forward to seeing and hearing of the spintron development, it's some undertaking thats for sure.
The issue of the bending valve stems is unfortunately one that cannot be completely eliminated when rocker actuation is used. A centered rocker end pad will centralise the rocker contact on the end of the valve stem, but there will still be a small side loading component present.
The conical valve spring is not new, but is now perhaps better understood for the benefits it brings to an installation. Progressive winding of the coils combined with wire of ovate cross section makes for a really remarkable spring.
Your development work on the short stroke engines is probably of great interest to many members. I suggest it warrants a thread to itself instead of being added to this present.
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hobot said:
Steve,
Here is a repeat of the final test except at 8000 rpm. A little better lighting and better conversion software. You can see the valve hits the seat 3 times every time it closes. Definitely not good.
[video]https://youtu.be/KYEgnELuFzo[/video]
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Jim,
Would compression in the cylinder change the way the valve behaves? Would it stop the bounce? The dynamics of the test rig precludes heat suck and blow. Maybe my mind can't wrap around the slow motion time.
Tom
CNN
Would compression in the cylinder change the way the valve behaves? Would it stop the bounce? The dynamics of the test rig precludes heat suck and blow. Maybe my mind can't wrap around the slow motion time.
Tom
CNN
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What camshaft lifters are setup with the spintron?
Tom
CNN
Tom
CNN
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Jim,comnoz said:
If time allows, Try one component at a time to see where the money maker lies (Biggest bang for the Buck). e.g. pushrod / rocker type / spring type or cam type. Or a total package of all the right stuff.
This is a great post. I wish to be a fly on the wall in your shop right about now. :mrgreen:
Thanks for making this happen.
Cheers,
Thomas
CNN
Fast Eddie
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CanukNortonNut said:
It's not usually that simple when it comes to fine tuning IMHO. The synergy effect of a group of changes can be very worthwhile whereas individual elements hardly register when looked at in isolation.
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I will not disagree with you Fast Eddie but it would be interesting to record the dynamics of the pushrod behaviour with a stock flat lifter to one with a 3 or 4" radius. Or comparing the BSA type lifter style, or between 2 pushrod materials etc. Lightening the valve train is the way to control valve float at the limits of racing this engine. There are lots of ways to skin a cat. 8) I was kind of interested if Jim could show the Pushrods in action at 7500 to 8500 RPM. I think it was Peter Williams that noted some issues with stock pushrods. I can't find where I read that...a... long... time... ago.
Cheers,
Tom
CNN
Cheers,
Tom
CNN
Fast Eddie
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CanukNortonNut said:
And I ain't gonna argue with you either Tom, understanding what actually goes on with some of the key / common mods would indeed 'add to the body of knowledge' ...
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