Unofficial Royal Enfield Community Forum
Royal Enfield Motorcycles => Bullet Electra & AVL => Topic started by: ace.cafe on February 02, 2014, 02:38:34 pm
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Here's a slow motion video of one cycle of a valve that has gotten out of control, and is bouncing off the seat when closed.
This is similar to what seems to happen in the AVL at that certain rpm around 5800 rpm, when the valve spring can't handle the harmonic surges and bounces, causing the engine to not be able to rev past that limit.
(http://vid163.photobucket.com/albums/t313/GrocMax/valvetrain videos/th_almost_tossing_rocker_zpse955b687.jpg) (http://s163.photobucket.com/albums/t313/GrocMax/valvetrain videos/?action=view¤t=almost_tossing_rocker_zpse955b687.mp4)
The S Cams have been found to have a profile that seems to not excite this harmonic reaction, at least enough to avoid it to the extent that the engine can rev past that rpm. However, it is my feeling that accessing any rpms above the spring's harmonic frequency is probably asking for a different valve spring. So, even with the S Cams, it wouldn't be a bad idea to put in some better valve springs with a higher 1st order harmonic frequency.
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Interesting clip of what can't be seen by the naked eye. Some pretty violent stuff goes on when valve bounce occurs, as you no doubt know, Ace. But for anyone who doesn't realise the implications, it can quite quickly rip the end of a valve right off, damage ridges on collets, which then let the valve stem slip through them, accelerate wear on ANY kind of valve seats and cause piston crown damage [even total destruction], as well as just limiting performance.
The AVL 500 [Electra X] suffers very badly, probably on both valves, but the inlet valve bounce is the one restricting the RPM's - I held one flat out [WOT] in neutral on the centre stand, at first believing there was a built in rev limiter somewhere. There wasn't :o :o On a dyno run, clouds of fuel mixture blowing back from the [open] end of the carb, accompanied by a very loud and hard version of a pinking [pinging] noise at around 5,800 RPM, made the penny drop very quickly. followed shortly afterwards by the inlet valve itself !!
A big bang will be on the cards sooner or later for anyone trying to rev much past 5,500 RPM on a standard engine because of this 'inbuilt feature' which prevents the full use of the porting, squish set up and pretty robust bottom ends that these machines are already blessed with.
B.W.
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Here's a slow motion video of one cycle of a valve that has gotten out of control, and is bouncing off the seat when closed.
This is similar to what seems to happen in the AVL at that certain rpm around 5800 rpm, when the valve spring can't handle the harmonic surges and bounces, causing the engine to not be able to rev past that limit.
The S Cams have been found to have a profile that seems to not excite this harmonic reaction, at least enough to avoid it to the extent that the engine can rev past that rpm. However, it is my feeling that accessing any rpms above the spring's harmonic frequency is probably asking for a different valve spring. So, even with the S Cams, it wouldn't be a bad idea to put in some better valve springs with a higher 1st order harmonic frequency.
Wow! How many FPS can that camera handle?
What's the speed on the ground in 5th at 5800?
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What's the speed on the ground in 5th at 5800?
Give or take a couple of MPH, about 100 MPH, a standard machine will not reach these revs in top gear, but will do so in the first three gears with ease.
B.W.
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Wow! How many FPS can that camera handle?
What's the speed on the ground in 5th at 5800?
I didn't do the video, but that engine was turning at 9250 rpm, and it's a Mitsubishi overhead cam engine. I read that the camera was synchronized to the engine, and was a very specialized high speed camera designed for slow motion work.
Tooseevee, we will be putting the beehive valve spring kit from the Fireball in your AVL head. No worries.
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Hm, 9250 rpm? Shouldn't worry most RE owners, though I don't like the idea of a dropped valve at 5500+
Next time the head is off, new valve collets recommended, guys...
Best an Electra-X can do on stock cams and gearing in 5th is mid to maybe high eighties mph.
A.
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It can happen at lower revs too, if the conditions are present to cause the valve spring to oscillate. It seems that that magic number is somewhere around 5500-5800 rpm in the stock AVL, according to those dyno charts that Bullet Whisperer posted a while back.
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I don't know where ACE got the video clip, but sometime back I had seen one with detailed view of valve bounce and rotation as visible from inside the engine, near the end of this video. Not an RE engine though.
- http://www.youtube.com/watch?v=_REQ1PUM0rY
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I don't know where ACE got the video clip, but sometime back I had seen one with detailed view of valve bounce and rotation as visible from inside the engine, near the end of this video. Not an RE engine though.
- http://www.youtube.com/watch?v=_REQ1PUM0rY
It can be other than just insufficient spring pressure. The harmonic frequency of the spring itself can be an issue. The 1st harmonic frequency of the valve spring needs to be above the redline rpm, preferably by quite a bit higher.
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Give or take a couple of MPH, about 100 MPH, a standard machine will not reach these revs in top gear, but will do so in the first three gears with ease.
B.W.
So going by that - Redlining an AVL might be disastrous ? I mean with the stock cams and stock top end setup?
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So going by that - Redlining an AVL might be disastrous ? I mean with the stock cams and stock top end setup?
Put simply - you would literally be 'asking for it'.
B.W.