marlintec Posted September 20, 2004 Report Share Posted September 20, 2004 Thanks Nigel, I didn't catch it. About reliability, sure we won't know anything until the first year of use. I would like to know more on these bikes. Technically, I mean. Cheers, JM. Quote Link to comment Share on other sites More sharing options...
its a kinda magic Posted September 21, 2004 Report Share Posted September 21, 2004 i heard the sherco's dies after a few sections of continus riding, bit like the 2-stroke! Quote Link to comment Share on other sites More sharing options...
the artist formerly known as ish Posted September 21, 2004 Report Share Posted September 21, 2004 As you can see Marlintec, we have a lot of school kids who share their new found knowledge with us on TC, shame one had to make a mess of your post on comparison of the two fourstrokes, but my kids scribble all over their books too. I have a question for you, on the Sherco cam it looks like roller rockers , I was told that this type of system follows the cam better and allows for a steeper cam lobe, also less floating of valves at high rpm, I know at high rpm on my old four strokes you could get the misfire and popping, I find topics like this interesting and would like to learn more. Quote Link to comment Share on other sites More sharing options...
marlintec Posted September 21, 2004 Report Share Posted September 21, 2004 Thanks for your explanation, Ishy. ;-) About your question, the use of rollers on the rocker arms is not related to the cam timing or valve elevation, but only with the lobes sizes. I have some math to show but this is not the place, better take two coins, fix one to the table with your finger and roll the other around the border. Imagine now that your fixed coin is lobed, then it's easy to see that as bigger are the rolling coin, smaller has to be the fixed coin to describe the same movement of your moving finger. Do you remember those children artifacts with "sprockets" inside a teethed circle, drawing flower-like forms? Is just the same. The use of rollers permits very tiny cams but also affect to the form of the lobes, being more acuted (steeped?) as bigger is the roller, being the valve timing the same. Another advantage is that lubrication could be less strict because there is no friction between surfaces but there are rolling points (like a bearing). A secondary advantage is that, being equals the rpm, the linear velocity of the lobes peaks is slower than in a traditional cam (the same angular velocity, but less radius = less tangential (linear) velocity) then the better following. The counterpart of this system is more noise and the more frequent setting of valve-rocker gaps. The problem of floating valves is more related to the weight of valves and the respective fractions of springs and rocker arm (so I use forged aluminium rockers in mi Bul4T). BUT if feel that our little TLR engines (I have also a TLR 200) don't suffer of this problem below 8000 rpm. Do you really go over this? Before the valve floating, we will suffer blowing problems at the valve ports (more diameter is needed and more valve overlap timing is needed): beyond certain velocity of gas (gas = gasoline + air) the flow becomes turbulent and almost is stopped at the entrance of valves. This may be felt as the symptom you explain. Respect to this, I like very much the Sherco design: it has a very reduced cam (in diameter and lenght) and also uses the vase-shim system to do the valve-rocker ajustment. I think Honda also uses roller rockers but only for 2 valves and uses the screw-locknut system (I was surprised to see "4-valves" in the Cota brochure, an error?). Well, anyway, I imagine that none of us is going to rev these bikes beyond 9-10.000 rpm. Cheers, JM. Quote Link to comment Share on other sites More sharing options...
its a kinda magic Posted September 21, 2004 Report Share Posted September 21, 2004 nice information there, very good Quote Link to comment Share on other sites More sharing options...
marky boy Posted September 21, 2004 Report Share Posted September 21, 2004 I dont want to detract from Marlintecs informative answers and technical advise , so would like this to be seen or unseen as a sub comment.!! And do not wish the topic to go astray , but ... I take exception to Dabster taking exception to anything i or anyone may have said , i dont know how he has the cheek!! A man with his reputation!! Please continue , all childish comments now withheld. sorry to interupt Quote Link to comment Share on other sites More sharing options...
subira Posted September 22, 2004 Report Share Posted September 22, 2004 Hmm....fork tubes look like they're plain black Quote Link to comment Share on other sites More sharing options...
brian r Posted September 22, 2004 Report Share Posted September 22, 2004 Marlintec, I would have thought we would be looking at a 13000 to 15000 red line. Do you think the bikes have titanuim or sodium filled valves? In the future we should be looking at variable valve timing, tuned intakes, possibly variable runners, and wild differances in exhaust. This coupled with the digital fuel injection should make amazing little motors. One other thing. On a thread a long time ago was the discussion of kill switches and how they don't work at high RPM. Now the kill switch could be wired into the fuel management system to starve the engine as well as kill the spark. What about a little NoS for those big hills! Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted September 22, 2004 Report Share Posted September 22, 2004 Starving the fuel won't it pink or worse hole pistons at 13000 rpm??? Quote Link to comment Share on other sites More sharing options...
brian r Posted September 23, 2004 Report Share Posted September 23, 2004 Good question. I know that modern cars and trucks cut off fuel to electronically limit the speed though. I would think that if it cut off the fuel completely it wouldn't predetonate. The four strokes I've ridden just ran out of gas when they ran out of gas. I do remember a 250 CZ (2 stroke) that went like a bat out of hell just before it ran out of gas completely. Quote Link to comment Share on other sites More sharing options...
terry Posted September 23, 2004 Report Share Posted September 23, 2004 With a four stroke, I would think that as long as the engine is turning over then oil is being pumped so how would you burn a piston? Quote Link to comment Share on other sites More sharing options...
subira Posted September 23, 2004 Report Share Posted September 23, 2004 The Road Race boys have a mercury switch to shut off the fuel if the bike goes down. Don't forget that the injection system runs under higher pressure than a gravity fed carb, you have to shut the engine down somehow - most likely the HRC engineers have given it some thought and testing Quote Link to comment Share on other sites More sharing options...
brian r Posted September 23, 2004 Report Share Posted September 23, 2004 Terry, the burning comes from a lean out condition. The other problem would be predetonation acting like a hammer on top of the piston. Quote Link to comment Share on other sites More sharing options...
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