01-22-2004 07:18 PM #1
Streets check this site out. http://auto.howstuffworks.com/camshaft3.htm They want this cam to side back and fourth, has anyone seen this before. this is supposed to give you bottom and top end power. Wonder how good it works???? Streets I would like your opion on these camshafts please. thanks
Last edited by vara4; 01-22-2004 at 09:01 PM.
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How about the pneumatic valve springs on an f1 car? The ship at my school has 2 seperate lobe profiles per lifter, the cam can be shifted so the lifter rides up onto the other profile, which allows the engine itself to run in reverse.
76GMC1500; This is all new to me, I just think it will be great if they work the way they say the camshafts will. Power at the low rpm's and at the top rpm's too. I want to try one of these cams.
P.S. why would you want the engine to run in reverse???
Last edited by vara4; 01-22-2004 at 07:52 PM.
Originally posted by techinspector1
Vegas, if you have no transmission and cannot switch the pitch on the propeller, I guess you'd have to run the engine in reverse to back the ship up.
Direct Reversing Engines
In order to manoeuvre a ship, the propeller thrust must be reversible, by means of reversing the propeller drive or by altering propeller pitch. Controllable pitch propellers, or diesel-electric drive, allow the use of unidirectional (non-reversible) engines. In systems of limited power using medium or high speed engines through gearboxes, arrangements of clutches and reverse gears may be used. In many ship, however, it is necessary for the main engine to be reversible and able to operate efficiently in both ahead and astern directions.
To run in the astern direction, all the operations in the engine cycle may need retiming. The starting air must first rotate the engine in the reverse direction and this will require retiming the distributor to supply compressed air to the appropriate cylinders in the correct order. The retiming may be carried out by altering the position of the distributor cam with respect to its drive from the main camshaft.
The number of the readjustments to be made and the methods used depend upon the engine cycle and type. Four-stroke engines will require a change in timing of fuel pumps, a different change for the air inlet valves, and yet another for the exhaust valves. To obtain all these changes on the same camshaft, a separate set of astern cams is fitted. Each astern cam is fitted to the camshaft adjacent to its corresponding ahead cam (below). The reversing procedure is then carried out by moving the whole camshaft axially, which moves the ahead cams clear of their followers, which now engage the astern cams. Ramps (sloping sides) fitted between corresponding ahead and astern cams cause the follower’s roller to slide smoothly from one to the other. The axial movement is carried out by a hydraulic cylinder fitted to the camshaft; locking devices and safety cut-outs ensure that the camshaft has carried out its full axial movement and is in the correct position before the engine can be restarted. To maintain alignment of the camshaft drive, a spline coupling may be necessary.
Turbo chargers are of course unaffected by reversal of the engine, but engine driven pumps must be reversible.
Large two-stroke engines have scavenge ports which control scavenge timing. This must therefore be symmetrical and will thus be unchanged when reversed. Engines operating with constant pressure turbocharge have almost symmetrical exhaust valve timing. Consequently no change in timing is necessary for exhaust cams.
Fuel pump timing must be readjusted since it will be the opposite flank of the cam, which will now raise the pump plunger to deliver fuel. There are alternative methods employed to change the fuel pump timing without altering the main camshaft. Two such systems are illustrated and described.
In both cases the main camshaft drive timing is not altered and therefore any other drives taken from this remain synchronised with the engine while running astern. This is important if a balancer system is fitted.
Sulzer RTA engines have oil pressure operated hydraulic ‘lost motion’ servomotors on the camshaft, which rotate the fuel pump cams to their astern positions. Fuel pumps and their cams are grouped in pairs along the camshaft and servomotor is fitted for each pair of adjacent cams. Oil pressure located and secures each servomotor in its correct position while the engine is running. A similar servomotor is used to re-time the starting air distributor and its drive from the camshaft. ‘Lost motion’ is the term used to indicate that the timing has been retarded, or moved back, through a given angle with respect to the ‘new’ direction of rotation.
MAN – B & W MC engines have their fuel pump cams fixed directly to the camshaft but the follower rollers can be displaced to alter the pump timing as shown below. The link, which displaces each follower, is actuated by the pneumatic cylinder and piston, powered by compressed air from the starting system. The link is self-locking in either position and a sensor is fitted to each pump to cut off fuel delivery if the link is not locked in its correct position.
Earlier models of two-stroke engines use elaborate systems of servomotors to rotate their whole camshaft to reverse the timing.
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Thanks; Techinspector, Viking, Streets and Robinson. I got to learn some thing new, I didn't know a ship's engine could reverse like that, Odd but interesting thanks. I have no problem with using a alternate power source as long as that is what it is,and by that I mean it has good horse power like the gas engines of today,and I don't have to stop and search out a power outlet some place or worse charge it up every couple hundred miles.Let me say this, I haul fuel to these power company's and I'm not talking about a few gallons I'm talking billions of gallons, for thier diesel generators to generate power. Now if every one has to charge thier cars up that means the power company is going to produce that much more power and use that much more diesel. So what is the differance if i use it or they use it ??? Right now this is the easyest and the best way to get from point A to point B!!! Plus I get to have a little horse power and a lot of fun. Oh and I don't have to drive some thing that looks like a go cart instead of a car or truck.
Last edited by vara4; 01-23-2004 at 09:39 AM.
Apparently BMW has just built an engine whihch eliminates the cam, lifters, timing chain, push rods and rockers comletely. Each valve is opened by an electric plunger by computer. In the crusing mode the valves open only slightly and for a short duration of time in relationship to most engines and thus achieve incredible fuel mileage. However, when the hammer comes down, the duration and lift equal that of high performance cams.
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TyphoonZR; I did know that some companys were working on that but I didn't know that anyone had made it work yet. Now if we can build them with compression and be able to buy high performance parts for them it will be great!!! Or maybe we could adapt the technology to older existing engines.
TyphoonZR; Where did you see that, I did find a new engine that BMW built but they still use a cam and rockers but it does look like they are headed in that direction. Their calling this new technology valvetronics but they still use camshafts and other components like rocker arms. The valves are only partially controlled electronically. The valves are not controlled completly by electronics yet, from what I've seen. Here's a website where you can check it out for yourself: www.canadiandriver.com/articles/jk/020213.htm
Last edited by vara4; 01-23-2004 at 04:00 PM.