GJM
Posted a lot
Alloy engines; like communism- great in theory.
Posts: 1,393
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Nov 21, 2005 18:11:32 GMT
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Then crank goes to front or rear axel..this provides power to the wheels how?? Heh, i can do 1) undo nut 2) take this off 3)replace this by... etc but buggered if i know how it all works
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Elementry engine questionsslater
@slater
Club Retro Rides Member 78
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Nov 21, 2005 18:18:30 GMT
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well on the end of the crank you have a fly wheel and bolted onto the fly wheel you have the clutch. And attached to the clutch you have the gearbox. Crank turns - flywheel turns - clutch turns - gearbox turns - drive shafts turn - wheels turn
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Nov 21, 2005 18:32:01 GMT
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has anyone got any info on diffs...i'm finding them very interesting atm
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Nov 21, 2005 18:37:23 GMT
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pushrods for teh win ;D
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once again rocking with 1117cc and 4 gears!
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Mr K
Posted a lot
Posts: 2,993
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Nov 21, 2005 18:48:35 GMT
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LSDs and auto boxs.... they confuse the hell outta me... the rest i understand no problem - i think building a ride on mower that did 40 - 50mph at the age of 12 and rebuilding various engines has tough me well! oh and flux capacitors, don't under stand them either.... i beleive some deloreans used them to great effect? pioneered by doc brown i beleive?
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Panda Matt
Part of things
Datsun Owners Club Wannabe
Posts: 734
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Nov 21, 2005 20:54:35 GMT
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This sounds like it could be a great idea for the features section...
what's a hemi?
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Nov 21, 2005 20:58:36 GMT
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Either a belt or chain from the crank...... ...or gears (Ford V4/V6) ...or shaft (1930's OHC Morris Minor/1950's Morris Six)
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... the only injury I sustained was a bumped head when I let the seatbelt of without realizing the car was upside down and that's not really the car's fault.
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Mr K
Posted a lot
Posts: 2,993
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Nov 21, 2005 21:01:28 GMT
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hemi = a domed (hemispherical) combustion chamber in the head. instead of the heart or kidney shape.
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Nov 21, 2005 21:10:38 GMT
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this should help.
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Nov 21, 2005 21:50:56 GMT
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so normally, where the two valves are what shape is it? Is it not normally flat, or is there a slight radius?
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Nov 21, 2005 22:54:12 GMT
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Few other points to note. Not in any particular order.
Some over head cam engines can run onto rockers rather than direct onto the tappets (Ford Pinto).
Cam in head engines have the camshaft in the head but then run onto push rods and rockers before the valves but in principal are same as OHV engines.
Camshafts open the inlet valves to allow the air fuel mixture in as the piston is going down (piston close to Top Dead Centre). Inlet valves close to allow the combustion process to take place (roughly at Bottom Dead Centre). The piston will now come up compressing the fuel mixture ratio approx 10:1, spark plug will start igniting the mixture around 10 degrees before the piston comes to the top by the time it reaches the top the full amount should have ignited forcing the piston back down to drive the crankshaft. By this time crankshaft has rotated 360 degree and camshaft 180 degrees. As the piston reaches BDC exhaust valves will open and as it rises again the gases are forced out of the now open valves. On a four cylinder engine pistons 1 & 4 and 2&3 are normally moving at the same time so while 1 is compressing and igniting 4 is exhausting.
Ignition timing varies with engine speed the faster the speed the more advanced the timing needs to be to allow the most power to be generated. And can go from 0 degrees upto 30 degrees on standard engines. Which is why distributors have advance mechanisms fitted.
Camshafts can be modified to allow more lift/ or duration depending on engine spec and generate more top end power or more low end torque.
Combustion chambers used to be mainly flat. IIRC hemi`s and semi hemi`s were developed originaly for racing to help increase swirl in the chambers and to help the flow through the valves on a crossflowing head. Modern 16V engines are usually called a pent roof but are basically a hemi style but less rounded.
This is just a very basic guide to the workings of a 4 stroke four cylinder that probably has a lot of glaring errors but should give the gist of what happens.
VRSSkodaNorm what are you wanting to know about diffs?
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well this is gonna sound really bad, but i was in an exam yesterday and got doodling (had answered all the questions)... so the crank is driven by the pistons, that goes through the gearbox, drive shaft, then the diff has to get the power from turning clockwise long ways to turning closewise at a 90degree angle ... I wanted to know how it does that? And don't they have to go slower on one side than the other to go round corners, how is that done?
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This is great stuff,.. All the "simple" engineering questions you wanted answered, but were afraid to ask! I have a modifying question. Why is overhead camshaft 'better' than pushrod? I can see why 2 cams would be better, different profiles for intake and exhaust. Therefore is possible to convert a pushrod engine to be overhead cam or to be a tiwn cam push rod?
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This is great stuff,.. All the "simple" engineering questions you wanted answered, but were afraid to ask! I have a modifying question. Why is overhead camshaft 'better' than pushrod? I can see why 2 cams would be better, different profiles for intake and exhaust. Therefore is possible to convert a pushrod engine to be overhead cam or to be a tiwn cam push rod? The main reason is less moving parts so its easy to make a higher rervving stronger engine. But to be honest for the most part you can still make an engine that will rev to 7,500 using pushrods they are generally noisier, people generally say more tappety but thats not strictly true as its just more metal to metal contact. Rover V8`s and most american V8`s are pushrod and its never been a problem for them. Its not really possible to convert to OHC unless its a specially built head. I know you used to be able to get a twin cam head to go onto an A-series engine. And the ford cosworth BDA was a 16V OHC head that was built to go onto a x-flow OHV block. But for the most part not practical.
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ImpManiac
Part of things
Imps... Imps... Imps...
Posts: 868
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Nov 22, 2005 11:06:52 GMT
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This is great stuff,.. All the "simple" engineering questions you wanted answered, but were afraid to ask! I have a modifying question. Why is overhead camshaft 'better' than pushrod? I can see why 2 cams would be better, different profiles for intake and exhaust. Therefore is possible to convert a pushrod engine to be overhead cam or to be a tiwn cam push rod? Pushrod engines often have camshafts sited down lowish on the cylinder block. The camshaft followers slide on the cams themselves, "following" them - also known as tappets. These operate the valves in the cylinder head via often fairly long pushrods. The pushrods lever the valve stems open via rockers (levers, really) that convert the upwards motion of the tappets into downwards motion of the valves. An OHC engine, on the other hand, often uses a camshaft whose tappets operate directly on the valve stem (an Imp engine, for example). Tappet adjustment is via a shim that sits between valve stem and tappet. There is no pushrod, no rocker arm and the tappets are often lighter and simpler, so there is much less mass to move. This lower inertia means that much greater acceleration can be used to unseat valves more rapidly and to enable them to seat more rapidly too. The effect of this is to allow valve timing that is good for torque but also allows the engine to breathe at high speeds. Pushrod engines can also do this but often need tappets with roller tips so that the tappet can follow the camshaft profile. They also need very special, often short-lived valve springs. Also, with fewer parts to wear or distort, OHC engines can last longer than older pushrod designs. American V8s last for ages because they are well designed but also because they are low-speed sloggers rather than small, revvy, European and Japanese designs. Big V8s suit the vast expanses of American roads and where petrol is a fraction of the price it is over here. Pintos, SOHC BMWs and other engines use an OHC but valves are operated by rocker arms. The camshaft operates part way along the rocker arm, with the valve being actuated by the end of the arm. This converts the displacement at the camshaft into valve lift in a ratio determined by the relative position of the camshaft, valve stem and rocker arm fulcrum point. Hemispherical combustion chambers are performance-orientated designs. Hemi chambers are actually bad for combustion because they are open and tend to allow pre-ignition, or knock, or pinking. Also domed-top ("pop-up") pistons are required to increase compression ratios. Many more modern hemi designs use two OHCs (DOHC) to enable the inlet valve(s) to face the exhaust valve(s). Modern 16-valve designs almost invariably use DOHC layouts. Each valve has even less inertia than one larger valve, enabling valve timing to be optimised further to give better torque but still retaining turbulence in the incoming fuel-air charge by generating "tumble." Turbulence is essential for good combustion. Fresh fuel-air mixture is forced into the area of the flame in the combustion chamber by turbulence. Older engines rely on swirl. Modern 4-valve per cylinder designs rely on tumble, which introduces less resistance to flow and allows cylinders to be filled efficiently. Engine power depends on how much fuel and air you can burn completely in the cylinders. If you can fill 'em more and burn it all, you get more power. That is why two carburettors or throttle bodies allow more power than one, etc. Oh dear. You've got me going now. I'm gonna bore everyone in the office all day now. I'm
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Last Edit: Nov 22, 2005 11:09:20 GMT by ImpManiac
1966 Singer Chamois sprint/hillclimb car in white over blue two tone 1975 Triumph Stag long term project (over 20 years so far) in colour TBA 2003 Vauxhall Vectra GSi 3.2 in black sapphire
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Nov 22, 2005 12:02:33 GMT
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Aren't engines the most wonderful, neat and ingenius devices!? Most adults own there very own 'Suck, Squeeze, Bang, Blow' machine and take it completely for-granted I've a couple of queries.... - Isn't it true that each Cam lobe on the shaft of a flat four Beetle engine guide the push rod controlling the valves for each opposing cylinder meaning that when the valve for one cylinder is open the valve for the opposing cylinder is shut - i.e one cam lobe each controls two valves, hence a Beetle camshaft having only four cam lobes - Also with a 16v engine, obviously for a given cylinder there are two inlet & two outlet valves. Do each pair of valves (inlet or outlet) Open at the same time or are they staggered to aid combustion/exhalation in any way? BTW i've been reading a brilliant Haynes book - its called Rebuilding and Tuning the Ford Crossflow by Peter & Valarie Wallage. Although its crossflow specific the principles and techniques can be applied to most engines & is very interesting
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Nov 22, 2005 13:00:30 GMT
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It really depends what you want to do, there are benefits to all systems. Illmor built a "Stock block Pushrod" Normally aspirated V8 and wiped the floor with everyone else including the turbo Motors !! Current F1 engines use Rockers as designed properly they are lighter, give better valve train geometry with longer duration. Not so much of a cam now, more an opening ramp and a step Nascar Pushrod v8`s ....US Spec roller this and billet roller rocker that Max revs were 7800 using Titanium springs. Redesigned using steel.... yes that heavy old skool steel we ended up with a lighter Valvetrain with less inertia, that would take Higher Valve acellerations and rev to over 11,000 ;D Fords Big V6 in the explorer... 4.something ? Started out as a Pushrod v6, its now an OHC, as the Cosworth V6 was. You have the Mass of the Cam drive to take in to account as well and 2 cams if you go that route... The accuracy suffers too. Its not all about whats best, its whats best for the job that is required of it..... Honda Vtec, single OHC, Rockers, screw and locknut lash adjustment...... simple, reliable, lightweight, easy to service, does just what it needs to do theres also a lot to be said for a Steel 1760 x-Flow that will rev to 9K ;D Especially on a modern Management system to get the driveability back ;D
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MWF
Posted a lot
Posts: 2,945
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Nov 22, 2005 13:23:14 GMT
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I was going to mention the Vtec system, there's a whole new world of complication!
In fact after a few attempts I can't word an explanation of how it works.
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MWF
Posted a lot
Posts: 2,945
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Nov 22, 2005 13:24:11 GMT
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LSDs and auto boxs.... they confuse the hell outta me... www.howstuffworks.com has a section on auto boxes
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ImpManiac
Part of things
Imps... Imps... Imps...
Posts: 868
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Nov 22, 2005 14:03:11 GMT
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I was going to mention the Vtec system, there's a whole new world of complication! In fact after a few attempts I can't word an explanation of how it works. I am sure that V-TEC must be explained somewhere on the web. My understanding follows. In addition to the usual two camshafts most 16-valve fours use, a third camshaft lives in the centre of the cylinder head. Under normal running, the short-duration, tractable camshafts are used. When you reach a certain engine speed, oil pressure is used to lock cam followers idling on the third camshaft. These followers are articulated and normally just flex. When locked using hydraulic pressure, they act on the valve stems and take over from the normal camshafts, effectively giving you deep-breathing valve timing optimised for maximum power. So you get the low-down driveability of short duration cam profiles with the usually peaky but shatteringly powerful blast at the top end! And Honda have engineered it all to be pretty seemless AND reliable! They are VERY clever, those guys! Short duration camshafts control the airflow effectively, allowing engines to develop excellent torque characteristics but tending to stifle top-end breathing and power. Longer duration cam profiles can tend to cause inlet charge to want to reverse in the ports because valves open earlier and close later. At low speeds, the flow can stall or actually reverse - hence carburettors that spit fuel out, etc. But as speed rises, the resonances and inertia in the "tubes of air" that are entering and leaving the engine can be arranged to enhance cylinder filling within a very specific range of engine speeds, dependent on valve timing, port volume, port velocity, etc. This is true "tuning" - the use of resonant sound pressure pulses to maximise power. DerbyDan, yep, engines are pretty cool! So many people have them and yet very few appreciate their nuances! They continue to fascinate (and bankrupt!) me! ;D I'm
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1966 Singer Chamois sprint/hillclimb car in white over blue two tone 1975 Triumph Stag long term project (over 20 years so far) in colour TBA 2003 Vauxhall Vectra GSi 3.2 in black sapphire
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