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Pros and Cons gear-driven cam vs. Chain-driven cam


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Hi bmw2002faq 

Just wondering about the pros and cons between gear driven camshaft as in the different m12 versions of the m10 and the pros and cons for chain driven ( single and double row chain ) 

 

Seen the gear driven in several older motorbikes and old porsche engines.. 

 

1. pros i heard in geardriven is when the gears are new it can be made lash free inbetween the gears.. 

1. Con is noise with straight cut gears in gear driven.

 

But what else is there ?? 

 

Hope you nerds know 😂😉

 

 

 

 

 

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Well, yeah, gear driven cams, sure.  I've got a motorcycle that runs on a gear driven cam.  But is it a ready option for the M10?  Are the M12's that common?  Typically it's full race stuff, hardcore, very sexy...

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As far as i know about the m12(correct me if im wrong) that is that they machined previous used m10s from road cars.. they used some kind of magnesium alloy for the end plates Where the gears where mounted and yes suddenly agere that nothing beats the look of gear driven.. but if you want to buy original parts for the m12 here in europe is very expensive.. And not all of the parts are available.. a fully dresed race m12 2.0liter  n/a is like 60-80.000 dollars so pretty much out of reach.. 

I found a british Company that makes replica cylinderheads.. those are 6000-7000 dollars.. 

 

But back to gear vs chain what are the pros and cons in a street and race car. The old porsche's have it mounted for Street aswell.. 

 

 

 

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Most modern (i.e. post WWII) street (i.e. production) engines that use a gear driven camshaft are OHV engines, vs OHC.  An OHV engine only needs three gears to drive the cam:  one each on the crank and cam, with an intermediate gear.  With even a single OHC there would need to  be more than 3 gears to fill in the space between crank and cam.  Otherwise the intermediate gear would be very large to span the gap. 

 

A chain drive is less expensive to produce than four gears (six--or more--if its a DOHC engine), so until the advent of belts, chains were the choice for most OHC--and some domestic pushrod V-8s,  while most European small, inexpensive engines used gears.   Japanese cars were a mixture--depending on what the engines were based on.  As Japanese engine design came into its own in the 70s, most were chain driven.

 

Gear cam drives are noisy, so cut down on gear whine, the intermediate gear was often phenolic resin or aluminum.  That became the weak point on the drives, as that phenolic gear eventually sheared teeth as they wore down, while aluminum gears shed bits of aluminum into the oil, which was (hopefully) captured by the filter.

 

So:  gear drives are quieter and less expensive to produce for OHV engines, but don't generally last as long.  Chain drives are noisier, require some sort of tensioner but last longer.  Belt driven cams are both quieter and cheaper to produce than either gears or chains, and have the added advantage to the car company of frequent replacement and lots of parts sales when they fail, which is more often than either chains or gears.  Ya pays yer money and ya takes yer choice...  Having worked with all three, I'll take duplex chains, thank you very much.

 

mike

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One draw back to a gear driven ohc engine is if the head is milled the gears need to compensate, not a easy thing to do while maintain the same gear ratio, Also a gear train whether new or not needs to be set up with gear lash to provide clearance when the engine heats and cools. 

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21 minutes ago, uai said:

one way of getting rid of the many gears is an upright shaft and bevel gears-now we're talking

20s and 30s vintage Bentleys used this method--and they won LeMans three times with the setup.  Some cars even used the vertical shaft as the armature for the engine's generator...

 

mike

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My experience with these has been in very modern, very sexy motorcycles, like some MotoGP stuff before, I think, they went pneumatic, a la F1.  Mine uses split gears that are spring loaded to deal with lash.  Typically not anything to do with street engines, at least from what I've seen on modern stuff.  I'm sure for reasons that Mike brought up- just too much money for what you get. On the street.

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2 hours ago, uai said:

one way of getting rid of the many gears is an upright shaft and bevel gears-now we're talking

This is also the way both Rolls Royce and Allison went in their ww2 v12 aircraft engines.

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