# Gear or Shat Driven Overhead camshaft? **URL:** \ **Category:** Factual Questions\ **Created:** [November 29, 2015, 5:57am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910 "2015-11-29T05:57:06Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![botsgotme](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@botsgotme](https://boards.straightdope.com/u/botsgotme)\ **Post date:** [November 29, 2015, 5:57am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/1 "2015-11-29T05:57:06Z")
OHC engines are popular, because they make the operation of the valves efficient. However, driving the camshafts presents problems-you can use a chain or a belt, but either can slip or break. has anyone designed an engine where the camshafts are driven by gears off the crankshaft? Or by a shaft with spur gears? ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [November 29, 2015, 6:19am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/2 "2015-11-29T06:19:37Z")
We might get a better answer in General Questions than in Great Debates, (although I guess it might come back). ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [November 29, 2015, 6:36am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/3 "2015-11-29T06:36:35Z")
i’ve never heard of one. Offhand, it seems to me it would much more problematic than a chain or a belt, both of which are well-proven designs with low failure rates (given proper maintenance). ---
**Author:** ![IT\_Guy](https://avatars.discourse-cdn.com/v4/letter/i/3ec8ea/32.png) [@IT\_Guy](https://boards.straightdope.com/u/IT_Guy)\ **Post date:** [November 29, 2015, 7:23am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/4 "2015-11-29T07:23:45Z")
Both. See [here](https://en.wikipedia.org/wiki/Overhead_camshaft#Bevel_shaft). ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [November 29, 2015, 7:46am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/5 "2015-11-29T07:46:14Z")
The venerable [Cosworth DFV](http://www.movinggraphics.ca/V8_Engine.htm)most certainly was gear driven. ---
**Author:** ![cochrane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cochrane/32/10441_2.png) [@cochrane](https://boards.straightdope.com/u/cochrane)\ **Post date:** [November 29, 2015, 8:40am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/6 "2015-11-29T08:40:57Z")
The U.S.S. Enterprise was Shat-driven. 😃 ---
**Author:** ![madsircool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/madsircool/32/3432_2.png) [@madsircool](https://boards.straightdope.com/u/madsircool)\ **Post date:** [November 29, 2015, 9:22am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/7 "2015-11-29T09:22:31Z")
We could provide our own fuel for our shat driven cars. 😉 ---
**Author:** ![Richox](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@Richox](https://boards.straightdope.com/u/Richox)\ **Post date:** [November 29, 2015, 10:19am UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/8 "2015-11-29T10:19:40Z")
a chain can’t really slip. it provides drive @ rated speed (reduction) or it doesn’t. possible failure modes that don’t mean the chain has physically broken might include chain stretch such that sufficient tension is lost and teeth skip, or teeth wearing such that skipping occurs. Both of these would still essentially mean the chain drive arrangement is in a failed state. Basically i think chain drive camshafts are not an engineering problem and therefore no solution is needed. Belts I would agree are less than desirable, especially in the majority of diesel engines where higher cylinder compression means valve and piston interference if cam timing is lost and therefore a likely totaled engine. in these situations I am more comfortable with chain over belt, but never have a personal reliability concern with chain drives unless the engine has some serious mileage on it. ---
**Author:** ![Mr.Me](https://avatars.discourse-cdn.com/v4/letter/m/d2c977/32.png) [@Mr.Me](https://boards.straightdope.com/u/Mr.Me)\ **Post date:** [November 29, 2015, 1:35pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/9 "2015-11-29T13:35:15Z")
[Ducati](http://www.rcycle.com/2009_Italian_Motofest_WV __20__ cropped.JPG) used shaft driven cams in the 750 Sport, even had a little window so you could see the gears. ETA: Norton had a similar arrangement starting in 1927 in the CS1. ---
**Author:** ![Mr.Me](https://avatars.discourse-cdn.com/v4/letter/m/d2c977/32.png) [@Mr.Me](https://boards.straightdope.com/u/Mr.Me)\ **Post date:** [November 29, 2015, 1:42pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/10 "2015-11-29T13:42:57Z")
Just missed the edit window, [here](http://www.racingvincent.co.uk/05%20Reference%20Photos/5.11%20Line%20Drawings/1927%20CS1%20Engine.jpg) is a cutaway drawing of the Norton engine. ---
**Author:** ![Nefario](https://avatars.discourse-cdn.com/v4/letter/n/59ef9b/32.png) [@Nefario](https://boards.straightdope.com/u/Nefario)\ **Post date:** [November 29, 2015, 1:59pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/11 "2015-11-29T13:59:44Z")
[Crosley](https://en.wikipedia.org/wiki/Overhead_camshaft#/media/File:1948_Crosley_COBRA_engine_OHC.jpg) and others used bevel gears. There was a 1930’s luxury brand - Pierce Arrow? Cord? Duesenburg? - That used a 3-phase crank arrangement with linkage to drive the overhead cam. It was quieter and more reliable than the roller chains and gears of the day. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 29, 2015, 3:17pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/12 "2015-11-29T15:17:15Z")
The wiki ref at post #4 says Leyland and Bentley used a multi-crank drive. I wasn’t able to dig up a diagram or picture of how the linkage worked. Anyone? ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [November 29, 2015, 4:08pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/13 "2015-11-29T16:08:34Z")
I think that drag race engines are frequently built with gear drives replacing the timing chain to eliminate timing issues caused by the timing chain slapping around. [Link](http://www.jegs.com/p/PRW/PRW-PQX-Dual-Gear-Drives/3149294/10002/-1?itemPerPage=90&pno=1) ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 29, 2015, 4:33pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/14 "2015-11-29T16:33:07Z")
Those replacement gear drives are pretty standard motor-head hop-ups for high output engines. They also make a cool noise. But they’re for engines with non-overhead camshafts and hence not relevant to the OP. Still a good cite ref the mini hijack about concerns about timing chain/belt unreliability. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [November 29, 2015, 4:46pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/15 "2015-11-29T16:46:54Z")
On bikes, the Honda VFR 750R had gear driven cams. This is because they had built the VF750 which had serious problems with tolerances and led to massive reputational damage because the cams were lunching themselves in very short order. The over engineering resulted in an engine that was near bullet proof, and could be very heavily tuned. Aprilia also had a homologation machine where they sold a gear driven cam kit, so they could then go world superbike racing - the kit was horrendously expensive and few were sold, but it served the purpose of having a world superbike that complied with the regulations of certain parts being readily available for rod going machines. I also believe it gave distinct advantages on the track, such as better control of the valves, less valve bounce etc. ---
**Author:** ![Nefario](https://avatars.discourse-cdn.com/v4/letter/n/59ef9b/32.png) [@Nefario](https://boards.straightdope.com/u/Nefario)\ **Post date:** [November 29, 2015, 6:10pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/16 "2015-11-29T18:10:56Z")
> [@LSLGuy](#): > > The wiki ref at post #4 says Leyland and Bentley used a multi-crank drive. > > I wasn’t able to dig up a diagram or picture of how the linkage worked. Anyone? Bentley is the one! Try wrapping your mind around the scanned page 18 shown on [this link](http://www.motorsportmagazine.com/archive/article/january-1964/17/random-thoughts-about-ohc) :eek: (scroll down) Also found the linkage arrangement on a [_moped_ engine](http://www.dansmc.com/camchain_nsu.JPG)! ---
**Author:** ![Bert\_Nobbins](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@Bert\_Nobbins](https://boards.straightdope.com/u/Bert_Nobbins)\ **Post date:** [November 29, 2015, 6:11pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/17 "2015-11-29T18:11:49Z")
> [@Richox](#): > > Belts I would agree are less than desirable, especially in the majority of diesel engines where higher cylinder compression means valve and piston interference if cam timing is lost and therefore a likely totaled engine. in these situations I am more comfortable with chain over belt, but never have a personal reliability concern with chain drives unless the engine has some serious mileage on it. There are also a lot of high-compression petrol engines that are interference engines. It’s an uneasy feeling to know that if that belt breaks you are going to need a new engine. I have a TFSI engine and I am happy to report it has a timing chain. 🙂 These are claimed to be good for the life of the car. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 29, 2015, 6:56pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/18 "2015-11-29T18:56:59Z")
> [@Nefario](#): > > Bentley is the one! Try wrapping your mind around the scanned page 18 shown on [this link](http://www.motorsportmagazine.com/archive/article/january-1964/17/random-thoughts-about-ohc) :eek: (scroll down) > > Also found the linkage arrangement on a [_moped_ engine](http://www.dansmc.com/camchain_nsu.JPG)! Excellent finds. Thank you. What a convoluted mess of waggling machinery! But it would be fun to watch in operation, net of the oil shower you’d be getting. As to the others and their timing belts vs. chains … That seems to be a religious issue these days. We’ve certainly had threads and threads about it. The consensus I got from the pros’ posts is that several manufacturers introduced belts just a bit before they were quite reliable enough. So belts got a bad reputation that is no longer valid for current belts in current (post 2010ish?) engines. But the bad rep is believed all up and down by shade tree mechanics and motor heads everywhere. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 29, 2015, 7:08pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/19 "2015-11-29T19:08:16Z")
> [@Bert\_Nobbins](#): > > There are also a lot of high-compression petrol engines that are interference engines. It’s an uneasy feeling to know that if that belt breaks you are going to need a new engine. I can’t imagine a belt holding timing for very long at all. Belt stretch alone will start to throw off the timing which will lead to high vibration and slippage and hopefully the engine just conks out instead of shaking itself apart. It’s an uneasy to know that if anything that breaks in the valve train you are going to need a new engine. There has to be a better way to deal with high compression valves. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 29, 2015, 7:27pm UTC](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910/20 "2015-11-29T19:27:22Z")
> [@TriPolar](#): > > I can’t imagine a belt holding timing for very long at all. Belt stretch alone will start to throw off the timing which will lead to high vibration and slippage and hopefully the engine just conks out instead of shaking itself apart. > > It’s an uneasy to know that if anything that breaks in the valve train you are going to need a new engine. There has to be a better way to deal with high compression valves. Here we go again. 🙂 These aren’t your great-grand-daddy’s leather belts. They stretch no more than steel chains do. And their teeth are just as good at staying synced to the sprocket teeth as a chain’s are. They’re lighter and quieter than chains. And don’t need or want lubrication. They’re good for the life of the engine in some cases and have 100k mile warranties in others. Without periodic adjustment. [Next page](https://boards.straightdope.com/t/gear-or-shat-driven-overhead-camshaft/738910.md?page=2)