Push rods or cam chain?

[lingeringstin...]

Which is better, and why?

And yes, I already know gear driven is superb, but it's not that common.

[Pete.]

Many engines have both. Do you mean OHC or OHV?

In purely mechanical terms OHV because or the reduction of reciprocating masses. All of those long pushrods have to be accellerated and braked thousands of times a minute where the cam just goes round and round.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[stinkwheel]

Are you beltist? Belts seem to be shite. Armstrong owners are constantly fucking with them but in fairness, they are also easy enough to change. Seen it done in a rally field. Mainly because they are mounted on one side of the engine more like a car.

Or you could go CX500 style and have both chain and rod?

I have both OHC and OHV bikes. They have pros and cons. Although it must be said my OHC bikes are gear-driven so the worry factor of a worn/loose camchain isn't something that happens for me.

OHV is very simple, easy to work on, easy to adjust. Failure mode is generally pretty safe, if a rod jumps, it generally means you have a bent rod and a closed valve and no piston hitting the valve.

OHC doesn't need messing with much but if a pain in the backside once it does. Adjustment can be fiddly, replacement is a major operation if the chain is in the middle of the bike. Failure mode is usually catastrophic.

The main argument for OHC is you can achieve higher rev speeds. Try that with OHV and you'll eventually experience valve float.

Or you could go back to 2-stroke and forget about all this valve nonsense.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[lingeringstin...]

Actually I was just curious what people thought. I don't think I've ever had gear driven cams that I knew of. Mostly older bikes with cam chains and the associated troubles old cam chains bring to an engine. I've gone a bit hooligan before and had the chains jump a few teeth. probably my own fault for being rev and clutch dump happy and it means a major tear down to fix.

My current wee engines are cam chain jobbies with those horrible Honda style cam bearings. I've got four of those engines now, all slightly different mods and experiments. Luckily there's a readily available needle roller bearing that fits where the Honda type cam bearing goes and at least a couple of my engines have them in. So far not problem.

I also chuck the automatic cam chain tensioner and do a bolt and nut modification for the rear cam chain blade. Seems to work better. Once the cam chain is adjusted and the bolt locked down I never need to touch it again. I can't help feel that the constant spring pressure of the automatic adjuster might have an effect on cam chain stretch and rob a bit of power. Might be microscopic but on my engine every little bit helps.

But to me cam chains seem a bit over the top for a sub-25 horsepower motor. They're small and weak looking and I always have this nagging feeling something either needs looking at, adjusting, replacing or is probably due to fail.

Actually I'm more of a sidevalve man myself. I like a plodder. I do like an old 40's-50's army BSA single. Unfortunately they aren't two a penny any more. Lovely bikes but not worth what people want for them now.

I rode a mate's old Panther sans sidehack and it was a wonderful thing. Probably only did about 60 at the most but it just felt sedate and in no way stressed or about to explode like a spluttering Yamaha RD always feels like.

To be honest I'm not bothered about high revs. If I wanted that sort of thing I'd go straight two stroke twin of some sort which I do really like but they are getting hard to find, all knackered and spares are becoming dear. Anything with the word "vintage" in front of it automatically doubles the price and "vinage" Jap two strokes are rare now. I see "vintage" MZ's on Ebay for hundreds of pounds when not that long back you literally couldn't give them away. Dreadful engines anyway and I'm glad to be rid of them.

[xX-Alex-Xx]

[MarJay]

Push rods come from non overhead cams. Overhead cams are superior for efficiency, and it means you can have two of them (per head) Hence why so many Japanese car engines from the 80s and 90s have DOHC embossed on the cam covers in MASSIVE Letters.

In order to make overhead cams work, you need a way of driving them, and generally a chain is the way most motorcycle manufacturers have gone. Honda dipped into gears for a while but it's expensive and requires extraordinarily tight tolerances to work. Ducati used belts, but then found that when their bikes stood for a while they would often fail.

Camchains have the advantage of low maintenance and can last the life of the bike, however you need to be able to keep their tension, and some bikes chains weren't man enough meaning they often wore or failed in early camchain engines.

So, in summary you're asking the wrong question. The question should be are overhead cams better than cam in block, and the answer is in most circumstances, absolutely yes.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[WD Forte]

Side valve and magneto.
all else is effeminate poofery but I'll allow 12v over 6V
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bikers smell of wee

[tatters]

Never had an issue with push rod engines using solid lifters like on older bikes and older V8s but Dodge/GMC/Chevy V8s took a proven design and decided to add a roller on there valve lifters which fails. Which is what happened to my 2012 5.7 hemi one roller failed at 60k and destroyed the camshaft. Common issue that requires a engine rebuild.

Mine not only took out a camshaft lobe but caused the shaft to seize, breaking the timing sprocket off the end of the shaft and in turn bending all the valves and pushrods....

https://external-preview.redd.it/W4UxreOM9ur1AV24fGFsQJExiEl0Dgaoz_KHqM5oY3I.jpg?auto=webp&s=ff7edcc6a61b979978c799a55b97b814633af477
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Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV