[nicholastanguma]

Fair warning: longish post, maybe not for the faint of heart.

I'm a luddite, but not an unreasonable one. You can like what you like, that's cool with me...but it's not okay for you to try forcing your likes to be my likes, too. We can disagree agreeably. I think electric everything is blind ideology, you think carburetors are for neanderthals--we can still be 100 percent courteous to each other.

Technology always progresses, and therefore marketing must always progress commensurately. Or, when not commensurate in their progress, sometimes the tech or the market will helpfully nudge along whomever is being slow at the time.

I'm heavily involved in the vintage air cooled auto and moto cultures, old VWs and Porsches and Hondas and NSUs and Fiats and Triumphs and all of it, all the air cooled carbed stuff makes me happy all day long. So I still like pushrod engines. I don't dislike overhead cam engines at all, I like 'em just as much as pushies, it's just that in the vintage air cooled world pushrod tech tends to be more prevalent than overhead cam tech. Way more Porsche 914s out there than NSU TTs, for instance. Admittedly, in the moto segment the prevalence of vintage Japanese powerplants makes things a pretty even split, you can just as easily find an old Honda CG or BMW airhead as an old Honda CB or Suzuki Bandit.

Here in the real world, where there exist stoplights, stop signs, police enforcement, speed limits, pedestrians, speed bumps, pot holes, school zones, and just general consideration for other road users traveling at their own paces...having to rev an engine way up high to get into my power curve simply doesn't make sense. The real world is not a race track.

Marketing is sexy when the copy reads "redlines at 15,000 rpm" and "makes 200 hp at only 600cc size" and other such sexiness (all of which I do appreciate, as long as the engine is carbed and air cooled), but if you're not a professional racer on a dedicated race track this marketing copy and this technology are just jewelry.

A hot rodded pushrod boxer four connected to a five or six speed transaxle is more real world usable torque and horsepower than any sane motorist can use without maiming or killing himself or others on the road or trail. Many scoff that a hot rod pushrod boxer in a VW or Porsche is "only making 200hp," but with five or six gears to play with on trails and roads that aren't dedicated racing courses that 200hp is real world fun as long as the sun is shining.

A hot rodded Enfield Bullet or Triumph Bonneville mated to a five or six speed transmission is exactly the same.

Restomodding old autos and motos with weight reduction and frame bracing and modern suspension and modern carburetion and modern gearboxes and other such upgrades is wonderfully emotionally satisfying, while keeping the pushrod engine's lower-hp-but-more-useable-torque powerband in place for real world fun. Where are you safely going to rev over 9000rpm on public trails and streets?

Your CRF450 or 350Z makes way more peak hp than a restomodded Honda CG250 or VW Beetle, but you're not actually a pro racer and your vehicle's peak hp output doesn't actually make you a sexy beast. Your machine is not you and you are not your machine--you are still fat or bald or ugly or stupid or dull or poor or selfish or arrogant or whatever no matter how sexy your machine is. A poser with a Kawasaki H2 is just as cringeworthy as a poser with a straight piped Harley-Davidson.

So I continually find myself burrowing deeper and deeper into the vintage pushrod lair. I very very very much enjoy track days! But I do not live on the track, either motocross or autocross.

Anyone else find they still enjoy hot rodded old pushrod engines for real world fun? Anyone else found endless emotional satisfaction in restomodding something obsolete into something actually usable for real world trails and roads?

[AzCal Retred]

My Pre-Unit I.B.'s are readily repairable with hand tools. At 10,000 miles the old iron barrel top end's rings were gone, so not much oil control, and it contained the infamous "potmetal" slotted piston. I had a "new old stock" standard alloy barrel and acquired a forged 6.5/1 piston for it. After getting the exhaust pipe & carb off, the rockers come off, the pushrods come out, six head bolts later you are looking at the old piston in your hand.
Cleanup takes what it takes. The new piston & rings fit easily into place, base gasket, barrel over rings & piston, head gasket, head, six bolts hand snug and you are home. Replace pushrods, reattach rockers, check & adjust valve clearance, put the carb back on and you are ready to test fire. What a user friendly machine - the high wear items are easily serviceable.

This old skool tech is perfect for my usage. The heavy flywheel aids traction, the mild compression allows predictable slow speed operation. You need to pick tech appropriate for the intended usage. Points and a carburettor are perfectly adequate for this machine and my use. The pushrod adjustment and point adjustment locations are conveniently located for routine maintenance, just like the designer actually rode these machines themselves. At roughly 22 - 25 HP and 65 - 75 MPH, it's still viable transportation today.

The alloy barrel was a concession to local 105F summer ambient temps. The forged slug was for greater mechanical reliability and the steel rings it runs last longer in service. The barrel feels warm within 30 seconds or so after startup, the cast iron unit stayed cool for maybe a couple minutes. Better heat transfer is a good thing for air cooled engines.

A fun little bike is the CSC SG260, a "CG" 250cc pushrod counterbalanced electric start Honda clone with a carb. At about 280 pounds all up and 18 HP or so, it looks like a nice ride. The SSR Buccaneer is another fun choice, based around a Yamaha XV250 clone.

About the only Japanese pushrod bike widely available I know of is the CX500 & CX650 liquid cooled "Guzzi" knock offs. Runners are still available relatively cheap. They had stubby pushrods and could routinely hit 10,000 I think.

[nicholastanguma]

You need to pick tech appropriate for the intended usage.

Yes, but the general buying public isn't interested in mechanical engineering, they like sexy marketing.  Meh, the economy has to keep chugging, I'm not going to pretend everyone in the world should like what I like.

About the only Japanese pushrod bike widely available I know of is the CX500 & CX650 liquid cooled "Guzzi" knock offs. Runners are still available relatively cheap. They had stubby pushrods and could routinely hit 10,000 I think.

Yes!  The shorty pushrods allow these machines to pretty much rule their classes at the Bonneville salt flats, from what I understand.

Interestingly, the short pushrods of the Honda CG thumper also allow an unusually high rev limit; from what I've read the current 250cc pushrod class land speed world record holder has its limit set at 9200, and that's with a 65mm stroke.  At only 229cc it was dynoing at 23whp.  For an engine that makes about 9whp stock that number 23 is outrageous.

For similar reasons the Toyota 3TC inline four's short pushrods keep it a popular hot rod engine with the Japanese restomod tuner crowd, even in a landscape completely dominated by SOHC and DOHC architecture.

[Bilgemaster]

That was a splendid "manifesto" that made a lot of good points, and I enjoyed reading it. No "tl;dr" ADHD syndrome here!

Yesterday, with a glorious sunny day finally creeping up into the 70s, I finished re-proofing that original model Aerostich Darien-Falstaff wax-cotton "wonder jacket" that 'olhogrider' had been kind enough to shed in my direction (Thanks OHR! It's splendid! And with the fresh Barbour Wax is now even a close match to my "Military's" hues) and then went for a nice long "pootle" (the term the youngsters are apparently all using nowadays) on my Iron Belly Bullet. It again occurred to me how much I enjoy hearing that flamenco tattoo of the pushrods and tappets when they're dancing happily. They accentuate that "elemental" experience. I don't need no stinkin' tacho. Their tippity-tapping tells me when we've found that sweet spot. And that's kind of the point of satisfaction with one of these old fossils, isn't it?: taming that roughly elemental lurching of that big lonely piston into a gentle canter or occasional spirited gallop, while not brutalizing the beast. It's all very "equestrian," I've often said. While I totally get the powerful appeal of a raging Hayabusa, or whatever, wailing about near redline, I've never shared that fascination for "flogging it", even as a youngster. This is not to make a virtue of necessity. Most of my rides have been elderly hoopties--ex-police surplus, basket cases, or other rescue dogs that I've nursed along somehow and would have soon expired if I'd given them the lash.

So yeah...I'm a big fan of the humble pushrod. Its sun may have set elsewhere techwise, but not on my watch.

Oh, and speaking of "shedding jackets", here is a charming tale for you rocker Anglophiles out there: https://youtu.be/g6ICapcRo38

[AzCal Retred]

I wonder how much the CG design can be stretched? 400cc? 600cc? It's a nice "clean sheet" stone axe design. A 400cc unit with 12/1 piston running on propane should be doable, you'd avoid the EPA/DOT hassle. There are propane tanks are made of spun carbon fiber now, probably could be designed as a stressable frame member as well.

[nicholastanguma]

I wonder how much the CG design can be stretched? 400cc? 600cc? It's a nice "clean sheet" stone axe design.

As the CG architecture is one of my all time fave vintage thumper designs, I have often wondered exactly the same thing.  However, as the CG is a small displacement machine, and my personal affection for hot rod minibikes and hot rod small displacement motos is essentially unbridled, I've more specifically wondered how much the design can be stretched while remaining within the small bike category. 

Calling Tom Lyons!  Taking into account the above, here's an interesting scenario, then, Ace, since as far as I know you are literally the world's most knowledgeable tuner of vintage pushrod thumpers.  Basically, what kind of hot rod performance could be had from this kind of engine?

Let's assume the following general guidelines:

1- A clean sheet design, or at least a mostly clean sheet design.

2- A six speed transmission.

3- Carbureted with a modern carb.

4- Air and oil cooling.

5- 300cc or so displacement, perhaps a 77mm bore and 65mm stroke?

6- Must retain the Honda CG's simple overhead valve design that uses a rocker arrangement allowing both exhaust and intake valves to be operated by a single cam; camshaft operated by a gear right off the crankshaft and low in the engine to provide constant lubrication.

7- As long as no. 6 above is maintained anything else goes, any valve angles and sizes, roller rockers, 2 valve or 4 valve head, beehive springs, exotic Ducati alloys, anything as long as the engine could still recognizably be called a "Honda CG" in name and architecture.

8- Must be a streetable hot rod engine, not just a high rpm racing engine, with enough torque for an enduro application and not just a cafe racer application.

9- Ooh, and no budgetary constraints for design, materials, or construction, smile!



For reference, here's the history of the CG engine:  https://www.janusmotorcycles.com/2019/10/22/bulletproof-the-heritage-of-the-janus-250-engine/

[Karl Fenn]

I have never had any issues with push rods apart from the odd bent rod or loose seat, many of my old singles were all push rod design and my BMW s, in fact only in the last 40 years have cams and chains become the norm, in the 70s many high performance engines were all pushrod design, every British bike was pushrod, but now it's all gone over to cam design these engines are easier to produce less moving parts, and no valve train or pushrod tubes.

[zimmemr]

Great post! More to the point, anyone that thinks the pushrod engine is antiquated should go to a Nascar. NHRA or Outlaw Sprint car race, or any other oval track race, and see for themselves how a well built push rod engine performs. There's nothing wrong with an OHC design, they've been around since the dawn of the IC engine, but there's just something about a pushrod engine that stirs my blood.

[AzCal Retred]

A Current In-Production design engine to compare specs to:

Jawa Perak motor; 1 Cyl., 4 valve, Liquid Cooled, DOHC, 6 speed, 334 cc, Max Power 30.64 PS, Max Torque 32.74 Nm., 81 mm x 65 mm, 11/1 CR, Emission Type BS6

With a single lobe cam you probably have less design leeway in the power department, but it would still be sufficient for purpose. Pumping it to 500cc would give a practical torque boost, a 95mm x 72mm B/S would let it rev a bit. The new CG design has a counterbalances anyway, so it should be relatively smooth. 4 valves with "forked" rockers and screw adjusters could handle the intake & exhaust requirements with that wide flat piston.

[axman88]

About the only Japanese pushrod bike widely available I know of is the CX500 & CX650 liquid cooled "Guzzi" knock offs.

Don't forget the Yamaha Road Star 1600  https://en.wikipedia.org/wiki/Yamaha_XV1600A,  and their 1900 Roadliner.   https://en.wikipedia.org/wiki/Yamaha_XV1900A

When I saw these, I thought, "they are taking Harley emulation to the next level".  I figured this was done mainly for style / marketing, but the valid engineering reason for pushrods, is to shave a few cm off the engine height.  Which takes me to my next point, ...

I like SIDEVALVES!

Yes, not afraid to go there.  Sidevalve engines are substantially shorter than overhead valve engines for the same displacement, and un-excelled for ease of removing the head, and general simplicity.  Great for burning the free fuel you pump out of the big tank behind the KFC under cover of darkness, or for conversion to wood gasification technology.

[Keef Sparrow]

BMW have recently introduced their new R18 motorcycle. The engine is a brand new 1800cc design - and has pushrods.

[AzCal Retred]

AxmanLXXXV!!! @ #9:

Thanks for the info on these Yamaha ginormous pushrod V-Twins! I always assumed everything was OHC design.

I'm with you on flarhead design - having the engine stop at the top of the cylinder makes for a short motor.

I want to see a Turbo-ized flarhead. Intake & exhaust are on the same side, perfect for a turbo. Boost cures any cylinder filling issues. Exhaust just serves to pressurize the turbo anyway. A tiny, POWERFUL motor. A V-4 would be ideal.

I'd also like to see a flathead "de-conversion" for the UCE &  Pre-Unit Bullet, an even more "antiquey" looking old tech retrofit!
An alloy one could probably be made up from a 535 barrel, a die grinder, some TIG time, maybe an end mill for the valve seats. The rest should be factory parts from H's, maybe 1940's era flathead bits. Real Old Skool!

!

[zimmemr]

Flatties rule. I forget who it was, maybe Gas-Gas, that built a prototype Trials bike with a 350 flathead, it worked great but they decided to go with a two-stroke, I presume to save weight and cost.

[Karl Fenn]

As far as l'm aware the latest BMW is chain driven cam and half pushrod engine, wet clutch quote me if l'm wrong.

[Richard230]

As far as l'm aware the latest BMW is chain driven cam and half pushrod engine, wet clutch quote me if l'm wrong.

The latest 1250 boxer engines use a "shift cam" to spread the power out and to meet the latest emission standards, so it is easy to loose track of what is going on inside that engine. Looking at this video (after about a minute of nothingness) it appears that the latest version of the boxer engine is a full OHC, unlike previous the models: https://www.youtube.com/watch?v=brNIxQ7Cwns