Author Topic: How Big Can Displacement Get Without Needing A Counterbalancer?  (Read 260 times)

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nicholastanguma

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Since the 80s the Japanese have been putting at least one counterbalancer on all their thumpers, from 200 up to 800 ccs of displacement, and in some cases the larger sizes even get 2 counterbalancers.  The Europeans do likewise these days, too.

Mass market machines must only meet a certain bare minimum of tolerances to pass quality control, therefore counterbalancer assemblies make sense since each machine's engine is not going to be individually balanced to the minutest degree possible, as though it were being assembled by a master craftsman taking great pains for the utmost in precision.  Pre-1980s thumpers were of course most characterized by their boneshaking vibration, and the appearance of counterbalancing measures was inevitable.  Imagine for instance the tooth shattering vibes that would accompany the DR650-800 single cylinder engines if they had not been counterbalance equipped.

But by all accounts Tom Lyons hot rod Fireball thumpers are individually balanced so well people are perplexed to outright shocked at the smoothness.  And clearly no RE Bullet has a counterbalancer or rubber engine mounts or other vibration mitigation in place, so I'm left wondering just how big can a thumper get without needing a counterbalancer if a master engine builder such as Tom is the fellow putting it together?

700cc?  800cc?


AzCal Retred

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Karl Fenn

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Well l reckon without a balance the 650 would have vibrated like a T140, BMW have a counter balance on the singles, of course the old bikes had no counter balance, but we accepted it as just being normal, you used to end up with tingling feet and fingers on a long run but at the time just accepted it, norton tried the revolutionary isolastics to overcome engine vibration but this was not a magic bullet


Richard230

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Ask Allen Millyard how big a motorcycle engine can get:  https://www.youtube.com/watch?v=I-Xr1bmbZ_s
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viczena

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Ask Allen Millyard how big a motorcycle engine can get:  https://www.youtube.com/watch?v=I-Xr1bmbZ_s

Good answer!
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AzCal Retred

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A single cylinder, opposed piston, twin axial crank machine would be inherently low vibration. Might be a good application for sleeve valves too. It would keep the weight low. The Panther Sloper big singles were an attempt to keep cylinder height reasonable with a long stroke design. The opposed piston concept hits all the marks, it's just tough to get mixture in and exhaust gasses out without exotica like sleeve valves. A opposed piston 2-stroke would be a lot easier as there are no valves to deal with. Fuel injection might get you past the EPA. A "sealed" bottom end and electric blower might be good enough for intake mixture admission duty. No substitute for cubic dollars...
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gizzo

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A single cylinder, opposed piston, twin axial crank machine would be inherently low vibration. Might be a good application for sleeve valves too. It would keep the weight low. The Panther Sloper big singles were an attempt to keep cylinder height reasonable with a long stroke design. The opposed piston concept hits all the marks, it's just tough to get mixture in and exhaust gasses out without exotica like sleeve valves. A opposed piston 2-stroke would be a lot easier as there are no valves to deal with. Fuel injection might get you past the EPA. A "sealed" bottom end and electric blower might be good enough for intake mixture admission duty. No substitute for cubic dollars...

Now you're talking. A "single cylinder" Commer Knocker 2 stroke diesel powered bike... You'd have to love that.
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AzCal Retred

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Thanks for the heads-up Gizzo! With titanium or carbon fiber rockers it might be able to spin up a bit. If not, a hydrostatic transmission might be useful. Lots of possibilities...

"There's nothing new under the sun" & " Materials Science drives innovation"

https://en.wikipedia.org/wiki/Commer_TS3
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zimmemr

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That was fascinating, thanks Gizzo and ACR. I'd never heard of them before.


Richard230

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Why design a simple engine when you can make it more complicated like the Commer Knocker ?  What's the fun in that for an engine designer? ::)   I suspect that complication and manufacturing expense is why we are not all driving around in Knockers.  ;)
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Karl Fenn

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They can get as big as he wants Allen is a pure genius the only one as far as l can see. His creations are like something from the land of the gods.


AzCal Retred

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@ #10: From the Wiki article:
" Rootes' intention for the engine was for it to fit under the QX "cab forward" design fitted to the R7 7ton truck released in 1948. This very advanced design had been built with the engine under the seat to allow three men to fit comfortably across the cab. "

A compact powerplant is a good thing.
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Arizoni

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Would 20,175 cubic inches be big enough?
It does have counterbalancer weights on the crankshaft but no special "counterbalancer shafts like modern engines use.

https://www.youtube.com/watch?v=2MLkbHkxk-g
« Last Edit: March 25, 2021, 04:20:16 pm by Arizoni »
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Karl Fenn

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Mind you, you could get along with the vibration in the old days just a bit of a tingle that's all.