Author Topic: How Big Can Displacement Get Without Needing A Counterbalancer?  (Read 707 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?


« Last Edit: March 24, 2021, 03:27:05 pm by nicholastanguma »


muezler

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I would say 2.000cc

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ace.cafe

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It's unlimited.
No engine ever needs a counterbalance shaft. The crankshaft has counterweights built into it which balance it.

The purpose for a counterbalance shaft is to counteract the remaining vibration forces for perceived comfort.

Counterbalance shafts are totally unnecessary for engine function.
You might notice that cars and other vehicles do not have them.
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TrianglePete

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Most modern 4 and V-6 engines have balance shafts.  It does wonders for singles or the other
manufactures would not spend the extra $
Balancing is a compromise. I use 65%.
Two thing I learned
   The heavier Bullet crank helps stalling in the 535
   Steel pushrods create bad vibrations


Keef Sparrow

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I think an old British motorcycle manufacturer called Panther used to make a 700cc single many years ago - I doubt it had balance shafts as it was so long ago.
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johno

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I think an old British motorcycle manufacturer called Panther used to make a 700cc single many years ago - I doubt it had balance shafts as it was so long ago.
The biggest Panther was the M120 which was 650cc, not far off though. ;)
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Richard230

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How about a homemade 5 liter V-twin?   ;D
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nicholastanguma

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It's unlimited.
No engine ever needs a counterbalance shaft. The crankshaft has counterweights built into it which balance it.

The purpose for a counterbalance shaft is to counteract the remaining vibration forces for perceived comfort.

Counterbalance shafts are totally unnecessary for engine function.



The solid mounted H-D Evo Sportster is well known for its heavy vibrations, so when Buell lopped off the rear cylinder to create the 500cc Blast single they essentially created an old school big single, as they did not add counterbalancing.

Since an Evo Sporty engine can be bored up anywhere from 88 to 100 cubic inches a Blast can be commensurately bored up, obviously, making somewhere around 750 - 800cc I think. 

Ace, could such a monstrously sized solid mounted thumper actually be made tolerable for daily riding without use of a counterbalance shaft?  I know you've already proven it can be done with 535cc Enfields, but a 750 - 800 cc engine is just so massive...


ace.cafe

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The solid mounted H-D Evo Sportster is well known for its heavy vibrations, so when Buell lopped off the rear cylinder to create the 500cc Blast single they essentially created an old school big single, as they did not add counterbalancing.

Since an Evo Sporty engine can be bored up anywhere from 88 to 100 cubic inches a Blast can be commensurately bored up, obviously, making somewhere around 750 - 800cc I think. 

Ace, could such a monstrously sized solid mounted thumper actually be made tolerable for daily riding without use of a counterbalance shaft?  I know you've already proven it can be done with 535cc Enfields, but a 750 - 800 cc engine is just so massive...
If the crank is made right, no counterbalance shaft is needed.
Now, some people might want one for added comfort, and that's why they exist.
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nicholastanguma

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If the crank is made right, no counterbalance shaft is needed.
Now, some people might want one for added comfort, and that's why they exist.


I suppose then the question more specifically might be: could such a monstrously sized solid mounted thumper actually be made "comfortable enough for daily riding" without use of a counterbalance shaft?

Let's say this enormous single was powering a dedicated hack, so between the bike and the sidecar there would be lots of metal to help absorb vibes, including a heavy flywheel, and the engine itself would be mated to a six speed transmission so there would be plenty of gearing to help things along and keep piston speeds from going astronomical.
« Last Edit: March 24, 2021, 10:50:15 pm by nicholastanguma »


ace.cafe

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I suppose then the question more specifically might be: could such a monstrously sized solid mounted thumper actually be made "comfortable enough for daily riding" without use of a counterbalance shaft?

Let's say this enormous single was powering a dedicated hack, so between the bike and the sidecar there would be lots of metal to help absorb vibes, including a heavy flywheel, and the engine itself would be mated to a six speed transmission so there would be plenty of gearing to help things along and keep piston speeds from going astronomical.
It's based on a personal desire for comfort.

There is no reason that any size engine "needs" a counterbalance shaft, if it is made properly.
The only "need" arises if a designer or the consumers want more vibrational comfort than the basic design provides.

For my opinion, I think counterbalance shafts typically add unnecessary weight and complexity because I have never felt the need for one in any vehicle I have owned, including many "crude" vintage vehicles.
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TrianglePete

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I like my bike as smooth as possible.

The balance shaft was invented by a Brit

named  Lanchester in 1904.

The shaft takes care of the second order .

The manufacturers would not spend $ if they

didn't think it was necessary.


Bullet Whisperer

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Modern singles with balance shafts generally have much lighter cranks than older, traditional machines, which had enough flywheel mass to enable quite effective counterbalancing by removal of material in appropriate areas. Where the more modern cranks are concerned, they may not have enough material in these crucial areas for removal of mass in order to be balanced anywhere near ideally. The counterbalance shafts take care of this instead, but absorb some power while doing so, just as heavier flywheels also do, so it is six of one and half a dozen of the other, to some degree at least.
 B.W.


nicholastanguma

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Modern singles with balance shafts generally have much lighter cranks than older, traditional machines, which had enough flywheel mass to enable quite effective counterbalancing by removal of material in appropriate areas. Where the more modern cranks are concerned, they may not have enough material in these crucial areas for removal of mass in order to be balanced anywhere near ideally. The counterbalance shafts take care of this instead, but absorb some power while doing so, just as heavier flywheels also do, so it is six of one and half a dozen of the other, to some degree at least.

Good explanation of the differences between two generations of thumper tech, thanks for your insight.

And you're right: engineering is always a compromise somewhere.  Make something better here and you have to make it less better somewhere else.



nicholastanguma

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I like my bike as smooth as possible.

The balance shaft was invented by a Brit

named  Lanchester in 1904.

The shaft takes care of the second order .

The manufacturers would not spend $ if they

didn't think it was necessary.


I like smoothness, as well...but not too much.  I don't want my motorcycles to become dull anonymous modern appliances.  If I wanted dull and anonymous and modern I'd be riding something like a Husqvarna Svartpilen or a BMW F650.

The thought of an 800cc, carbed, air cooled thumper makes my heart sing, but I'm not willing to be naive--while my heart is singing my head is wondering just how much vibration I would in REAL LIFE consider too taxing to enjoy beyond a half hour.

A DR650 engine can be bored up to 790cc, and then stroked up to 900cc if so desired, and of course that engine has been counterbalanced since its inception in 1990, so the potential for huge hot rod power is well documented while still maintaining reasonably low levels of vibration.

But as terrific as the engines of the Suzuki DR650 and Honda XR650 and Yamaha XT660 are, with their overhead cams and four valve heads and compact dimensions and counterbalancer assemblies, none of them quite strum a luddite's heart strings like the raw thunder of an even older school pushrod two valve head Royal Enfield 535 or a Sportster "halfster" 800.


TrianglePete

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BW
    What % do you balance your cranks to ?

Royal Enfield engineers put a balance shaft on

the Himalayan ??


Bullet Whisperer

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BW
    What % do you balance your cranks to ?

Royal Enfield engineers put a balance shaft on

the Himalayan ??
Hi Pete, originally I worked out the mass required to put through the crankpin holes of individual flywheels of 350 and 500 Bullets, based on a factor of 0.66 and I made up mandrels for each size of engine in order to do this when lightening the flywheels and rebalancing them between centres in the lathe.
 What I have learned over the years though, is good truing of the flywheels and mainshafts seems to be far more vital than getting the balance factor to the last few grams with the Bullet engines. There are no doubt some who would be quite horrified at the rather, shall we say, crude way I balance the flywheels, but it works and the only mention of vibration from any of my 'Asbo' engine owners to date, has been from one whose engine bolts turned out to be loose!
 I can't comment on the Himalayan, or the 650 twins, even, as I have no interest in them and I haven't really done much with the UCE engines, either and am quite happy to keep it that way!
 B.W.
« Last Edit: March 25, 2021, 11:45:33 am by Bullet Whisperer »


TrianglePete

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I agree with getting the crank true  For Sure.

I found 65% for all around.


TrianglePete

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I mean TRUE...


Bullet Whisperer

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Nice rig in that second pic, Pete, I assume that is a mandrel for pressing the flywheels up to a pre set overall width?


Richard230

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One of the claimed advantages of additional engine vibration control devices are that they allow lighter frames to be designed to withstand engine vibes and therefore save both weight and money. Plus, most customers prefer fewer vibrations, or at least a lower vibration frequency, than more. Not everyone appreciates big single vibes, but no one likes the buzz you get from some 4-cylinder motorcycles, especially when operating in hot, dry weather.

Speaking of big singles, didn't Suzuki market an ADV 800cc single some years ago called the "DR Big"? I don't think it was imported into the NA market, but I believe it was sold elsewhere for just a few years before it faded away never to be heard of again.  ???
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nicholastanguma

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One of the claimed advantages of additional engine vibration control devices are that they allow lighter frames to be designed to withstand engine vibes and therefore save both weight and money. Plus, most customers prefer fewer vibrations, or at least a lower vibration frequency, than more. Not everyone appreciates big single vibes,

All good points.

Speaking of big singles, didn't Suzuki market an ADV 800cc single some years ago called the "DR Big"?

Yes.  Lasted longer in Europe, if I recall correctly, and was a very successful Paris-to-Dakar rally racer, I think a winner in fact.  From what I understand the 800 engine was simply a DR650 engine with a bigger bore.


ace.cafe

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I would note that there is a big difference in "needing" it and "wanting" it.

The question was "could it be done".
My answer is yes it can be done effectively.
If the question is "Might some people prefer a balance shaft for comfort?"
My answer is yes for that too.
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nicholastanguma

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I would note that there is a big difference in "needing" it and "wanting" it.

The question was "could it be done".
My answer is yes it can be done effectively.
If the question is "Might some people prefer a balance shaft for comfort?"
My answer is yes for that too.

Interestingly, I'm forced to wonder if the sort of folks who LIKE vintage tech, air cooled, carbed, pushrodded big singles prefer the more visceral experience of heavy flywheels and heavy crankshafts in place of counterbalancer assemblies.

This technology is so obsolete these days even the 80s Japanese big singles are advanced by comparison. 

For instance, if some restomod shop were selling turnkey Sportster adventure hacks with 800cc "halfster" thumper engines, carbs, kickstarts, and Baker 6 speed transmissions then they'd be marketing such machines as modern vintage artifacts...and experiences.  Each machine would indeed be real world usable as a dual sport overland rig, but as an intentionally modern vintage experience too, and not just a travel appliance with an accompanying Motel 6 weekend mentality.

Ergo, anyone who actually purchased one of these things would be intentionally looking for just such an artifact and just such an experience.  Such a buyer would be intentionally eschewing a smooth modern EFI Honda machine and experience.

Note that people keep spending a base minimum of 20,000 USD on brand new Ural hacks every year, and if you peruse any Ural forum you quickly see an oft repeated standard list of wishes that the Ural factory never delivers either because of government regs or too much production cost:

- A return to carbs
- A kickstart that actually works
- A 5 speed transmission, but preferably a 6
- More engine power

Yet year after year people keep buying new Urals.  Modern vintage experiences are as important to some buyers as the modern vintage machines themselves.   :)
« Last Edit: March 25, 2021, 02:52:57 pm by nicholastanguma »


nicholastanguma

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If such an 800cc "halfster" adventure sidecar as I described above was available and I had the funds on hand I'd absolutely be plunking down a deposit with the shop poste haste.   ;)
« Last Edit: March 25, 2021, 02:24:38 pm by nicholastanguma »


TrianglePete

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BW,

     Went thru time and money to make that Jig

I can repeat 0 runout and keep small end clearance .
      The other photo is the balancer.


Richard230

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Interestingly, I'm forced to wonder if the sort of folks who LIKE vintage tech, air cooled, carbed, pushrodded big singles prefer the more visceral experience of heavy flywheels and heavy crankshafts in place of counterbalancer assemblies.

This technology is so obsolete these days even the 80s Japanese big singles are advanced by comparison. 

For instance, if some restomod shop were selling turnkey Sportster adventure hacks with 800cc "halfster" thumper engines, carbs, kickstarts, and Baker 6 speed transmissions then they'd be marketing such machines as modern vintage artifacts...and experiences.  Each machine would indeed be real world usable as a dual sport overland rig, but as an intentionally modern vintage experience too, and not just a travel appliance with an accompanying Motel 6 weekend mentality.

Ergo, anyone who actually purchased one of these things would be intentionally looking for just such an artifact and just such an experience.  Such a buyer would be intentionally eschewing a smooth modern EFI Honda machine and experience.

Note that people keep spending a base minimum of 20,000 USD on brand new Ural hacks every year, and if you peruse any Ural forum you quickly see an oft repeated standard list of wishes that the Ural factory never delivers either because of government regs or too much production cost:

- A return to carbs
- A kickstart that actually works
- A 5 speed transmission, but preferably a 6
- More engine power

Yet year after year people keep buying new Urals.  Modern vintage experiences are as important to some buyers as the modern vintage machines themselves.   :)

Sounds a bit like what you want is a Buell Blast.  :o
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I modified my uce 500 cc engine toe a 612 (Hitchcocks crank), wild cams , power commander . etc...  All beautiful - a lot of vibration but too scared to take it to max - problems with the frame I think... handle bars are starting to wobble too aggressively at acceleration - need some more work. I also was unable to kick start it so far. Sure my bike is over 200kg and will do more than 100 miles/hour but I cannot experience it for now.


AzCal Retred

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Roeland - Who did all this work? What's the cranking compression? Are the tyres stock? In good shape & rated for 100+ MPH? Are they aligned & balanced? Steering stem bearings properly lubed & adjusted? Rear shocks OK? Stock? Modified? Front fork oil clean, proper level & viscosity? Any bags, fairings or luggage bolted on, that could affect stability at speed. What's your skill level? Things happen really fast past 85 or so, it's best to approach speed incrementally. How do you really know your bike runs 100 MPH if you can't ride it? Does it have a compression release? Didn't the builder show you the starting technique?. These 612's can require 3mm or more of compression plates to reduce cranking compression to levels that won't harm the engine. Has that been done? If the cranking compression is 125 -- 130 PSI it should be as kickstartable as it was before. Talk to the builder, you need answers.
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OMFBullet

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I used to walk past a Panther combination on my way to school in the 60s.  I remember the chap who owned it used to have to give an enormous kick to start it. The Panthers were famous for knocking their big ends out at regular and quite short intervals. It was unmistakably a single, and indeed the definition of a thumper.


Roeland

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Roeland - Who did all this work? What's the cranking compression? Are the tyres stock? In good shape & rated for 100+ MPH? Are they aligned & balanced? Steering stem bearings properly lubed & adjusted? Rear shocks OK? Stock? Modified? Front fork oil clean, proper level & viscosity? Any bags, fairings or luggage bolted on, that could affect stability at speed. What's your skill level? Things happen really fast past 85 or so, it's best to approach speed incrementally. How do you really know your bike runs 100 MPH if you can't ride it? Does it have a compression release? Didn't the builder show you the starting technique?. These 612's can require 3mm or more of compression plates to reduce cranking compression to levels that won't harm the engine. Has that been done? If the cranking compression is 125 -- 130 PSI it should be as kickstartable as it was before. Talk to the builder, you need answers.

I did the work myself, except for the porting of the head and the beehive valve springs; that was done by ACE. The compression is standard. The back tire is a larger size and together with the sprockets should give a theoretical speed of just over 100mph. I dismantled and re-installed the front fork, changed the oil, etc.  The back shocks are still standard at their hardest setting to avoid the tire rubbing against the fender. The tires are knobbly….that could be the problem. I also fitted the Carberry vibration reduction plate and changed all the bearings, oil pump, hydraulic lifters etc. The previous engine was a 535 cc high compression configuration which was able to go about 93 mph (GPS tracked) with a pillion - the extra weight gave it more stability. I do have saddle bags fitted but I noticed not much change with them or without them. One thing I did note is that the actual frame alignment is not very accurate - the engine bolts did not line up exactly - I loosened everything and tightened the bolts with the engine running. In actual fact with the removal of the engine block one of the engine bolts (nearest to the kick starter) was seized to the engine - I had to cut the engine out of the frame and drill out the entire bolt. The engine is a 2012 C5 UCE engine; it does not have a dedicated compression lever; only the little lever next to the left-hand handle bar grip which I believe acts a bit like a choke? I'm actually not sure how to lower the kick start compression on this engine - I may have to look into this? The engine got now about 2500 km on it and to be honest I'm not that much into high speeds anymore. If I want to go a little faster I take the Harley.


AzCal Retred

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Roeland - to be clear, what frame is this? B5? C5? Continental GT?
This is a standard 500cc 2012 C5 with a ported head, factory piston?
What is the measured cranking compression?
I believe that the electric start has a decompressor mechanism built in. If the cams aren't stock, this feature is likely gone.
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PART No. 570309 ; CAM GEAR ASSEMBLY-EXHAUST WITH DECOMPRESSOR ASSEMBLY ; £147.79
As far as I know from this forum, people install a "button" decompressor or Bullet decompressor unit in the head if that function is desired. I don't see a "exhaust valve lifter" unit offered for other than the Bullet.
What kind of knobbies are these tyres, trials universals? Motard? If you are on the street at more than maybe 65 MPH on trials universals you're rolling the dice.
Wheel alignment is checked with a string, front to back, on the centerstand. You are verifying that the front & rear tyre contact patches are absolutely in line, not offset. Spokes can be tuned to move the rim a bit, otherwise it's machine work & spacers. The rear sprocket needs to stay centered on the front sprocket while you are doing this as well.
When you oversized the rear tyre you reduced fork rake geometry. More rake generally translates to stability, less for turning ability. All of this interacts in complex ways.
I would put S (112 MPH) or H (130 MPH) rated street tires of the OEM size back on it. The cams should go back to stock, then you should be able to use the e-start. These are 27-30 HP machines, it takes about 35 HP to "reliably" run 100+ MPH, rider blended into the paint. Then you'd have something you could ride. If it easily runs freeway speeds, that's good enough. That ACE head will buy you some there!
If you want to go fast, it's too easy to acquire a 600 class 80 HP+ Japanese asphalt scratcher that'll run 130+ for $2500 - $4000, less than the cost of any hop up you could ever do to the Enfield, and safer too. You are buying race-proven geometry & suspension and a current-tech motor that will move it down the road at terrifying velocities. I've even seen a few rideable Hayabusas & ZX12's for under $5000 with their 170+ top end speeds. Enjoy a rideable Enfield, leave real speed to the "clean sheet of paper" designs. Or get a Royal Enfield 650 Interceptor or Continental, they'll broach the "ton" right out of the box and don't weigh much more than the singles.

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