Well Charlie, I'm practicing to be a politician...

 

I still have my original 1990 clutch in the bike, with a Barnett clutch spring to beef it up for the 107, it was stock for my stroker. I am with you on not changing things unnecessarily. Had a new crank sprocket and chain fitted with the 107, because the sprocket was beginning to get sharp! I had a Crane ignition on my bike from long before the stroker, to iron out emissions related timing quirks, which the TC may also suffer from, so consider a new adjustable ignition module.

 

Uh-oh…

Went down and met face to face with the machinist/engine guy today. Previously I only spoke with him on the phone. Nice guy and much easier to talk to then the guys on my side of town with their “A EVO CAN’T GO 115,00O ON CAR OIL BUT I HAVE 30HP MUFFLERS FOR SALE….AAAHHHHHHHH” nonsense. We get to talking and when the T&O Torquemonster flywheels come up he is adamant that those are the wrong choice!? He says that if I was looking to launch myself across the intersection faster, then go with those but they take more power to keep spinning. We go back and forth but I’m not knowledgeable enough about this subject to put up much of a fight. His friend from across the parking lot comes over and when he is asked about this subject….well now its 2 on 1 and not in my favor!! They reminded me that Harley has gotten lighter flywheels as they progressed through the different motor types for a reason and that the heavier wheels will actually ADD to the vibration?? I don’t know about that vibration part but still, he’s a nice enough guy, just so happens to have an opposing viewpoint to what I went in there with.

So after I left I called the T&O guys again and explained what I was just told. They of course said the exact opposite and told me how they thought these flywheels were perfect for my application. They also said these Torqumonster flywheels are designed just like the original shovelhead flywheels use to be, adding mass to one of the lower wheels. So, while Harley has gone to lighter wheels, these guys still offer the older, heavier kind.

From the inputs I’ve gotten, and my own experiences, this is the way I see it and please, feel free to pick this apart:

Harley has gone to lighter wheels for a reason right? What is that reason? They have also gone to larger displacement and higher RPM ranges then the old days. My FLT red lines at 5500 rpm for example. Is it the increase in motor size and efficacy that allows them to get away from lighter wheels? Like a V8 in a truck vs. a straight 6 – the V8, with its increase in cubes and overall power doesn’t need the help down low where the smaller, stroked, straight 6 uses a larger flywheel to help get it going. And then there is the old John Deer tractor my grandparents had – really slow spinning 2 cylinder motor and a massive flywheel. I’ve seen dyno sheets to some of these larger cubic inch V-twin motors and they pretty much start with massive amounts of torque, where the smaller motors start low and need to build as the motor spins up. There is stored energy in the spinning mass and I believe this will help at lower rpm while pulling. Motors do not produce much power at idle (or slightly off idle where you let out the clutch) and the stored energy in the spinning mass will help get under way, especially in a smaller size motor under load. There is no free lunch so what is the trade off? I can see spin up speed a.k.a. acceleration but from the inputs I’ve gotten, this won’t be noticeable. Going from 4 ź stroke to 4 5/8ths helps cover this up. Why doesn’t Harley do this….Longevity.

Because of production cost Harley makes a one size fits all motor for all their bigger bikes. Where a smaller Low Rider for example would want acceleration, the bagger (and that trike thing) needs torque. I wonder how differently they would build the bagger motor if it was built solely for the bagger? And if they can rubber mount a Sportster, they could if they wanted to stuff a twin cam in there. But those motors are built different for a reason. They want a lot of acceleration and don’t have the same load to pull around.

How am I doing? My head hurt and I need a drink!! Luckily for me IT’S SATURDAY AFTERNOON (almost) and I have nothing better to do today!!

And as of now…….I’m sticking with the heavier wheels.

 

Thanks for sharing that scenario and the mechanics views are of no surprise.

In the old days, the guys doing the really "trick" setups for speed and bragging rights would actually use 2 right side flywheels to lower the weight from that end. Why would they? Lighter wheels allow for quicker acceleration and that's it - period. And back in those days the guys were working with relatively tiny 45 cubic inch engines, spinning flyweels that weighed near what an Evo wheel does today and they were doing it with basically half the piston size... but when the design is appropriately balanced, the moving parts really don't care what the other ones weigh. A light flywheel will vibrate same a heavy one if not balanced to the geometry of the design.

Let's face it, manufacturers (and builders for that matter) do whatever sells (within limits from EPA, mfg costs etc) and quick, arm stretching acceleration is a powerful aphrodisiac, especially to the current generation of motorcycle buying/riding population. And your idea of a different bagger engine is correct. When "bike bikes" first came out there was what on the road? - 74" Harleys and that was it. Then came the Sportsters, British bikes and eventually Hondas - lighter, quicker accelerating (and if they'd had loctite back then most would have dipped Sportsters in it). But like every other manufacturer trying to capture every possible corner of the market, they started producing any and every combination of size, weight, style imaginable to get every motorcycle purchasing dollar they could. Using a similar or identical engine was simply good business sense from a manufacturing and profit standpoint.

And there's no right or wrong to any of this. It's simply a matter of whether one wants to roll a heavy load along at whatever speed with the least amount of effort, or zip around quicky from slow to fast - as in, 0 to 70/80 in "x" amount of seconds, or sit out there and roll at 70-80 all day long... that's my perception of it all.

PS - I don't have my notes here, but there's only a few pounds difference between the TorqueMonsters and stock wheels...

One more thing that just came to mind about the carb. I have zero Twin Cam experience, but I'm thinking you'll need to find the intake manifold for an Evo. The cylinder/head combination is taller on a TC and don't quote me, but I'm thinking the angle won't mate-up. Also, the Evos had a vacuum nipple just behind the diaphram chamber of the carb for the VOES and the TCs had that fitting plumbed into the manifold.

 

Charlie,

Interesting stuff, but I can't help thinking there is some folklore hiding in there! I bought a shovel new in 1974, when Harley engines were bolted in as God intended, none of the rubbery stuff. That thing vibrated like nothing I had ever owned while new, but as the miles rolled by it eased up and I could ride it at any speed in comfort, up to 115mph on the clock. So I am sceptical about the flywheel weight/vibration thing. It had no problems launching from standstill in second gear, a party piece I used for shaming all my mates on their other brand bikes - took'em ages to catch up! But that is partly a gearing thing and I have bored the pants off some of you with my theory on that!

Once Harley went to rubber mount and also bigger engines, balancing the engine would have required different characteristics. It is possible they reduced flywheel weight as part of that, but also having owned BMW twins since the 70s and sampled them since the late 60s, they reduced flywheel weight over the years (they were bloody awful in the 60s versions). So I think that is partly the development of the reciprocating engine, rather than a Harley specific thing.

I went to a talk given by a Jaguar car engineering director some years ago, on the new V8 engine they had just introduced. It is entirely developed by them and he described how they had reduced parasitic losses (friction to you and me) by using higher grade materials to reduce component weight, like smaller valve stem diameter. This sort of stuff hasn't escaped the attention of all the manufacturers, and if Harley are using lighter modern pistons they won't need as much counter-balance, hence lighter flywheels. I can't see any problem with a well built motor with your proposed 'heavy' crank.

I hope that drink worked for you!

 

Consider this -

Two 8.5 diameter discs of steel with shafts centered in each, connected by a pin (crankpin) that was also centered between the discs. Assuming whatever was connected to the center pin was free to rotate, then what would the discs look like? They would be flat and uniform with the only removal of material being what was necessary to compensate for tiny differences in density and mass of the material to make a perfectly balanced rotating assembly that would theoretically spin at any speed without vibration. My point being, it wouldn't matter whether those 2 discs weighed 2 lb or 2000 lb, the result would be the same, either balanced or not. Weight of the total assembly has absolutely nothing to do with it.

But in the case of these flywheels we're moving that center pin approximately 2.25 inches toward the circumference of the discs, throwing an otherwise balanced rotating assembly into radical unbalance. Hence, material is removed from the (now offset) pin location of the discs (flywheels) to a point the assembly is once again balanced... but not exactly. The downforce of the compression plus the upstroke of exhaust, friction of the pistons, weight of the now offset parts and timing of all that must be compensated for.

In the old days when they first started producing these types, the mathematical formulas may have gotten them close, but it remained trial and error as to what would rotate in that manner without shaking the fenders off. So that was the procedure of the day in determining how much heavier the wheels had to be opposite the rods to allow for the least amount of vibration. That is what we now call the "factor." When you put a completed assembly (rods pistons and all) between 2 dead centers, the spot away from the crankpin and rods will be heavier regardless if it's an Evo, Shovel or what have you. So it's not the weight of the wheels, rather the balance "factor" incorporated that determines how smoothly all this will rotate.

So for an already too long of a story short - heavier the wheels, the more inertial energy is stored - period. And regardless of the total weight, the "factor" of compensation incorporated into the assembly determines how smoothly it will operate. And in the vernacular of Forrest Gump - "that's all I have to say about that."

 

Ok, time for me to chime in. You stated that you ride two up and pull a trailer sometimes. The heavier wheels will help you. Lighter wheels will allow you to rev up quicker, but you aren't looking for that as you run 3,000-4,000 RPM's. Remember the first law of inertia: "Objects in motion tend to stay in motion" That's a basic law and cannot be argued with. For touring and plain old cruising-heavy wheels. For acceleration-light wheels. Secondly a heavy flywheel will smooth out vibrations caused by the 45 degree V-Twin design firing pulses. If you could get the engine to run with a heavy enough, properly balanced flywheel you would have a smooth running V-Twin. However the weight would be prohibitive. Now there you have it!!!

 

[QUOTE]Hey T150, passing along something I just learned. I am currently working on my 4 5/8 89", I ran the S&S cast pistions because that was it. The guy I sent my heads to asked me about the pistons and laughed "you can't find forged can you" He let me in a builders secret and told me a Wiseco 1200 flat top sportster piston will work and ranges from 0.00 - 0.015 deck height.

I"m saving up some more change to get the pistons, I'm pretty sure what part number of piston he uses but going to get them from him to eliminate guessing, he has treated well so far and forgot more than I will ever know.

 

[QUOTE=1997bagger;6253418]I don't know if they are forged, by the chap who built my stroker used KB Sportster pistons. I think in a Sportster they give 10:1, but a little less in my motor.

 

So now that the motor size and design decision has been made I guess its time to start. I parked it up on the lift yesterday (114,940 miles) and this will be the first time since April 2, 1998 that she will NOT be ready to go at a moments notice! And until I actually break it down, would still jump on it and go cross country without hesitation….just PLEASE not into a head wind!! And I’d have to remember to bring along oil.

Thanks everyone for your inputs. t51vej - I (as well as others I’m sure) really appreciated your detailed explanations as to why things are, or are not, a certain way. That is way better then “because I’m anonymous Internet guy and I say so” with no reasoning to back it up. Graham, your input was also very helpful and that 6 speed has been moved back to the bottom of the list. I started this looking for way more motor then I needed I guess and am glad I was talked out of cutting this thing up (thanks Rufus).