The Chopper Compendium

Contemplating the potential of increasing my stock flywheel stroke from 4.250" up to 4.500". Any advice would be appreciated.

Any advice would be general, since you don't say what motor your using.
There is more than one way to do this, and there are several pros and cons.
There are many things to consider. Best to buy a current high performance book for the engine you have and study, study, study.

If you want more detailed advice, give more details. What kind of motor, how are ya gonna ride, what do you want to accomplish, etc., etc., etc.
What else do you plan to do to it? Stroking is just one feature of a true performance package.

*Edit* AND, stroking is not always part of a high performance motor.

Check out www.victorylibrary.com , Panic has some good info posted for free and a lot mre for sale in his books !

Bike started life as...1980 flt, 80 ci shovel. 4.250" stock stroke, want to bump it up to 4.500" stroke and increase piston/jugs to 3.625".
I have the v-twin tuners & performance handbooks as reference for building performance engines. Riding style or desired outcome is hot street/stop-light drags (bar hopper).

So you want a 93 incher, if you plan on running it hard, I would get a set of stroker wheels, they are stronger and if you S&S wheels they are lighter = faster into the Rs, at one time there were offset crank pins out there, but I don't think there to be had anymore. If you want to use your stock wheels you can go to 88 inchs with 3.625 big bore jugs, which I do all the time, in fact I'm biulding a 88 inch EVO right now. I like to lighten the stock flywheels when I use them in a 88 inch GO FASTER.

Sadly, the purchase & installation of new flywheels is well outside the constraints of my budget. Hence the reasoning for my quest to obtain info & advice on modifying/stroking the stock assembly.

Those are good books. That style of riding requires torque more so than HP, so stroking is a good way to go.
For that bore, you'll be using diff jugs, and pistons, so likely the best way to stroke wold be to use longer con rods.
Otherwise you get into machining the wheels for different crank pin placement. IMHO.

It's good to discuss this to research options and for planning, but if you plan to use a local shop, they can give you face-to-face info and recommendations,
and let you know what they are capable of. You can also ask around for other rider's recommendations. See someone riding a hot set-up, ask them about it.
What did they do, where, and are they happy with it.

Whatever you do, don't rely solely on answers you get on ANY internet forum. There are a lot of knowlegable people here and elsewhere with good answers, but...
sometimes you'll get some bad info from a well-meaning person wanting to help.

FYI, when I built my Evo motor, I was told that 3 & 13/16" (3.8125") was the largest bore that would fit under a stock HD head.
I started my build because the orig cases developed a crack. I decided since the motor was apart, I would use the biggest jugs I could.
I planned on long cross country riding, so kept the stock wheel/rod assmbly. Wound up with a screaming 96" motor that went from 57HP to 72 and considerable seat of the pants improvement.
Delkron cases, Axtell 3.8125" jugs, stock heads, S&S Super E, Andrews cam EV-46, Screaming Eagle ignition.

Stroking a motor needs to complemented with fuel/air flow, and a hotter spark than stock is very helpful. Be prepared for shorter longevity as strokers
have more piston/cylinder wear.

gearhead1951...thanks for that link, lots of great info

railroad bob...
I certainly won't go off any one particular source. And, I'm not overly worried about fitment issues as I'm also planning to build a custom hard-tail frame & girder front end to resurrect this previous heavy old-tired bagger.
As for finding a local shop, well I work in a machine shop (as a welder/fabricator) and have been discussing this with the machinist I work with and plan to do all the work "in-house" as it were. His actual suggestion was just to make a complete new set from scratch.

Your machinest is right, you need new flywheels, 4.5 with 3.625 jugs is a good combo. 93". If you can't afford the wheels how are you going to afford the the big bore kit? the wheels are cheaper then the big bore kit. if your budget is tight then I would just stroke it, more bang for your buck, 4.5 stoke with your stock jugs will give you around 86 inchs, if you go 4.625 you'll have around 89 inchs, and both those engine sizes will be great fun in a light chopper that you want to build. also you can't stroke a motor with longer rods, the crank pin has to be moved away from the flywheel center line to make more stroke.

Early Iron wrote:SNIP... also you can't stroke a motor with longer rods, the crank pin has to be moved away from the flywheel center line to make more stroke.

There ya go, I gave some bad info without meaning to. Thanks for the correction.

Early Iron...
I know rod length only changes piston position, not stroke.
As for the financial issues, its comes down to one or the other. That is why was looking for advice about modifying the stock wheels. I figured given my access to a machine shop & a very experienced machinist, it would be something that could be tackled.

Questionerofall, It could be done, but it would take a lot of work and like your machinest told you, it would be better to make new wheels, no matter what you do, you are going to have to make fixtures and find some datum points to work with if you want both wheels to match, you will also need some tooling and that wont be cheap, you can buy new aftermarket wheels cheaper than modifying yours or making new ones.

we stroked some stock flywheels one time by changing the pin location, went together OK, just didnt last very long.

Riceburner...
Can I ask, what was the process you went through to stroke those flywheels? I'd be very interested to learn if its along the same ideas that I & the machinist I work with have been bouncing around.