79cc Sportsman Flyer build

Tom from Rubicon

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Apr 4, 2016
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Just from video #1. lapping in the flywheel / crankshaft taper contact area never crossed my mind. That AGK does not give a hoot for woodruff keys is telling. It looks like AGK is content with only 60% contact superseding key positioning. Allowing metal to metal contact grip to supersede key retention.
Now I gotta hunt down the two tins of water soluble lapping compound lurking somewhere in the shop.
The other interesting value of a keyless flywheel according to the video is setting way beyond the keyed timing advance.

So, this will be my approach. Lap the mating flywheel and crankcase surfaces, but start at the keyed position.
If someone has empirical experience with spark advance beyond 28degrees BTDC. let me know.
Tom
 

Tom from Rubicon

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Apr 4, 2016
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Rubicon, Wisconsin
Just from video #1. lapping in the flywheel / crankshaft taper contact area never crossed my mind. That AGK does not give a hoot for woodruff keys is telling. It looks like AGK is content with only 60% contact superseding key positioning. Allowing metal to metal contact grip to supersede key retention.
Now I gotta hunt down the two tins of water soluble lapping compound lurking somewhere in the shop.
The other interesting value of a keyless flywheel according to the video is setting way beyond the keyed timing advance.

So, this will be my approach. Lap the mating flywheel and crankcase surfaces, but start at the keyed position.
If someone has empirical experience with spark advance beyond 28degrees BTDC. let me know.
Tom
Edit to say Lap the mating flywheel and crankshaft surfaces.
I surely thought 54 foot pounds torque could draw two tapers into full mate.
 

indian22

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Dec 31, 2014
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What accent Tom? LOL ....good video. Two things I'd really ditto proper key attitude when installed on a taper shaft & this is not just a motor thing it's a taper topic. The second is his insistence on having a clean taper, male and female, prior to installation. It's critical! This too is a taper thing & is 101 machine tool info for any tool using tapers. Both accuracy and wear result by ignoring clean taper fit up.

I use the "Clover" brand of lapping compound and one small tin is a lifetime quantity for most hobbyists.It works for what it's intended to do and will also cearance anything it strays onto.

Building a puller for your motor is a simple project Tom. I have pullers for each motor type I use. I think I paid $20. for the 125cc Honda clone puller that I use on my Simplex and Harley "Pea shooter" builds, just in case. It's a bit more complex than the one used for the ARC flywheel, so I opted to buy rather than make.

Rick C.
 

indian22

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Tom that was an element I thought they omitted in the video. I use blue on taper fits as well as head work or just anytime I want a precise fitment. The old time gun smiths used "smoke tolerance" before blue entered the scene. They had a sooty flame burning and smoked the part being filed and fitted to locate the high spots until the "tolerance of smo ke satisfied them. Blue is a nice substitute I'd think breathing smoke shortened life spans.


Rick C.
 

Tom from Rubicon

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Apr 4, 2016
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Quote Rick C. "I'd think breathing smoke shortened life spans."
Think candle smoke. Been there, done it when I had not Prussian Blue. Magic marker works fairly well to witness a fit.

Didn't get much done today. Made a copper scraper and cleaned up the clinging gasket on the crankcase.
Still have to clean up the side cover.
Made a tap guide block to squarely tap 5/16-18 four holes in the tooling plate for mounting the engine head right side up.
When I pressed the valve guides flush with the valve pockets, the valve guides got taller by 2.5mm top side.

If I don't cut down 2.5mm of the valve guide of intake the valve seal flange will not set flush on the spring boss.
After that, flush the crankcase. Amazing all the nasty metal grunge in a fresh engine.
Give the modified head a good soapy wash and rinse. Reassemble the valve train contained in the engine.
The fussiest part and important part to me is the valve lash adjustment. AGK spec's .004" for intake and exhaust.
If I get anything done tomorrow after our Sunday driving Miss Daisy (Mona) I can only hope.
Question: Does anyone use Permatex on their gaskets on a reassemble? Factory sure doesn't.
Tom
 

indian22

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I still grab a black marker for my quick markups Tom but have my Prussian blue handy for real layout work. I have yet to order a granite plate and new height gauge. By the time I get my layout tools together for the lathe I suppose a Mill order won't be so expensive an add on.

Rick C.
 

Tom from Rubicon

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Once I clamped the tooling plate head assembly in the Mill vise I was able to mill down the intake valve guide 1.9mm.
Allowing the intake valve seal flange to seat properly on the valve spring boss.
This was done after I pressed the valve guides flush in their respective intake and exhaust port pockets.
Monday is going to be soap and water washing day. If you never have soap and rinsed aluminum. Be surprised.
Tom
 

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Tom from Rubicon

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Apr 4, 2016
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Thursday will be knocking the stock cast iron flywheel off the crankshaft, and begin the lapping process to ensure proper fit of the ARC flywheel to the Predator 79cc crankshaft. Youtube does decent documentation both AGK and ARC.
The ARC video does not dwell on the time it takes for a proper lap job.
Fifty years of experience lets me say. 75% contact is good, 90% contact better in steel. Aluminum unlike steel compressed has no spring-back.
Tom
 

Ralph hop

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Nov 14, 2019
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Tom, is the lap for timing advance or is it a wise thing to do for aluminum fly. Got an ARC fly that says it has 8 degree advance built into the key way. You using a key or just mating it?
 
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indian22

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I really like the ARC flywheels. I prefer the look of the smooth version and when running without a housing cover the finned flywheel is a big safety
issue. Got to keep that pretty "cheese cutter" enclosed. The fins are mainly for stationary cooling use on the industrial motors and serve little purpose for cooling on an all aluminum motor which has open exsposure and is primarily moving while in use. Not idling in heavy traffic. Motorcycles got by without fins for over a hundred years..Of course if you are using the pull start recoil mech then the housing is required and a fins are a good factor. Either/or the ARC wheels are really nice.

Rick C.
 

Tom from Rubicon

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Apr 4, 2016
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Tom, is the lap for timing advance or is it a wise thing to do for aluminum fly. Got an ARC fly that says it has 8 degree advance built into the key way. You using a key or just mating it?
Ralph, at the outset I will do a fit check with Dykem Prussian blue Marking blue - Wikipedia as the shaft and flywheel tapers may not be the same. After that, I am going to go with the keyed timing. If needs be I will do the lapping.
ARC going keyless for 34 degrees advance has to have a perfect taper fit.
Tom
 

Tom from Rubicon

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Apr 4, 2016
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I really like the ARC flywheels. I prefer the look of the smooth version and when running without a housing cover the finned flywheel is a big safety
issue. Got to keep that pretty "cheese cutter" enclosed. The fins are mainly for stationary cooling use on the industrial motors and serve little purpose for cooling on an all aluminum motor which has open exsposure and is primarily moving while in use. Not idling in heavy traffic. Motorcycles got by without fins for over a hundred years..Of course if you are using the pull start recoil mech then the housing is required and a fins are a good factor. Either/or the ARC wheels are really nice.

Rick C.
I decided to go with the blower fly wheel Rick, incase I ever get parade duty. If the mood strikes me I can always turn the blower fins off as I don't think they effect dynamic balance. Somebody on the forum already has.
Tom
 

Tom from Rubicon

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Apr 4, 2016
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Ralph, I was surprised of the weight of a ARC 6671 flywheel. 180 from the epoxy encapsulated rare earth magnets is a encapsulated counter weight. The stock ARC has a bit of spark advance. When I get the cast iron flywheel off so I can compare weight, will be worth documenting. Never gave it any thought until right now.
Those d**n fan blades create drag too ! Grrr!
If I don't get the performance I expected, chips will fly. Four jaw chuck to the rescue.

I got a 1953 Ford Jubilee needs loving too, and a 1973 Boston Whaler powered by a 1966 Homelite 4stroke needs loving.
And a Wife, who gets all my love.
Surplus is what sustains my projects. I had more ambition for things when I was a wage earner.
Ralph, you saw the skeletonized flywheels ARC has? But I don't think your 212 is not a concern. Those engines got steam.
Use one and enjoy,
You have the option having lapped the flywheel of offset keyway timing advance.
Not being a Small Engine Mechanic, I assure you, I ain't got a clue. Empirical data eludes us.
No dyno graphs.
So be it. If the reworked engine in my Sportsman Flyer can climb the Glacial Eskers which have been a challenge.
The time and expense will be worth it.
Tom
 

indian22

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Dec 31, 2014
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Good points & questions guys. I'll add my observations to the conversation. The stock flywheels have shown weakness when the revs go up & pose a real danger to the rider. Switching to the ARC billet wheel is to me a great safety modification. The lighter billet wheel should balance out just fine if the fins are cut, but if a balance issue occurs it's simple to balance out in your shop. Shaving the fins allows you to shape the flywheel & it's nice not to see another motor just like yours, though all the ARC wheels look great. It's cool to look different. Shaving flywheels to shed weight and improve acceleration is an old rodders trick that works, to a point, but taken to far it's a problem. The loss of a few ounces shaving the fins etc. would not seem to be a problem if you have significantly improved the H.P. with the mods made & I'd think you will double the advertised power of the 79cc mototor and that is going to feel huge! It's a fact that removing the governor and running heavy valve springs will put the revs way up there so getting rid of that cast bomb between your legs is worth way more than the cost of a billet flywheel.

I like where your taking this with or without the fins.

Rick C.