Flywheel safety?

FlatheadsForever87

FlatheadsForever87

Member
I recently joined another forum (old mini bikes) because that's my newest hobby. While exploring the site I found they have a b&s section upon it I discovered it is mostly flathead discussions and a few intek and animals too. I ended up reading about 10 years worth of threads but one really stuck out to me. A few of the "top guys" of the forum were claiming that the flathead flywheels were extremely dangerous above the rated rpm 3600, and any one that kept it on the engine after any modifications or removal of governor were ignorant and had no regard for the safety of their self or anyone riding it or anyone close to it. If this statement is true why wouldn't wka or any other sanction madate a billet flywheel? I have looked around in magazines and online, all I can find for sale is the billet 3 hp flywheel. Also what is the max rpm you can run it safely? Just want to get solid info before I make a reply. Thanks anyone who can help.
 
That’s funny because they turned those flywheels over 6 thousand and even higher for many years and they only came apart a number of times out of everyone running them. I am not up to date on the certain rules but I swear I read somewhere you could use a billet flywheel in wka now. Don’t quote me on it but I feel like I remember reading that. I want to hear what others have to say that have ran flatheads back in the 90s and early 2000s and up to 2010s and the people running them now because they are all familiar with the stock flywheels
 
All the years I have been at the track and in numerous flathead kart racers garages I have yet to see a single 5 hp billet flywheel. I'd like to have a few of those and the 3hp as well just cause they ain't rust magnets and I'm sure they are lighter. Who knows it may even save my life one day when I accidentally Rev my raptor over 20000 rpm. Lol. 20000 rpm is almost as likely as blowing a cast flywheel.
 
5 HP cast iron flywheels (and 3 HP for that matter) will all pull 7000 rpm just fine. It's when you get above that I get nervous.
5 HP billet aluminum flywheels are readily available (as are 3HP which are made on the same taper and timing/magnet location) and have been for probably going on 25 years or more now. (That's when WKA mandated the billet flywheel for limited and opens.)
If you are turning more than 7000 rpm, I'd seriously consider the upgrade -- if not, then keep it simple.

^ DEFINITELY the stock cast aluminum flywheels are a total disaster waiting to happen.
-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
CarlsonMotorsports said:
5 HP cast iron flywheels (and 3 HP for that matter) will all pull 7000 rpm just fine. It's when you get above that I get nervous.
5 HP billet aluminum flywheels are readily available (as are 3HP which are made on the same taper and timing/magnet location) and have been for probably going on 25 years or more now. (That's when WKA mandated the billet flywheel for limited and opens.)
If you are turning more than 7000 rpm, I'd seriously consider the upgrade -- if not, then keep it simple.

^ DEFINITELY the stock cast aluminum flywheels are a total disaster waiting to happen.
-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Click to expand...
Did they ever make it a rule on stockers
 
Screenshot_20211030-172119_Facebook.jpg
 
Absolutely.

If you get it started without breaking your arm, it was never intended for more than 3600 rpm. These are lightweight, pressure cast units from an alloy which is best for production applications, not racing applications.

The mower blade provides the inertial mass in the stock applications where these were used.

I would never stand anywhere near a 20 inch mower blade turning 7000 plus rpm.
 
Well that's what I was thinking but the 2 theat I have came off of side shaft model 11 4 horse leaf vacs. Basically identical to the 3 hp side shafts just with a huge bore and these flywheels.
 
I'm trying to remember from the old days.

The 3.5 hp vertical used the same piston as the 5hp horizontal.

The 4 hp horizontal used same crank and block as 5 hp with smaller bore. Also used same head, with less cc's.

I bored one to 5hp dia, but offset the bore.
Back then, my racing engine supply came from old fertilizer pumps.
 
The model 11s that I have are quite a bit bigger bore than a stock 5 flathead. Just a shorter stoke. Thinking closer to a 3 hp stroke. In fact I just checked. The 4hp model 11 piston is right at 2.760 in.
 
95 shaw said:
Absolutely.

If you get it started without breaking your arm, it was never intended for more than 3600 rpm. These are lightweight, pressure cast units from an alloy which is best for production applications, not racing applications.

The mower blade provides the inertial mass in the stock applications where these were used.

I would never stand anywhere near a 20 inch mower blade turning 7000 plus rpm.
Click to expand...
I think we maybe discussing different pieces because although it oil smoked like heck the model 11 wasn't hard on my arm at all to start . I'm not sure if it would be an advantage because when I weighted them they were darn close to the 3 hp steel flywheel.
 
flattop1 said:
Its never a problem till it is .
What's the rpm the leaf blower spinning ?
Is it direct drive ?
How bout a picture of the under side of flywheel
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I'd imagine it is turning the original 3600 rpm but to be honest I didn't tach it before tearing it down. I will note that not all non point coils would fire with it but it also may have been a few junk coils. Doubtful but possible. Let me get fired up this morning and I'll send some pics your way. Also yes vac blade was direct mount to the pto. The other one was alone when I got it. Just a short pto model 11 complete othere than tank and carb.
 
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