Arc 6619 stock or 8 degree keyway?

slufoot78

New member
Hello, just received a arc 6619 flywheel in buy out. I have read in some of them the keyway is in stock location but newer ones are preset at 8 degree. How do I determine which one I have with out installing it and using a degree wheel? It does have a 06-13 stamp on it if that makes a difference? Thanks and have a great day.
 

JPR57

Premium User
That flywheel has a 2013 date code (06-13) which will be at 24 degrees BTDC with a STOCK KEY. The new 8deg advance flywheels will have a 2014 date code and "32 degree timing advance" engraved into the flywheel body and will be at 32 degrees BTDC with a STOCK KEY.
 

slufoot78

New member
Thanks for the info. Can a stock key be filed down enough to gain 7 to 8 more degrees or should I go with a factory offset key? I know sone guys dont use a key at all but i prefer there was one in there. Thanks again. Have a great day.
 

sCREamnClones

New member
That flywheel has a 2013 date code (06-13) which will be at 24 degrees BTDC with a STOCK KEY. The new 8deg advance flywheels will have a 2014 date code and "32 degree timing advance" engraved into the flywheel body and will be at 32 degrees BTDC with a STOCK KEY.

Just a suggestion, but....wouldn't putting a dash # indicating the advance (ie: 6619-32) support 'marketing' and 'inventory' in addition too the customer? Prayfully..."Cams" could be next (??)!
 
I run no key used a key and field my own keys.
stick in a vise and mic it.for every .006 you take
off is 1 degree.you can use a hand file just takes
a little time.Now I just use the adjustable hub
flywheel 6618 arc.love it and worth the money.
 

Flash06

New member
For those of you that are running with no key, how often if ever do you see the flywheel slip?
No keyway in any of mine, do it just like tunnel vision said and you won't have any problems. 32 degrees is very normal in fact I run anywhere between 32-35 deg.
 

RadialFin

Member
No key is fine. The keys arent really meant to drive these things, they are just a handy locating tool.

Many 100cc direct drive (no clutch) motors run their drive sprocket on a taper without a key. Most of them are putting 25-35HP down through that taper, so you can be sure that the flywheel will stay in place if you lap it properly. Same with the ignition rotor on these 100cc motors, often turning 20,000, will drop to near zero and back up to 16,000 in less than a heartbeat braking over a bump.
Tapers are just fine if done properly.

ENGINE%2010T%20SPROCKET%201.jpg
 

mikey56

New member
while i haven't had any slippage on my flywheels (thanks cr!), i do like to have the ability to "tweek" the timing. for this, i'm going to get two of the adjsutable timing flywheels from ARC or at least one of the new ones that are "preset" to 32 degrees....my way of thinking is simple....if you lap the flywheel and don't use a key and it slips, it could cost you the race....if you have one that is set straight up with a stock key and you can adjust your timing or if it's already set, then you lessen the chances of slipping or (because of the "thinness" of the keys) shearing a key at the worst possible moment....
 

rab3rd

New member
No key is fine. The keys arent really meant to drive these things, they are just a handy locating tool.

Many 100cc direct drive (no clutch) motors run their drive sprocket on a taper without a key. Most of them are putting 25-35HP down through that taper, so you can be sure that the flywheel will stay in place if you lap it properly. Same with the ignition rotor on these 100cc motors, often turning 20,000, will drop to near zero and back up to 16,000 in less than a heartbeat braking over a bump.
Tapers are just fine if done properly.

ENGINE%2010T%20SPROCKET%201.jpg


So what is the proper way to lap it? Never done that before.
 

RadialFin

Member
does that tapered sprocket have a key? just need to clarify this in my mind
Yes some have a keyway (how did the pic get so damn big!) but it's very rarely used, same with ignition rotor. There are others that simply have a taper on the shaft and sprocket, cant find a pic though.

Lapping it just involves patience (less with alum wheel!), grinding compound and ensuring it stays square during the process.
 
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