5 degree advance flywheel on Mc101

[philrock]

I have a pair of Mc101 M/Cs, freshly re-built, but have never been run. They have 5 degree advance flywheels. Ignition point timing has not been set. I'm getting conflicting information about whether these flywheels are appropriate for these engines.

Comments?

I'll be running alky, and I understand that standard point timing for this is 22 degrees BTDC. If I use the 5 degree advance flywheels, would I still use the standard point timing?

[Tom Smith]

101 flywheels have more counter balance weight. If you want to advance the flywheel a 5 degree offset key will do the job. According to Mcculloch engineers, 101s like less advance than the smaller Macs do for some strange reason.
Lighter flywheels on dual 101s will probably knock the bottom end punch down and raise top end rpm some. Not exactly what works best for sprint racing. Personally I used standard uncut 101 flywheels, slightly hot plugs, 22 degrees, and 20-1 methanol with Blendzall or Burris castor for my dual sprint 101s.
BTW Mcculloch machined their various flywheels differently and off center on purpose for balance factors.
Tuning duals is a different deal than tuning a single. For one thing they don't get as hot so you can compensate for that some with the heat range of the plugs.

[Jeff Campbell]

Phil,
I'm running 5deg advance flywheels on my Chaparral with dual MC101s, with stock 22deg timing, straight Alky, and Autolite 411 plugs. My 101's are bone stock, including the carbs, porting, and head gasket. So, this combination works, my Chaparral is fast.

The 22deg optimum timing is based on the stock motor with std flywheel. The stock motors have a huge head squish, due to the fact McCulloch at the last minute before introducing the 101's, stuck a extra thick head gasket in there as a bandaide fix for "thermal issues". Good motor builders correct the squish, timing and advance the flywheel (or put on a 5deg advance flywheel).

FYI - the std flywheels are easy to advance 5degs, if I remember right, you file off one side of the flywheel key (only the portion that extends above the crank), lap the flywheel to the crank and carefully assemble it (check the true advance of the flywheel to be sure its done right). I've run std flywheels this way on my 101's, no issues.

Jeff

[jmendoza]

I have almost the same set-up as Jeff, twin MC-101A using 5 degree flywheels, Azusa exhaust, BDC- double pumpers for methanol, stock timing, stock ports & head, squish, 411 plugs, coil moved as far as it can go for maximum maveric advance. Dart twin A-Bone. Runs great!

[philrock]

Thanks for your responses.

Sounds like there should be no problem with the advance flywheels. Since I already have them, I guess I'll give them a try.