Ring gear choice, 122 vs 149

[Larry DeCamp]

I have a magnaflite starter with 122 ring gear. It seems alittle weak even with 7:1 0320 and new solenoid and pc680. My goal is NO problem!! I plan to buy a light weight no pully flywheel and B&C starter. B&C says 149 tooth has slight advantage in crank torque. I have read this is a myth.
what is truth ???

[jrs14855]

My 320 with 10-1 pistons cranks extremely well with 149 ring gear and sky tec starter

[airguy]

What prop do you have? A heavier prop adds angular momentum and will help a starter overcome the compression stroke, while a very lightweight prop will have trouble, especially with a weak starter. I had the combination of a relatively light prop (Whirlwind RV200) with the Magnaflite starter on my IO360, and it would not handle the compression stroke worth a flip. I changed to the SkyTec 149NL and my problems were solved, though it comes with it's own set of maintenance inspection quirks (no free lunch).

[jrs14855]

Sterba prop on mine. Direct ground from battery to starter mounting bolt makes a huge difference.

[RV6_flyer]

Originally Posted by Larry DeCamp

I have a magnaflite starter with 122 ring gear. It seems alittle weak even with 7:1 0320 and new solenoid and pc680. My goal is NO problem!! I plan to buy a light weight no pully flywheel and B&C starter. B&C says 149 tooth has slight advantage in crank torque. I have read this is a myth.
what is truth ???

Should be no difference.

It is possible to sometimes replace the starter ring gear with one of a different size. There has been problems doing this with some starters. Read this to learn about possible problems. http://www.skytecair.com/RingGearTech.htm

I have changed a 122 tooth ring gear to one with a 149 tooth ring gear like listed in the above link. In my case, it worked but in some cased it may not work due to clearance issue documented in the above link.

[jrs14855]

I disagree almost entirely with the skytec info. Many early Pipers with the low compression engines had the 122 tooth starter and had at best mediocre cranking capability. The same starter on a Twin Commanche with high compression engine but 149 ring gear(with matching starter gear) cranks the engine noticeably better.