SST-120 Left to Right Hand Turning


Want to turn your Mercury Racing SST-120 powerhead from left to right hand turning to run COR?

1) Remove and replace the LH Mercury Racing Light Weight Aluminum flywheel (usually marked with a yellow ring around the hub mount) with a RH flywheel (sometimes blue but not always). You could also just swap the hubs.

2) Replace the LH starter with a RH starter. Make sure the ring gear and starter bendix gear match. Most LH motors have 94 tooth ring gear on the flywheel and 10 tooth bendix on the starter, Most RH motors have a 92 tooth ring gear on the flywheel and an 8 tooth bendix on the starter. Regardless of LH or RH, these tooth counts news to match... 94 tooth ring gear only matches a 10 tooth bendix starter gear. A 92 tooth ring gear only matches a 8 tooth bendix starter gear.

3) Add the upper throttle arm from a fishing motor if you want the variable the timing. (Most SST 120 motors have fixed the timing at 25 or 27 degrees BTDC).

4) Use a dial indicator to "degree" your new flywheel. Instructions here:

5) Set the idle timing somewhere between 8 and 12 ATDC as a starting point and the full advance to no more than 25 degrees as a starting point.

6) Fire an go.

Capnzee88's picture

I'm just not sure you can swap hubs, maybe yes, maybe no--just don't think so, but would not swear to it.

007's picture

You might be right but just the other day I bought a flywheel from an experienced OPC racer who confirmed that hubs can be swapped although some might be different heights so that would need to be checked. Also, the key would need to lined-up properly before reassembling.

Capnzee88's picture

Mike, you seem to be cornering the market on COR stuff, Good for you! Every class needs a reliable place to go, whether it be for knowledge or parts--U DA MAN! I just bought a 1978 175 2.0, bote and tandem trailer for 600 bucks (fresh water). 2.0's are all around, they just don't fall out of trees. Next you will be building engines for COR guys? Keep up the great work!

007's picture

Sounds like a runner. She might have some good parts left in her!