Motor Bracket

[KevinMc]

I have been given a Johnson 9.9 as a gift from some very good friends. My old Mac Motor bracket was difficult to use. So I purchased a new one. The holes did not match up so I drilled new ones, sillicon chalked the old ones. Then some one pointed out that I had the bracket for a two stroke engine and my motor is a 4 stroke ... I had asked what the difference was and the guy who sold me the bracket had told me that the only difference was the weight factor. So I made the purchased and installed. Now I am told that there is a major difference ... engine torque. How big of a problem do I have??? What should I do now?I hate not knowing what I should know. And I hate being sold something with bad adice.

 

[Peter]

no problem

You don't have a problem. O'day recommends a 4-6 hp engine for the 22. With the original 1975 mount I've used a 4-stroke 8 hp (currently), 2-stroke 9.9, 4-stroke 9.9 and I've had no problems. Yes the engine is heavy, but the boat has been pounded at the dock by storms and the bracket has never failed. Nor has it ever failed in actual use. The 9.9 really pushes the boat around. On the subject of engine torque: the mean engine torque delivered by a 4-stroke is about the same as a 2-stroke. The reason people say 4-strokes produce more torque is the higher cyliner pressures. However, only 1 turn of the piston is the power cycle, so the mean torque is half, and if anything, is less when compared to a 2-stroke. If you've seen the infomercials for the E-tec (a 2-stroke), this is the case as they've beefed up the injection to boost torque. Engine torque does not present a problem for the mount because the pistons oppose each other's stroke, cancelling each other out. Nor is it gyroscopic because their motion is along a line, not circular. The torque of the prop does matter, but is comparable between the two engines. After all, the props a similarly sized and pitched and the boat will go about the same speed for a given hp whether 2- or 4-stroke.