Viper/Merc 85 Shortshaft Conversion


I've got a quick question that I was hoping you could answer in a quick email reply.   I've got a mid to late 70's 85 hp merc, long shaft, with a blown power head.  I don't have the serial number handy, but it has the 850 red letter cover, and am fairly confident it came original with my 77 Viper.  I'm looking at buying a late 70's 115 short shaft, sn 4396336.  First does my Viper need a long shaft motor?  If so can I use the extension parts off from my 85 to convert the 115 to a long shaft without much trouble? 





Yes you could put the 115 powerhead on the 85 tower housing. The gear ratios should be different so you could either prop up or change the gear set to the 115 set. With more power you'll want to stay with the 115 gearing. Be sure to use the 115 down stack assembly. The Viper works best with the 20 inch motor. A 15 inch works but takes very special rigging. 

                                                 Have fun with your project!




Please submit whatever questions you have to  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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