small gearcase interchangeability

[fieromx3]

i have a 1973 evinrude 50 with a small gearcase on it. i want to buy a 1973 evinrude 85 for sale locally that needs a new gearcase.... will the small gearcase fit the 85? they are both longshaft

 

[jimmbo]

Re: small gearcase interchangeability

The gearcase on a 1973 50hp is identical in size to the V4 and 3 cyl models, but just because it looks the same size does not mean it is the same casting number.The smaller gearcase came along in 1975. Even if it did bolt on, the gear ratios are so different I doubt you would be able to find a propeller for it

 

[fieromx3]

Re: small gearcase interchangeability

well as long as the bolt pattern is the same and the shift rod and drive shaft fits the 85 im ok with it! the gear ratios may be different but there is a variety of propellers that can work

 

[jimmbo]

Re: small gearcase interchangeability

you might be looking for 9 or 10 inch pitch

 

[fieromx3]

Re: small gearcase interchangeability

:O this is an 85 horse i have a 12.25x15 pitch on my 50 and it turns around 5500rp on the 85 id be looking at probably a 19! though my current 15 would rocket me out of the hole with the 85 horse!

 

[jimmbo]

Re: small gearcase interchangeability

Please post a model number for your motor so we can figure out what year it is. a 1973 85 hp has a 2:1 gear ratio, a 1973 50 hp has 32:12 ratio and like the 85hp uses 13.5 dia props. an 1975 50hp has 29:12 ratio.

 

[fieromx3]

Re: small gearcase interchangeability

the 85 is a 85393M and the engine i have a 50373r but it has a small gearcase from 1978 55 55875S

after looking very carefully at diagrams and such it looks like the shift rod will not fit

 

[jimmbo]

Re: small gearcase interchangeability

Ok. why didn't just say at the begining you had a gearcase from a 1978 on it? Any way the gear ratio will be the biggest issue. going from a 29:12 to a 24:12 will be a fairly large increase in prop rpm for a given engine rpm and will overload the engine. you would most likely have to drop down to a 12.5 in pitch to maintain 5500rpm, maybe less because of the greater load of the 1 inch bigger diameter