79-80 (85-115hp) Block changeover

[dpancheri]

I am new to this forum so I appoligize if this topic may have already previously been discussed. My current outboard is Merc. but I am looking at an older jet boat with a Evenrude 115. The owner says he had an 85hp Evenrude on it until it broke a piston. He says he found a 115 of the same series at a local dealer that had been taken off of another jet boat because of low compression and changed the jet foot over to this upper unit. My question for anyone familiar with late 70's early 80's Evenrude's of this size is , did these motors use the same block and and if so, what was the difference between them ie.(bore, stroke, running rpm, timing curve ect.) to get that much difference in horse power? He says he still has the 85 hp block for parts. Also what would this motor be worth approx.? Any info would be appreciated.
Thankyou
Dave Pancheri

 

[emdsapmgr]

Re: 79-80 (85-115hp) Block changeover

By the late 70's OMC standardized the crankcase on the V4 engines. They were identical cases for 85-100-115, same part number. Same pistons, crank, heads, etc. Most difference in the carb throat size. Some carbs 1", some 1 1/4", some may have been 1 3/16". Some 115's had the intake filler blocks like the 140. They were all hp rated at 5000, and were recommended to be propped turn up to 5500 by the factory. Timing was to be set according to the decal on the engine airbox. Many on this board will advise turning the engine at least 5500 for longer life. Good compression is the one requirement for a 2-stroke. If your 115 was removed from another boat due to low cranking compression, it may need either a decarb, or rebuilding. A rebuild block should have 125 lbs of compression. If it needs rebuiding, factor that into your purchase price.

 

[dpancheri]

Re: 79-80 (85-115hp) Block changeover

By the late 70's OMC standardized the crankcase on the V4 engines. They were identical cases for 85-100-115, same part number. Same pistons, crank, heads, etc. Most difference in the carb throat size. Some carbs 1", some 1 1/4", some may have been 1 3/16". Some 115's had the intake filler blocks like the 140. They were all hp rated at 5000, and were recommended to be propped turn up to 5500 by the factory. Timing was to be set according to the decal on the engine airbox. Many on this board will advise turning the engine at least 5500 for longer life. Good compression is the one requirement for a 2-stroke. If your 115 was removed from another boat due to low cranking compression, it may need either a decarb, or rebuilding. A rebuild block should have 125 lbs of compression. If it needs rebuiding, factor that into your purchase price.

Thanks for the info.
I think the compression runs about 85lbs however this is at 5000' elevation, My experience with sleds is 125lbs at sea level equals about 100lbs at our elevation so 85lbs sounds a bit low but probably not unusable. One of my other concerns is this is alot more motor than this boat is tagged for( 17' flat bottom ). I have not owned a jetfoot before but I do know that it is common practice out west to run about 30% more motor than normal because of lower jet effiency and elevation loss. My concern is, and have I done this with my 25hp Merc for a long time, is it ok to run this motor at 75% throttle as normal practice.
Thanks again for your help I have learned alot already.
Dave Pancheri
Idaho Falls, Id

 

[jimmbo]

Re: 79-80 (85-115hp) Block changeover

1969 - 1978 85hp 92.6 ci
1979 - 1996 85 -90 hp 99.6 ci
1969 - 1970 115hp 96.1 ci
1971 - 1972 100hp 92.6 ci
1973 - 1996 115hp 99.6 ci

The late crankshaft rated 85hp and 90hp used same blocks, the 115s used different blocks because the porting was different. The carbs were different sizes. Thing were a bit different after 1986 when the engines were propshaft rated. The old 115 became the 90 and the old 140 beacame the 115/110hp, The main difference between the old 115 and the 140/new 115 was the exhaust tuning and stuffers in the intakes.

 

[dpancheri]

Re: 79-80 (85-115hp) Block changeover

1969 - 1978 85hp 92.6 ci
1979 - 1996 85 -90 hp 99.6 ci
1969 - 1970 115hp 96.1 ci
1971 - 1972 100hp 92.6 ci
1973 - 1996 115hp 99.6 ci

The late crankshaft rated 85hp and 90hp used same blocks, the 115s used different blocks because the porting was different. The carbs were different sizes. Thing were a bit different after 1986 when the engines were propshaft rated. The old 115 became the 90 and the old 140 beacame the 115/110hp, The main difference between the old 115 and the 140/new 115 was the exhaust tuning and stuffers in the intakes.

Thanks for the additional info, very helpful! One final question. Did these motors have any reoccurring problems ie.(CDI,stator,crank,ect.) that I need to ask the owner about before purchasing?
Thanks again:
Dave P

 

[emdsapmgr]

Re: 79-80 (85-115hp) Block changeover

The only thing I would recommend has to do with the poor gas quality of today. I'd run a can of Engine Tuner through the engine crankcase on an annual basis.