Classic AquaSport
Aquasport Mechanicals - things that need a wrench, screwdriver or multimeter => Engines & engine woes => Topic started by: love2fish on June 25, 2013, 02:53:19 PM
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been looking for a new (used) motor for my boat and have found a large number of 25" shaft length motors, I know you can get the extension to convert a 20" to a 25" or a 25" to a 30"... but is there anyway to go the opposite way? Making a 25" to a 20? more trouble than it's worth?
while on this topic, would putting a 25" on the original transom cause to much stress on the existing original transom? have also been looking for a short setback jack plate- movable or stationary.
Thanks
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Hey Chris,
Good question. I did the 5" Bay kits on Scotty's 75's. They could easily be converted back to 20" from 25". The most arduous part would be changing all of the lower unit studs back to shorter lenght in the case of his Mercs. Take out the driveshaft, shift shaft and water tube extensions and you're back to 20". Now if you have a factory 25" engine with the XL midsection made from 1 piece; thats a whole nother can of worms to convert back to 20". That would be a complete mid section teardown and exchange including changing driveshafts, shiftshafts and water tube. Basically a complete engine teardown.
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Thanks Fitz! Sounds like I'm going to keep looking for a 20".
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All and all, the Bay extension kits worked well. The downside was the diagrams and instructions were lacking. On the Mercs, the shift shaft extension proved to be the most challenging because of having to relocate the stock shift coupler on the gearcase to the top of shift shaft extension. I thought we had the wrong shift extensions because of the spline configuration. I slept on it and had an revelation at 4:00 am and went out to the shop and figured it out. Now that I've done it, I know what to do. So my advice is buy a 20" engine for the current transom height and when you decide to go to 25", buy the Bay kit for $400 and extend the engine the 5" for the new transom height. Atleast it gives you an option. I never liked putting a 25" engine with a jack plate on a 20" transom. Rarely can you adjust it up high enough to get the right height plus it just looks like a :*: in my opinion.
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I converted a 200hp 2.5L Merc 20" to a 25" shaft the hard way. I bought it from a guy who said it was a 25"... I did a quick measurement and yeah it looked right... "wrong!" Turns out the seller was measuring the shaft of a spare lower unit he had. NOT the measurement from the cavitation plate to the mount. He made good on it by getting me a newer 25" mid section and a freshly overhauled 25" lower unit. I took the motor apart and swapped the parts. Creating a Franken-Mercury that had a 1998 factory power head, a 2001 mid-section and swivel, early 90's hood, fuel system, electrics etc, and who knows what year lower unit. Thing ran like a scalded ape too boy!