5" Driveshaft Extension. Converting 20" Lower Unit to 25"

**bigshrimpin** · 04-24-2006, 09:42 PM

Does anyone have experience using the 5" extension kits to convert a 20" motor to 25"? Are these reliable or should I just do an ebay swap?

I have the 5 inch housing spacer, a 25" shift shaft, the longer bolts.
Just need the longer water tube and this drive shaft extension . . . I think?

**tj309** · 04-24-2006, 10:52 PM

You are in luck. I just did this to my PM300's. What kind of motor do you have? You will also need a shift shaft for a 25". And depending on the lower unit you may need different bolts/studs which are not readily available - but I know where to get what you need.

**tj309** · 04-24-2006, 10:56 PM

Sorry I did not read your post close enough. Yes you will need the 25" driveshaft. Luckily it is cheaper (by alot) than the 20" driveshaft. Other than that you are set if you have the proper bolts and studs.

Why are you doing this? I have been blasted by forum members for doing this but it is really the best thing to do for my rig and what I want it to do.

**bigshrimpin** · 04-25-2006, 12:31 AM

I bought a second 20ft seacraft fishin boat. It had a 20 inch transom that had rotted out. I raised the transom to 25". After I raise the transom . . . I found a 1979 Merc v200 (20") that had been sitting in an old guys garage for many years (got that for a song).

Now I have two lower units, both are 20". One is the preload type that came with the v200 and the other is off an 87 150 xr2 . . . both are 2:1.

. Rather than trying to locate a 25" shaft and paying a few hundred bucks to have it chaged out, I was thinking that a 5" drive shaft extension would be the easiest way to convert the gearcase to 25". I'd also have a backup just in case I colide with one of the many breaching tree stumps that lurk beneath the surface of the Sac River.

**150aintenuff** · 04-25-2006, 12:42 AM

brand new 5 " shift shaft and driveshaft extension and water tube extension costs TYD less than the cost of a 25" drive shaft call bay manufacturing and tell them you need some pieces for a 611 kit..

they quit doing full length driveshafts as the extensions have proven 90% of the time just as strong as the shaft its self... on poorly cleaned up exhaust can equipped mid you may have to take a drill and de burr the inside of the lower motor mount castings to clear the buldge for the 5" extension.. ive installed probably 50 of these kits and none have had a problem.. twisted 1 set of extension shaft splines but that was easily replaced for less than 50 bucks...

no need for longer water tube... just go to home depot and buy 1/2" schedual 40 repair section 2 foot long, cut a piece 8" long and slowly using a bench grinder or lathe remove JUST enough of the outer wall to FIRMLY seat into the water pump housing... cost less than 3 dollars and is stronger and is a perfect gasketless ultra tight seal into the water tube and it gives you PLENTY of room for a had to align the tubes and you will need 2 hands to align the pieces properly as it is VERY tight fit.. as a matter of fact for 10 dollars ill send you out a prebuilt redy to drop in and run water tube gauranteed not to ever break or wear out and is preasure rated to over 60 PSI.... bay mfg charges over 30 for thier water tube extension... and it requires the use of a tapered rubber seal that is prone to failure at the mating surface of the water tube..

**bigshrimpin** · 04-25-2006, 11:03 PM

Thanks 50 for the info. I'll try it out this weekend . . . hopefully Bay can hook me up with just the 5" shaft extension piece. I might take you up on you offer for the tube, if it's not too much trouble.

**Aaronhl** · 12-04-2019, 08:04 PM

How easy is it to go from 25" to 20" by not using the spacer? I know you would need a 20" lower unit but what about any other parts?

**ChrisCarsonMarine** · 12-06-2019, 07:54 AM

I cut and re-spline driveshafts and shiftshafts,Chris

**Aaronhl** · 12-09-2019, 06:04 PM

Originally Posted by ChrisCarsonMarine

I cut and re-spline driveshafts and shiftshafts,Chris

Approx how much? And is it done with driveshaft installed in the lower unit?

**ChrisCarsonMarine** · 12-10-2019, 11:09 AM

Yes,can be done in the gearcase.generally 125$ for standard shafts,150$ for hardened shafts,out of the gearcase.25$ more if in the gearcase.Can also add a coupler near the water pump to run whatever length/spline you want,Chris

**Aaronhl** · 01-22-2020, 10:55 PM

Anyone know the part number for the long lower unit studs that are used with the 5" spacer?

**bigshrimpin** · 01-26-2020, 12:27 AM

Originally Posted by bigshrimpin

Thanks 50 for the info. I'll try it out this weekend . . . hopefully Bay can hook me up with just the 5" shaft extension piece. I might take you up on you offer for the tube, if it's not too much trouble.

I remember posting this in 2006. 14 years ago. I still have a set of these kits. I even made some 30" 2.5L 200's over the years. Thanks for reviving an old thread and reminding me how helpful folks have been on here. Where did all the time go!!!