Alpha One (gen) One Lower Unit Impact!

Went down to a river system close to my shop to water test boat. Everything went well for about two hours. Was not familiar with the area but the guy who went with me assured me there was plenty of water. Anyway, was going upstream and struck a rock travelling about 20-25 mph. Immediately tried to raise drive and again struck another rock with prop. Turned boat with drive trimmed up as far as I could get it and started downstream and away from the area. I knew that I had done damage. The drive and prop were still spinning and was able to limp back to the dock area. Shut off engine and trimmed up as far as possible. Immediately saw mushroomed prop and proceeded to load boat on trailer. After loading, looked at the lower unit and to my horror (lol) could see a hole on the front side of the lower unit about parallel to the center line of prop shaft. Obviously, the lower unit housing is junk as well as all of the internals. Pulled the lower unit off of boat with upper unit still attached to boat. Took off the bearing cap on upper unit and saw that there was still oil in upper unit gear housing but had some water droplets mixed with the oil. The gear oil still looked green but there was water intrusion. At the time, I was not aware of how much damage that I had done. I did not see any oil slick when I struck. I knew the aluminum prop was shot but when returning to ramp, there was very little vibration from the damaged prop. However, after spinning prop on trailer, I could see that the prop shaft was untrue. (not running perfectly straight) My worry is this: I travelled after the initial impact about two miles back to loading ramp not knowing the extent of damage. Like I said, there was still oil in the upper drive. Actually looked quite full when I pulled the bearing cap. I also felt the upper drive housing right after I loaded up boat thinking I probably heated everything up but that was not the case. It was actually cool to the touch. I know that I will be replacing lower unit without question. The question is this: How do I know how much damage was done to the upper housing and where should I start investigating? I have alot of questions but have not gotten far enough to do any visual inspection of the upper gears, etc. I am in the process of draining the upper unit of oil as I said with the bearing cap removed and the lower unit removed. Any suggestions or advice would be greatly appeciated at this point. bummed out, Tom

Ayuh,... Buy a Complete SEI replacement drive....

You can't buy the special tools needed to service yer's for the price of a New SEI, Complete drive...

There are many good used drives out there for $500 to $600

What ratio is your drive?

That's the problem bondo. "The tools" Can't set the gears without michrometer or whatever. i'm not going to give up on the upper unit just yet but if if requires lots of breakdown and such I will go ahead with what you suggested. Thanks, Tom

Depending on how bad the hole is in the lower unit I would do this if it were me and I did not have any tools to do a rebiuld myself.

Most likely the upper is fine.

Most likely everthing in the lower is fine with th exception of the case and the prop shaft.

Remove the lower, bring it to a shop, have them dissassemble it for you and order a new shaft or try to find a good used prop shaft that is true. Also while the lower is apart have all the gears looked at closely for damage and if so the replace them or make a decision on replacement or repair.

If you can just repair with only a case repair and prop shaft replacement then Take the case home, clean and repair the hole if it not too bad. I would say take it to a welder who can do aluminium and weld it up, grind down all excess on the inside and outside, Clean thouroughly and have shop reassemble the unit. No need to check any gear lash for a prop shaft change. all internal set ups are not relevant to the prop shaft. Most can be done without the prop shaft bieng used at all.

If all this can be done, clean everything, pressure check it when reassembled and if all is good fill her up and reinstall.......


One other area to look at is the vertical shaft in the lower, where it engages into the upper, look at the splines and make sure they are straight and not twisted.

If money is a real object and you know someone with a good lathe, the prop shaft can be straightened to under the .003" total runout spec with a good lead hammer and some patients......

WHere do you live? if you were close enough to me i would happily help out as I have all the tools for this type of work....

Chris, thanks for responding. That's how I got boat to work originally! lol I saw a 1:84 ratio on ebay but it is kind of a crap shoot. I was originally able to break down my drive. Don't ask how but I did it and it is a pain in the ass. The problem that I cannot overcome is synching the gears with a dial indicator as you would do with an automotive drive. That's the hard part! Right? If it's not right it will blow shortly after reinstallation according to merc. and alot of threads I have read. The tooling is not cheap so you more or less have to do it for a living in order for it to be worth the money. The drive is a 1988 Alpha One generation one 1:84 or (1:81 for the later gearing) I was more concerned about water intrusion,metal,dirt and water getting up into the upper half thus damaging seals,bearing and races, etc. I did see some silver fines in the oil in the upper. I just changed the oil before I trashed the drive so I am thinking it should look clean but again the oil from the damaged lower unit may have sent alot of that crap up to the top end. That is my biggest concern at this point. The upper unit is still attached to the transom along with cylinders. Next question: Is there something that I could pour down the top of the upper drive to wash it out. I don't want to kill the seals (if indeed they are still good? Would carb cleaner or something like that in a spray can be safe to wash out all the crap?

kghost, thank you also for your quick response. I messed up buddy! lol I blame myself for even going to the darn place where I launched. What a mistake! I blame it on being totally unfamiliar with the river I was running in along with distractions from passengers and the sun right in my eyes. Hey, I guess it is bound to happen sooner or later. Chris, I bet if I had done the same at the shore I would probably only trashed the prop and maybe bent prop shaft. Sand is more forgiving than boulders but there are other things down in those waters that could be just as dangerous. Thanks guys for your help. kghost, I am right outside of Philadelphia Pa. I know I can get her back together but just bummed about having to start over again knowing that the thing was running so nice before the impact. Oh well, could be worse I guess. As long as nobody got hurt, that's all that counts. Right? I have to go for Easter dinner at my parents so I'll talk to you guys tonight or tomorrow. Thanks again for all the support. sincerely, Tom