Help?!? Cavitation plate went bye bye

[cawhite6814]

Hello,

I have an issue I would like some help with.
I have a 91 Mercury 2.0l 150hp. I have it hanging on the back of a semi heavy 17ft procraft fishing boat. I took the boat out this weekend in pretty rough water and didnt seem to have any problems. When I put the boat back on the trailer I found out the whole cavitation plate including the trim tab was snapped off at the lower unit. I mean the whole freakin thing is gone. I was wondering what damage this could cause to the motor, running it without it while I was out. Im not sure when it actually happened. And I was also wanting to find out what upgrades could be made from here, since I will be needing to replace at least the case. Would a gear ratio change or lwp or anything else help get a little bit more performance out of the boat? What would the best gear size and case size ect be as a replacement, and how will it effect rpm's?

Thanks,

chris

[flabum1017]

you can have a fabricator weld a new plate on, unless you plan on using a Doel-Fin

[cawhite6814]

There is nothing to attach it to, It broke off even with the lower unit. The fin, trim tab, The whole plate is gone, all that is left is a hole in the lower unit and what is left of the factory fin on the sides of the lower unit. Everything that extends from the lower unit over the prop is no longer.

Chris

[HStream1]

There is nothing to attach it to, It broke off even with the lower unit. The fin, trim tab, The whole plate is gone, all that is left is a hole in the lower unit and what is left of the factory fin on the sides of the lower unit. Everything that extends from the lower unit over the prop is no longer.

Chris

Post some pictures. But based on what I'm reading. Get another case. If you want to use the existing internals go with a Bobs LWP. If not then seek a CLE or Sportmaster off this site. I have a complete 20" CLE in Great condition. PM me if interested.

[cawhite6814]

I will get some picks up when I get home from work.

Thanks,

Chris

[HStream1]

I forgot to mention. And not knowing the history of your engine/lower. I'd suspect that there was some prior damage or welding issue(s). I could be wrong.

[Action Dave]

Don't worry about CLE or nosecone case. You dont need one. Just pick up a used 2 liter gearcase housing and swap all the internals. Shouldn't be overly expensive.

[cawhite6814]

Here is what it looks like now. Pretty ugly right? lol. What is the best gear ratio to go for as a replacement? And can any damage happen from running it like it is?

Thanks,

Chris

[T-REX]

U beez a lucky man....Ya lost tha only part ov tha geer case dat don't hurt any other mekaniks...

I've seen tha whole geercase break off, and even tha mid break, and loose tha geercase, but never a break like dat, az ta leeve all tha hi dollar stuff intact....Lookz like a geercase, case, an ya bace in bussiness!!...

Did U have a whale tail on that case??

[cawhite6814]

Ya I had a bob's aluminum tail on it. I dont know that I will be putting another one on the next one tho. The motor had it when I got it. I do have a hydrofoil that attaches with a clip with no drilling, so no holes, nuts and bolts. maybe it would be better?

[tlwjkw]

What part a Texas ya in? Bobby V. in Ft. Worth can help ya out.........T

[captglm]

I have seen several lower units that broke off almost exactly the same with the bobs aluminum tail plate. they are great in calm water but it adds alot of stress in rough water. if you notice, it breaks right where the tail plate starts.

GM ><>

[TEXAS20225]

yep 8176751224

[jody504]

thats broken from a lazy ass not putting the bolt back under the fin.Happens on the newer modle motors more than the older but they crack with or without a extra fin. So that answer the ? of if that bolt was needed the answer is yes

[cawhite6814]

I live in Houston, Tx.

If I wanted to go ahead and change out the lower with a complete case is there some tips on what to go with? I have been reading and it seems like most everyone uses the 1.87 gear ratio and the large diameter case without the preload pin. Does that hold true in my case or is there a better setup? I think I was told mine was 2.1 if im not mistaken.

Thanks,

Chris

[cawhite6814]

Dont know if there were any missing bolts under the fin, Everything seemed secure, went out and i suppose i wuz mistaken. I will live and learn i guess. Sucky as it may be.

[jody504]

There should hve been a 3/8 bolt under the fin at the back most are left out that would have kept the back from flexing right where it broke is the weak spot because of the air slots are the newer units have the anoid there instead of the air slots.The back don't have anything eles to hold it from moving but that bolt and a dow pin to line it up

[T-REX]

Well, az fer tha geerz, U betta stay wit tha 2:1 geerz...Wit yo tank, dat po lil 2liter will sholey suffer if ya go to a higher geer.....You'll prolly binifit from a set ov hi altitude geers(2:33) on yo bote......2liters iz only 122 ci's and on a heavy bote, that lack ov ci's makes a big differnce gitt'in out tha water and goin...JMO

Oh, sum people don't replace that bolt Jody iz talk'in about(I have been guilty myself) and it will kum back to bite ya in tha ass.,..Especially wit a whale tail...Them Bob's tails loads tha back ov tha geercase too much, and on a heavy bote, tha geercase kan't handle tha pressure, then when ya drill tha holes, thats tha beginn'in ov tha end....Juss my unprofessional opinion!!

[cawhite6814]

Ok, Thanks for the advice. I dont wanna be boggin down. So this may be a dumb question, but... if i happened to come across the 2.33 gears how would that effect the rpm's. And is it true that changing out to perfomance reeds gives you some extra rotations? Im wantin to change to a tempest prop and I wanna get the best pitch to get the most out of what I have to work with. I plan on doin the reeds, and someone told me to take the liner out of the exhaust tuner. I will do what ever other bolt ons I can, and eventually get the heads shaved to up the compression.

[TEXAS20225]

i been doing this for a couple of days:D i have not seen any high alltitude gears sets arouind my neck of the woods wnt more power buy a 200

[cawhite6814]

Ya I thought about that too, My boat has a 150 limit and I fish sum tourneys that require you to stay within the limits, but on the other hand..... I did find a 94' mariner 200 efi for a good price that I was considering but he said it bogs down at 3500 rpm so i wonder if it is more trouble than its worth. he said he replaced the ecu and had it checked out but couldnt pin point the problem and believe it to be something minor, possibly a fuel issue.

[baja200merk]

that happened to my buddys 280 on his mirage at RR, prolly cause the case was loose (his was).. He doesnt know when it happened but all we do know is the fastest the boat went the day before the plate broke was 114, plate broke off and it got to 118 the next day with 2 on board faster then it ever got to 114 :D

im tempted to beat my plate off with a hammer :thumbsup:

[Action Dave]

I actually have an OMC gearcase housing with the cav plate cut off. The exhaust is relieved and routed out the back courtesy of two aluminum half-pipes welded to the case above where the cav plate woild be.

[Action Dave]

Here's a pic.

[cawhite6814]

So I guess if I needed to run it like it is until I switch it out I could??

[baja200merk]

my friends runin his with no plate... the sporty is only a year old :eek:

dave ive seen that before, wasnt it on ur uncle bobbys red and white action a few yrs ago?

[Action Dave]

dave ive seen that before, wasnt it on ur uncle bobbys red and white action a few yrs ago?


It's not the same case but the cut-n-weld was done by the same guy. The only negative is you loose the slight bit of drag a cav plate might give you if you stand the boat straight up in the air.

[Action Dave]

So I guess if I needed to run it like it is until I switch it out I could??


I really don't see why not. As long as none of your internals are damaged and there arent any leaks. From your pics it looks like you'd be OK.

[cawhite6814]

Thanks for the info, I had a trip comming up and I dont think I can have it done before then, so I was wondering.

[captglm]

As long as you still have the 2 bolts/nuts under the back (near the break) and the 3 up front and they're all tight. you shouldn't have any problems.

GM ><>