catinaround

have tried the JB Weld and it was gone in a weekend ,don't bother

CB-BLR

I have had similar problems with my IMCO lowers and cav burning behind the water pickup. My friend owns a marine repair buisness that specalizes in fast boats...so he has a lot of IMCO lowers sitting around. What I noticed looking at a lot of them is that IMCO is not consistant about where they place the water pickup notch fore and aft on the underside of the lower. Some start at the very front...and some start two or so inches back from the point...point being...unless the pickup notch starts as far forward as you can get it...notching out under the pointed part...most of the lowers I saw had cav burns on them.

My suggestion would to be to open up the notch as far forward as you can...and make sure that the front part of the notch is parrallel to the prop shaft...or even slightly pointed up...not down as your entrance ramp is...and then shorten up the notch by that same amount by welding up the rear of it....basically moving the notch as far forward as possible while retaining its original length. Water than can come in straight from the front of the drive instead of getting slightly pushed out of the way by the nose or downward sloping entrance ramp.

I did this on my current lower...and the cav burns stopped completely.

Chris

P.S. I will try to go over to the storage place and take some pics of what I did.

P.P.S You should also weld up the current cav burn area so it doesnt get worse...it is like cancer, and the rougher it is...the faster it will get eaten away

thirdchildhood

iTrader: (6)

CB-BLR, that IS interesting and explains some things. I have elongated my inlet after consulting with an Imco rep about losing water pressure at positive trim. The cavitation burn started before I did any grinding and continued after. I just cleaned up the rear of the opening and filed a slight bevel on the sharp edge. I also did the JB weld fill in. Now I'm waiting for some warm weather. Here is what my inlet looks like now:

CB-BLR

You need the front of the opening deeper into the nose...the taper where it gets narrow at the front...should be the same width as the rest of the notch...not narrowing.

ie...the water should be able to go straight in from the front...the way you have it now...will still produce cav burns.

Chris

Michael1

So is this just an IMCO phenomenon, or does this happen to standard Bravo's, too?

Michael

thirdchildhood

iTrader: (6)

Thanks Chris, I will look into that.

Michael, this thread started out about burns on a Bravo. I kind of hi-jacked it because it was dead.

Airpacker

Considering what IMCO charges for a SC lower, you would think that they did their hydrodynamic homework but alas, NO.

I have been dealing with the same issue on my cat and am just about ready to weld the hole shut and use another thru hull to feed my inter cooler.

thirdchildhood

iTrader: (6)

I would love to see pictures of the water inlet on other Imco shorty lowers. Please state if the inlet is stock or if not, what you did to it. Pictures of any kind of cavitation burn on any drive would be interesting too. Thanks.

tylogan11

I'm getting ready to pull the trigger on a Imco and to be honest this issue concerns me, I read a thread a while ago that a person drilled two holes on the top of the nose or tip of the imco that faces the rear of the boat I wonder if that would help reduce cavitation burns?

Also does anyone know if this problem exist with IMCO's that are painted black?

I don't mean to hi-jack this thread by any means just trying to do my homework before I shell out the cash.

thanks,
Gregg

thirdchildhood

iTrader: (6)

Gregg, you're not hi-jacking any more than I did! Your boat does need the shorty and worse case scenario is that I will need mine welded up a little every couple of years. I service the drive every fall anyway so popping off the lower and taking it to a welder will not be a big deal. I do hope to find the solution to my problem though. I will probably widen the front of my inlet mod as suggested unless more info comes out that says otherwise.

And hopefully we'll get a chance to run together again this summer on the big lakes.