Burning up bravo 3 impellers

[ericcarr2000]

Ok as many of you may know I just got my repowered 7.4 running for the first time. I took it to a shop to get the timing & carb all tuned up and the break in procedure done on the cam. They told me that during the tuning that they had done it was running real hot. After I picked it up I brought it home and hooked it up to the muffs and started it. I started to notice that it did begin to run hot... I didn't let it get so hot that the audio alarm didn't go off though. At this time I pulled the impeller housing and noticed that the impeller was shot of course. So I installed another impeller, started it up and noticed it began to run hot yet again. So I pulled the impeller housing yet again and of course it was shot. So I thought ok I'll pull the damn outdrive.. When I did there were chunks of my exhaust flappers there along with pieces of the impellers. I pul the drive on the stand hooked the muffs to it and turned on the hose. I noticed that there wasn't any water reaching the upper part of the drive. Am I missing something here as to why the water wouldn't be reaching the upper?
I hooked the hose to the housing after the drive was off to make sure water was going through it and it is. Somethings stopping the water from even going to the motor.. Any suggestions?

 

[Bt Doctur]

Was the drive unit dis-assembled? the impeller pieces could never enter the exaust system?http://www.boatfix.com/merc/Techbk/97/97hs3.pdf

 

[ericcarr2000]

I guess the rubber pieces could have possibly been just the exhaust flappers. When you hook up a hose to the bravo 3, should the water easily come out the top of the drive?

 

[alldodge]

I put the drive on the stand hooked the muffs to it and turned on the hose. I noticed that there wasn't any water reaching the upper part of the drive. Am I missing something here as to why the water wouldn't be reaching the upper?

It would be helpful to me to read through your other threads but I go with this;
with muffs connected and the drive off, the water should very easily flow out the water port in the top half of the drive. If it is not doing this, I would suggest you need to split the drive and check the hollow tube from top to bottom.

I hooked the hose to the housing after the drive was off to make sure water was going through it and it is.

Which housing is this, thermostat or other?

The belt driven seawater pump has a in and out. If your not connecting them to the right one you will not be pulling one. As an example, my Rinker has the inlet side on the bottom, and the Formula has the inlet on the top of the pump housing. This all depends on how the housing is rotated and secured

 

[Bt Doctur]

Yes ,it free flows thru the drive/ Does it have dual water pickups? outdrive source and a thru hull with a strainer

 

[ericcarr2000]

It looks just any other bravo drive with them little jokes on both sides of the drive. I separated both halves of the drive today and cleaned out the rubber material from the exhaust area. I'll re attach them to each other tomorrow and then try to hook the hose up to it on he stand and see what it does then. I'll get back with yas tomorrow and let ya know what I find out.

 

[HT32BSX115]

If this is a used 7.4L engine, did you or anyone else pull the oil cooler and ensure it is free of debris?

If the engine is NOT new, previous impeller failures will clog it so bad that water flow can be completely blocked.

The discharge from the raw water pump usually goes directly to the oil cooler before it goes to the engine/heat exchanger etc...

When I unclogged mine, I had to use needle nose pliers to pull the pieces of impeller vanes out of the oil cooler.

 

[ericcarr2000]

Update... Well I just got done putting the drive back together setting it on the stand and turned the water on and water still wasn't coming out....until I used pressure on both sides of it to push the most on and then it started pouring out of the top.... I did this with a brand new pair of muffs also.... I guess my days of running it in the driveway are DONE... I just hope no damage way done to the motor.... My exhaust flappers got so hit they they actually looked like the plastic part melted.

 

[thumpar]

The impeller should suck hard enough that you wouldn't have to push them together. Are you turning the hose on full? How is the water pressure at your house?

 

[thumpar]

Also, have you tried backflushing the system? When I had my impeller go I took the hose off the housing and put a hose into the feed hose to get all the pieces out.

 

[ericcarr2000]

Ok here's my conclusion... The motor is new...took it in to have it tuned up....carb/timing adjusted. They supposedly hooked it to muffs, ran it for 20 minutes @ 2000 rpms...
I'm going to assume that they pretty much fried the impeller along with my exhaust flappers. When I picked it up they had told me that during the break in process, which I did not ask them to do, that they had noticed that it was running real hot and that they could smell rubber and hear some crackling noises coming from the bell housing area. Upon me arriving home I thought that I'd replace the impeller and try that. I burnt through that one within a few minutes. I pulled the drive and that was when I had noticed the pieces of the flappers in the exhaust portion of the drive.
With all this being said, am I correct to think that these bravo 3 drives really shouldn't be run on a hose?

I'm praying that they didn't fry the engine when they overheated it for the 20 or so minutes....

 

[thumpar]

I run my B1 on muffs before every outing. The B1 and B3 are the same except for the lower end with 2 props.

 

[alldodge]

With all this being said, am I correct to think that these bravo 3 drives really shouldn't be run on a hose?

As Thumper said there is no issue running them on muffs, been doing it for years. From my reading it was kind of telling me there was some clogging, maybe not. What I would say more then anything, don't run your drive with a low pressure, or reduced pressure on the hose. Open it all the way and let the water spray all around it before starting. It has no problem sucking the water but water must be there to suck

 

[HT32BSX115]

If no one physically checked the oil cooler, it's likely still clogged.

 

[ericcarr2000]

Oil coolers not clogged I did check it. The problem I'm having is with the drive off the only way I could get the water to come out the top of it was to squeeze the muffs with my hands with it running.

 

[thumpar]

There have been problems at the transom where the water comes in. It can get clogged up.

 

[ericcarr2000]

I sprayed water directly into the bell housing and it worked fine. The problem I'm having is not enough water going through the outdrive. I guess I'm all done running it on muffs.

 

[alldodge]

Oil coolers not clogged I did check it. The problem I'm having is with the drive off the only way I could get the water to come out the top of it was to squeeze the muffs with my hands with it running.

Not real sure because I have never put muffs on the drive to see if water would come out, but something doesn't sound right about that.

I have a other B3 on a stand and will try to see what happens with mine tomorrow

 

[thumpar]

There is something going on. If you can't run on muffs what makes you thing it won't overheat on the water? If there is water at the intakes on the drive it should suck it up. Do your muffs completely cover the intakes?

 

[ericcarr2000]

Yeah they cover them completely but like I said I can't get the water to go all the way up the drive until I press on the muffs, otherwise most of the water just doesn't seem to enter the water inlets. I'm just as baffled as you guys are..