Mercruiser 5.7 exhaust bellow blowing

[QBhoy]

Hi
A friend in the marina had his exhaust bellow blow off for the third time since the new season started.
Eventually I had a look at it for him, expecting the usual situation where he hadn't fitted it properly and having roughed up the surfaces.
This was not the case....
Having pulled the transom in against the jetty for a look...it was very apparent that the casting on the exhaust outlet pipe on the leg was cracked.
Upon further investigation, we managed to get the whole fitting off for inspection. It appeared to be a crack in the casting.
After asking him about it....he then said that it's the second such part he had been through in the last 3 years.
What would the forum think to this ? Surely it can't be unique to his application. ??

 

[alldodge]

Have not seen one that cracked that was not very old and corroded. So is the crack on the bell housing or the transom assembly?

That said you can run it without the exhaust bellow, or even just install an exhaust tube

 

[QBhoy]

Hi alldodge

It's on the transom assembly. Thought it might be a casting failure at first glance...then he said it's the second time it had happened. Totally confused me as to what may be causing this.
It's literally the piece the bellow attaches to, on the transom side.

 

[alldodge]

Hi alldodge

It's on the transom assembly. Thought it might be a casting failure at first glance...then he said it's the second time it had happened. Totally confused me as to what may be causing this.
It's literally the piece the bellow attaches to, on the transom side.

Wow never seen that happen and never heard of it happening twice.

What year is it and is it and Alpha or Bravo?

 

[QBhoy]

It's around 2002/03. Alpha.

 

[QBhoy]

Here is a picture.

 

[alldodge]

That is real strange

The item kind of looks like it would come from the bell housing side instead of the transom. I know your right but just to make sure we are on the same item.



I would remove the transom assembly and then put a straight edge on the boat transom. It has to be in a bind and something is not flat

 

[QBhoy]

Alldodge...of course...you are right. From the bell housing side.
If it helps any, the initial problem was that the exhaust bellow kept blowing off.
When he told me this, I instantly presumed it was the old problem when you don't put it on right (without roughing up the surfaces) and you trim leg up and it pops off...this wasn't the case. It happened when engine was started and a little revs applied.
The boat was in the water at the time, so we pulled the back end in to the jetty and had a look. After 2 mins, it was clear to see the casting had cracked here.
Just so unusual for it to happen twice. Can't think what is so unique to this boat that would cause it to happen twice ! Once is a freak occurrence and perhaps understood and put down to a dodgy casting, but when he told me it had happened before I was dumbstruck.
He now has another second hand assembly fitted and ready to try out tomorrow.
So strange.

 

[alldodge]

I'm thinking there is something that comes in contact with the exhaust, it shouldn't but don't see anything else that could break it. Move the drive up/down/left and right. In each of the positions see how much play is in the pins.

 

[QBhoy]

I'll be down there later. I'll have a look and see.

 

[QBhoy]

Looks like the bellow jubilee clip screw may have been positioned at the bottom and hitting the exhaust cast section. Only thing I can think of and it lines up.
Think he has been positioning the screw section of the clip in wrong position.
Another picture of damage.

 

[alldodge]

I think your right, it does look dented in, and also the manual shows (Sort of) to place the screw on the starboard side



While this should have no effect, but the hydraulic ram comes with a spacer inside to reduce the amount of trim in by 1 1/2 degrees. It should not have been removed, but even if it was it should have no effect. Another spacers could be added to decrease the travel further. I would make place the screw clamp to the side and trim the ram all the way in to see if it still makes contact

 

[QBhoy]

I shall do that. Think we have it sorted now.