Replacing exhaust manifolds, risers - Page 2 - Maxum Boat Owners Club

shrew · 10-13-2017, 02:54 PM

Quote:

Originally Posted by rwc

I have an aftermarket thru hull uptake and the drive uptake has been capped off.

This is a Bravo III. They are known to slowly corrode and crush the intake hose where it passes through the transom assembly. The resolution is to replace the transom assembly. What some folks do as a work around is to cap off the intake through the outdrive, then install a through hull, with a seacock and a sea strainer like a full inboard.

The water intake through the drive also cools the drive, so if a through-hull intake is installed, then an external drive shower also needs to be installed on the drive.

Do you have an drive shower?

Those manifolds and risers look like they were ready for replacement LAST season.

rwc · 10-14-2017, 07:31 AM

Quote:

Originally Posted by shrew

Do you have an drive shower?

Those manifolds and risers look like they were ready for replacement LAST season.

I don't know about the drive shower. Where would I see it?

According to the mechanic it should have been changed three seasons ago. I reduced the price accordingly, but hopefully no surprises lurking in there. Going to get it done ASAP.

mmwjr · 10-14-2017, 04:17 PM

Quote:

Originally Posted by rwc

I don't know about the drive shower. Where would I see it?

According to the mechanic it should have been changed three seasons ago. I reduced the price accordingly, but hopefully no surprises lurking in there. Going to get it done ASAP.

The shower is a bolt on to the upper drive, would be SS tubing that has a lower scup pickup and a head to spray the water on the drives top.

bman440440 · 10-14-2017, 11:38 PM

Quote:

Originally Posted by rwc

I don't know about the drive shower. Where would I see it?

According to the mechanic it should have been changed three seasons ago. I reduced the price accordingly, but hopefully no surprises lurking in there. Going to get it done ASAP.

there are 2 types of showers... here are pic's

Phillbo · 10-15-2017, 04:10 AM

There is no reason a well maintained B III should ever need a shower.

rwc · 10-15-2017, 04:14 AM

Quote:

Originally Posted by Phillbo

There is no reason a well maintained B III should ever need a shower.

Now that I've seen the pics, I know I don't have one. That said, the aftermarket uptake isn't recent and the engine has 766 hours on it with no apparent drive issues. Maybe this is an issue in hotter climates?

I would think immersion of the lower end of the drive would provide plenty of cooling.

mmwjr · 10-15-2017, 04:31 AM

Typically when one does the modification you have the block off plate is on the inside water passage and the outside hose is cut which allows water pressure to push water through the lower intake then through the drive and out the cut hose.

Phillbo · 10-15-2017, 07:13 PM

The transmission is not submerged when under way.

shrew · 10-16-2017, 01:55 PM

Yes, the drive ABSOLUTELY needs a drive shower if the drive intake is blocked off. Yes, it is because once up on plane the drive is out of the water from the anti-ventilation plate up. The water being drawn through the drive cools the outdrive. absent water there is no cooling of the drive on the upper half of the outdrive.

So someone did a hack job to solve a blocked intake problem. The proper solution would have been to either replace the transom assembly, or do what was done on your boat AND add a transom shower. This sounds like a shadetree mechanic had his hands on this boat.

rwc · 06-20-2018, 01:02 AM

Just to follow up on this conversation, I went over the question of the drive shower in detail with my mechanic and he said that while it might be necessary in warmer waters, in his experience it's unnecessary around here. The cooling mod is common, but no one has drive showers.

He said, drives can overheat, but around here, it's always symptomatic of some other problem and if you are maintaining the drive properly, there are warning signs (discoloured drive oil, discoloured drive paint), which my drive is not showing. The drive has 768 hours on it, so I presume if the cooling system was going to be a systemic issue, it would have been by now.

With respect to the subject, I've decided to hold off for now on replacing the risers due to indecision. I'm aware that this risks hydrolocking the engine and destroying it, but the replacement is about $4k installed, while a whole new engine is $12k. I can get a new engine with fuel injection, better fuel economy, less emissions, and more power density, which will probably last the remaining life of the boat, or I can spend $4k on this engine and then possibly have to replace it in a few years anyway because it is too tired. I figured I'd use it for the season before deciding because at worst, I risk being forced into the former decision.

mmwjr · 06-20-2018, 02:26 AM

Your boat, your money. Best of luck.

rwc · 06-20-2018, 03:42 AM

I'll wind up doing a whole ROI study before I'm able to decide, because engineer.

All the rest of the maintenance went fine. Replaced bellows, painted and did all the fluids. No surprises, which was nice.

Determined that the water leak is rainwater through the hull seam, so that's my project before winter.

mmwjr · 06-20-2018, 12:23 PM

Understand the ROI however there is always the wildcard of emotion where you fall in love with another boat so the planned duration for the ROI goes out the window.

jrsick · 06-20-2018, 12:39 PM

Why don't you put in the manifolds and risers yourself? There's 8 bolts and 3 hose clamps. You get a look at the system to determine condition. Spark plugs are right there too. Cost of parts is $1500. No better time than present to dive in.

rwc · 06-20-2018, 05:37 PM

Excellent points fellows. Thanks.

I'm pretty enamoured with this boat right now, but it's true that could change. It's my first boat, so I guess that's part of the reason I'm hoping to make it through the season without having to make the decision. I really don't know what to expect from anything.

I had it out on the weekend with four adults and two kids and discovered that I had to send my dad into the cabin in order to get enough weight forward to get up on plane. That made a more powerful engine quite appealing at the time.

As for doing the work myself, I really should. I've replaced several car engines and done just about everything else wrt rebuilding a car. The boat scares me a little more for some reason. Also and annoyingly, the serial number for the engine wore away over the years, so I'm worried about buying the wrong parts. I think I've deduced what it is, but I can't be sure. I guess I should just ask if I can exchange them if I get it wrong the first time...

jrsick · 06-20-2018, 06:00 PM

Your title should have the engine serial number. If not, a 2004 5.7 mercruiser is enough info to get you the right parts. I see manifolds and risers on craigslist every week.
Regarding getting up on plane, since your WOT is 4000, you are over-propped. What size props do you have? You could go down 2 or 3 pitch and get better hole shot and on plane quicker. Smart tabs help with this also.

rwc · 06-20-2018, 06:21 PM

Quote:

Originally Posted by jrsick

Your title should have the engine serial number. If not, a 2004 5.7 mercruiser is enough info to get you the right parts. I see manifolds and risers on craigslist every week.
Regarding getting up on plane, since your WOT is 4000, you are over-propped. What size props do you have? You could go down 2 or 3 pitch and get better hole shot and on plane quicker. Smart tabs help with this also.

Unfortunately, it's not in the title, but here's hoping you are right that they are fairly standard by year.

I didn't mention, but after the boat was maintained, she makes 4300 RPM. At first, I thought my mechanic must be some sort of wizard because I couldn't figure out what he did that would make such a big difference. Then I noticed that the drive trim was a little up. I pushed it all the way down (because for some reason I thought that's where it should be) and the boat dropped back to 4000 RPM max again. I think that issue can be chalked up to operator error.

It occurred to me yesterday that if prop angle made that big a difference, maybe dynamically adjusting trim while getting up on plane would make it easier? I also have to figure the trim tabs. I just sort of randomly poke them at intervals.

mmwjr · 06-20-2018, 10:53 PM

Tuck the drive all the way down to get on plane then trim out for best speed. Same with trim tabs but you can also use them to balance side to side depending on where weight is distributed.

jrsick · 06-21-2018, 12:12 AM

yep, what he said ^
You want the front of your hull to be out of the water and above the bow wave when on plane. By trimming the drive all the way down you force the bow to stay in contact with the water surface. This increases drag and reduces efficiency.
When trimming out, make an input then ride it for a minute to see the effect. I know boaters that like their drives trimmed just short of cavitation.
Practice this weekend and you can let your dad be part of the family and put his days as boat ballast behind.

rwc · 06-21-2018, 01:38 AM

Thanks guys. I will give that a shot.

I think the prop was cavitating quite a lot when up on plane, trimmed down fully and at WOT. I expect that was the main source of the difference, pushing against that extra bit of resistance. The sound from the prop was remarkably different with a few degrees change in trim. Went from an angry growl to a happy whir.

I design ships for a living, but have somehow managed to avoid learning anything at all about planing craft, so your advice is much appreciated.