Maxum 3100 SCR Issues

[srdiamond]

I bought a 2002 Maxum 3100 SCR last year.... it was in pretty good shape .... the only issue was that there was some weird electrical issue in that with only one good battery, there was no way to start both engines... ends up both battery switches were bad .... now all is good.... it has the 5.7 Mercs with Bravo3 ... bilge is clean and engines seem solid.... but at WOT of 4500-4800 I have never got the boat above 30mph.... I assume I should be getting another 10mph with this package.... but since everything else was solid with the boat I just assumed a previous owner had weird ratios installed somewhere along the way.... but a few days ago a major issue has popped up in that I cant get on plane at all now... it seems to rev fine and I am not bleeding drive fluid but it feels like I am dragging an achor or something..... any ideas all? I am assuming if the engines were not producing enough power that I never would have been able to get to WOT so I cant imagine that is it... neither engines nor drives are burning oil...

[pascavone]

1. use your cell phone gps or iphone app fir a speedometer to check if your actually going the right speed.
2. make sure your garmin is set for MPH and not NMPH... miles per hours, not nautical miles per hour.
3. how much fuel are you carrying, and how many bodies?
4. Stick your hand under the water and see if your trim tabs are attached or hanging off. The hinges do rot.
5. Raise the drive, with engine off, put the boat in froward gear and try to turn your props by hand. This will check if your engine coupler is slippping.
6. Look behind your engine at the input drive shaft and look for black rubber fragments, this would be your engine couple falling apart.
7. The WOT of 4500-4800 is correct.
8. Sea water, growth build up on the hull?
9. You could compression check all cylinders of the engine, which should be +150lbs, but more importantly all equal per engine.
10. I don't think you'll get any more that 34mph going in slack water to begin with. You are sailing around with 12,000lbs.

[srdiamond]

Great feedback.... let me answer a few that I know offhand...

1. use your cell phone gps or iphone app fir a speedometer to check if your actually going the right speed.
speedo isnt connnected on the boat and the speeds I mentioned are confirmed from both the boats GPS and my phones....

2. make sure your garmin is set for MPH and not NMPH... miles per hours, not nautical miles per hour.
Definitely MPH

3. how much fuel are you carrying, and how many bodies?
The last time with the problem was just a few people and half a tank - the week before I had 11 people and a full tank and I was able to get on plane without issue (although I have always had a top end limit of 29mph)

4. Stick your hand under the water and see if your trim tabs are attached or hanging off. The hinges do rot.
They are solid and are set down for maximum lift

5. Raise the drive, with engine off, put the boat in froward gear and try to turn your props by hand. This will check if your engine coupler is slipping.
This is the most interesting idea I have heard yet - I assume you are talking about the threaded shaft with the universal joint in between that connects the engine and drive? I have certainly taken many drives out before and I cant imagine how that could be slipping without some serious damage being done internally, not to mention the sounds it would cause? But if that could somehow slip (like a loose clutch), that would explain the top end speed problem and plane issue now, yet the engine is still reaching WOT.... very interesting....

6. Look behind your engine at the input drive shaft and look for black rubber fragments, this would be your engine couple falling apart.
I would definitely notice this - my bilge is amazingly clean and dry - I am confused what is rubber in the coupling? I guess I am thinking of the solid 1 inch think steel shaft from the outdrive that goes thru the gimbal bearing into the engine...

7. The WOT of 4500-4800 is correct.
8. Sea water, growth build up on the hull?
boat just went in 4 weeks ago in Lake Michigan with a decent bottom paint so I cant imagine this is an issue...

9. You could compression check all cylinders of the engine, which should be +150lbs, but more importantly all equal per engine.
This could be an issue, although how could the engines be reaching WOT, unless the props were slipping?

10. I don't think you'll get any more that 34mph going in slack water to begin with. You are sailing around with 12,000lbs.
Unfortunately I have been unable to talk to another Maxum 3100 owner to see what they are getting - but I have a friend with a 2005 rinker 34 with volvo 5.7s and I have clocked him at 40mph personally..... we certainly seem to have the slowest boat around for our size.... very irritating.... :-)

I appreciate your help... let me know your thoughts...

[pascavone]

Ok,

The engine coupler is a aluminium insert spline, pressed into a 2" thick rubber donut, that is bolted to the flywheel of your engine. This is how your drive shaft connects to your engine. The rubber is to kill vibration.

A few sand bar hits, and the splines can shear, or the rubber slip under high rpm's. (this is why people sell boats, because you have to pull the engine to get to them).

There is a zurk grease fitting back there, that need to be serviced every year.

Next,

Tabs down is pure drag in the water.

You need to get moving and get up on top of the water before tabs will be effective.

Try having your bodies move to the center of the boat next to the captain, and not the ass end, just to get on plane, that will pull the bow down w/o tab drags.

there are a lot of 3300 owners on here, so they will give you the details about their 40mph runs.

Rinkers are way lighter boat, so can't compare.

[biggerseagar]

What happen to the survey when you bought this boat? Did you get one done? That would of answered alot of your questions. I do say this with all do respect:-)

Roger

[ss3964spd]

Sr.,

I would first physically verify that when you have the drives all the way down via the trim switch that they are indeed all the way down.

I find it unlikely that both couplers would go bad at the same time. Regardless, if they did I would think that you'd see it at the tachometer. Meaning, when you hit the throttles to get on plane the RPM's would likely jump up way higher, and much faster, than normal - just like if a clutch in a car was slipping.

Dan

[CountryME]

Sr,
Check to see if you have spun the hub on your props. Matchmark the hub and prop, go try and take off a couple of times, then check your match marks. If they are off, it's time for new props.
You may have had one spun hub and now spun the other one from over use.

-JP

[srdiamond]

Thanks all.... drives are definitely all the way down and I have played with all possible variations of the trim tabs - remember that it used to get up on plane fine until a week ago (still had top end issues though)....thanks for the clarification on the spline.... I know when I have taken off previous outdrives to service them, the 'dick' of the outdrive with the splined end slides thru the gimbal bearing into the female end in the flywheel - I assume you are saying that this female end contains the rubber donut piece which would explain why I have never seen it......my starboard drive does have a slightly different sound which could be this - the more I think about it, this really could be the issue.... is this a plausible theory?....maybe the starboard drive coupling has been slipping and has only been able to transmit 50% power since I bought the boat and thus that explains the low top end speed (btw, my friends Rinker weighs 15000) ......and maybe now it is slipping more and thus isnt even able to get enough power from the starboard drive to get the whole party up on plane.....

How does one possibly check the status of the coupler without removing the engines? I assume you cant see it well enough to examine even after taking off the drives?

[pascavone]

well,

lets hope its something simple, but usually the tach will bounce as the coupler holds, then gets hot, and spins then peg the RPM's.

Since your able to still run, I'd keep working with it this season, and then deal with it after the winter.

if you end up pulling an engine, the jobs about $2k, then your should replace your transom pin seal at the same time, since the boat is due for its age.

[srdiamond]

I am amazed that I have never had a coupler go bad all these years of owning boats - I have had 4 different mercruiser / bravo combos and they were all in the 10 year old range? Is there no way to know for sure if its the coupler or you just have to pull the engine? And shouldn't we do both if we are in there already? It sounds like there would not be any major grinding noise since it is rubber but it also sounds like I should be seeing rubber debris in the bilge?

[pascavone]

I'd call a mobile marine mechanic and let him look at it.

I was getting WOT and not going anywhere ither.

I can tell you backing off a sand bar, can really piss a coupler off.....

Who knows what the last owner did?

[Painter]

srdiamond,
What was the final outcome of your problem?

[srdiamond]

It is a long and sordid story....after a full tune up it got only marginally better.... we finally started testing the compression in each cylinder.....bingo!...... I had 3 dead cylinders on the same side.... we assumed it was a head gasket - took it apart and sure enough it was blown between 2 of them (but not the third one).....but the valves didnt look right so we took it to a valve shop and he immediately said it had been hydrolocked and needed a new head / valves....i.e. water had gotten into the cylinders and screwed it all up. So now the question is what was the source of the water - bad exhaust manifolds, flapper valves, etc....oil looks fine and piston rods dont appear to be bent....so do we risk just replacing the head for only 1k hoping it was just a fluke or the entire motor for 5k and eliminate all possible issues (including knowing if there is any coupler issues)?

[Painter]

Sorry to hear that srdiamond. I have to replace a coupler on mine but that's it, I am replacing both engine couplers with the steel ones. I was hoping someone with a 3100 would be able to let me know how difficult getting the engines moved ahead enough to change the couplers would be. I will be doing it myself but there is very little room to work with. I have a shop to do this in it's just that I have never worked on boats before. Anyways good luck with yours and let us know the final outcome was.
Also if anyone else out there has done any work like this on a 3100 please let me know, as I don't see many posts on this model.