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Author Topic:   Merc 115 4 stroke shifting problem
ocuyler posted 07-28-2003 01:46 PM ET (US)   Profile for ocuyler   Send Email to ocuyler  
Hey guys,

A 2003 Mercury 115 4 stroke EFI came installed on my new Boston Whaler 16' Dauntless. It a terrific motor. No choke starts, runs very quiet, especially at idle, great mid-range power and a perfect 2.5 to 3.5 mph troll at idle. Indication so far show amazing fuel mileage.

The only problem that started almost immediately was the linkage became sticky trying to go from forward back into neutral. It binds a little and then jumps into neutral or even past it into reverse. Ouch! Also neutral is hard to find and it occationally will start in gear.

I dropped it off at the dealer, who's immediate reaction was "welcome to the world of Mercury". The comment FLOORED me. I asked why he would say something like that to a first time service customer. His reply refered me to the dealership owner. His reply today was that they have have this persistant problem with the lower units being too "tight" and that Mercury customer service was BALKING at acknowledging the problem, much less a fix. So they are going to do the "best they can".

Any comment out there?


Jarhead posted 07-28-2003 03:47 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
I don't think this is going to help but I have the same out fit [boat and engine]. Never had the problem you mentioned.

The "welcome to the world of Mercury" crack was uncalled for and would have me going to a different dealer for the service work!!

Marlin posted 07-28-2003 06:38 PM ET (US)     Profile for Marlin  Send Email to Marlin     
I also have the same boat and engine. I agree that there's no positive feel for going into or out of neutral, and the first couple times out I had a tendency to go from forward right through to reverse. It's particularly hard to make sure the engine is in neutral when it's not running. I was surprised that there was no button or trigger that you need to push/pull to leave neutral.

As I've gotten a feel for the controls, that problem doesn't happen anymore. The motor has certainly never started in gear, and not from lack of trying on my part!

Overall, it sounds like your control could use a little adjusting of the cables. It shouldn't be that big a deal.

Jamie 20 outrage posted 07-28-2003 09:02 PM ET (US)     Profile for Jamie 20 outrage  Send Email to Jamie 20 outrage     
Yes, Merc has been having that problem, but what an insensitive jerk to say that. The fix is to replace your new cable with either platinum, extreme or any other premium cable. Then lower the idle. Trust me, if they had done this before they gave you the boat, you wouldnt be posting here. Now, unfortunately, you will be looking for this problem and and always will. The problem occurs because of the increased lower end torque that the 4 stroke has, that the 2 strokes don't. This makes it physically harder to get the clutch dog to back off the gear dogs. Again the cable and lower idle[less torqe] will do the trick.
jimh posted 07-29-2003 08:57 AM ET (US)     Profile for jimh  Send Email to jimh     
I had some repair work done on a Yahama engine at a dealership that sold all three major brands (OMC/Mercury/Yamaha). The service guy told me "We don't like to work on Yamaha's." I was not impressed with their work and never went back..

I am confused by the comment that 4-stroke engines have greater torque at lower crankshaft speeds (than 2-stroke engines). I thoughy, from the comments about poor accelleration under load ("holeshot"), that the 4-stroke engines had less torque at low crankshaft speeds.

bsmotril posted 07-29-2003 10:26 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
My understanding is that all mercs that use any kind of ECU for injection have a shift interrupter that momentarily kills a few cylinders (1 bank of 3 on V6 Optis) to help ease the shift dogs. This has been common practice on Mercs and Mercruiser electronically controlled motors, and even on older carbed mercruisers. Having this interrupter out of adjustment will certainly cause the symptoms you are having. I don;t know what kind of controls come with the smaller mercs, but the Quicksilber conrols on the bigger motors have an adjustable detents for the gates on either side of neutral.
OutrageMan posted 07-30-2003 05:35 PM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
I can speak to this issue with some authority. The rescue boat I run has twin 115 Merc 4S's on it and we have had problems with the shifting also. We also have the benefit of the president of Mercury Marine being a neighbor and the donator of the engines.

Jamie, you are both right and worng with your cures and causes. Yes the motors do have more torque (but it is very, very small), but that is not what causes the problems. To shift the motor, an ignition retarder comes into play, effectively shutting down the engine to allow for the shift to occur. However, it will not do so until the RPMs come done to a preset level. Depending on how many turns you were making to begin with before the shift attempt, this could take a few seconds. Additionally, the solution is not different shift cables (although this is an improvement in any boat). In this case what actually does help the problem is the instalation of heavier satinless steel props. The added weight actually acts as a brake when coming down, allowing for a faster shift.

I would be happy to answer any other questions you may have.


Perry posted 07-31-2003 03:25 AM ET (US)     Profile for Perry  Send Email to Perry     
I always thought the inertia of the heavier stainless steel prop makes it spin longer.
jimh posted 07-31-2003 09:17 AM ET (US)     Profile for jimh  Send Email to jimh     
I think you mean momentum, not inertia. But yes, it would seem that a heavier propeller would have more momentum, and, like a flywheel, cause the propeller shaft to keep turning longer.

We now have two conflicting areas in this discussion:

--does a 4-stroke engine have more torque at lower RPM than a similar 2-stroke engine?

--when reducing engine speed to idle, does a heavier propeller tend to keep the propeller shaft spinning longer than a similar size propeller which is lighter?

Comments are invited.

OutrageMan posted 07-31-2003 12:58 PM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
I am completely oblivious to the physics involved. I just know that our solution came right from Mercury tech dept., via its President.


Jamie 20 outrage posted 07-31-2003 10:04 PM ET (US)     Profile for Jamie 20 outrage  Send Email to Jamie 20 outrage     
I also was told about the advantage of a stainless props to help shifting from Merc. On the boats that I worked on, we were able to correct the problem without going to stainless. Nothing was mentioned about rpms needing to come down. Our problems occured just by trying to shift at idle. I am a big fan of fixing the easy and cheap stuff first, when possible.
jimh posted 07-31-2003 10:47 PM ET (US)     Profile for jimh  Send Email to jimh     
I have confidence that Outrageman has observed this solution, but why it works is the focus of my additions below.

If the boat has a stainless steel propeller which is heavier, then it ought to have more momentum. When the shift interrupter momentarily cuts the engine off, the engine loses power. The engine slows faster than the propeller. The engine is fighting compression in its cylinders to continue rotation. The propeller, which had been being driven by the engine, now continues to spin. The boat may still have some way on, so the water flow makes the propeller keep spinning, too.

Down in the lower unit, the shift mechanism is a sliding clutch dog. If the propeller spins slightly faster than the drive shaft, it is easier to shift out of gear. This is because the drive shaft will tend to slow and come off the clutch dog, and then the shift can more easily slide the dog back to neutral.

This analysis does not violate any laws of physic, and seems to explain making a shift from forward to neutral easier. This analysis also does not require making the 4-stroke have more torque than the 2-stroke.

If the engine uses an aluminum propeller which has less momentum,
the propeller may slow down faster than the drive shaft (at the time of shift interruption), in effect laying on the clutch dog and making it harder to pull it off the engaged dog and back to neutral.

Making a shift from neutral into gear should not be affected if the propeller is not moving.

I am trying to think how the torque would effect this situation. When the engine power is interrupted at the shift time, it seems like the engine doesn't have much torque, either 2-stroke or 4-stroke. The ignition is off.


OutrageMan posted 08-01-2003 07:44 AM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
Jim, I think that you hit it right on the head. Makes sense to me.


Peter posted 08-01-2003 10:54 AM ET (US)     Profile for Peter  Send Email to Peter     
The best that I can tell from Mercury's website is that the foot of the 4-stroke and 2-stroke Mercury are the same because the gear ratios are the same. Thus, from the foot's perspective, there should be more momentum on the drive shaft side of the gear case in a 4-stroke motor than in the case of the 2-stroke motor due to the increased number of moving parts. That leads me to think that getting the engine speed down before shifting is even more important in a 4-stroke than in a 2-stroke, although it is important to get the engine speed down in all cases for the foot's health.

I'm not entirely sure from the dealer comment according to the original poster that the comment was necessarily specific to 4-strokes. I read the comment in a more general light that these lower units are "tight".

jimh posted 08-01-2003 01:02 PM ET (US)     Profile for jimh  Send Email to jimh     
Peter, et al.

Yes, I like the concept that when the ignition is interrupted, the 4-stroke may continue to rotate better than the two stroke due to the following:

--two-stroke has less momentum, fewer moving parts
--two-stroke hits more compression cycles
--four-stroke has more momentum, more moving parts
--four-stroke hits fewer compression cycles (right?)

This situation would cause more difficulty in shifting with the 4-stroke, and again, no laws of physic are violated.

ocuyler posted 08-11-2003 10:40 PM ET (US)     Profile for ocuyler  Send Email to ocuyler     
Thanks for all the comments. The dealer was very quick to arrange for a new lower unit and the correct stainless steel prop. They installed during the week and we sea trialed Sat morning. The 115 4S jumped out of the hole and ran up to 6000 rpm's with 2 pob and 10 gallons fuel. Speed at wot is 44 with a light load and is MORE than enough speed in a 16 footer. What a teriffic little boat!

I had the occcation to have 7 adults and 40 gallons on board and there was NO WAY this boat would even think about getting on plane. But it gave us that much longer the finish the beer!

I'm a happy camper. Thanks again for your help.


dogfish2 posted 08-12-2003 09:13 AM ET (US)     Profile for dogfish2  Send Email to dogfish2     
Glad to hear that your problem has been resolved. Did the dealer install a lower unit with the same gear ratio (2.07) as the malfunctioning one or with the newer version? Just curious, as I have a 115 4s on a Montauk. With a S/S prop, and waiting for the rpm/s to drop a little before shifting, the "clunking" problem is minimized. Good luck and have fun with your rig.
Perry posted 08-12-2003 04:08 PM ET (US)     Profile for Perry  Send Email to Perry     
Ocuyler, are you saying that your boat cannot get on plane with 7 adults and a full tank of gas? Did ou try? I have the same boat as you but with a 90 4 stroke Honda. With a 15 pitch prop and 6 large guys and 30 gallons of fuel I am able to plane though it takes around 10 seconds. I can get to 5900 rpm and 35 mph at wot.
ocuyler posted 08-13-2003 12:25 AM ET (US)     Profile for ocuyler  Send Email to ocuyler     

Yes the lower unit was the same spec. Yes, I tried to plane with that load. I'd estimate the weight of that particular "sea trial" at 1600 pounds, with 7 adults, fuel, beer, luggage and unmentionables. There was NO WAY getting on plane was going to happen. I was dissappointed, but not surprised.

However, with 600 pounds, It jumps up in 3 seconds and runs up to 6000 RPM's in a flash, finding 43 MPH.

The prop is a stainless steel 16" VENGEANCE. Would you try something else?


Perry posted 08-13-2003 01:48 AM ET (US)     Profile for Perry  Send Email to Perry     
Otto, 1600 lbs is a lot of weight. The one time I had 6 guys I estimate I had about 1200 lbs. I think if you can achieve 6000 rpm with 600 lbs on board, you are propped right. I use a 15 pitch stainless for better hole shot and increased performance with heavy loads. With a light load it will rev to over 6200 rpm and 38 mph but I rarely take it that high. With only 90 hp, I need that 15 pitch prop to get my heavy Dauntless on a plane quickly. My 16 pitch stainless will push me to 40 mph but the hole shot suffers.

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