2002 MFS25A noise in neutral and 2300 to 3000 RPM

So, I finally get this thing running good, get the boat propped right and my first real problem occurred while on a 5 day vacation last week!

While idling the engine is noticeably loud, but it is smooth running. When you put it in gear, the noise goes away and it's super quiet and smooth. Also, I'm getting what sounds like a screeching noise (almost like a belt noise or bearing noise) that starts around 2300RPM and stays until around 3000RPM. It almost sounds like a defective air pump (if it had one).

So, I need to troubleshoot this. Does the pull start mechanism have any components, that ride on top of the flywheel or come in constant contact with the crankshaft? I figure I can remove that whole assembly and see if the noise goes away. Also, I notice there is an idler or tensioner pulley for the timing belt. Is there a way to remove the timing belt easily to check this pulley and put it back to rule out the bearing in the pulley being bad? Assuming there are timing marks somewhere around the crank and cam?

Finally, is it possible to run the engine with the lower unit removed to rule out a bearing problem in the lower unit transmitting noises up to the powerhead? I do have the upper flush attachment that connects to the powerhead.

FWIW. The engine runs excellent otherwise and it did not affect our trip at all. We used the boat every day, 1 to 3 hours per day.

Yes, the motor will run fine with the recoil starter removed. No, nothing inside the recoil should be riding on the flywheel or crankshaft.
Yes, a bad tensioner could whine. Cam timing is straightforward, using the Factory service manual as a guide.
Yes, you can run with the LU off. Have plenty of cooling available; you will not be pumping. Do not over-rev when not under load.

Thank you!

OK... So, before I started taking stuff apart, I figured I would check the lower unit oil. It seemed like there was not that much in there, it was very black and had a little water coming out at the end. It was not like a milkshake though.

The gears and bearings all look pretty good to me and they all spin freely and are very smooth.

The only thing I can see that does not look right is that the upper bearing below the water pump has an issue. That upper race is "spinning" in the bore? It seems like that when you assemble this engine, that race should be "pressed in" and should "NOT spin". Does this sound correct? I took a video of me showing how easy this race moves up and down and spins in the bore. I'm thinking that this is the idle noise and the screeching noise between 2300 and 3000 RPM is what I was hearing.

My first thought is to replace that upper bearing and race, replace the driveshaft o-ring and seal below the water pump, replace the o-ring and seal at the back of the prop shaft and replace the shift rod seal (if I can figure out how to remove it). Does this sound right? If so, I'll order the parts tomorrow.

Here is a video that shows what I'm talking about: https://www.youtube.com/watch?v=uRNp0yKzGiM&feature=youtu.be

If there was water in the LU, a new seal kit is in order. I sometimes use a stainless dental pick to remove the inner cam rod o-ring. Installing the new one will also test your patience. Black, stinky lube is an indicator that it was definitely time for an oil change. If the oil level was low, you could damage the upper bearing -- a common problem when LU lube changes are ignored, or the refilling is rushed.

When changing lube, in order for the LU to be filled completely, you are supposed to fill to the top, and then the gears need to be turned to dislodge any air bubbles, then the LU topped up again. The o-ring, shim and seal typically put enough thrust load on the upper bearing that it doesn't spin in the LU bore. It is not pressed, or it would be impossible to get the drive shaft out. Yours looks pretty normal. If it did spin a lot, the aluminum casting would wear first, as it is softer than the hardened race of the bearing.

Thanks again for the info.! The lower unit oil only has about 30 hours on it. I remember you saying in many threads about how Tohatsu was worried about upper bearing failure. So, I was very careful to top it up properly. I actually did it 3 times over 2 days to be sure it was all the way to the top. I used Penzoil Marine 80/90 gear oil.

I'm just hoping that age, ozone and other environmental factors got to the seals and that this "re-sealing job" and fresh oil fixes the problem.

So, that race is supposed to spin? Weird... I can see in the lower unit and on the race where it is black. It has obviously been very hot from spinning. I wonder if I just lightly score in the inside of that bore with a scribe?

Also, regarding that shift rod... There is a brass bushing where the rod passes through. I have removed the 10mm bolt and washer securing it in there. But, how in the heck do you get it out? I was thinking about clamping some vice grips on there or using a slide hammer? That sucker is really in there!

No, the race isn't supposed to spin in operation, but you do have to be able to pull the drive shaft out. If the rollers and race faces are OK, it wouldn't hurt to "stake" the aluminum to increase the compression (friction) to keep the race in place. Just don't get it too far off center, or the roller cone won't seat properly.

If the lube was actually low, you may have had some leak out. Maybe a marginal prop shaft seal, etc.

I usually push the cam rod down and then jerk it up (hard and fast) and the whole rod and bushing pop out. Sort of like a slide hammer.

Again, thanks for the info.! After going through the parts diagrams and re-reading your post about the shim and thrust load, I found something interesting. In the parts catalog, it lists 4 different shims of varying thickness. Perhaps all I need is a little thicker shim, or maybe 2 of them?

I'm not really sure which one I need, so I guess I'll just flip a coin... Those little shims are $10 a piece!

Not a good idea. The shims come as a kit, and you use the appropriate one that gives the correct backlash.
If you have not changed anything in the LU, I would stick with the shim you have now.

I got it back together. Getting all of those seals in was a piece of cake! I was surprised. So much easier than the old OMC I used to own. The Tohatsu lower unit comes apart really easy. Pretty brilliant design IMO...

I found that the aluminum plate below the water pump that puts pressure on that shim, had quite a bit of corrosion on it. I think the corrosion was "lifting" that plate just enough to cause some play between it, the shim and the bearing race. It is much tighter now that it's all cleaned up.

I put it on the hose and it is MUCH quieter than before, so I think I can call it fixed. I plan to go out Friday, so I'll know for sure then. The loud idle noise seems to be completely gone, but I'm afraid to rev it until I'm out on the water to see if the "Screech" is gone.

Thank you again for the advice and help!

Good luck and happy safe boating!

I was finally able to water test this thing yesterday. Not happy!

On start up and pulling away from the dock all was good. In fact too good. At idle out of gear at the dock the noise was gone and as I pulled away, I was thinking that I never remember the engine being this quiet!

After a short burst of WOT and then a 4 minute cruise at a cruise RPM of 4700, I backed off the throttle and came back to neutral. The noise I previously had at idle had come back. After about 20 more minutes of use at various speeds and RPM's the screeching at the previous mentioned RPM's came back as well.

After about an hour of idling through manatee zones and no wake zones I headed back to the ramp. On the final leg back to the ramp I ran it up to cruise RPM again and it seemed like there was an "oscillating vibration" sound? It almost sounded like something you would hear if you ever had a truck with a 2 piece driveshaft that had a bad carrier bearing. Or I just could be imagining it, thinking it is worse than it actually is.... Either way, the idle noise and screeching noise is back and I am thinking again that it must be that loose race on that top bearing since everything else in there looked so good?

I am going to pull the lower unit here again in a few minutes BEFORE I drain the oil, remove the water pump and have a peek in there again. I'll drain the oil afterwards to see how it looks and report back what I find.

Frustrated. I need this thing fixed! Right in the middle of Snook season too!

OK... To add to the above. I pulled the lower unit (again). This time I did not drain the oil. I put it on the bench and pulled the water pump and found that the oil was not covering that top bearing and the oil looked milky? So, I then drained the oil and it was not clear like honey but rather opaque like crystallized honey. That to me looks like water. I don't see how though?

After draining everything, I pulled the prop and pulled the propshaft carrier out again and everything looked good. So, I reassembled everything and put 25 psi in the lower hole and could not hear or see any leaks. Perhaps one of the seals was not seated properly and when I did all of this it seated? I don't know. After I put it together last time, I did not pressure check it.

I am perplexed as to how the water got in and why the oil level was down... Since the pressure check was good, I'm going to fill it with oil again, run it, check the oil again to be sure it's "oozing out' that top hole and water test it again

UGH!

Had it out on the water again today. Just like last time, it started out super quiet. After about 15 minutes of running at various RPM's the louder than normal idle and screeching at 2900RPM came back. You can accelerate past the noise and it's fine. And just like before, it's really quiet in gear and a little louder out of gear in neutral. I ran it pretty hard for about 20 more minutes and them came back and pulled it out.

However, when I got home I drained the oil into a glass container and it was crystal clear! So, it is definitely sealed up now. Now I just need to figure out what is causing the noise.

Recently I went from a 11" pitch prop to a 9" pitch prop. I guess the next thing to do would be to put the old prop back on? It seems like all of this crap started literally right after I put the new prop on.

Snookwhaler,i read your entire thread again, Was the suspect bearing ever replaced,along with the race, Did you repack it with grease on install for breakin,couldn't hurt. Does your engine have a mid shaft bushing/bearing,not familiar with that brand. Was water pump impeller and housing replaced recently with a good quality unit? have you asserted where the noise is emitting from,Upper engine or lower unit? A wooden dowel with an ear on it might help with an assistant on board,a makeshift stethoscope .Keep us posted about putting old prop back on and running, maybe new prop was damaged! Out of balance?

Hello. No, I never did replace that bearing. I may go ahead and do that at some point. The bearing and race are in good shape with no apparent damage. This goes for the bearings on propshaft as well. The upper bearing is bathed in oil from the lower unit and does not require grease. I still suspect that the noise is coming from that race spinning inside that bore in the top of the lower unit as pictured in my video, but I am not certain? My guess is that "under load", that race begins to spin in the bore and that is the screeching I'm hearing? Once the engine is warmed up I suspect that is the idle noise too. Although it's not too loud, It's not as quiet as it used to be.

The water pump and seals were all replaced with Genuine Tohatsu parts and it is all brand new. I went through all the parts diagrams and I did not see any additional bearings or bushings in the driveshaft housing (mid section). All I see is an oil seal at the very top just beneath the engine.

It really is hard to tell exactly where the noise is coming from and it is most pronounced "under load" at around 2900RPM. The screech starts at around 2600RPM, is very pronounced around 2900RPM and then gone after about 3000RPM.

I really am at a loss.... The only other steps I can think of are to put the old prop on there just for fun and "see what happens". Then go back to what was mentioned above and "Stake" the bearing race in the house or at least "score the bore" so it does not spin and last resort, replace the upper bearing/race.

Thanks for the input!

OK.. Here is what I have been able to figure out. I took it to a local fresh water lake yesterday and ran it just over 3 hours at various RPM's. Same problems with noise as before.

Today I before I dropped the lower unit I noticed oil coming out of the water pickup plates on each side. So, I drained the lower unit again and this is what I found (pic attached below). The seal letting the water in, is the upper driveshaft seal around the driveshaft. There is still a little bit of play in that upper bearing and putting force on that driveshaft for and aft or up and down causes a little movement. My best guess is that "under load" the shaft is pushing that seal hard to one side and letting water in.

Now, the obvious thing to do is either replace that upper bearing and see what I got as far as play and hope that it is tight? I'm hoping this is the best course of action. I also plan to get a replacement upper seal and a shim kit just in case, as now it is obvious that "the play is the problem".

Does it matter which way the driveshaft and propshaft seals get pressed in? On one side of the seal the "groove" is a little wider than the other and the spring is more visible than the other.

I have since replaced the upper driveshaft bearing and there is still lateral play in the shaft. The water is definitely coming in the upper driveshaft seal on the water pump plate. Engine torque is pushing the shaft hard to one side and it appears that this is what is letting the water in. So, now it appears that the needle bearing that is pressed into the lower unit housing must be worn and needs replacing and then shimming, measurements taken, etc...

At this point, I'm thinking this is beyond my expertise as I do not have access to the tools required to measure the tolerances and replace the needle bearing. I have found a local Nissan/Tohatsu/Mercury dealer and plan to go in there and get their take on what to do... Any advice on what to tell them or how to handle dealing with them is appreciated to avoid getting ripped off. This is about to get expensive.

The parts catalog shows which way the seals are to be installed. The diagram shows a cut-away side view if the seal, so you know which way the lip faces. They will work backwards, but not as well. Very rare to get that needle bearing worn, but it could happen if you had contaminated LU lube or water in the LU.

If the seat for the upper ball bearing is significantly out of tolerance, you will need to replace the LU casting. If the bearing merely does not seat well, staking it in position may get you through. When you installed fresh drive shaft seals, were they oriented in the correct direction, or did they go in backwards?

I would tell the service tech that it seems water is coming in through the drive shaft seal. Then give him the whole history, so he can help you diagnose the reason for the leak.

Hmmm... Thanks for the info. I'm not seeing that in the parts diagram. Just the seal but no picture showing the cut away.

On one side of the seal, the inner lip is much closer to the outer edge. This side has writing on it. On the other side the inner lip is farther away from the edge. This side is thin and has no writing on it. When I installed them the first time, I installed them with the inner lip closer to the edge facing "out" or towards the water. The sides that had the writing on them were facing the water.

Hmm. You are correct. The cutaways aren't in that catalog. Sorry.
Normally, the side with the thicker metal is away from the oil. The side where you can see the spring goes towards the oil.

OK... Yep. That's how I had/have them in there. Thanks!

I was just thinking about this again. Yep... I'm an idiot! I definitely installed the driveshaft seal upside down! Dang it! Such a simple thing... When you install the seal, you have to flip the plate over. I installed it facing up, which means when you flip the plate over to mount it and the water pump, the seal is upside down.

Propshaft seal is correct. Hopefully I can pry the seal out of the water pump plate without damaging the seal. So, one more water test and if this does not fix it, it's going to the shop. I really hope all of this nonsense was that simple!

Still leaking. Just dropped it off at the local shop today. We'll see what they can find (if anything).

Got it back from the local shop a few days ago. Rebuild prices for lower units are ridiculous considering what this engine is worth now! I found a used 2007 Mercury 30hp engine. Fuel injected model, but the lower was identical except for the shift rod (which I swapped out). I could have bought the entire engine for $700 or so. Paid $200 for the lower unit because of unknown issues and possible bad ECM. The oil in the lower unit was black and smelled bad. BUT, it had no water in it and for the cost considering everything else I have run across, I could not pass it up. If it works, I can get rid of this engine and upgrade. The boat really needs a 70 to 90hp anyway.

I plan to water test it tomorrow and use it for a couple weeks to get me through the 4th of July weekend. Then sell it and look for a nice used 70-90hp 2 stroke.

It's a shame, because the damn engine (my engine) runs so good otherwise... No issues at all. When I take people out, they are always shocked at how quiet the engine is. You hear more water and prop wash noise than engine noise up until about 4500RPM.

4-stroke Mercs 30 and under are re-badged Tohatsu motors.

Hey, pvanv... I just wanted to thank you again for all of your help in this ridiculous mess. It has been ridiculous on so many different levels, I'm not sure where to begin? The first is the "let down" in the local area for support and repair of an issue like this at a reasonable price (more on that later).

In the end, I wound up finding a used (smoked) lower unit from an ex law enforcement craft that only had 280 hrs. on the clock. The engine was a 2007 30hp Mercury 4 stroke with the "non big foot" 1:92 lower unit.

I had been looking for weeks everywhere trying to find a decent "used" lower unit to no avail. Most places that replace all the components and rebuild it and "do it right" charge close to or just over $1000! Seriously? Not seeing the logic in that since the engine is not worth $2000 or less now anyways. Most of the cost seems to be in the ridiculously expensive parts which should be half of what they are (more again on that later as well). Then again, the ridiculous cost on labor in most shops which I found quite shocking varying as much as $50 or more per hour depending on where you look.

My conclusion is that if you have a small outboard and have a problem like this, is to just sell the damn thing, because unfortunately most shops lack the knowledge to rebuild them (lower unit) or cannot even handle it in the first place because they are so used to selling and pushing their "new product".

My biggest complaint and most shocking is the wild variation on parts pricing! It is literally INSANE! The 2007 Merc 30hp lower that I have in my possession and is now currently installed on my old 2002 25hp Tohatsu are literally identical except for the shift rod and the "end of the shift rod".

I had recently replaced the water pump on my old 25hp Tohatsu and wanted to use it on the Mercury 30hp lower unit. No problem! All the parts were LITERALLY identical and dimensionaly EXACT! BUT, i wanted to use new gaskets on the water pump plate and a new lip seal for the drive shaft. Here is the shocker! Paper gaskets for the Tohatsu were only around $2 a piece, but for the Mercury they were over $7 a piece!!! This is for the EXACT same parts! Same goes for the lip seal on the driveshaft on the water pump plate. For the Tohatsu it is just over $7, for the Mercury almost $12 for the EXACT same part "each"!! The list goes on and on. I could not believe it.

It really is a shame. It is such a let down, I'm thinking about getting out of boating all together. It's a shame, because it has been a big part of my life since I was a child. With all the water quality problems, dealing with algae and red tides every year... Sea grass die off, lack of fish, the fishing sucks, etc... What's the point?

If I wanted to, I could literally start my own shop because of my background. But, at what cost? Apparently I would just be adding to the problem....

Anyway.... The damn thing is finally fixed thanks to a "rare as hens teeth", cheap used part. Forget rebuilding it! Just throw it away if you have a problem!

Yes, yes, and yes.

Due to low volume of outboards in general, and the fact that marine engines are built to non-explosion standards (non sparking alternators, starters, etc.), costs are higher than similar items would be if they were "automotive". Likewise, the motors must be tested and certified to EPA standards... since they make so few motors compared with the Auto industry, the cost of certification per motor produced is much higher.

Tohatsu makes many many motors... they are the largest OB manufacturer in the world, motor for motor. That's because in addition to their product, they make Evinrudes 20 and down, Mercurys 30 and down, and made every Nissan produced. They also did a lot of Mariner and similar smaller brands.

Tohatsu is the lowest-cost motor in North America. Their products, when re-badged, carry a markup. For example, the water pump kit for the 4/5/6 costs about $20 more if purchased as an Evinrude part; It's actually in a Tohatsu box, with a BRP/Evinrude sticker over the top of the original Tohatsu sticker.

Most OB shops around here charge about $100 an hour (I do), based on flat rate shop times. If a technician has done a particular job several times, s/he may meet or beat the hours quoted in the flat rate chart... but if it's the first time for a particular procedure, they will take longer... effectively reducing the amount per hour. When you figure-in insurances (surprising expensive), overhead, payroll, etc., the rates are about what an auto repair shop charges. The tech must attend manufacturers schools every so often to remain certified, flying to/from the factory, spending a week in a motel, and studying/wrenching on motors... and that's not cheap either; Payroll goes on while the tech is in school.

Many times, changing shaft length, converting to/from Remote, etc., is more costly than selling the current motor and buying one that is the proper configuration; That's due to parts and labor costs. Your LU is a typical situation; The labor to replace the case (swapping all internal parts, etc.,) is not a trivial thing. Backlash adjustment requires shim kits, special backlash measuring tools, and pricey machinist's dial indicators. It's not a 5-minute job. As you found, many times the best financial (and time) deal is to replace a major component rather than rebuild it. Due to labor costs, many shops don't even bother cleaning small OB carbs -- they just replace them. Sure, it seems wasteful, but the bottom line is that depending on the skill and patience of the technician, it may well be a lower cost to replace a $200 carb, instead of spending hours cleaning and repairing it.

It's fixed. I had it out today for many hours. I ran both props too. The one with 11 inch pitch will only hit about 4900 RPM, but is smooth. The prop with 9 inch pitch will hit 5700 RPM. But, there is still "screeching" at the RPM's previously mentioned in the post? I cannot see any visible marks on the prop. There is no physical contact? Weird... It runs best with that prop and idles smoother, handles better, etc...

There is a water pumping problem though. I used the bearing/seal plate off the Tohatsu because the Mercury one was heavily corroded and would not seal properly with the paper gaskets. I also used the stainless plate and impeller off the Tohatsu. BUT, I used the top portion of the pump and cup off the Mercury. They look exactly the same. But, there must be a difference, because the only way I can get the tell tale to stream is to "goose" the throttle. Before It was a solid stream all the time. Hopefully putting the Tohatsu "top portion" of the pump on there will fix the problem. I remember having an alignment problem once and the pipe "kicked off to the side" and missed going in the top of the pump. Maybe I pushed that pipe up in there too far? I don't know.... I'll figure it out tomorrow. At least now I can paint the lower unit the right color and get on with selling it. I really need a 70-90hp anyway. I need gobs more power for this boat. Deep V and heavy.

Shame, it's a great engine. Now that I've fixed the stupid thing, it will probably go for 10 years without an issue! LOL!

Minor wear grooving in the impeller cup with increase side clearance, reducing pump efficiency a surprising amount. The water pipe has a flat end that seats into the "adapter plate" at the bottom of the motor, so it should never push up too far.