1993 Force 150 flywheel - need answer quickly

[HotTommy]

Preparing to take my pontoon boat out of town for a week tomorrow, I noticed a new ding in the engine cover. Inside I found this on the replacement flywheel I installed last summer.

Two of the four ears used for rope starting the engine are missing. The four bolts that hold them are broken off. I need answers to critical questions so I know whether or not to cancel tomorrow's trip.
1. The flywheel must be out of balance now. If I remove the remaining ears and bolts, can I safely run it like that temporarily?
2. I assume the broken bolts were deficient or installed incorrectly. Is there another likely reason that suggests I should not run the engine?
3. What have I not considered that suggests I should cancel my trip until the engine is completely repaired?
Thanks in advance for your advice.

 

[HotTommy]

As I removed the remaining ears to examine their bolts, I discovered those 8 bolts hold both the ears and the starter ring to the flywheel. I found one of the missing ears, but not the other. So my plan for now is to remove and replace all the bolts (including the broken ones), and replace two ears on opposite sides of the flywheel. I'd still like to know why the bolts broke, but for now that's the best I can think of. I'm still hoping for input from those with more experience with these things.

 

[Frank Acampora]

The four ears on Mercury flywheels are held with 1/4 X28 fine thread bolts. These bolts have deformed threads on the inside and are not meant to be removed.

In your case, yes, I would remove the last two rope starting ears to hopefully restore balance. The bolts should be a bit difficult to remove. Yes, the flywheel will be safe because it was designed to have the treaded bolt holes. Removing the bolts will not cause any added stress and the broken bolts will not add enough appreciable weight to affect balance.

My questions are: 1. If you installed the flywheel last summer, why did you not see the ears missing? 2. Did you run the engine all summer? 3. did you find the missing ears laying in the lower cowl, indicating that the bolts themselves had snapped?

 

[HotTommy]

Frank,
The ears where there as recently as a month ago. I assume the bolts snapped within the last few hours of use. I didn't notice the engine running differently. If it weren't for the telltale hole in the engine cover, I might have run it all summer. ... I found one missing ear inside the cowl. It did not appear damaged. The other must be there somewhere, but I can't see it. ... The remaining bolts came off with an 11 mm socket, so I assumed they are metric. I'll find out when I take one to the hardware store today. Other than having to brace the flywheel to keep it from turning as I removed the bolts, they were not hard to get out. ... And thanks for the quick reply.

 

[gm280]

Since you did find one of the two rope ears missing, did you also find the broken bolt heads as well? Because at least two bolts had to break for the rope ear to fly off. So there has to be at least two bolt heads there as well. I would certainly look and find all the parts because if they are attached to the magnets in the flywheel, other serious problems can occur and it won't be pretty either... I know you want to go boating, but think about the consequences first and be safe. If that means removing the flywheel to verify everything underneath is good, then so be it... Safety has to number once priority... And when you replace the 1/4 X 28 fine thread bolts, use grade eight to make certain they will be stronger and not shear off as well... JMHO!

Taking another look at the pictures, it looks like the bolts holding the last two rope ear are attached with grade eight bolts... What caused them to shear... IDK :noidea:

 

[Frank Acampora]

Yeah, most likely metric. I was thinking of the older Mercury flywheels.. Because of normal engine vibration you would not have felt the imbalance condition. however with long use it may have caused wear on the upper bearing. This would take a good long time because the upper bearing is a relatively large ball bearing capable of carrying some decent loads.

The bolts may have been torqued past their yield point --none of us would ever do that: because torqued to specs is too loose, tight is almost right and too tight is just right LOL-- and eventually snapped. Happens with parts and engines you don't have a history on.

 

[Jiggz]

Since you found one of the two ears that got loose, is there any indication it "hit" something hence shearing the bolts? Have you tried testing the flywheel and crankshaft for too much "play" (horizontally and vertically) which could indicate worn out main bearings? If there is an indication of too much "play", I would not recommend running that engine until the cause of the problem is resolved.

 

[HotTommy]

Here's the latest. The flywheel is off because one of the sheared bolts was difficult to remove. No missing parts beneath it. I"ll have to retap that hole for a slightly larger bolt. ... I don't know how to test for excess play. If its referenced in the FSM, I'll check it out. ... The only thing beside bad bolts that may be worth considering is a minor change I made a few weeks ago. Even with a new, fully charged battery and a new starter, my motor never sounded like it was spinning up quickly to start. Then, after using the battery to listen to the radio while out of the lake one day, it sounded downright sluggish when I went to start it. Not wanting to get stranded someday, I added a second battery and wired it in parallel with the original. By my understanding, its still providing 12 volts, but with more amps available and more staying power. The engine has not sounded sluggish when starting since then. .... The bolts that broke are the ones that connect the starting ring to the flywheel. So if the starter is now applying more starting torque than before, and the engine's compression is good from my recent rebuild, I suppose it could be putting more demand than before on those bolts. And if one failed, that could have led to a cascade of failures for other bolts. All I know to do is replace the old bolts in new, properly torqued bolts, and then monitor what happens. If it happens again, I'll look at disconnecting my second battery.

Jiggz - It looks like the ears hit the cover after the bolts sheared. No signs that anything hit them first to break the bolts.

 

[Frank Acampora]

The same starter is used on all 3,4,and 5 cylinder engines. So, it is no wonder it sounds sluggish. My 150 does the same thing: It cranks like it is going to stall the starter then starts to crank faster, but no where near the speed of my 3 and 4 cylinder engines. It does start easily BUT--When the engine starts I still breath a sigh of relief. 12 volts is 12 volts and if the starter is drawing the full amperage it doesn't matter if it is drawing from 2 batteries or 1. The starter is designed as a constant speed motor which delivers high torque at almost all speeds except stall.The torque is a small function of speed and attaching two batteries and increasing the speed due to increased amperage will not apply much more appreciable load on the flywheel ring.

As for the flywheel: I have never seen a flywheel where the starter ring gear was not shrunk onto the flywheel. They heat the ring and slip it onto the aluminum flywheel. As it cools it shrinks and will be as secure as welding. Reason: Can not weld dissimilar metals and there is nothing to break .

Therefore I am very interested in yours. Please post a photo of the underside.

 

[HotTommy]

The flywheel assembly looks like this one:
Link
The part with the key that attaches to the crank is like a hat that sits over the donut that holds the magnets and has the starter ring. The only thing that attaches the hat to the donut is the eight bolts that also hold the ears for rope starting. ... BTW, if anyone ever sees me write anything about outboard motors that is contrary to anything Frank Acampora has said, just ignore me and pretend I didn't say anything. The bolts that snapped were indeed 1/4" fine thread bolts.

I reassembled everything with new Grade 8 bolts torqued to about 10 ft-lbs, and secured with thread locker. It cranked and ran easily with no apparent difference in vibration from anything I've seen before. I'll monitor those bolts closely for the next few hours of use to see if any work loose or break off.

 

[Jiggz]

No Title

Looking at the flywheel, it looks like the ring gear is welded on four spots thus permanently attaching it to the flywheel. Or could this be a mod that was done by the owner? The pictured flywheel looks like it's brand new so I do not think this was a mod. Did you check your flywheel if it has the same welded spots? Or could it be this was a mod by the manufacturer on later models?

 

[HotTommy]

I didn't think to note whether or not my old or new flywheels had welds. I may have misused the term flywheel in my early post above and led to the confusion. It wasn't until I disassembled my unit that I discovered one part that connects to the crank and another part that holds the magnets and starter ring. I referred to the part that bolts to the crank as the flywheel and the other part as the starter ring.

 

[Jiggz]

It probably has the weld. Looking at the schematic diagram it seems those 1/4-28 bolts holds nothing but the manual starting ears. But then you mentioned these bolts also hold the unit that houses the magnets (which is technically is the flywheel) to the ring gear, if that is accurate it means for the bolts to shear the welds would have been broken off first. So if none of the welds is broke, then it means the bolts just failed on their own under centrifugal force created by the weight of the "ears" which be all account is rare but not impossible.

 

[Frank Acampora]

Hmmm! So Mercury went to an all steel flywheel. Interesting.

 

[HotTommy]

I put about ten hours on the engine last week and everything looks and sounds normal. So unless the problem returns, all is well and this is my last post on this thread.

 

[Jiggz]

Great update! Enjoy.