Alternator Pivot Mount repair suggestions

[Captain Bill]

I started my starboard engine this morning and something started screaming which was coming from the area of the alternator. I quickly shut the engine down and started feeling parts and found the alternator pulley to be very hot. The belt looked fine so I thought I had lost my front alternator bearing. This was not the end of the world because I have a spare alternator on board. So I dig out the spare and start taking off the old alternator, cursing myself for buying a cheap aftermarket 80 amp alternator 2 years ago. I grabbed the alternator and it seemed a little loose, not at the top on the adjustment bracket, but at the bottom at the pivot bolt. I could not see the pivot bolt until after I had removed the adjustment bolt and rotated the alternator out of the way. It was obvious that something was very wrong with the pivot bolt mount. My first thought was that the bolt had broken as the alternator was movable in all kinds of un-natural directions, but the bolt appeared to be in place. I put a wrench on it and sure enough it was still completely intact. As I backed it out it soon became obvious that it was not the bolt that had failed, but the hole in the casting. Upon removing the bolt and getting the alternator completely out of the way I could now see the the inside bottom corner of the pivot hole was completely destroyed. I'm not exactly sure how or why it broke. The adjustment bracket is fixed in place and while I can see that perhaps as I tensioned the belt put some pressure on that portion of the pivot hole but find it hard to believe there was enough force to break a solid 42mm thick casting. My next thought was the casting was hollow because there were not enough metal pieces to account for the entire thickness of the casting and was afraid that the missing metal had fallen down into the waterpump gears. I stuck an angled probe in the hole and found that the interior appeared to be solid. I am now assuming that the casting actually had a defect in that area and the bolt was only supported by a thin outer edge. I checked out the alternator and the bearings seem to be fine, no play, no noise, and the alternator spun smoothly by hand. I'm now assuming that the noise was casued by the belt and the alternator getting out of alignment because of the failed pivot mount hole.

Now comes the big problem. I'm in Georgetown, Exuma and am pretty sure that there is no chance of getting a proper repair done here in anything that approaches a reasonable amount of time. My thought is to use some Marinetex to fill the hole and use a bolt or dowel of the proper diameter (coated with silicone grease) to make the bolt hole open. I would use a block of wood and some rubber bands to hold the dowel/bolt in the proper position. I've looked at the parts manual and this casting is essentially the whole front of the engine and would be very difficult id not impossible to remove with the engine in place. It is also not possible to drill an accurate hole as there is simply not enough room for a drill. If I could figure out a way to tension a belt I would simply run that engine without an alternator since I have one on the other side and have a genset as well as solar panels to charge the batteries.

I am open to any alternative suggestions to my repair thoughts. Please feel free to contribute.

I have attached a picture of the hole. In the process of taking the picture I think I found the source of the problem. One of the bolts is missing from the adjustment bracket......Duh. anyway looking for any repair suggestions that might be better than my current idea.

[Captain Bill]

I screwed up the attached image, hopefully it will work this time

[Captain Bill]

I thought that the missing bolt in the adjustment bracket was the cause of my problem but such is not the case. The arm gas 2 bolt holes, but only one bolt. Apparently the arm has two possible positions, but not 2 bolts to hold it position and the arm is not loose when I try to move it. Consulting the manual, it showed only 1 bolt holding it on. I am again at a loss to explain the cause, but clearly no matter how it's repaired I'll have to keep an eye on it.

[Reefmagnet]

Can't really get a handle on the problem without a wider shot. Your idea should work for temp repairs but perhaps consider using jb weld as the filler. A bit of grease paper wrapped and taped around the bolt/dowel should work better than grease with no chance of accidental adhesion.

At the end other day the only long term repair is welding or replacement.

Sent from my SGP521 using Cruisers Sailing Forum mobile app

[DougR]

Your repair idea seems as good as any, but I think perhaps instead of filling the gap with 100% Marine Tex you might carve a piece of hard wood to fit snugly in the void, and then Marine Tex that in place. The wood will spread the load and help prevent creep when the epoxy gets up to engine operating temp.

Also, one or two wraps of wax paper on the bolt or dowel rod is easier to deal with than silicone grease.

DougR

[Blue Stocking]

Wrap the bolt to clearance tolerance with plumbers Teflon tape. Always releases cleanly. Can also use this method to set bolts and screws into filled epoxy. Lag screws in wooden engine beds prime use.

[Captain Bill]

Thanks for all the suggestions. I like the teflon tape idea as an improvement over my silicone grease. Unfortunately I don't have any hardwood on board, but I might be able to find another hard filler.

[Sailorman Ed]

Bill,
I assume you have a 2GM or 3GM Yanmar. I kept noticing that my alternator belt would come loose and when I was near a Yanmar dealer ( Deaton Yatchs - Oriental) , I asked about this and they said this was a known problem with these engines. And you are correct, that casting is large and costly to replace. They did tell me that if you were very careful, it is possible to drill out the one side and sleeve it. I have not tried this so cannot confirm. From your picture, I would oversize the hole, use the Marine Tex but also sleeve it as large as you possibly can. I think I priced this casting and it was $$$.
good luck!
Ed

[TrentePieds]

JB weld and teflon tape to get you to a professional. A satidfactory permanent repair is IMO more than you can do yourself while on the hook in some remote place.

TrentePieds

[wayne.b]

Originally Posted by TrentePieds

JB weld and teflon tape to get you to a professional. A satidfactory permanent repair is IMO more than you can do yourself while on the hook in some remote place.

TrentePieds

===

I had a very similar problem 5 years ago with the 4 cylinder Yanmar on my primary generator. The hole in the engine casting had become elongated and it was no longer possible to tension or align the alternator. The guy at my local auto electric shop gave me some circular stainless steel shim stock the same diameter as the bolt. I greased the bolt, put it inside the shim stock, and then cemented it in place with JB Weld. It's been fine now for over 2,000 engine hours. I cleaned all of the metal surfaces with acetone before applying the JB Weld.

[Captain Bill]

I cannot get a drill bit aligned from the front even with a 90 degree drive. I might be able ro clear enough space to approach it from the rear by removing the exhaust and heat exchanger, but I don't have replacement gaskets should one be damaged in the removal process. I have MarineTex, but not Jb weld. I compared the specs on line and they are not that much different. I would like to reinforce the MarineTex with a piece of metal and will have to see what I can find. I've used MarineTex in the past to repair a compressor block where a headbolt broke off and had to be drilled out. It worked well until I could get back to the states and get a proper repair done. I'm pretty sure that a MarineTex repair will be good for several hundred hours and if I can get a piece if steel embedded in it it might be permanent.

Marine Diesel Direct lists the housing at $910.06 so it;s not exactly cheap. There are of course a number of seals and gaskets associated with replacing it. One gasket is part of the oil pan assembly and if damaged requires the removal of the entire bottom of the engine to replace. This is not something I'm willing to attempt at my current location.

I had already decided to clean all the metal with acetone so I'm glad to see someone else had success doing that. I'm also thinking of using a dremmel and a diamond burr to make a couple of “keyways” in the casting, perpendicular to the hole, to lock the MarineTex in place.

[hellosailor]

I think wayne.b has the best temporary solution but would join the chorus is suggesting a good machine shop when you can. It should be possible to weld in a permanent repair, perhaps fill it then insert a helicoil, or weld in a stud--not sure how the support would have to be fitted around that. But a machinist or welder should be able to come up with a permanent fix.


Regular JBWeld is supposed to have steel filling material in it, partly to dissipate heat. I haven't tried to kludge MarineTex that way, but have successfully used metal kitchen scrubbing pads (copper, bronze, stainless) embedded in silicone seal, in order to make a heat-resistant patch on exhaust pipes. Normally the silicone seal would overheat and burn off--but the embedded metal took the heat problem away. Fine steel wool might be better in your application, because the area is so much smaller and tighter.
I wonder if you couldn't also fit the bracket in place after your temporary repair, and holding it with some straps or clamps, reset it with epoxy to the engine body itself, to spread the load over more than just the repaired bolt. If that repair failed and the alternator "flew" off...potential for a lot more damage.

[Blue Stocking]

Is the alternator of the type with the single mount on the front plate, usually either 1 or 2 " wide, called the Ford mount, or is it the saddle type, with mounts extended off the front and back pates. There is often a difference in the alt. and the engine hole size, anywhere from 6mm to 1/2". Repair shops carry a range of thin wall bushings to correct this eventuality. I know I do.

[unclemack]

That hole doesn't look accidental to me, more like a bodge job to extend (move) the hole - best guess being that it was re-drilled so a non-standard alternator could be made to fit where it wasn't intended to fit.

The metal scrap that you found loose - on close examination does it all have the same shaved-off look as that piece at the edge of the hole in your photo? If so then I'm wrong... again... but a hole like that would need a hell of a lot of vibration for a hell of a long time. I'd expect to see shavings & debris all over the place.

If the bits you found are in fact packing added by Mr. Fixbuggerall then I'd suggest you just need to replace with a better packing - a single, carefully-shaped or moulded-in-place piece preferably.
Casting still looks strong enough - I first thought you meant the whole lug had broken away.

Pulleys need to be aligned with a straightedge, obviously.

[Captain Bill]

OK, here are pictures of the alternator and mount. There is a little distortion caused by the camera lens that makes the alternator look a little bent. It's not. The mount consists of the two alternator tabs, a spacer and two bolts, Both bolts were absolutely tight when I took them apart and and required considerable effort to crack loose. The gap between the spacer and the front alternator tab is 42mm and the thickness of the casting at the undamaged portion is 42mm. The long bolt at the undamaged portion measures .375 inches on the calipers and the internal diameter of the hole in the alternator was .395 inches which seems to me to be what one would expect to allow bolt clearance. I did find it a bit odd that this seems to be an SAE 3/8ths bolt. Obviously you can see in the pictures that the bolt has been damaged and will need to be replaced. The bolts and spacer were taken from the original Hitachi alternator so were the original bolts that came with the engine. I installed the alternators myself so I know that there was no modification made to the mounting hole. The only thing I can think happened is that there must have been a defect in the casting and the belt tension must have eventually caused the failure. Like I said previously there was simply not enough metal pieces to account for 42 mm of casting x perhaps 8-10mm of failure area. The upper adjustment arm was tight and could not be moved by hand and the the bolt connecting the alternator to the arm was tight when I removed it.

I had the engine room door open while the engine was running a couple of days before the failure and noticed nothing unusual. I had run the engine the day before for about 3 hours with no unusual noises. When I started the motor the next morning, the noise was immediate and very loud. It was not possible that it had been doing this the day before and I had not noticed it. I opened the engine room door to determine where the noise was coming from and it was obviously the alternator. I then shut the engine down. The total run time was about 45 seconds from the time the noise started until shutdown. It seems to me to indicate that the the final failure was somewhat sudden. I find it a bit hard to believe that that much damage could have been done to the bolt n 45 second so something had to be going on for much longer.

The engine to answer an earlier question is a 3jh3ce.