Addtional alternator bracket on Yanmar 4JH3

[brian48]

Can anyone advise me on a permanent solution to keeping my second alternator attached to my engine block? I have a Yanmar 4JH3 TBE with a 175 amp Leece Neville (Prestolte) 24 volt alternator attached as a second alternator. Needless to say this alternator is a seriously heavy lump which takes some driving. It is controlled by an Adverc. Despite the size of the alternator I have never seen the adverc call for more 70 amps charging which at 24 volts is perhaps about 2 - 2.5 Kwatts with losses. The drive is by double vee belts from the engine crankshaft. The alternator is mounted on a fabricated 12mm steel plate bracket (not Yanmar) which is bolted on to he front of the engine (originally with 4 M8 bolts ) and onto the top of the engine with 2 more M8 bolts. (Steel screws into aluminium alloy castings.) I bought my boat 8 years ago when it was 8 years old and had 900 engine hours. On my first long trip, with quite a bit of motoring needed, my routine check of the engine compartment revealed 2 loose bolts and some oil under the engine. These were from the alternator bracket to the front of the engine. When I put them back it was obvious that the threads in the aluminium engine block (actually it is the drive train cover plate) were all but gone. I stuck them in with yaksh** and it held until we reached port.
I found a Yanmar technician and we took off the alternator and bracket. As always on boats it was in a pretty inaccessible position. The drive train cover plate with the 4 tapped holes could not be easily removed from the engine (said to 2 -3 man days work) However between the 4 tapped holes was a round 10 cm opening in the cover plate giving limited access to the other side of the tapped holes. The solution was to put long grub screws through the holes with nyloc nuts inside, reinstate the bracket, then another nyloc nut outside tightened against an allen key in the grub screw.
This held for 400 hours but I have just found 2 sheared grub screws with nylocs under the engine. The grub screws had fatigued through (not helped by the grub screws being a bit short and the allen key recess being inside the nut when tight).
local technician here in Turkey has made a temporary repair with some studding but it was not possible to get any serious grunt on the nuts. I am also not really happy with nylocs inside the engine near the drive train.
My thinking for the proper repair is : longer high tensile grub screws if I can get them, aerotight nuts, long allen keys to get serious tension on the grub screws to reduce chances of fatigue.
However I would welcome any comments or alternative suggestions.
I hope these pictures work as it makes it much easier to understand.

 

[coopec]

I've been giving some thought to mounting my alternators which are 24V 60amp and rather than using the 12V alternator on the Perkins I have thought of buying a 12V 120amp as well. (I haven't got room for a stand-alone generating plant)

My preference is to use a serpentine belt and, to balance the load on the main bearing, mount an alternator on each side of the engine.

I think the way the extra alternator mounted in this kit is excellent
http://www.boundlessoutfitters.com/Balmar-AltMount-Second-Alternator-Kit-p/bal-yda.htm

I have considered using air-conditioner pulleys/clutches so I can switch the alternators off/on. If any experts are reading this maybe they can comment that idea.

Clive

 

[rogerthebodger]

This is a pic of my twin alternator arrangement

I have used 3 separate Alpha section belts that have a greater load carrying capacity that the more normal Z or A section belts.

The belt driving the water pump has a jockey pulley for tensioning.

The brackets will be different for each engine due to different mounting holes and space in engine room.

 

[earlybird]

M8 bolts seem very small for mounting an alternator of that size and belt loading, together with vibrational inertia loads, especially off an alloy cover. Presumably there is a fair amount of overhang, making things worse.
If your new nuts break off inside the cover, then that could be expensive.
Don't know your engine but could you modify the alternator mounting bracket to get extra support from the front engine mounting bracket? If so, then that might be much more solid.

 

[bristoljim]

Why not fit a switch in the alternator field circuit - a bit technical - some alternators are easier to do than others but cheap & simple compared with clutches.
Jim

 

[bristoljim]

Sorry this was for Coopec
Jim

 

[pvb]

However I would welcome any comments or alternative suggestions.

Adding a second alternator, especially a large-case alternator, is fraught with difficulty. If Yanmar offer a bracket, go for that. Otherwise, you'll probably have a major problem trying to engineer your own bracket which will survive extended use. I put a second alternator on the engine in my last boat, a Volvo Penta 2003T. VP offered a second alternator bracket which was ridiculously expensive, but it worked, and there's no way I'd have ended up with such a robust solution on my own.

 

[brian48]

Many thanks for the advice so far. The Balmar setup does indeed look good but they seem to want USD1000+ for the bracket and then you need a new alternator as well. They seem to be using mini vee belts for transmission which I think I have seen on more modern 4JH series engines at boat shows. I thought of converting to mini vee belt drive but the pulleys have to be made up and are quite expensive. I haven't had any problem with vee belt wear or slippage. Maybe the adverc has a soft start function. Earlybird your suggestion of extending the bracket to fit onto the engine side of the front mounting bracket is a very good one. There seems to be space and the bottom of the bracket is quite close. It will have to be fabricated pretty precisely. On the nuts inside the cover you are obviously right that if one comes off it could ruin the engine and that is why I was concerned. Another thought I have just had is to get 2 short lengths of 10mm bar stock tapped with 2 M8 holes each at the correct spacing and use them inside the cover as semi captive nuts. I could then use bolts instead of grub screws. I can buy the Yanmar gasket to get the exact spacing. Does this sound like a better idea?

 

[coopec]

Why not fit a switch in the alternator field circuit - a bit technical - some alternators are easier to do than others but cheap & simple compared with clutches.
Jim

I don't want to hi-jack the thread but I realise now there must be a switch on the alternator field circuit of the alternator already.

The power steering pump is piggy-backed onto the alternator on the Toyota HiAce (small bus) and the 24V alternator powers the air-conditioner. There must be the option for the driver to switch the air-conditioner on/off as required.

Thanks for that

Clive

 

[bristoljim]

Another way to consider is to mount the alternator off the engine on the boat,you can then have a decent bracket & tensioner & the longer v belts are very forgiving of the slight engine movement.I have used this successfully on a number of installations.Worth a try before spending megabucks.
Jim

 

[coopec]

Another way to consider is to mount the alternator off the engine on the boat,you can then have a decent bracket & tensioner & the longer v belts are very forgiving of the slight engine movement.I have used this successfully on a number of installations.Worth a try before spending megabucks.
Jim

That's what I hoped I could do because although the engine is rubber mounted any movement would be very small and as you say the longer belts would be forgiving. (I prefer the serpentine belts to "V" belts though)

I think picking up good mounting points on an engine for a hefty alternator(s) is a bit of a problem.