Help with alternator mounting bracket

[robertsapp]

I purchased a '95 H336 last September, and have been fixing various things the previous owner didn't attend to. I have a 3GM30F engine. I discovered that the regulator was fried in the alternator, so I took it off to have it rebuilt. I had noticed that when the engine is running, the alternator was wobbling around a bit, and there was quite a lot of belt dust on the inside of the engine enclosure. When I removed the alternator, I discovered that an undersized bolt had been used in the top mount, which allowed quite a bit of play, causing the wobble. It had even worn the hole in the mount into an oval shape due to the wiggling around. When I went to remount the rebuilt alternator, I picked up a 10mm bolt, which fits the mounting holes in the Hitachi alternator perfectly. The bolt won't go through the mount, however. So my question is, does anyone know what size and type of bolt is used in the top bracket? I'm considering picking up a 10mm drill bit and enlarging the top mount holes so that my 10mm bolt will work, but before doing that, I'd like to see if anyone can tell me if there's something else I should be using.

 

[Dan Johnson]

Robert...

I have the same engine in my H34 and have had the alternator off a couple of times. My Yanmar parts manual specs an M8x120 bolt that mounts the alternator pivot ears to the engine mount (part #26116-081202 for all GM models). That's 8mm dia by 120mm long.

You sound like you're trying to fit too large a bolt for the mounting hole. You could possibly go to an SAE size slightly larger if the hole is that ovalled. Drilling out to a 10mm size may weaken both the mount and mounting ears on the alternator.

I do get belt dust over the season and usually run about 60 hours on the engine each season (only 30 last year, however). I've not noticed any wobble in mine. That may be from tightening everything up very snug once I'm satisfied with the amount of belt play I've dialed in.

 

[robertsapp]

Re: Robert...

OK, I'll pick up an M8-120. I'm curious though why the alternator accepts a 10mm bolt but the mounting bracket is an 8mm. Thanks for the part reference, at least I'll know I have the right hardware.

 

[petersea]

I'm also curious why the 10 mm bolt fits and if it fits correctly the 8 mm will not fit correctly. What ever you do you are going to have to make sure the bolt fits tight and will not back out. If in fact the alternator hole threads ovaled out or enlarged you will still have the same "wobble" you had before if the bolt is not tight. May want to use some lock-tite on the threads. Think about using an oversize locking washer, if you have to enlarge the bracket slot so that the bolt fits as it should. The belt dust is common on these engines but just to to sure make sure the pulleys are aligned. The belt should run straight on the pulleys not on an angle.