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TR6 Alternator bolt keeps shearing - replacing the spacers - are these correct?

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Bruce100

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Twice now the lower alternator bolt has broken. The first time I believe the bolt was original. The second time it was replaced by the shop that was doing my differential mount reinforcement, and broke a year later.
shearedbolt.jpg

Why is it breaking? I cannot for the life of me remember if both spacers were present both times. The bigger one was, just don't know about the smaller one. If the smaller one was not, that might explain it.

The alternator is a Bosch.

A friend dropped by yesterday with a couple of spacers. He was confident of the bigger one, but not so much of the smaller. The hole is 5/16" on the larger, 1/2" on the smaller. Is the smaller one in the picture correct?
altspacer.jpg
 
Bruce- I can't remember anymore .
But I have the bigger one powder coated in my collection box
I had no idea what it was for when I put it back together.
Guess it should have gone to the recent owner.
 
The spacers look right. I remember having 2 and maybe a lockwasher as well.
As far as the diameter..if the bolt fits thru and the nut snugs up, I don't know what else might be required.
 
Would also suggest also a "Grade 8" bolt be used next time.
 
The important thing is that they are spacers...Do they take up all the slack in the bolt and allow the nut to tighten up firmly and clamp the alternator so it does not roll down ?
 
poolboy said:
The important thing is that they are spacers...Do they take up all the slack in the bolt and allow the nut to tighten up firmly and clamp the alternator so it does not roll down ?
Click to expand...

As well as keeping it properly aligned on a flat plane with the crank pulley. I had a similar problem with an old British sports car I had, I think my TR4A, after breaking one or two I replaced with a Grade 8 and never replace it again. But certainly visually inspect it and make sure nothing is out of order as well.
 
Can you post a picture looking straight on the fracture surface? Bigger is better and it must be in focus. Bolts fail either due to fatigue or over load and the fracture surface should tell the tale.

Regards,
Jim
 
Whenever this problem occurred on the generators on the early cars, it was more usual to have the bracket crack or break close to the bolt. Which is what may happen if you use a grade 8 with too much space between the six's alternator brackets and the spacers. so in reassembly, use a feeler gauge and make a shim washer to take up any space. That way the only load the bolt has to handle is the torque.
 
I had this problem with an alternator conversion on my 3A. Broke several bolts, but breakage due to vibration, not shear or anything like that. My problem was that the alternator bottom swivel mounting waas not captured tightly enough and it cause the entire alternator to vibrate to the point of breaking the top bolt. Grade 8 made no difference (stronger but more brittle?). Solution was to 1st make sure that the belt is true to the pulleys, 2nd make da$m sure that the alternator is completely mounted tightly to the engine. That solved it (after 2 years - everything "looked" fine) for me.

When the bolts breaks, I was lucky not to have the head go through the radiator, big pow!
 
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