Alternator Bracket Failure - Check Engine When Running

[Stu Jackson]

Noted this last weekend.  Having a new bracket made, would take two + weeks to get from supplier.  Managed to limp home with no wind at idle speed.  Alternator cracked the oil filter...

Critical Upgrades suggests you check your engine when it's running on a regular basis.  Glad I did.

[Ron Hill]

Stu : WOW!!   

A chunk of metal that thick should not have broken, you've got a vibration/stress problem.  As I recall your M25 factory alternator modification kit was put on about 2000 ? 

Something is going on!!  You need to check your alternator mounting and alignment.

[Stu Jackson]

Ron, very, very good memory!  1999.  Stuff fails.  The alternator is lined up just fine.

[DaveM]

Stu
I recall you went through a period when the alternator thru-bolt was undersized and the alternator was loose. That may have been when the initial fatigue damage kicked off. Appreciate you sharing. Another check to make when changing belts.
Thanks
DaveM

[Stu Jackson]

Good point, Dave.  For those not familiar with what Dave referred to, it's this:

Alternator Pivot Bolts for M25 Bracket Upgrades:

http://c34.org/bbs/index.php/topic,5127.0.html

[Ron Hill]

Stu : You can insert a sleeve into the mounting hole on the alternator case so it will snug up on the bolt.  Then make sure that you use large diameter washers on both sides of the case hole for alignment.

That's what I had to do with the new engine and the old Balmar.   A thought

[Stu Jackson]

Here's the new bracket that I had Metal Magic (Oakland, CA) make.  About twice the price of the replacement from the OEM supplier, but much thicker.

[Stu Jackson]

When I first installed it just the other day, I found that even with the alternator bracket tensioning tool, I couldn't get the 7400 belt tight enough.  We'd been using the 7400 successfully for many years before this "exercise."  The 7390 belt was too tight, and I couldn't even get it on the pulleys.

It seemed like we had no choice. I could have had Metal Magic make the slit on the bracket at the top part longer, but that would have left almost NO metal underneath the the bracket.

On the way home from the boat, I had another thought.  What if there was a belt size between the 7400 and the 7390?

Do they make a 7395?

YUP!!!

$16 for a true NAPA heavy duty belt, and a day later, everything is working just fine.

Here's what I learned:  A long belt works if the slit at top of the alternator bracket is long enough to get the alternator WAY out (the 7400, worked for us for four years).  The alternator HITS the engine block if your belt is too short (the 7390).  The middle sized 7395 works.  The alternator adjustment arm doesn't adjust a whole lot!

I'll purchase a backup 7395 tomorrow.

I also made note of this on the C34 Tech wiki.

[Ron Hill]

Stu : Good for you!!  I used a "395" length belt for over 20 years.

FYI, Gates makes NAPA belts.   

[efhughes3]

Thanks for the heads up!

[Indian Falls]

http://www.ebay.com/itm/151034376320?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

bracket replacement... 

[efhughes3]

http://www.ebay.com/itm/151034376320?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

bracket replacement... 

Thank you for this link! Bought! 

[mregan]

Would this bracket also work on the M25?

[Stu Jackson]

Would this bracket also work on the M25?

Yes, but only if you've done the alternator bracket replacement, see the Tech wiki and Critical Upgrades:

http://www.c34.org/wiki/index.php?title=M-25_Alternator_Mount_Conversion_Kit_%22B/M_256891%22