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PTSD (Post Traumatic Saab Dysfunction) Engine Vibration
Posted by Gary Piland [Email] (more from Gary Piland) on Mon, 4 Mar 2019 22:40:39
PREFACE - If anyone has any theory as to why this is happening, please jump in. Don’t make me beg!
I’ll try to keep this as short as possible. Hang in there, it gets weird. This story spans about a year and a half.
My ‘67 96 V4 daily driver has a ‘73 1.7L bored, big valves, MSS exhaust, F4 cam, HD oil pump (all per Jack Lawrence’s recommendations). Runs great. Blah blah blah. With an electric cooling fan and Davies Craig electric water pump the v-belt goes around the balance shaft pulley and the alternator pulley only. Nothing else.
All is good, then after a few months...
The engine begins to develop a sharp metallic buzzing sound that comes on suddenly at 3100 rpm and disappears just as quickly again at 3300. On closer inspection It’s some kind of vibration/resonance between the balance shaft pulley and the alternator.
NOTE: I have a non-stock 60 amp alternator. But, trust me, you’ll agree this isn’t the culprit.
I discover the vibration has fatigued and cracked my beautiful 1/4” thick custom top aluminum alternator bracket at the top bolt on the engine block. Thinking it must be the alternator causing the problem, I replaced it and make and install a nice new bracket. Vibration gone. Cool!
Vibration returns after about two months and on checking, I have another broken 1/4” aluminum upper bracket in exactly the same spot.
Fine. I replace the upper bracket with steel and fit another rebuilt alternator. (O’Reilly’s lifetime guarantee. Can’t be too careful, right?) Vibration/buzzing stops. Yes!
No. After some weeks the buzzing returns and low and behold one of the bottom spacers in the stock steel alternator bracket that fits snuggly over the outer bolt hole in the timing cover is MIA. Bad weld? Sure why not.
Not one to mess about, I replace the bottom bracket (thank you Tom Shipman) and install another rebuilt alternator. Success! No bees under my bonnet.
Fail. A few weeks and the buzzing’s back, so I remove the alternator and try a different pulley on the alternator. I’d been using the same reverse fan pulley from the stock unit. Maybe...? Buzzing ceases.
You guessed it. About a month and half and the buzz is back. This time it has actually broken off the bolt hole where the bottom alternator bracket bolts to the engine timing cover.
WTF. (Pardon my French abbreviation.) Guess I’ll steal the timing cover off my ‘68 parts car and order new gaskets and seals.
Only now I have PTSD (Post Traumatic Saab Dysfunction) about this whole scenario and can’t help fearing it will continue to dog me.
Any and all suggestions are welcome. Call me if you want - 785-221-2246.
posted by 72.209.18...
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