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Got Engine Vibrations??

 
Old 09-22-2017, 11:10 AM
  #1  
SeanR
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Default Got Engine Vibrations??

I did, and have had since I purchased my '88 some 12 years ago. I've changed out engine mounts, trans mounts, new torque tube etc. When I dug in to my 3rd belt job a month back and took off my damper it looked like crap and knew it was time to change it out.

It was about to become two separate pieces.





Our options are limited as Porsche doesn't have these in current stock or production, and I'm sure if they did uber expensive would be an understatement. We all should know that Greg has an affordable option and I took advantage of that with his ATI damper modified to fit our cranks.





After getting it all back together and a couple of drives I am amazed at how smooth this engine is now. Put this on your list of things to do in the future. All of ours are old, most likely worn out or getting to that point. So a huge thanks to Greg for getting these things done so we have that option.
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Old 09-22-2017, 11:46 AM
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Tony
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Ive never really thought of that?

Whats actually inside the stock one?
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Old 09-22-2017, 11:55 AM
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Think it is a big ole puck o rubber vulcanised
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Old 09-22-2017, 12:39 PM
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dr bob
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Center metal hub slides over the nose of the crank, indexed by a Woodruff key, clamped by the bolt in the crank nose. There's a metal ring outside that, the one you see with the ignition and crank timing marks on it. The outside ring fits from the engine side of the hub, with a rubber ring vulcanized to both pieces to hold them together.

The crank is subjected to uneven twisting forces by the pistons and connecting rods arrayed down its length. The twisting is opposed by a springy shaft connected at the rear, and a transmission at the other end of the shaft. Each motion of a piston and rod tries to make the crank turn faster or slower where it connects. The crank is stiff but not rigid. Each attempt to turn it in a different direction in a different plane and different time twists the metal. The crank has some natural resonant frequencies, like a bell. If allowed to self-reinforce a vibration at a resonant frequency, the vibration would eventually cause the crank to fatigue and fail.

The damper does what its name implies, "soaking up" the torsional vibrations in the crank, thereby delaying the fatigue failure.
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Old 09-22-2017, 03:17 PM
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FredR
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That is one ratty damper!
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Old 09-22-2017, 03:30 PM
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PorKen
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I assume Porsche specified a rubber damper for a good reason. Why install some aftermarket product?

Do the TDC marks line up? (EG. tested with piston stop?)
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Old 09-22-2017, 03:35 PM
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Originally Posted by PorKen View Post
I assume Porsche specified a rubber damper for a good reason. Why install some aftermarket product?

Do the TDC marks line up? (EG. tested with piston stop?)
LOL, I see what you did there.

Yes, everything lined up perfect.
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Old 09-22-2017, 03:41 PM
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I just want to know what you did to make your HB look like that? I'm pretty sure almost all of my cars have more miles on them than yours, but none of my Hbs look as torn up as yours.

Any ideas?
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Old 09-22-2017, 03:43 PM
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SeanR
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Originally Posted by soontobered84 View Post
I just want to know what you did to make your HB look like that? I'm pretty sure almost all of my cars have more miles on them than yours, but none of my Hbs look as torn up as yours.

Any ideas?
219,xxx miles on it. Lived in AZ and TX for most of it's life. Can't say I've seen one in worse shape but some close to it.
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Old 09-23-2017, 12:02 AM
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What kind of vibrations were you feeling? Only at idle, or a particular rev range? All the time?
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Old 09-23-2017, 02:46 AM
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Originally Posted by SeanR View Post
219,xxx miles on it. Lived in AZ and TX for most of it's life. Can't say I've seen one in worse shape but some close to it.
I've got several samples thst are missing chunks of rubber on the outer perimeter, just like yours. And a couple that became two piece dampers, when the rubber completely let go.

It's my guess that once the rubber starts loosing chunks, it doesn't take too long to get the "two piece" unit.

I've been testing these things for four or five years, now. I'm deep into my second "batch" of custom 928 mounting hubs, so I guess I've used about 30 of them, so far.

I install one when I can't cure engine vibrations by changing mounts and there are not issues with the clutch in a manual or flexplate and torque tube in an automatic, even when the rubber looks perfect.

I've yet to have a client that hasn't noticed a significant reduction in vibration.

My conclusion is that the rubber, which transmits the harmonic from the inner hub to the heavier out hub, has become so hard that the pieces effectively become one part, with almost no dampening of crankshaft harmonics.

This has been further supported by observation of main bearings and crankcases. Main bearing wear and crankcase "fretting" with elongation of the housing bores has become much worse, in the past 10 years, regardless of mileage on the engines.

The lack of harmonic absorption is, in a nutshell, tearing these engines apart.
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Old 09-23-2017, 08:45 AM
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hlee96
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Greg and Sean, thank you for the new product and insight to the dampener. However, now that I am almost ready to finish putting together an euro s cis engine on the engine stand, should I be putting this dampener on now or only when 99% of the engine is done? Sean mentioned that this dampener has zero tolerance so once it's on, pretty difficult for a home hobbyist to remove, right?
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Old 09-23-2017, 09:53 AM
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SeanR
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Originally Posted by hlee96 View Post
Greg and Sean, thank you for the new product and insight to the dampener. However, now that I am almost ready to finish putting together an euro s cis engine on the engine stand, should I be putting this dampener on now or only when 99% of the engine is done? Sean mentioned that this dampener has zero tolerance so once it's on, pretty difficult for a home hobbyist to remove, right?
As Greg pointed out on FB, and I hadn't even thought it through that far. Once installed you don't have to take the hub off to do a belt job. The damper is a two piece system and the damper is easy to remove. Undo the 9 bolts holding it together and wammo, off.

The hub can be removed with relative ease with a decent hub puller, and you can get them at any local parts store or ebay.
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Old 09-23-2017, 09:54 AM
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I'm simply amazed at how much of a difference there is on my engine. Will be doing another one this before November on Jarrods GT as we've been hunting down the same issue on his car and the only thing not replaced is the damper. He's got it in hand already, so thank you.

Originally Posted by GregBBRD View Post
I've got several samples thst are missing chunks of rubber on the outer perimeter, just like yours. And a couple that became two piece dampers, when the rubber completely let go.

It's my guess that once the rubber starts loosing chunks, it doesn't take too long to get the "two piece" unit.

I've been testing these things for four or five years, now. I'm deep into my second "batch" of custom 928 mounting hubs, so I guess I've used about 30 of them, so far.

I install one when I can't cure engine vibrations by changing mounts and there are not issues with the clutch in a manual or flexplate and torque tube in an automatic, even when the rubber looks perfect.

I've yet to have a client that hasn't noticed a significant reduction in vibration.

My conclusion is that the rubber, which transmits the harmonic from the inner hub to the heavier out hub, has become so hard that the pieces effectively become one part, with almost no dampening of crankshaft harmonics.

This has been further supported by observation of main bearings and crankcases. Main bearing wear and crankcase "fretting" with elongation of the housing bores has become much worse, in the past 10 years, regardless of mileage on the engines.

The lack of harmonic absorption is, in a nutshell, tearing these engines apart.
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Old 09-23-2017, 09:57 AM
  #15  
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Originally Posted by Snark Shark View Post
What kind of vibrations were you feeling? Only at idle, or a particular rev range? All the time?
It seemed to be all over the map. I could be cruising at 40 and feel it, not at 45, 120 and everything felt fine, get to 125 and it would happen. Cruising along was when it was most noticeable.
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