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Sheared flywheel bolts...

Just picked up an engine that has some issues. Unbeknownst to me, it fell off a jack while mechanic was removing it from chassis. Fell forward on fan housing and caused damage to fan, housing, fiberglass shroud, plenum /vents on back of alternator, fan housing support (two cracks) as primary damage. Talked to Ollies and Supertec yesterday about repairing the housing support. I also asked them about the crank which as it turns out has three sheared flywheel bolts (out of the six) that I presumed were broken by an overzealous mechanic. Talking with the seller, he said that when he was removing the pressure plate, the heads of the Allen bolts (10 x 1.5mm) rolled onto the floor...looking very polished. I take him at his word, but have never heard of this before.
I have heard of bolts being sheared by accidentally tightening instead of loosening them, or by being overly aggressive with bolts that were installed with loctite...instead of heating and soaking with penetrant first. Personally, I have never sheared a flywheel bolt, but I always go slow and use heat and penetrating fluid.
On the assumption that the crank sheared the bolts...what does this suggest? An out of balanced crank? Engine turns ok, but that only tells me that it turns ok. Could the fall have torqued the crank somehow to create a situation where it stressed the flywheel bolts. Other than the fact that the crank is 50 years old, and needs to be dealt with as such, should I be worried about the rest of the engine internals, knowing the crank (supposedly) sheared these bolts?
Looking forward to the responses...
Old 02-06-2019, 10:24 AM
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The 70.4mm stroke 6 bolt cranks have harmonic issues that cause flywheel bolt problems. Eventually Porsche changed the 70.4mm crank to 9 bolt and those extra 3 bolts add enough additional clamping force to eliminate the loosening of the bolts when tightened to spec. But the harmonics are still there.

Walt Fricke has posted about this a bunch of times and his method of overtightening them with red loctite and 150 ft-lbs appears to work.

Aluminum Flywheel keeps coming loose!!
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Old 02-06-2019, 11:27 AM
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Walt Fricke has posted about this a bunch of times and his method of overtightening them with red loctite and 150 ft-lbs appears to work.

[/url]
^^^ this. absolutely

red loctite or even green loctite 680 retaining compound for ultimate strength. Caterpillar tractors use loctite 680 to retain BIG engine studs and the like torqued to some 500lbs+
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Old 02-06-2019, 03:07 PM
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flywheel bolts

I know Walt well... and familiar with the 70.4 flywheel issues.
This is a 66mm counter balanced crank. I am worried about the #8 bearing and saddle...as well as any other collateral damage that might have occurred. Basically I am concerned about what might have caused this (something "upstream") and caused other damage either at the same time, or what damage might have occurred as a result of this...(continuing to run an engine with a flywheel supported by three bolts vs six). Would improper use of a bent/damaged/repaired/unbalanced crank cause this? The human error factor is not lost on me either...someone could very well have forgotten to torque the bolts to 110 ftlbs...but that would likely have caused them to back out, not shear. To my knowledge, the only thing that would have caused them to shear would be initial gross over-tightening (creating a stress crack), using a loctite variant improperly and then being over-excited when trying to release them without penetrant or heating first, or the idiot factor of trying to loosen the bolts by tightening them (righty-tighty vs lefty-loosey). Previous owner claimed when he recently dropped the engine (to sell it to me), he removed the pressure plate and the allen bolt heads all dropped out. How they didn't get mixed up between the pressure plate, the clutch disc and the flywheel is beyond me.


I'm open to ideas guys. Do I keep it and roll the dice?
Old 02-06-2019, 05:22 PM
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I assume you'd tear it down completely if you keep it? If yes and you got a good deal on it, I'd vote to keep it.
Old 02-06-2019, 06:12 PM
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Sheared flywheel bolts

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Originally Posted by stownsen914 View Post
I assume you'd tear it down completely if you keep it? If yes and you got a good deal on it, I'd vote to keep it.
This is all relative. I value everything..."at a price" to make it "right", or return it to the condition in which it was represented. I paid a fair price for a running engine while in a driving car. A lot of water has gone under that bridge since then.

The effort here is to determine the potential downside to the internals. The two current "known" issues require that I break down the engine to evaluate and repair. If I go this route, it is analogous to "driving the car off the lot"...I own it. A bad crank and/or issues with the case bearing journals is a game changer for me. Thus my desire to seek the collective knowledge from the board as to what might have cased the sheared bolts issues.
Old 02-07-2019, 06:59 AM
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Looking at the area around the flywheel bolts shows all the tumbling marks the bolt heads did on the flywheel while the engine ran. I wonder how long it was driven with only 3 bolts holding the flywheel on?
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Old 02-07-2019, 07:29 AM
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If it was sold as a running engine, I think Id be unhappy with what youve found so far. For a core engine price, maybe it would be ok ....
Old 02-07-2019, 03:07 PM
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Sheared flywheel bolts cont...

After discussing this soap opera with a few resident experts...the consensus seems to be (if the story that the bolt heads were found on pressure plate disassembly is true), that the bolt heads were over torqued on assembly and "waiting" for the opportunity to "shear".
My only option at this point is to try to remove the last three bolts. They will either come quietly and release, or shear like the other three. Either way, it needs to be done to separate the case halves as there are bolts behind the flywheel holding the case together that need to be accessed. I am however wondering if I do attempt to remove the last three bolts...if this is akin to "driving the car off the lot". I think I should have a quick conversation with the seller...before I attempt this.
Old 02-08-2019, 09:32 AM
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Good point about messing with the other three bolts and "driving it off the lot." Best to ask before you go taking things apart.

I agree with Scott that this flywheel bolt situation pales in comparison to the damage caused by the fall. It feels like we're focusing on the wrong thing here? You paid a fair price for a running engine from a running car and that's not what you received. So why try to figure out what else may be wrong in addition to the known exterior damage, the sheared flywheel bolts? I have to assume that this engine has a lot of value and you don't want to pass on it if the cost to fix the problems isn't too much to bear?

But I too am still intrigued by the sheared flywheel bolts. Like you said in your first post, maybe they were overtightened because somebody thought they are left handed threads? Wouldn't surprise me at all if someone was naturally thinking left hand threads

(tried to righty loosen one, ah man, nope, this one ain't coming loose let me try another one, nope, this one ain't coming loose either, what the heck neither is this other one........? Maybe they aren't lefty threads. Let's lefty loosey them. Ooops, they ARE right hand threads!)

I recall over the years here on the forum where some people asked in advance if the flywheel bolts are left hand threads on these engines, since there are other makes of cars that do indeed have left hand flywheel bolts. Just a shot in the dark guess on my part

But in the end I don't think the fall would have impacted the flywheel bolts. It would have to fall just right to get the flywheel in contact with the floor. It sounds like the contact was at the other end of the engine to damage the fan area.
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Old 02-08-2019, 10:44 AM
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Quote:
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I think I should have a quick conversation with the seller...before I attempt this.
100% agree. Don't know if the seller was aware of all these problems and hid it, or if the seller truly did not have any idea the damage sustained. If it was me, I'd not take it apart any further or you will have "driven it off the lot". Have an estimate of what the known repairs are so far, and there are likely to be more issues upon disassembly. Unless you really want this engine regardless.
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Old 02-08-2019, 10:57 AM
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This is a 66mm crank, so no need for more than 110 lbs/ft or whatever the factory spec is. Which leaves a rather large safety margin of the elastic range of the bolt. Engineers have always told me that a bolted joint like this uses friction of the joining faces, which is created by the stretch of the fasteners, to resist rotational slippage. Put another way, the force path is through the joined surfaces, not the bolts. So it is hard to see that any forces created while running this engine would shear off three bolts.

I guess there was enough room between the central hub of the clutch disk and the flywheel for these bolts to have room to rattle around (which the photo suggests they did). My experience with bolts backing out (which maybe could put a bending force on the bolt?) is that they contact the clutch disk hub. As a result, depressing the clutch does not cause the mainshaft to quit moving, so you grind 1st or reverse when you start the car and try to move. Hard to ignore this. You can get going by putting the car in gear before starting, at least for a while, and when driving you may be able to shift basically normally (I finished a race that way) because the synchros will help match speeds which are a lot closer than when at a dead stop. It would seem to me that the central part of the clutch disk must have been pretty messed up, and loose bolt heads would have caused the same issues as backed out bolts.

This is very strange - maybe someone used a 3/4" or 1" semi tractor/trailer impact wrench and didn't pay much attention to the torque setting?

The fracture faces look, maybe, like they broke pretty much at once, rather than the fracture gradually getting bigger?

Very strange.
Old 02-10-2019, 06:15 PM
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All Porsche boxer flat 6 cranks suffer from harmonics. The longer the stoke and the heavier the masses involved the greater the noise levels. More mass was added to the cranks in later models to help deaden the vibrations and the twisting.

From experience harmonics typically will loosen the bolts and cause the flywheels to come loose and transfer material to the crankshaft hub. Typical on the earlier 6 bolt cranks.

In this case, I agree that the bolts probably sheared from over stretching. But check to see if the mating face to the crank is flat too.

As for other internal damage, I think you probably will have other repair work to do but not from the flywheel coming loose.
Old 02-10-2019, 07:04 PM
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Quote:
Originally Posted by Walt Fricke View Post
This is very strange - maybe someone used a 3/4" or 1" semi tractor/trailer impact wrench and didn't pay much attention to the torque setting?

The fracture faces look, maybe, like they broke pretty much at once, rather than the fracture gradually getting bigger?

Very strange.
Did it fall on the flywheel as well? Or is this an older issue?
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Old 02-12-2019, 11:50 AM
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The seller apparently forgot to mention that when taking the pressure plate off the bolt heads fell out.
Old 02-13-2019, 12:34 AM
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More work to do...

The seller was going to take the engine back...so I re-assembled and prepared for shipping. Then in a strange twist of events he offered to refund half of my purchase, so I decided to roll the dice and keep the engine. Now that it is back together, I can re-dis-assemble and address the sheared flywheel bolts. It is what it is...and we shall see what we see.
I'll report back.....
Old 02-21-2019, 05:07 PM
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Quote:
Originally Posted by speedo View Post
The seller was going to take the engine back...so I re-assembled and prepared for shipping. Then in a strange twist of events he offered to refund half of my purchase, so I decided to roll the dice and keep the engine. Now that it is back together, I can re-dis-assemble and address the sheared flywheel bolts. It is what it is...and we shall see what we see.
I'll report back.....
Good choice. And nice that the seller was willing to work with you several different ways. Now the real work begins.
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Old 02-22-2019, 03:26 AM
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Sheared flywheel bolts...ending

The remaining three non-sheared bolts were tight...very tight. So I applied patience, Kroil, and heat and vibration. Making sure the socket was buried in the bolt head...they came out slowly. So far so good. With the flywheel and washer removed, I had a decent amount of bolt protruding.

Several ways to attempt to skin this cat...
Reverse drill bits
Easy out
Notch the stud for an impact flathead
Std stud removal tool
Weld a short bolt to the broken stud
Vicegrips
I couldn't find my reverse bits (first choice) but used Kroil and heat and vibration again as prep. First one spun out with my fingers...second and third needed just a bit of tempting with a small vicegrips. What could have REALLY sucked was a non-problem. Pretty sure I was due....
Flywheel looks ok...for having bolt heads bounce around between it and the disc and the PP. Still not convinced that was the real story, but it doesn't matter now.




Thanks everybody for the guidance!
Old 02-24-2019, 04:59 PM
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All things considered a pretty good outcome!
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Old 02-25-2019, 02:21 PM
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