GPA951s

Not sure why those mounts would fail so early, What comes to mind is possible undue stress in the form of a bad transmission mount. With the "Tail" of this entire assembly swinging from the rear it could possibly be tearing the front mounts. The Trans mount usually manifests itself in the form of screwing up your CV joints first, due to the whole assy. getting out of alignment. I am running factory front motor mounts on my racecar and I did the "Urethane trick" to the Trans mount. I Really liked the result of that BTW. $30 worth of that 2 part casting urethane from McMaster Carr and a little bit of work and that mount is solid as hell yet still absorbs vibration.

As far as your bearing life, the only way to tell would be if you still had some oil left over or possibly on your next oil change to send the oil out to a lab for analysis to see how much bearing material is in it. Shutting the car off (if you haven't modified the lock mechanism is usually not a good idea anyhow) Many people when they build racecars / Track cars Dis-able the steering lock for this reason as well as making it easier to move around the garage or steer it into the trailer ECT. I disabled mine, so in an emergency I can turn the key off and it wont lock the steering wheel.

MAGK944

First, are you sure about how old your mounts are as there is some discrepancy in your posts, are they genuine Porsche or OEM, there is a big difference in OEM claims for engine mounts and you mention both terms.

Second, do they show any sign of oil contamination or heat damage, are all your heat shields in place and are you running a stock-sized turbo and factory exhaust manifold.

Third, as already mentioned ^^ is your trans mount in good condition, the whole drivetrain (engine, torque tube, transmission) is supported by only three mounts so if one is bad the other two will quickly fail.

So, it’s my belief that something external to the mounts design has caused them to fail. Fact is there have been many track cars over many years using genuine Porsche mounts without experiencing this sort of failure.

With all that in mind and after everything that’s been stated on this thread, if you feel solid mounts would suit your situation, and are confident that you have any possible vibration issues covered, go for it. It seems from past comments here that there are cars running solid, semi-solid and even URO mounts “without issue”.

Cloud9...68

Thanks for the quick and informative responses, and sorry for the mount age discrepancy. My current mounts are actually much older than five years - I was getting my dates confused. I did a complete track car conversion about five years ago, including an engine rebuild, but I didn't replace the mounts at that time, because I had replaced them about five years earlier with OEM Porsche mounts (they were definitely not URO or any other aftermarket brand - they definitely had the "Porsche tax"), and they looked to be in good shape, at least visually. So they are actually about 10 years old, but the car has been "down" much of that time for various reasons, so they really don't have more than 3-4 years of actual run time on them, so their recent catastrophic failure is pretty unexpected. The heat shield was in place, and my exhaust (stock factory) is ceramic coated, so it should be somewhat cooler than on a stock car. It's a 968, so no turbo. And the left mount failed almost as badly, so it doesn't appear that heat was a major factor. There was no oil contamination on either of them, either.

Interesting theory about the transmission mount. I did have the left CV boot fail recently, but the right one is fine. Would a bad trans mount give any symptoms? GPA951S - could you please elaborate on the "urethane trick"? Given the car's age, I should probably replace the trans mount, regardless of which direction I go with the engine mounts.

It's good to hear that there is experience with track cars running OEM mounts without issue, which supports the theory that something external caused my mounts to fail. But on the flip side, while a lot of concern has been expressed over the extra vibration from the solid mounts, is there any actual "solid" evidence of the use of these mounts directly causing a failure that likely wouldn't have happened anyway?

Jay Wellwood

re: Urethane trick. Assuming GPA951S4 is referring to the tranmission mount, Have you read through this thread?

https://rennlist.com/forums/924-931-...-tutorial.html

Cloud9...68

Yes, I did some searching and found that thread. It leaves a few steps out, though. I assume you have to strip the rubber out of the stock mount, correct (excuse my ignorance - I haven't ever seen a transmission mount of any kind in person)? And how much urethane are you supposed to pour into it? How does the urethane assume the correct shape? Probably dumb questions, but if anybody has done this mod, and has some more pictures, could you please post them? Thanks.

V2Rocket

Just look at the photos in that link and it's self explanatory.
You don't need to remove any old rubber, just clean it well enough.
The Urethane fills all the gaps between metal and rubber in the stock mount.

968 should be mostly the same as a late 944 mount.

JustinL

Here's the mount that I did for the chumpcar. Inside the steel "cage" there is a rubber mount contained and attached to the aluminium hanger. There's a lot of airspace inside the cage and rubber that allows a lot of movement of the transmission. The urethane is a viscous liquid that you pour into that airspace to stiffen it up. It doesn't make it rigid, but much more stiff. The tricky part is keeping the fluid from sneaking out of the mount while it solidifies.

MAGK944

Thats very strange, if both mounts were changed at the same time with genuine parts it’s unheard of that they would both fail at the same time, especially in such a catastrophic manner. It’s been my experience on all the 944’s I’ve owned that the RH mount fails first and the LH is still very much in spec even though I change them as a pair. This further leads me to believe something else caused the failure. Could you have ruptured the mounts with a sharp tool while you were working on it during that long lay-up time? Did you support the engine from above while dropping the crossmember to do other work? Did you accidentally Jack the car up by the sump?

There is more to this story

GPA951s

I left everything together and filled that sucker all the way up to the top... It just pours in like water, its not very thick in its liquid state. So "Damming up" the sides is Critical as it will leak out. Foil tape is the way to go.. Duct tape kind of sucks for this... But the result was amazing... This was one project I have ZERO pics of.. Sorry …

There is only one Drawback to this whole deal... when I remove the Right side CV half shaft I can no longer "Push" the tail of the Trans over to gain clearance around the cooler loop. So its a bit more Fiddle-ly… But WELL worth it...

Cloud9...68

None of the above - I can't think of anything I may have done that would have put any significant stress on the mounts since reinstalling them 5 years ago, nor were they stored in any sort of environment that would have created accelerated deterioration. So this is a puzzle at the moment. I'll check to see if there's significant side-to-side play in my transmission when I get home. I did install Bruce Karger's geometry correcting trailing arm attachment bar earlier this year, so I may have inadvertently put some stress on the transmission mount in the process. Maybe I somehow damaged an already very old transaxle mount which created extra stress on the engine mounts.

Thanks for the extra info on the urethane mod - it all makes sense now, and is something I will likely do.

Breakaway944

Are you sure they were OE mounts? You call them OEM mounts, which are not Porsche. OE=Original Equipment - what came on the car from the manufacturer. OEM= Original Equipment Manufacturer - if someone makes a rubber grommet for a Porsche they can now make a transmission and call it OEM. They are an OE for the rubber grommet (since it comes on a Porsche from the factory), but an OEM for the trans (they manufacture parts for Porsche (rubber grommet) just not transmissions.
I ask because you state there was no oil contamination on the mounts. My understanding was that the OE Porsche mounts were oil filled for dampening, compared to OEM aftermarket mounts that are solid rubber. So if they ripped open there should be lots of oil on the mounts where you saw none. I could be wrong about the oil filled mounts, maybe someone more knowledgable can confirm or deny.

V2Rocket

Side note, I got a set of URO mounts for free and just put them into the car a few days ago.
I can keep track of their lifespan for the group...plot twist, the motor doesn't have B-shafts.

MAGK944

You paid too much!

Cloud9...68

I confirmed my mounts are OEM mounts - they have a Porsche part number, and that little inverted triangle with something that looks like a modified "P" inside the triangle. I also talked to Jason at Paragon products, from whom I bought the mounts, and his records indicate they were OEM also. It doesn't look like they were ever oil filled - they just look like solid rubber. It's incredible how destroyed they are, but in different ways. The rubber completely split horizontally on the passenger side mount, and the rubber is very dried out and pieces of it are flaking - it literally looks partially disintegrated. The rubber is intact on the drivers side mount, but the part of the mount that connects to the bolt that goes through the cross member is sheared off. So my engine was literally resting on the cross member, with no means of support on either side.

I spoke to Jason about solid vs OEM rubber mounts. He told me he has sold about a dozen sets of solid mounts, with no complaints from any of his customers. Based on my experience, I don't believe the rubber OE mounts can take the abuse my car dishes out. I have a full race suspension, and super-sticky tires on 10.5" wheels all around, and routinely pull over 1.3G lateral acceleration in multiple corners on the very technical track I drive on, with a max of 1.37G. I have solid or spherical bushings everywhere, so the engine mounts are some of the very few "flex points" left in the car, so they must be under a lot of stress, which I think explains their very short life span. I did the mods to my suspension five years ago, at which point the mounts looked brand new, and only finally got everything sorted earlier this year. So, I'm leaning strongly toward getting solid mounts, but am suddenly concerned about what the next weak link in the chain will be after I install them. In other words, I think I'm exerting forces on this (28 year-old) car that are vastly in excess of what it was originally designed for, and the soft engine mounts failed as a result of being the next weak point in the system. I don't want to replace them with the same style and go through this again in a year, but am suddenly concerned that this may just be a symptom of future, possibly even more serious, problems as a result of the insane cornering forces my car is suddenly capable of.

H.F.B.

hm, just on the passenger side. Are your sure you have your heatshield in place? This protects the mounts from the exhaust manifolds. Not having this shield will greatly diminish the life of your mounts.
Some pics can be found here -->https://rennlist.com/forums/944-turb...d-install.html

Edit: just noticed #17 and #18, regarding heat shields