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This is the continuation of a painful saga, and was hoping someone here can shed some light on what may be causing my car (a 1992 968 mostly-track car) to devour engine mounts. Back in November 2019, I had event #1: Both of my mounts failed catestrophically, causing my engine to move enough for the power steering pump pulley to slice through one of my dual oil cooler lines, dumping most of my crankcase onto the track. These were 12-year-old OEM mounts I had purchased from Paragon. After considering my options, I went with a set of Lindsey Racing "Super Mounts", and after maybe 30 miles of street driving, the rubber isolator of the right mount split wide open, creating a noticeable vibration. Lindsey told me they had never had anything like that happen to one of these mounts, so they sent me a pair of new isolators, which installed yesterday. I did a track session today, and near the end of my session, to my horror and amazement, started dumping oil all over the track again. I didn't see an obvious source, so I had it towed home, put it up on my lift, and found that my brand new rubber isolator on the right-hand side mount has completely sliced through, leaving most of it protruding from the mount at a grotesque angle:
Second torn rubber isolator on right-hand engine mount
I still can't see the source of the leak - all the oil lines I can see look fine, although I havn't taken the belly pan off yet. So, at the moment, I'm not seeing the connection between the failed engine mount rubber isolator and the massive oil leak. My questions are:
1. Why is my car suddenly devouring engine mounts? And why is the right one always so much more damaged than the left?
2. I have a 17-pound (iirc) single mass aluminum flywheel, with the stock front pulley. Could this, in combination with the stiffer-than-stock Super Mounts be creating enough vibration through the chassis to destroy the mount's rubber?
3. After this experience, I'm strongly inclined to bite the bullet and go with Porsche OE mounts (oil filled, I believe), but am a little hesitant if there is some other factor that's causing my car to destroy one mount after another after just a very small amount of driving. So, it's kind of a chicken-and-egg thing - is there something else in the driveline setting up a condition that's destroying my engine mounts, or is the stiffness of the Super Mounts itself creating vibrations that end up destroying the mounts? The latter sounds pretty far-fetched. The transaxle feels solidly mounted (I can't move it by hand), but of course its mount is 28 years old.
Any insights would be greatly appreciated. Thanks.
Assuming that your stock ones failed due to age, it sure seems like something is causing stress on those Lindsey mounts.
If you are still running belts, did this by chance all start after a belt/roller change? Are you certain the balance belt is timed correctly? It is very easy to get that bottom roller 180 out and you will swear it’s correct. Does the 968 have a harmonic balancer and are you still running it?
Might be worth stiffening up the trans mount with urethane as you say it’s old, there is a well-proven write up for this mod. The whole drivetrain (engine, tube, trans) on our cars is only supported by three rubber mounts so a single failure will put undue stress on the remaining two mounts.
I agree that more than likely the BS is 180 out... It happens and you really dont notice it till Higher RPM, Yours is destroying Motor mounts... When I had the Issue.. I rocked my Power Steering pump apart, First the bolt broke then the clip came undone from the back of the pump and the pulley moved forward and dumped all the Ps Fluid....
Outside of that... Bad TT bearings could cause Vibration..
Vibration is Clearly causing this issue, You might have to look deeper...
Could well be but in my experience, having recently done the tt bearings on two of my cars, they generally don’t catastrophically fail to an extent they would cause such a severe vibration. On everyone I’ve done it’s the front bearing that goes first and it’s identified by a grinding noise heard only on deceleration with no other perceivable symptoms.
Ymmv but personally I would first look elsewhere for the cause of your vibration and leave the tt bearings as a last resort.
Thanks very much for all the inputs - several of them had crossed my mind, but maybe I need to re-evaluate my earlier conclusions. I did do a belt change after my event in November, but didn't think I had an isse with the orientation of the BS belt rollers, because not only was I very careful (including rotating the engine several times to make sure the marks were all in the correct places) because I'm aware that it is easy to get them 180 degrees off, but I had found the engine to be very smooth on the first drive I took with it. But maybe I didn't push it hard enough to notice an issue. I will definitely re-check the orientation of the rollers, as this theory does make objective sense. I've also sheared off and/or lost multiple bolts holding the alternator (my car doesn't have AC) and power steering tensioners, so there's definitnely something causing a lot of vibration that wasn't there before. I was thinking the vibration was caused by the failed mounts, but it makes more sense that there is some other cause of vibration that's destroying the mounts' rubber isolation pieces, which creates more vibrations, causing all kinds of havoc.
As far as the mount install method, it's hard to say. This is one of the more difficult jobs on the car, so I had to try multiple approaches to get everything to line up. I ended up loosening the M8 bolts that hold the mounts to the engine, raising the cross member with a floor jack, getting one of the mount bolts through the hole in the cross member, wrestling the other side into place, and hand-tightening the nuts that hold the mounts to the cross member. Then I raised the engine with a floor jack (I supported it from above with an engine support bar, but it still sank down a couple of inches) to allow me thread the cross member bolts, again just moderately tight initially. Then I tightened all the engine mount bolts and nuts, and finally torqued the cross member bolts. I don't thinlk there was anything I did that put unnecessary strain on the mounts' rubber isolators, but I suppose anything is possible.
Hopefully it isn't the torque tube, and from MAGK944 description, it doesn't sound like that's the issue. But it has the original, 28-year-old (split) TT and bearings, so I realize I'm on borrowed time.
And I agree a harmonic balancer would be a good idea. I've run my SMF for over five years with no issues until now, but it makes sense to use one. I see RS Barn sells one that looks pretty good from the description.
It happens to the best of us... unfortunately when I did my engine I let my Ego get in the way of my common sense.... I have done these belts, over and over, So when I aligned all the marks I was confident in the orientation... and didn't double check the book.... Rolled the engine over by hand like I normally do.. No Issue.. Drove it on the street, no Issue... Took it to the track... Snapped the PS bolt tensioner.. Then lost the PS steering... Didn't think anything of it... chalked it up to "Sh$% happens" as I was testing it on the street it felt totally fine.. until about 5200 RPM...Then I could feel it... Something wasn't right...VERY Slight..High Frequency... I just happen to have another engine on the stand and took a quick peek at it and compared it to the engine in the car... YUP 180 out on the balance shafts.... I was looking at the "U" and the "O" when I should have been looking at the the marks on the backside of the pulleys themselves.. never ripped a motor mount but the PS deal sounds VERY familiar :-)
GPA - Yes, your car's symptoms sound eerily similar to mine. The weird thing is that I didn't replace my rollers this time (I change them every other belt change), and I thought I was being very careful not to let anything move while I was putting the new belt on. Hard to imagine how I could have let the roller rotate a full 180 degrees by accident, but I'm willing to believe just about anything at this point.
Before I get too deep into this investigation, which could involve pulling a lot of stuff off my car, as a sanity check, I'd like to confirm that I have my engine at TDC. I don't have marks on my Fidanza flywheel, so I can't check through the opening in the bell housing. I've lined up the notch in the opening at the top of my distributor housing (the opening is normally filled with a rubber cap) with the mark in my camshaft, which is painted blue on my car. With the cam in this position, my rotor is pointing at about 11:00 oclock, which appears to line up with the contact for the No.1 plug wire in the distributor cap:
This is the way I've always found TDC on my car (which I verified with the flywheel mark when I had the DMF), but I want to triple confirm before moving on. Thanks.
Last edited by Cloud9...68; 02-23-2020 at 11:53 PM.
It happens to the best of us... unfortunately when I did my engine I let my Ego get in the way of my common sense.... I have done these belts, over and over, So when I aligned all the marks I was confident in the orientation... and didn't double check the book.... Rolled the engine over by hand like I normally do.. No Issue.. Drove it on the street, no Issue... Took it to the track... Snapped the PS bolt tensioner.. Then lost the PS steering... Didn't think anything of it... chalked it up to "Sh$% happens" as I was testing it on the street it felt totally fine.. until about 5200 RPM...Then I could feel it... Something wasn't right...VERY Slight..High Frequency... I just happen to have another engine on the stand and took a quick peek at it and compared it to the engine in the car... YUP 180 out on the balance shafts.... I was looking at the "U" and the "O" when I should have been looking at the the marks on the backside of the pulleys themselves.. never ripped a motor mount but the PS deal sounds VERY familiar :-)
This is interesting. I wondered why my AC compressor bolts on my 968 AND 951 both sheared. I wonder if it had anything to do with this. I just did the belts on the 951 and really haven't driven it since then because of the exhaust hitting the frame. I will triple check the balance shaft belt this spring.
in reading your install procedure it sounds like the mounts gets torqued before the crossmember (before the weight of the engine gets placed on the mounts/crossmember).
try putting the crossmember in place first, putting the weight of the engine on the mounts (finger-bolted in place), and then torque it all down to simulate real-life conditions on the mounts.
i could be wrong here but i am equating it to torquing suspension bushings with the car on the ground vs in the air.
What Spencer said, oh and replace your transaxle mount. And there called LR “ultra” mounts. Try a LR transmission “transaxle” ultra mount. 28 year old transaxle mounts that hang the transaxle on a track car probably is shot/blown out/used up/wasted/done for. And if that’s the case which it probably is, the transaxle will swing causing the engine mounts to fail.
in reading your install procedure it sounds like the mounts gets torqued before the crossmember (before the weight of the engine gets placed on the mounts/crossmember).
try putting the crossmember in place first, putting the weight of the engine on the mounts (finger-bolted in place), and then torque it all down to simulate real-life conditions on the mounts.
i could be wrong here but i am equating it to torquing suspension bushings with the car on the ground vs in the air.
What Spencer said, oh and replace your transaxle mount. And there called LR “ultra” mounts. Try a LR transmission “transaxle” ultra mount. 28 year old transaxle mounts that hang the transaxle on a track car probably is shot/blown out/used up/wasted/done for. And if that’s the case which it probably is, the transaxle will swing causing the engine mounts to fail.
That sounds like very good advice. The LR transaxle ultra mounts really look The Business. So I'll first check whether I got my balance shaft(s) 180 degrees out of sync. If not, do you think that a worn transaxle mount could cause a brand new LR engine ultra-mount to fail almost instantly? Seems a little hard to swallow, but maybe between that, the fact that I'm not running a harmonic balancer with a lightweight single mass flywheel, and the stiff-than-stock LR engine mounts (along with super-sticky tires on 10.5" wheels all around, full race suspension, etc.), set up a situation that generated a lot more vibration than normal. Could this be enough to cause both my alternator and power steering adjuster bolts to shear? The car was very smooth throughout the rev range before I installed the super mounts and the most recent belt replacement.
Oh, and does it look like I have TDC located correctly? Thanks.
I'm a fan of the "urethane trans mount" trick, you can search here and find how to do it. Cheap and very effective.
Yes, I've read about that. But I'm wondering about the compatibility of this approach with my LR super-mount engine mounts. Seems like using the LR Super Mount transaxle mount might be the safer option. After my recent experiences (waiting for the bill for leaving a 1700' oil slick on the track this past Saturday - imagine it will be well in the thousands of $$), I'm inclined to take the safest, most bulletproof approach to everything I do in the process of correcting what may be causing my current highly damaging symptoms.
02-23-2020, 01:33 AM
Eating engine mounts
