Captain_Slow

Including rebuilt/redesigned ECUs, cooling fan final stages, etc...I look forward to a day when Hans or several of the 928 vendors are offering these slick rebuildable engine and trans mounts. The prospect of keeping and restoring 928s becomes so much more attractive with options like these, which helps the value of these cars. It's the worry that OEM parts like these will be NLA or outrageously expensive for what they are that puts the largest downward pressure on 928 values, IMHO.

Carl's soon to be finished better-than-factory 'NEW' 928 would be an outstanding candidate to showcase Hans' motor and trans mounts.

hans14914

Made a couple tweaks to the mount design to slim it down a bit. I may do some weight reduction windowing on the final part (need to run FEA).

I am printing the prototype today, and have the isolators on order. Should have the fit worked out by early next week, and try moutning with a spare trans and crossmember.

Nice thing about this design is the isolators are a common part number, and $10 will rebuild both mounts. the pucks could also be replaced with a harder composite or any number of sheet-stock materials as an inexpensive short-run waterjet job.

I will start a new thread on those mounts next week after the first test fit, and then if it looks good, see if we can get volunteers for a small beta test batch. I expect these mounts to be competitive with current stock pricing.

Thanks
Hans

SMTCapeCod

This is a great project- both, but particularly the trans mounts.

I'm somewhat amused that the folks that piled on in other threads about use of poly in other applications have been conspicuously quiet here....and I'm pleased with that.
I'm still interested in info on the poly resilience in the face of all the heat and duty cycling? Previously covered?

Looking at the CAD drawings, and the mount design, I'm wondering how you account for loaded vs. unloaded profile on the trans mounts? Were new/installed mounts measured, or do the stock ones not sag/deflect until they are totally toast, such that an unloaded measurement works?

Also, can you talk a bit about how you expect they'll compare to stock with respect to noise/vibration dampening given the positive connection from the bolts that couple up the upper and lower halfs?

And, so, that price....is that the 2014 post-spike OEM price?

Again, great project.

hans14914

I have a set of prototype parts printing at the office now, and will confirm test fit with those.

The stock design is fairly solid, and the way the trans is mounted, all the weight sits directly on the mount, so if I had to wager, 80+% of the load will be carried in a vertical direction. Not much sheer force can be applied to the mount, just under launch/brake and it is aided by the engine mounts (they work in tandem as the torque-tube acts as a rigid coupler). I measured a good used mount for my parts pile, (unloaded) for the original model. I dont exepect there to be a significant reduction in height between a loaded an unloaded mount, as the total weight on each transaxle mount is relatively low for the durometer of the factory part. That is why they last significantly longer than the engine mount (firm solid mount with relatively low load).

Many people have reservations on using poly in suspension applications, and rightly so. A well designed bonded rubber part is almost always superior to a rotating poly bush. However, in a mount application, poly can be a superior choice as it has more predictable behavior over a wider range of temperature. I have chosen an isolator that has a medium/firm durometer of 88A. This is a bit firmer than the stock rubber, (which I estimate is probably somewhere between 75 and 80 with my calibrated thumbnail test). I have however allowed some gap on the inside of the bushing between the ID and fastener OD for some additional compressible space, which will reduce the effective "hardness" of the mount. The 7mm gap between the upper and lower halves of the mount allows some shift, further reducing the effective "hardness" of the poly bushings.

I have added a 1/4" shim stack inside the mount, with two washers above the isolator and three below. It is possible to remove the washers to slightly adjust the relative height of the transaxle, but also to reduce the gap between the upper and lower halves of the mount, which will have a firming effect. In conjunction with the adjustable motor mounts, the entire drive train can be raised or lowered to a degree to help accomodate spacers, custom pans, or a specific center of gravity (not a huge range of adjustment, but sometimes 0.25" makes all the difference. It also leave the native volume for a total 1" height allowing for use of common sheet stock materials. The poly bushing is 3/4" in height, so again, a very common raw material thickness. If someone wanted to use a firmer or softer material, it would be very inexpensive to have custom inserts cut via waterjet out of many materials.

As to price, I don't have a fixed quote yet, but did send the files over for a preliminary bid. I should have it back before Friday afternoon. I wont be able to get a final quote until I test the part and make sure its dimensionally accurate, and adjust accordingly.

Thanks
Hans

SMTCapeCod

Hans,

Thanks for taking my request for information for what it was, and for the time you invested in putting together the response. Great information. Thanks again.

hans14914

Assembled the V2 prototype today, and it was a bit stiff to my liking. I restricted the movement intentionally, and in doing so, did not allow enough room to adequately allow for vibration dampening.

V3 has just been designed, and the lower bolt holes have been increased in diameter, and a rubber washer added to allow upto a theoretical 3degrees of movement. These will still be much stiffer than stock. I am also adding an additional poly bushing in the trans mounting "eye" location. The cost of the poly is relatively low, but it will require a custom steel insert which will bump the cost. This will allow some, but constrained rotational motion, which my original design had no provision for at all.

I hope to get this printed and tested early next week, but think these changes should get close to the finished product.

Thanks
Hans

hans14914

Pictures of the V2 prototype if anyone was interested

SMTCapeCod

Bump, can tell by the thread trends folks are dusting off their stored cars and buying others', probably more than a few finding worn trans mounts on their to-do list.

yaskota

Still lurking... still liking. And yes, Eleonore needs new motor mounts. With all the driving I do & try to do on Hawaii's high quality roadways (sarcasm), it would be nice to replace my mounts with an upgrade... ;-)


PS: transmission needs a seal replaced, so that end may be a likely candidate too.

hans14914

Still need more people on board to make the mounts. Just too expensive for me to sit on a run of parts.

Its a turnkey project though. I still need to test v3 of the trans mounts. May try and do that next week.

Thanks
Hans

BC

I'm in.

hans14914

Bringing this thread back from the dead. I think we have enough people interested to make a small run of mounts. I am going to have the new shop I am working with quote parts for me next week, but there is still some time to make tweaks to the design. I am probably going to kick myself for asking, but does anyone have any comments/suggestions on the design before chips start to fly?

Livio928

What is the potential price point for these Hans ... one year on.

hans14914

Wont know till next week when I get the quote back. They will be significantly more than Volvo or Anchor mounts, and less expensive than Porsche mounts. That's all I know at the moment.

MattiasH

I'm still in for a set of motor mounts.