what i did to solve my problem. ( broke a motor mount while drag racing not good). I took the old ac bracket from an 85 and an old rear end bars cut the braket to where the rear end bar fit into it drilled it and ran a bolt through there. then i made to l brackets welded them the from rail. drilled them measured cut the middle out of the bar put a peice of all thread inside welded it abck together and put it in place the rubber bushings give it just a bit of movement but it keeps it from moving more than 1/4 of an inch and if your good it can be done on both sides then you some serouis solid motor mounts but make sure your welds are strong i broke the welds on the frame 3 times then i got made and used the stick welder it is not pretty but it will hold. the bracing to the strut tower does nto seem like to good of an idea.

jr

 

The motor mount itself broke?!??! How the hell...all i know is that the ones in my car are one pieced machined steel....not sure if its stainless or not...

 

i broke the studs off the mounts. So i went to this system.

jr

 

I dabbled in solid motor mounts for about a month and a half. It was an interesting experience.

In November, I got a bunch of large washers from Boeing Surplus and I think a number 10 stud from somewhere else (if it were a bolt, it would be as strong as our pressure plate bolts with the '10' on them). I measured the height of the motor mounts with and without an engine weighing them down. It was like 30-32mm or something. I cut the stud into two pieces of the correct length. I also used a thin rubber pad made from an old radiator hose on each side between the mounts and the cross plate/cross member/front cover mount (or whatever you call it).

I won't bore you with the details, but I will say that it had marked improvement with a few side effects that could be cured with new stock mounts and a torque brace.

The good: the stickshift didn't jiggle left-right anymore, and launches were more predictable. Small changes in throttle didn't cause a push-pull feeling as much as it used to, due to the engine no longer torquing left-right. The oil pan no longer would torque down and hit the crossmember.

The bad: way more vibrations than before. At certain RPMs, they would enhance themselves, and at others they'd cancel themselves out. I found myself unconciously trying to find them all the time. The noise was also much worse than before (and my exhaust lets you hear the engine pretty well). Sometimes something in my door or the driver's fender would vibrate really loudly while letting out the clutch at low RPM.

The result: I couldn't keep driving it like this. It would eventually crack the front cover; I just new it would. I got a good used motor mount to replace the one that had gotten soaked with oil from a bad upper oil line (I got a good used line at the same time). I replaced the line, then the motor mount. What a difference! It turns out that the oil soaked mount was not the bad one. Infact, the rubber part was in better shape than the passenger side mount. I blame the heavy exhaust system and the torque of the engine for wearing it out and allowing the oil pan to hit the crossmember. I moved the oil soaked one to the passenger side and the new (used) one the the driver's side. This will allow them to wear in the other direction for a while. Kind of like rotating your tires. I used to get a vibration with the old stock motor mounts. This was because the little metal bottom cover was rubbing the top cover (REPUs have the bottom cover; I'm not sure if RX-7s do too). Anyway, that old vibration seems to be gone now. The engine again torques over to the side when the secondaries open and I'm thinking of trying out peejay's cable idea to minimize it. I've got the cable and the clamps mixed in with some old junk I've got to throw away so maybe they'll work. Too bad I don't have a shock tower to use (REPU).

Almost forgot: the studs had dinged threads where the washers had slipped down and started rubbing. I should have used the stud protectors I made out of an old Fiat stainless steel tube. The rubber pads compressed which nearly loosened up the nuts. It needed to be retorqued. Oh well. I might still go with solid motor mounts in my MG project, thanks to this experiment. Or not. Also, the four front cover bolts had a little bit of aluminum gunk on them from all the vibrations. I'm glad I went back to stock motor mounts when I did.

 

Strange...as the car I was in experienced almost no vibrations at all. That was the beauty of it. At 8000rpm there was almost no vibration. At idle there is actually more vibration that when the rotars are spinning, but its not harsh or anything. It is not noticeable if you dont know that they are there.

I'll have to take a ride down to Seattle to show you

 

I have stiffer motor mounts in one of my cars. They're just hardened rubber, not steel, but the difference in both vibration and throttle feel was huge. The drivetrain feels more solid, more connected, and with the amount of torque I'm making, the whole car rocks to the side if I nail the gas

The next step up is urethane, and they're expensive. Steel is cheaper, but IMO too stiff for a street car with a lot of torque, but since the rotaries don't seem to put out too much torque, you may be fine with it.

As far as vibration goes, I noticed a lot more from a stiffer tranny mount than I did the motor mounts.

 

Woah, Jeff is near Seattle!! Holy cow man, I never noticed!! Come build my dlidfis system!! Haha, j/k man, but I wouldnt mind seeing some of the stuff youve done, or your REPU sometime .

~T.J.

 

I have some mounts made out of delron, and a mate has them in his rx3, no noticable vibrations at all, we are both using the cars for drag racing.

i have broken 2 stock mounts, i ripped the rubber in half and one broke one of the studs,

Dale

 

Ok, but where is Woodinville? I couldn't do it tomorrow as I'm going to bust some rotary stuff over at a fellow rotorhead's house tomorrow. Honestly, I've never done DLIDFIS on a 1st gen before, but there's always a first time.

Oh, and my REPU motormounts are holding up fine. I haven't done my MG project yet.

 

How did you go about making them?

 

"Just run a $2 cable from the top of the front side housing to the left strut tower... that way the engine isn't a stressed member and you don't have a ton of vibration, yet the engine doesn't rock over under acceleration."
pics of this i allways hear about this but have never seen a pic of it..

 

Ok, well I didnt expect you to be all excited about it, haha. You know anything about Webers? I have one I need to install...

~T.J.