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Index > Engine/Drivetrain > Thread: Solid motor mounts
Thread: Solid motor mounts
Jeff20B


Moderator
Posts: 661
posted April 19, 2002 03:55 PM

Solid motor mounts

Anyone tried them? I'd like to because I can't stand how soft my stock ones are. The rubber part of my driver's side motor mount has been damamged by oil over the years from a leaky front cover oil line and is very soft which allows my engine to jerk left-right a bit more than I'd like it to. My bro's old RX-7 had this problem too, though a bit worse. Anyway, I'd like to get some ideas as to what types of materials I could use.

To give you an idea of one possibility, I've thought about removing the stock mounts and replacing them with aluminum blocks with either rubber or urethane (sp?) pads. Even a little squish would be better than what I've got at the moment.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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repuguru


Redlining
Posts: 319
posted April 20, 2002 06:11 AM

It seems like there may be a larger amount of vibration transfered with aluminum blocks with rubber pads on each side. MAybe not.


____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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Jeff20B


Moderator
Posts: 661
posted April 20, 2002 01:26 PM

My friend's baja has a rotary in it and there are virtually no vibrations. It is bolted to a KEP adaptor and the tranny is attatched to the horns. It connects to the pan somewhere under there. The front cover is bolted to an REPU 'cross member' (is that what it's really called?) and the diagonal sections are bolted to some 'pads' on the pushbar metal to metal. Yep, no rubber or anything there to absorb vibrations. The 13B sometimes doesn't run completely smooth, but you never really feel any vibrations. This is kinda what I'm aiming for. The only problem on an REPU is the rear tranny mount which is rubber too. It think I'll keep it though to absorb driveshaft vibrations. This leaves the front cover mounts. I want to replace them with something that will still absorb a little vibration, but won't flex nearly as much (or at all).

My other friend and I thought this up: rubber motor mounts are for luxury cars with piston engines, not rotary trucks. What do you think?
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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rotarynews


Moderator
Too Many Rotary Websites
Posts: 206
posted April 25, 2002 06:25 PM

One other thing you might try...

You might try to rig up an engine brace (like RacingBeat's/Mazdatrix's).. Attach the engine fromt the top (somewhere) to the firewall or fenders (somewhere) I hear that if you make the connections to the firewall or fenders nsulated with a peice of rubber, you won't get any vibration. Your launching becomes very predicitable, and it should handle better.
____________
*rotarynews.com
*FD3s.net
*mazdarepu.com

The best way to predict the future is to invent it!
-- Tom Matano


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Klaus43


Rotorhead
Posts: 1259
posted May 08, 2002 12:23 PM

Yep, excess movement sucks!

...that's how my fan got broken ends during autocross--contacting the lower radiator hoseclamp! There must be some nice modern material suited to the task... tho I wouldn't wanna brace my motor to anything but the frame!

       
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jfaplanet


Redlining
Posts: 356
posted May 08, 2002 08:12 PM

Home made solid motor mounts

Back in my younger days when I autocrossed. We made a solid mount of a a stock mount by drilling out the bolt that goes through the mount and using one bolt to connect the block through the mount to the frame. You still have the coushion of the rubber, but impossible to break (if you use a good quality bolt). Also if you tighten the bolt enough it become very solid.
____________
74 REPU "Red"
74 REPU "Jethro" "TII"
74 RE-Courier vert
79 SA-SE(aka deathtrap)
79 SA-SE-FC (project
turbo)
http://home.bellsouth.net
/p/PWP-crgj
TN Forum:
http://tnrotary.10.forume
r.com/

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offline


1st Gear
Posts: 16
posted June 18, 2002 02:58 AM

My R-100 broke a Holley 650 double-pumper when the stock motor mounts allowed it to contact the right hand strut tower. Now I run stack of huge washers and large bolts as solid motor mounts. Solid mounting didn't make much of a difference, but the exhaust was deafening loud and I wouldn't have noticed if a jet was trying to land on the trunk.

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Jeff20B


Moderator
Posts: 661
posted June 18, 2002 04:34 AM

That's good news since I'm going to need to get rid of some potential engine twisting when I mount a 13B in my MG Midget project. It used to have a 12A with stock rubber motor mounts which allowed the passenger's side rear corner of the oil pan to contact one of the frame rails and started cutting into it. The 13B has 20mm of extra length, and I kept the front mounts in their current locations and moved the tranny mount back. As you can imagine, the extra length isn't helping things and will still allow the oil pan to cut into the frame. What is my solution? To replace the passenger side motor mount at least, but probably both?

I don't think I'll be drilling out the studs either. That would lead to lowering the engine slightly as I tightened the through-bolts. However, lowering it a bit may be ok, as long as it doesn't flex anymore. Or maybe I could just keep the stock mounts and add a torque brace? Interesting.

       
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Jeff20B


Moderator
Posts: 661
posted June 27, 2002 12:14 AM

Well, I've gone and installed a mock-up 13B in my MG project and there is a little bit of space between the pan and frame rails (like last time). I can push a shovel handle down the oil filler tube and really twist the engine left to right. It's not as far as if the engine were running, but it's still enough to flex the motor mounts quite a bit. Since engine height is critical in this project, I'll need to find something that is the same thickness as the motor mounts when compressed. I'll need a fully laden 'wet' weight engine for this to be accurate though. Once I get my measurement, I can try these out in my other rotary vehicles as well.

       
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bcrx7


1st Gear
Posts: 11
posted July 31, 2002 08:54 AM

well i've heard the having a solid motor mount, make every thing else become lose on the RX-7's, I don't know if it's the same in the REPU. Just polyurethene should do the job
____________

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Jeff20B


Moderator
Posts: 661
posted July 31, 2002 10:42 AM

That's a good point. Maybe an REPU will be different since it has a ladder frame. Too bad there's no shock towers in an REPU to bolt a torque brace to.

       
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bcrx7


1st Gear
Posts: 11
posted July 31, 2002 11:15 AM

Doesn't the Racing Beat Torque Brace bolt to the firewall??
____________

BC and Vancouver RX-7 Club

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Jeff20B


Moderator
Posts: 661
posted August 06, 2002 11:42 AM
Edited By: Jeff20B on 6 Aug 2002 11:42

Yeah it does, but I'm not sure if the REPU's sheet metal would be strong enough. We'd need to find a hard point like a corner where two sheets are spot welded together. My MG has something kinda like this, but the intake manifold is directly in the way.

       
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Jeff20B


Moderator
Posts: 661
posted November 27, 2002 08:27 PM

I rigged up some solid motor mounts in my truck yesterday. They consist of a stack of large washers, a metric stud of sufficient length and stength (which I hacksawed to the proper length), and one rubber pad for each side which lays between the top washer and the angled ends of the front cover mount. Some careful measurements and a couple nuts and lockwashers and I was done.

Have I ever complained about the vibrations my engine produces here before? Well, they're way more pronounced now. Yes, my truck's engine has an imbalance probably caused by the old REPU flywheel or something. It has always vibrated. At idle it was barely detectable, but at higher RPM (from 3k up), the engine felt very bad. After going with solid mounts, the vibrations are way worse and pretty anoying. Idle still isn't that bad, but certain RPMs just above idle seem to resonate in such a way as to cause me to try to get above them, or stay below them, which in traffic, isn't always practical. Forget about towing. Either way, the lack of slop is still a welcome improvement.

If my engine was better built, it wouldn't have those vibrations. I'm not sure how long I'm going to keep the solid mounts in there. I may just get a decent used set of motor mounts after I get a new oil line. No sense getting them before the oil line though, since the driver's side one will just get soaked again. Anyway, the solid mounts will probably go in my MG since any side to side movement is bad for the oil pan in that car (it hits the frame on both sides and warps it enough to let oil seep out). I'll try to rig up a torque brace on top of the truck's engine kinda like RB's. It will give the engine a triangle of support (top and two lower sides). The MG will probably be ok with just two mounts since it won't be producing anywhere near 200HP (I don't recommend going over 200HP with a front cover mount), and it's already sort of solidly mounted, what with the pan-on-frame and all.

Just updating my motor mount situation and throwing ideas out there.

       
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rotormunky


Redlining
Orlando, Florida
Posts: 424
posted November 28, 2002 12:18 AM

You might consider these folks. They revulcanise motormounts for vehicles that are difficult to get replacements for.

Let me know how it goes if you do try them. I'll likely just get them to revulcanise mine when I get to that stage.



Steele Rubber Products
http://166.82.96.9/homeframes.html



____________
-Martin
Orlando, Florida

http://www.themonkeyhouse.org/REPU

'77 REPU (Some assembly required :)
'91 Cabrio (Battered and bruised, but she's still my baby.)

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Jeff20B


Moderator
Posts: 661
posted January 15, 2003 11:50 AM

Here is a post I wrote on the RX-7 Club Forum...

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.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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