Solid motor mount concerns

[soup]

Hello all,

I will be making much more power than stock and was planning on replacing my stock 89+ style mounts with solid ones similar to the ones at AAP etc... A friend seems to think that running two solid motormounts on the 7M is a pile of garbage.

According to him the main reason to switch to a solid mount is to stop the engine from torqueing over in the engine bay. This is great, but isn't really necessary since the 7M is a straight 6, a very well balanced engine as opposed to the big v8's. The 7M doesn't torque all that much, again unlike those v8's. His main concern is that it changes the natural harmonics of the engine and therefore could possibly cause premature failure in the bottom end.

His other reason is that it shakes the car like crazy, which I kind of like. This extra vibration rattles parts loose which means more maintenance. Have you found this too be true?

His solution was to run one solid mount, or weld tabs to the stocker, to stop the engine torque and one stock to absorb the vibrations. This seems logical to me and was also seconded by a co-worker who is a big mopar junkie and ex-Dodge mechanic.

Also, is there any difference if the mount is made of steel or aluminum?

 

[YoNkErS87t]

Sonex2000 runs semi-solid mounts on his car and you feel alot of vibration. I personally don't like the vibration. It would drive me nuts to drive it everyday and i drive without P/s and no A/c. i don't know if it would vibrate something loose but it could be very possible.

I don't know about running one solid and one stock, but if you do run the solid on the side with the oil filter, so it would be easier for you to change the oil filter.

To me easier acsess to the oil filter is the only plus i see, but see what anybody else says about running one and one. I doubt it would be a problem.

 

[GrimJack]

Engine doesn't torque over much, hmm? Tell that to Jeremy, who tore his motor mount in half, then torqued the engine over hard enough that it pulled his wastegate line off and made him overboost at Mission.

The only difference between aluminum and steel is the weight for this purpose.

The other reasons I like solid mounts.
- Much crisper shifting
- No need to fun a flex section in your exhaust, as your engine and chassis both vibrate at the same rate.

I had issues with a couple bolts coming loose from the vibration, but only the turbo to downpipe bolts for some reason, and some lockwashers will fix that the next time it happens.

I don't buy the failure in the engine due to extra vibration... the engine will vibrate less than it does on soft mounts. I could see other components failing because they have more vibration - parts that are not usually subject to the extra wear, but I haven't seen this personally, at least not yet.

By the way, if you want to take mine for a spin so you can feel the vibration ahead of time, let me know and we'll get together.

 

[Ckanderson]

wonder if their is any change in chassis stiffness now that the engine is a "stressed member"

 

[chevyeater]

There are vibrations, they are not intolerable, rather they are quite moderate IMO. The engine is always subjected to these same vibrations so, bottom end or any other engine component life would not be affected at all. There isn't much reason for V8 guys to use solid mounts, unlike the 7M , they have had interlocking safety mounts since the '60, that will not allow the engine to flop around in the engine bay like a fish out of water when a mount breaks (wich the stock ones do regularly on the 7M).

The engine is not really a stressed member with solid mounts, still just a lump sitting on mounts.

 

[Ckanderson]

hmm.. always wondered that... I guess since it's not tied into the unibody, rather a subframe.. it wouldent be stressed much.

 

[soup]

I think Jeremy's problem was 15yr old worn out mounts. I've never thought about the engine being a structural part before. Time to break out the FBDs lol. The Formula SAE car at my university integrated the engine as a structural component of the go-kart, pretty cool stuff imo.

I was pretty skeptical about the harmonics concern, but I know very little about that right now so I threw it out to you guys.

 

[Allan_MA70]

solid mounts are for those that dont care about the car, 99.9% of the "semi-solid" ones are bullshit aswell, if you dont understand why, you should not be changing things on your car! someone who did know took probably a lot of time to carefully design when building the car

 

[Ckanderson]

Please explain.

 

[GrimJack]

Yes, please do. I find myself in direct contradiction of your statements.

 

[mkIIIman089]

*scratches head on Allan's anger filled post*

 

[Sonex2000]

My semi-solid motor are good. The reason i get vibrations is my RPMs are a little on the low side. gotta fix that. what r u up to later yo87t? "poop"

 

[lowbudgettarga]

i also have the solid mounts. at first when i had them on my car it was n/a and my crank had been reground and not rebalanced and my car vibrated like a mofo and i didn't like them. Then i went turbo and the engine had never bben apart and it hardly vibrated the car at all. Now i'm rebuilding my engine and having the rotating assembly balanced in hopes of virtually no vibrations. I love the mounts now by the way.

 

[soup]

Well thanks for voicing your opinion Allan, but you would care to elaborate for the rest of apparent ignoramuses. There's a reason I created this thread.

 

[Allan_MA70]

some reasons :
you have a big long heavy mass supported by only 3 points, 2 being solid - hello leaverage and cracked/stressed sub-frame,

every time you jump on or off the go pedal rather then the rubber absorbing the shock-load its transmited to the chassis thus trying to twist the front end of your car just NOT what you want entering or exiting a corner

rubber mounts also allow a little buffering of the engine over harsh bumps = better handling

"SEMI-SOLIDS" typicaly have a strait thru bolt this allows compression but after it compresses in a loading situation it springs back agenst the bolt so its only a matter of time before the bolt or its mounting will fail

 

[mkIIIman089]

hmm, interesting.

 

[YoNkErS87t]

YO sonex I realy don't think there is anything wrong with your RPM's, but when i get a chance we could get together and check it out

How did that electric fan turn out?

 

[drunk_medic]

I see a good theory about the solid and semi-solid mounts, but no proof.

Let's find some guys with higher horse/torque figures and see what their experiences are, then see if any can inspect their cars and see if they can see any signs of wear or twisting. The chances are that most of the guys who buy these items are going to be below the 400ft-lb mark, but we need to see what the guys with higher numbers are doing.

Seriously, I plan to use solid or semi-solids along with an engine brace for my 2JZ swap - and the "end goal" for that engine is to be AEM managed with a SP63 or a SP SS GT800 series turbocharger - I'm going to need a good mounting setup.

 

[chevyeater]

some reasons :
you have a big long heavy mass supported by only 3 points, 2 being solid - hello leaverage and cracked/stressed sub-frame,

every time you jump on or off the go pedal rather then the rubber absorbing the shock-load its transmited to the chassis thus trying to twist the front end of your car just NOT what you want entering or exiting a corner

rubber mounts also allow a little buffering of the engine over harsh bumps = better handling

"SEMI-SOLIDS" typicaly have a strait thru bolt this allows compression but after it compresses in a loading situation it springs back agenst the bolt so its only a matter of time before the bolt or its mounting will fail

1. The engine doesn't have any leverage on it's mounts, thank God. At least Toyota gave this a little thought.

2. Back this one up with some measured deflection readings please, see #1.

3. Engine buffering != better handling. No idea how you dreamed that up. Have a look at a racing chassis please before commenting further, or, just scroll back thru this thread to the part where soup mentioned the FSAE car at the local university.

4. Show me a broken semi-solid mount. I just disposed of a pile of broken stock ones.

Anything else?

 

[Allan_MA70]

1. The engine doesn't have any leverage on it's mounts, thank God. At least Toyota gave this a little thought.

2. Back this one up with some measured deflection readings please, see #1.

3. Engine buffering != better handling. No idea how you dreamed that up. Have a look at a racing chassis please before commenting further, or, just scroll back thru this thread to the part where soup mentioned the FSAE car at the local university.

4. Show me a broken semi-solid mount. I just disposed of a pile of broken stock ones.

Anything else?

1, so what the transmission hanging off the back of the engine has no leverage on the engine mounts???

2, im not going to run solid engine mounts on my road car just to measure anything!

3, Race car or road car?? Road cars to not travel on smooth roads and see alot more runing hours, think of this you have the engine mass traveling around a corner and hit a pothole mid corner its going to accellerate towards the ground what is slowing it down in order.. tire... spring/shocker/suspension bush ohh and look ENGINE MOUNT and then it reverses as the wheel climbs out of the pothole now if you have a SOLID mount its placing the mass of the engine strait onto the suspension no flex as all (well maybe the x-member twisting as the transmission bounces around on its rubber mount)

4, I highly dought any aftermarket mounts have seen the mileage of any broken stock mounts


Have you owned a car with solid mounts? and not just a bodgy engine mount only job im talking about transmission aswell the noise is PAINFULL from the drivetrain acceptable for a race car maybe but never on a road car again

Allan