poly motor mount vibrations?

[Craig 94 TA GT]

I'm looking for some new motor mounts to stop the header vibration. I see that OEM ones are going to run $125+. However, the poly ones go for less than $50. I know that I'm not making too much hp, so stock is sufficient. However, I'm wondering, is the $75+ difference worth the lesser vibration? I've been searching on cz28 and read that some haven't noticed any vibration with poly motor mounts, while others have noticed a little. Any experiences with these?
Thanks in advance.

[fastTa]

Since the poly mounts are stiffer they will actually do a better job at keeping the actual motor from moving around, but that comes at the cost of transferring that energy through the k-member and frame. It's not too bad, but remember you should do a poly trans mount along with it. I think Summit has the clamshell inserts for like $25 each.

I suspect you are trying to eliminate the motor from moving and allowing the headers to "rattle" against the k-member, so it definitely couldn't hurt.

[Craig 94 TA GT]

Thanks Kev. For the motor mounts, I guess I'll go for ES or Prothane, whichever is cheaper since they're probably the same. When I remove the clamshells with the old mounts, I'll have to drill out the rivets to remove the old rubber, correct?

I have the ES poly trany and TQ arm mounts, and initially they rattled my teeth out. However, when I removed the spacer plate on the tranny mount, and the vibration seemed drastically decrease.

And you're exactly right...the headers are vibrating on something. I could swear it has tons of clearance between the K-member, but I guess it's somehow making contact when the tranny is in "Drive." It happens sometimes at idle and all the time at 1700-1900 RPM. I'm getting kind of used to it, but it's still a bit annoying and I'm seeing up to 5-7* of KR from it.

One more quick question...I know I'll probably have to remove the headers to get at the mounts, so are the Felpro 1406s reusable? (< 1k miles) Or would I have to get new ones? Thanks...

[Joe K. 99 Zeee!!]

I did a lot of research before I installed an ES trans mount. From what I've read, it seems that ES may make their mounts a tad bit softer than Prothane. When I installed the tranny mount I didn't use the preload plate and I shaved off the little hump on top.

Some people at cz28.com were recommending the install of poly engine mounts along with the tranny mount. They said it would be a little quieter than just the tranny mount. I don't know about that one though, haven't seen it myself to say one way or another.

Let us know the results if you go poly!

[Craig 94 TA GT]

I did a lot of research before I installed an ES trans mount. From what I've read, it seems that ES may make their mounts a tad bit softer than Prothane. When I installed the tranny mount I didn't use the preload plate and I shaved off the little hump on top.

That's very interesting to know. Do you think the motor mounts would be the same difference between ES and prothane? If that's the case, maybe it would be better to go with the slightly softer one

I never thought of shaving the hump off the top. Thanks for the idea, Joe...when I removed the preload plate, I didn't shave anything. Maybe that would help a tiny bit, because even without the plate, it was still slightly taller.

[Joe K. 99 Zeee!!]

I'm assuming you're using an ES tranny mount. Here's a write up that I read before modifying mine.

http://www.ls1tech.com/forums/showth...n+tranny+mount

I have slightly more sound and vibration than stock. Not really that intrusive till I get up to about 75mph.

I don't know about a difference between the motor mounts, but I wouldn't be surprised. I didn't do too much reading on motor mounts specificly.

[fastTa]

You CAN get away with re-using the 1406's, but you always take that chance of making a small enough tear that it has the potential to blow out. I've always been a big fan of copper exhaust gaskets.

It's hard to say for sure if the Prothane stuff is slightly harder than the ES stuff since there can be varibles in each polyurethane batch, but I have heard people say they think the Prothane stuff IS slightly harder.

[Z Ya Later]

Gee, I wonder what I'm gonna be helping with when I get back in town lol

I've got the Prothane motor mounts in my Jeep...and they shake at higher motor speeds quite noticeably. However, my Jeep doesn't have OD and is running 3.54 gears, so the motor will obviously be revving higer at 75 than yours will.

By the way, should I anticipate a hood removal and motor lift? lol

[Craig 94 TA GT]

Gee, I wonder what I'm gonna be helping with when I get back in town lol

I've got the Prothane motor mounts in my Jeep...and they shake at higher motor speeds quite noticeably. However, my Jeep doesn't have OD and is running 3.54 gears, so the motor will obviously be revving higer at 75 than yours will.

By the way, should I anticipate a hood removal and motor lift? lol

Hood removal? Engine lift? Only if I replace both motor mounts at the same time Do I hear old calculus book and jack? lol

I'm not going to do this just yet. First it's a compression check to make sure the head gaskets are still OK. I have a feeling that there's something going on there, which is creating the high BLMs on the driver's side. Also, I learned a trick by reading a post from Joe...aluminum foil makes a good fill-in for areas that have tiny leaks It may save tons of headaches for driver's side header to y-pipe area.

[Craig 94 TA GT]

Well, the poly mounts are in.

A couple thoughts:
- To raise the motor, I used was a jack, soft cover 1000 page book, and block of wood.
- It was a complete PITA to do. It may have been easier with stock manifolds rather than short/mid-length headers. The headers needed to be moved out of the way.
- For the driver's side, the clam shell needed to be bolted together once the rivets were drilled out. They gave 5 bolts: two 3/8", and three 1/4" bolts. The 3/8" ones needed to be torqued down to around 36 ft-lbs, and 1/4" bolts to around 24 ft-lbs. At just over 20 ft-lbs, a 1/4" bolt snapped right in half. So I ended up leaving them around 20.
- The passenger's side needed finese to remove. The starter needs to be removed to get the whole mount shell/assembly out. And the edges of the mount cover part of the bolt holes. I used a hacksaw to cut about 1/3" off each corner.
- There are no extra bolts for the passenger's side clam shell because it naturally tightens down when bolted to the k-member.

I drove it around the block and noticed a tiny bit of vibration at low speeds. However, it isn't nearly as bad as the vibrations with worn rubber mounts and headers. And my annoying vibration at 1900 RPM is completely gone.

I'll post more results once I test at higher speeds

[Z Ya Later]

Hmmmm, do I sense a testing session or two in the near future?

[Craig 94 TA GT]

LOL, not really yet. I'm hearing a loud ticking in the motor bay. All bolts are tightened to 30 ft-lbs, so I'm not sure why the header is leaking.

BTW, remember that firesleeve protecting the wire/boot under the #5 primary? Well, guess what, it's almost burned through. The boot is already crusty in some parts. I don't think anything can stand up to that heat.

[Z Ya Later]

Looks like its time to invest in some better heat protection for wires. If I remember correctly, there's slack on the O2 extension, right? Maybe its time to zip-tie it out of the way?

[Craig 94 TA GT]

Ummm...O2 extension? Near the #7 primary? The #5 wire isn't long enough to curl around and go back to the plug. It's a straight line right underneath #3 and #5 primaries, which are together. Well, we could probably get a longer wire to curl it around and completely avoid coming close in contact. I'm just not sure how long this wire should be.

[Z Ya Later]

Ummm...O2 extension? Near the #7 primary? The #5 wire isn't long enough to curl around and go back to the plug. It's a straight line right underneath #3 and #5 primaries, which are together. Well, we could probably get a longer wire to curl it around and completely avoid coming close in contact. I'm just not sure how long this wire should be.

Well, we could always strip the boot off, cut about an inch or so off and crimp a new terminal on if need be.