Strange sound... Where's Waldo?

[Fishman]

I have had this strange sound coming from the front of my car as I accelerate from a stop. I looked, and looked, and looked,... to no avail. Sounded like a bad speedo cable. Finally took it to the shop today. I take the guy for a quick ride and he says he knows what it is. We pull back into the shop and lift the hood. With the engine running and in gear, he pushes the brake to the floor and hits the gas. We both then watch the engine fan blade walk up into the fan shroud. Bad motor mount. Any one have any opinions on getting rubber versus all steel mounts? I am putting out @350 hp and will be adding some headers later this year. My main concern would be vibration... I'm just not sure how noticeable it would be at idle with the all steel mounts.

Thanks in advance for any input. Brian

 

[bossvette]

I use polygraphite from PST
http://www.p-s-t.com/
do a search for them poly motor mounts there was a big discussion earlier about the pros and cons

I would advise against steel or solid mounts unless you are racing only

I personally have PST polygraphite everywhere except the diff mount
Craigsr

 

[Vettehead Mikey]

Hello from the resident hater of all things poly.

The poly mounts are no stronger than stock mounts, they're just stiffer.

The idea of a non-solid mount is that it should dampen vibration from the engine, not transmit it.

Your call.

 

[crause]

Excuse me if I jump in for a connected question. I think I may have the same problem on my 75. How big of a problem is it to change the mounts? Is it just a matter of jacking up the engine a little to get the pressure off and unbolting them?

Thanks
Andy

 

[Fishman]

Is it just a matter of jacking up the engine a little to get the pressure off and unbolting them?

That's my plan.

How big of a problem is it to change the mounts?

I'll let you know.

 

[bossvette]

Is it just a matter of jacking up the engine a little to get the pressure off and unbolting them?

that is pretty much it, do one side at a time use a 2x6 under the pan

 

[VRGSVET]

I had the same problem on my 80. I installed poly mounts by Energy Suspension. I definitely feel more engine vibration now, but I can live with that. It's a Corvette, not a Cadillac, after all. Changing them wasn't too bad. It's a little difficult to get a socket on one of the bolts, but with the right extension/universal combo you can get it. I also had a hard time getting engine up high enough to get one of the mounts out. I had to remove the fan to keep it from hitting the shroud when I jacked the engine. One other problem I had was reattaching the spark plug heat shields. Not sure if this applies to your car though. I agree with the earlier recommendation, don't go metal unless you're putting out extreme horsepower. It will rattle you to the bone. You might want to consider installing rubber mounts with the safety locks.

 

[cruzer99]

The GM mounts lasted 25 years......where's the desision??? Go with the GM unless you'll be upset if they go out in 2030. HA
Good luck

 

[Fishman]

Just called the order in two minutes ago... I have decided to go with all steel mounts. The reasons: (1) I checked all my part invoices today and found out that I did indeed put new rubber mounts on two years ago when installing the new motor! I changed sooooooo much, forgot I had this done. (2) I will be installing some headers in a few months and the additional heat generated will not sit well with the rubber (3) I have basically doubled the original hp with the addition of the new motor (4) In speaking with someone today that works on nothing but vettes, he said older vettes always have issues (eventually) with rubber mounts, especially with folks like me that have increased hp. The guy told me to go steel and if I am not satisfied with his advise, he would put a set of original rubber mounts on for no labor charge (kinda hard to pass that one up... it's almost like a test drive). (5) As VRGSVET put it so well... "It's a Corvette, not a Cadillac".

I really appreciated all the replies. THANK YOU!!!

I had to remove the fan to keep it from hitting the shroud when I jacked the engine.

THANKS for the tip VRGSVET... almost forgot about that. Though I am sure the fan blades would have quickly reminded me!

 

[Vettehead Mikey]

I know that name of several good dentists. Make sure your health insurance is paid up and will cover the cost of all the fillings that are going to rattle loose.

Excuse my french, but your motor isn't putting out more HP than many stock C2 or C3s which came from the factory with rubber mounts. Why would yours fail and their's (and mine) not?

Even the mighty L88s came with rubber mounts. Is not possible that either 1) you got a bad mount 2) maybe too many full power launches? :L

 

[Fishman]

Vettehead Mikey,

Make sure your health insurance is paid up and will cover the cost of all the fillings that are going to rattle loose.

Good one!

It's not a daily driver and I do enjoy getting into it. I think you hit the nail on the head with the number of power launches... no fun unless you can hear the sound of fuel pouring into the carb!

I'll keep you all informed. It's a pretty cheap experiment and can reverse my decision if my fillings start falling out.

Thanks for trying to 'save' me... you may very well turn out to be 100% correct. At which time, I will allow you a 'I told you so'! :gap

 

[Fishman]

OK... here's the latest game plan (after a quick call). I am going to my mechanics shop next week and we are going to put on the steel mounts. Additionally he just ordered some stock mounts from a vendor he hasn't tried before. This guy has been concerned with the quality of replacement stock mounts being produced for the past few years (especially around the glue and steel separation, case in point... my two year old mounts). If the steel mounts 'knock loose my fillings', we will immediately replace with the stock ones from his new vendor.

All of this is a result of appreciating & benefiting from all of you in the CAC. I love this forum... and thanks for the reality check Vettehead Mikey!

 

[Fishman]

Update....

Just installed the Moroso steel motor mounts last week. The 2 year old rubber mount was totally separated (the rubber & steel). Also I noticed 'Made in India' embossment on the old rubber.

I really do not see a very noticeable difference in the rubber versus steel mounts. When quickly launching the car, it actually seems to keep the car running straighter. I did notice that when the engine is cold, the steering wheel does have a slight vibration, but that goes away as the motor approaches normal temperatures. Additionally, after installation, there were two noisy vibrations coming from the interior... I simply retighten the parts and the vibration went away. I think the steel mounts do not make much of a difference because of the several factors: new engine, well tuned, a new suspension, new exhaust, and the new interior. I am sure the mounts would have been far more noticeable if the car wasn't restored recently.

Unless things dramatically change... the steel mounts are staying in.

Just thought I would keep everyone up-to-date. Brian

 

[cruisin-davey-g]

Brian:

I agree with your assement of the solid mounts not being too much of a difference, as long as you don't run over too many bumpy roads & hit a set of RR tracks too hard. Other than that, you should be OK. Those other posts about the 'teeth-rattling' experiences probably don't have the luxury of cruising down silky smooth roads all of the time. But, as soon as you do hit one of those bad roads, you'll know just what they're talking about.

The roads in Texas must be OK, because if they wern't, you sure wouldn't like the solids. At any rate, where I'm from, I'd be real leery about wanting to run with solid mounts.

Good Luck............your Vette sounds like a real 'Screamer'.