Engine mount replacement...

CliffBeer · 08-31-06, 03:14 AM

Wondering if anyone has any advice on replacement of engine mounts. The 302 in my CAV shakes excessively so I'd like to consider a change in engine mount. Presently there are rubber mounts between the block (directly below the headers) and the chassis which don't look that substantial. My car is a CAV.

Anyone have any experience with changing these out? Specific recommendations on suppliers and types (rubber or plastic or ?). Thanks in advance.

aji · 08-31-06, 11:35 AM

When I replace engine mounts I buy poly mounts.

With the headers you may want to fab a stainless heatshield. The poly will deform under heat above about 250degF
http://www.suspension.com/mustang.htm check it out

Not sure what you have now!

Howard Jones · 09-02-06, 07:39 PM

Cliff, Shakes excessively? If you already know this than I'm sorry. BUT did you rebalance the engine with the flywheel that came with your kit? A 50 oz motor will shake a lot with a 28oz flywheel as well as the other way around. It won't last very long either. The GTD V6 flywheel for instance that came with my kit was 128 grams out of balance from the ideal weight for a 50oz motor when I had it checked. I don't know what you have on your motor so I offer the idea for your consideration.

A properly balanced and tuned motor shouldn't "shake" very much unless it was really very radical I would think. Do you have any unusual vibrations when you run up the rev range?

I learned the hard way so I am only trying to save you some grief.

CliffBeer · 09-06-06, 03:15 AM

Quote:

Originally Posted by Howard Jones

Cliff, Shakes excessively? If you already know this than I'm sorry. BUT did you rebalance the engine with the flywheel that came with your kit? A 50 oz motor will shake a lot with a 28oz flywheel as well as the other way around. It won't last very long either. The GTD V6 flywheel for instance that came with my kit was 128 grams out of balance from the ideal weight for a 50oz motor when I had it checked. I don't know what you have on your motor so I offer the idea for your consideration.

A properly balanced and tuned motor shouldn't "shake" very much unless it was really very radical I would think. Do you have any unusual vibrations when you run up the rev range?

I learned the hard way so I am only trying to save you some grief.

Hi Howard,

Thanks. The shaking is fore/aft shaking, not side to side. Said another way, the shaking is not a problem of an inbalance in the rotating mass of the engine. Rather, it is a problem of too soft a mounting platform for the engine/transaxle accentuated by some grabbiness of the clutch. Said yet another way, the two front and two rear engine/transaxle mounts allow excessive fore/aft rocking under load/unload of the clutch. I believe it is a matter of too soft, or worn, front engine mounts so the poly bushings suggestion above is a good one I think.

Thank you for your thoughts!

Peter D · 09-06-06, 09:38 AM

Cliff, the pic below is of the engine mount that DRB use - rock solid. The RF's used the more standard style (in rubber or urethane), but needed a rose-jointed stay bar between the back of the engine & the rear cross member to control fore & aft movement.

Even with the more solid urethane DRB setup, there is absolutely no noticeable difference in "in-car vibration" between them & the conventional rubber mounts.

The was a thread on this some time ago (including a source in the US, I think), but being "search impaired", I can't find it.

Kind Regards,

Peter D.

aji · 09-06-06, 01:13 PM

Thanks for the picture.

A torque strap or strut is not a bad idea at all. The bolts on the engine mount are in shear under engine torque. I believe the mounts limits torque travel with mechanical stops. The stock rubber mount are far to soft for this application. In theory you are going to transmit more energy to the frame with Poly Mounts so you should expect more engine induced vibration is there is any involved. If you are going to stiffen things up besure and install at least Grade 8 bolts in the mounts and straps/struts.

best

Kenny J · 09-06-06, 02:07 PM

I have CAV#66 and I am aware of the problem. The motor mount bushings are small and can wear out quickly. I redesigned the mount system to look more like the original mounts. I also wanted them to be ajustable both up and down with shim washers and front to back.
I will try to attach a picture.

Ken

Kenny J · 09-06-06, 02:49 PM

I will try again to post a pic.
Ken

Kenny J · 09-06-06, 02:55 PM

Third time or strike!
Ken

Bob Putnam · 09-07-06, 08:42 AM

The stresses in the mounts are not the same as in a front-engined car because of the union between the engine and transaxle. The mounts only absorb a small rotational force from changes in crank/flywheel/etc. angular momentum.

Where the mounts take a beating is under accelleration, where they must transfer wheel torque into the chassis. It lifts the front of the engine and presses down on the trans mount. That's where some of the front-end lift from accelleration comes from.

If there's 3 feet between the engine and transmission mounts the lift reaction could be as much as 1600 lbs. Subtract the weight of the engine and you have 1100 lbs - 550 lbs lift at each mount. Normal mounts are not built for those stresses.

CliffBeer · 09-07-06, 09:09 AM

Thank you all. Some very good ideas and carefully considered thoughts here.

Obviously, there's a range of views as to what works best. I do like the idea of a better mount system with some adjustability. However, I'm looking to use stock mounts readily available from an easy source such as Summit Racing. I have a lathe and a press and all kinds of fabrication tools but on this one I'm looking to keep custom work to a minimum due to present time constraints.

Thank you!

Mark Worthington · 09-07-06, 10:59 AM

Summit (or maybe Jegs, or maybe both) sells the Prothane mounts that were recommended above. They are of much higher quality than the typical auto-parts-store mounts. I used them in my car and am happy with my decision.