Captured engine mount design

[rossman]

The engine mount that McKinney Motorsports designed got me thinking about how to design a captured engine mount with the added stiffness given by semi-hard urethane rubber. I here is my first cut at a design. Should be pretty cheap and easy to produce assuming the bushings can be found or made for a reasonable price. The drawing is not to scale and I have not taken any measurements yet. I'm not sure how much room there is on top and bottom for the urethane bushings. Comments welcome.

 

Edited October 26, 2010 by rossman

[Tony D]

A nylock style nut on the bottom independent of the attachment studs would be all you need. Drill the hole through the bonding discs on the McKinney mount and install two smaller bolts (maybe M6 or M8) with nylocks and a wavy-spring to keep the tension on it without limiting the vibration dampening advantages of the mount.

 

You wouldn't really be able to use the center bolt, it would have to be tight and that wouldn't really leave the isolator do anything other than be compressed.

 

Corvair motor monunts were like this---not captive. The engines would fall out. Remedy was to put a through-bolt on the laminates to keep it captive.

[rossman]

A nylock style nut on the bottom independent of the attachment studs would be all you need. Drill the hole through the bonding discs on the McKinney mount and install two smaller bolts (maybe M6 or M8) with nylocks and a wavy-spring to keep the tension on it without limiting the vibration dampening advantages of the mount.

 

Let me rephrase so I know I understand what you are proposing. Take the McKinney mount and drill two independent holes thru the machined aluminum plate, urethane disk and stock engine support. Then, install bolts in each hole with spring washers or belleville washers under the nuts to allow for some play.

 

I'll have to look closer but I don't think there is enough room for the bolts/nuts on the engine support side.

 

 

You wouldn't really be able to use the center bolt, it would have to be tight and that wouldn't really leave the isolator do anything other than be compressed.

 

Yeah, in my design all the bushings are in compression. It's definitely not ideal.

[Tony D]

The goal is to make the respective bonded discs to not be able to separate from the elastomer. Simply putting a bolt through the bottom side of the mount and thread it up into the aluminum spacer (as you have it drawn) with the bolt secured with loctite would do the same thing.

 

It's the same way you make the stock Nissan Mount tear-proof.

 

Really, it's easier to put a link or small chain to the K-Member to the Mount-to-Block portion of the stock motor mount.

 

Or a link from the upper starter bolt to a reinforced box channel laid over and secured to the unit body.

 

Keep the engine from moving (torqueover) --- either by solidly linking it to the chassis, or limiting it's movement to less than 0.125" will prevent the mount from being torn open from excessive forces. And if it ever does go, the link is there to hold it in place---same as a bolt through the mount itself.

 

Personally I prefer the links because you can preload them as you desire.

[rossman]

Really, it's easier to put a link or small chain to the K-Member to the Mount-to-Block portion of the stock motor mount.

 

Personally I prefer the links because you can preload them as you desire.

 

I agree. That seems like a much better idea. Thanks for the help Tony.

[bjhines]

The real trick would be to design the mounts for stiffness against engine torque and forward aft movement; while allowing more freedom of movement in all other directions. This means you would have left and right mounts or one design that can be flipped.

 

The later 280Z mounts were moving in this direction. It would also be nice to allow mounting the engine lower in the chassis and further back using slots or multiple bolt patterns.

Edited October 27, 2010 by bjhines

[Tony D]

One other thing to remember that our resident fabrication genius MONZSTER had a bitchen' captive motor mount design that utilized the moustache bar bushings and some round tube. That was pretty stout looking and really looked OEM.

 

The advantage was you could make it at home and used easily replaceable urethane bushings. A spunky individual could knock off an RTV or Plaster casting of the bushing and then cast their own in several different durometer polyurethanes (buy it from McMaster if nothing else...) and get a motor mount with damping and movement suitable to their tastes. With moustache bushings, changing from dampened to solid would be a matter of jacking the engine, and swapping the bushing inserts!

 

I'd forgotten how much I liked that mount until I saw a photo I'd taken of them while looking through my archive drive for impeller wheel attachment photos for work!

[240zip]

would you mind posting pictures of the motor mount you mentioned?

[rossman]

http://forums.hybridz.org/index.php/topic/86839-urethane-engine-mounts-for-l-series/page__p__824007__hl__%2Bmotor+%2Bmount__fromsearch__1#entry824007

[HowlerMonkey]

Somewhere here is a thread from a few months or year ago that had some very sweet looking captured mounts.

 

I seem to remember that they might have been based off of some jeep mounts and possibly red in color but not positive.

[rossman]

That thread is located here: http://forums.hybridz.org/index.php/topic/54341-captive-engine-mounts.

 

I am considering this as an alternative to the McKinney mounts. The hole locations in Jeep CJ mount are 1.25" wider than those on the stock zcar bracket. The two options I see are to slot each hole on the mount an additional .625" inwards or modify the zcar bracket. Just eyeballing the Jeep mount pictures, it doesn't appear to have enough metal to slot that much. NZeder chose to modify the stock bracket but he never posted the results.

[NZeder]

NZeder chose to modify the stock bracket but he never posted the results.

hmm good point....I am very slow with my project and the engine is still on the stand waiting for me to finish up my rewiring of the engine bay. The only other issue with the Jeep mount from ES is the lugs and centre stud are inline this is not the case with the stock L6 mount which are slightly offset.

[rossman]

I've decided to try out a slightly modified version of katman's solution (see link in post #11 above). Instead of a standard bolt as katman did, I'm going to try a shoulder bolt that is a little longer than the height of the stock mount. The shoulder will clamp the base of the mount to the lower support bracket while the head of the shoulder bolt will catch the top metal plate when it stretches the mount a set distance. Washers can be stacked up below the head of the shoulder bolt to adjust the distance the mount can stretch. I found a 5/8" shoulder bolt on McMaster Carr that should work nicely. I may even stack spring washers under the bolt head to soften the impact on hard launches. I just need to figure out the right spring force. The ~.625 ID Bellville washers that McMaster sells range from 530 - 1810 lbs to flat.