1 day ago in News
Click here for a review and full results for the Grassroots Motorsports $2014 Challenge.
So I ordered up a set of stock mounts for the Spirit R/T. Most of the time I just run down and buy some Urethane window weld and fill them up. It really works well.. Not as hard as most aftermarket poly mounts, but generally speaking it means they are perfect for a driver.
This time I ordered from Mcmaster Carr.. I plan on filling stock mounts again, but this time with the Shore 80A (hardness rating) stuff..
This of course gets the wheels turning.
Anyone around here cast polyurethane?
Why not suspension mounts and the rest of it?
What do you recommend for casting molds for trickier parts? (I have read plaster of paris has some problems that can be fixed with shellac and mold release)
What about degassing? Ect???
I've done a few items. Adding poly to fill the voids of a stock engine mount can work but there are special additives/primers that you need to make sure the poly bonds to the rubber. And if the poly is much harder/stiffer then the stock rubber the bond will fail anyway. I made a mount for my street car using shore 60 and it's held up well, much better then a stock replacement which was way to soft.
As for molds, I use whatever is handy, molding clay, plastic, wood, plaster will work. You just have to coat whatever you use so the poly doesn't stick to it.
I plan on buying a gallon or so ( I think it was shore 60 also) and doing all the bushings mounts for the camry since the aftermarket ones don't exist or are way overpriced.
I and just going to clean the old rubber out of say the control arms and cast in those. Everything else I am just going to cut some exhaust pipe up and re weld into the right diameter and cast in that
Why not buy some PolyBushings.com?
Johnny's supported the community from his home-based shop and is about as Grassroots as you can get.
With that said, I believe he said once that when machining or cutting polyurethane that freezing it beforehand helps. Molding it isn't too bad aside from the potential mess.
turboswede wrote: Why not buy some PolyBushings.com? Johnny's supported the community from his home-based shop and is about as Grassroots as you can get. With that said, I believe he said once that when machining or cutting polyurethane that freezing it beforehand helps. Molding it isn't too bad aside from the potential mess.
Polybushings rocks. Pretty high quality stuff and a good guy.
But I have some custom stuff in mind and really enjoy enjoy the process of learning to build my own.
As in building custom suspension parts. Ect.
Not to mention should I ever be able to make it I have to keep the challenge budget in mind.
In reply to ronholm:
You can use any type of plaster as the mold.. Coat the plaster with AMBER shellac, not clear. And then just use a paste wax (Johnson's will work fine). Plaster of paris is pretty weak stuff but will work fine for one or two pulls. Degassing the polyurethane will certainly help if you have access or can build a small vacuum chamber. I've even used a shop vac as the vacuum source.
I was just playing around with this and made a sample motor mount out of some emt that was laying around. It really is as simple as it sounds
I just taped the two pieces together. Mix equal parts and pour.
Remove tape after one minute
Bam! one urethane mount in under 3 minutes. This was just a simple test to see how feasible the process was. It is as easy as making a packet of Jello pudding. Easier actually.
I just filled the mounts on mndsm's challenge car with 94duro stuff.
Worked great, though i forgot to put the release stuff on the other side, so they ain't real pretty. They'll work well. Hard as HELL.
I just used the "kit" from energysuspensionparts.com. It was ~$25.
What type of primer the is needed to coat rubber engine mounts before filling with urethane? I have also heard about burning out the rubber before filling them, which is better? I have also seen people place mounts in a vacuum chamber to eliminate bubble, how necessary is that?
I need to do my engine mounts
None. Just clean them. The kit i bought was formulated especially for bonding to rubber.
I didn't vacuum them, but i was pretty careful when pouring, and topped off a time or two after i noticed bubbles rising.
These things are obnoxiously hard. These mounts had a LOT of void space, and the more void you fill, the harder they get.
OK, I'm just getting around to ordering a kit. I've noticed that one of my mounts is torn, should I replace it? Cut out the torn parts? Use as-is?
bgkast wrote: OK, I'm just getting around to ordering a kit. I've noticed that one of my mounts is torn, should I replace it? Cut out the torn parts? Use as-is?
Doesn't really matter. I recently filled the side mounts on my own MX6 and ended up just cutting out damn near all of the mount, only leaving enough rubber to locate the center bolt sleeve.
It's..... really harsh. Like really harsh.
Zombie thread! The horror...
Oh... and I ended up filling stock mounts for the project.. It really worked GREAT!
I've done a few. MR2, AE92, xA. Tape up one side of the mount. I use Duck Tape. If the mount is totally destroyed, then rig up something to hold the middle piece in the center of the outer ring. Screws, whatever, just something to hold it in place that you can take out later. Make sure the side you taped up is really really well taped. It doesn't hurt to add some saran wrap and an extra layer of tape. The urethane (I use the stuff from McMaster-Carr) will find holes like water does. Put in a bucket of sand to support the taped side. Mix and pour all at once.
When "fresh," they are really tough. Like back massage tough. After a few thousand miles, they smooth out.
Great, thanks! I ordered a kit from energy suspension, surprisingly they were cheaper than McMaster. I'm debating if I want to do my side mounts, or just the torque mounts. This isn't a plush cruiser, but I did pull the balance shafts so it may be a bit bumpy.
If you're going to do the torque mounts, may as well do them all. Just like most of the work is done by the torque mounts, most of the vibrations are created by the torque mounts.
I need to do this.
The one thing some people do is get to hard (high) of a durometer poly. Shore 60 is about the same as stock rubber but when you pour a solid mount as opposed to a stock one with voids you end up with a stiffer mount without the harshness that some have mentioned in posts here. IF you go with a short 70 you should duplicate some of the voids of the stock mount by installing something very soft to act as the void. Foam works well for this. IF you going to use this on a race car then sure use the shore 94, at least it has some give as opposed to a solid mount.
2 weeks ago in Articles
JG and David discuss the auction scene, and future collectible cars.
Also get your instant access to the digital edition of Grassroots Motorsports Magazine!Learn More