I'm at the point of putting some sort of bushing on my front suspension of the Locost.
Delrin is easier as it's just cut to length
I searched all over for a Poly bush the proper size but everything was too long. I ended up with sway bar end bushes thinking I'll just cut the length down a short bit, but I just realized the end "flange" is too thick so I have to thin that down a little as well so that it will fit within the confines of the bracket.
Is it worth that much work to use poly?
My understanding - as limited as it is - is that a lot of people consider Delrin superior to poly. It's not applicable in places where you need the deflection of rubber or poly, but it also doesn't need regreasing and doesn't "grab" the sleeve like poly does.
Obviously in a Locost, you'll have to consider the increased NVH 
.
There's a thread on Miataturbo about this, but I don't have a link handy right now.
Effectively Poly is a rubber with it’s compression measured in durometer (squish). Delrin is a POM polymer that is crystalline, like many of the other engine bay plastics. Delrin/POM is inherently lubricious meaning it should not make noise.
Hmmmm. I've made one set of poly bushings. It wasn't as hard as I thought. Yes, I am having trouble holding the bushing to do the initial cut, but the sanding to final dimension isn't all that bad nor is the thinning down of the flange ends.
I wanted some compliance is the reason I was asking about poly. I've ridden in a Locost with Delrin and it was harsh, but then even a Locost with stock bushings is harsh. Mine is to be a little civilized Locost without solid mounted anything. The car will still exceed my capacities
I don't like heims, but the poly also needs a grease fitting (more work) to tame the noise.
Delrin is just so much easier and if it's not a groaner surely it's not that much harsher than poly, is it?
I guess I'm probably going to make both and then see which one I like once I'm on the road.
Anyone have a dead nuts simple way to cut the poly? I used a chop saw as a razor knife was getting nowhere and was dangerous besides.
EDIT: WHOOPS just realized making both doesn't work, I have to make a choice. It's the grease fitting that's the issue. It protrudes into where the bushing wants to be. The poly has the flange to keep it towards the outside edge, but the Delrin doesn't.
I have used a 2 piece poly before with a 1/4" gap in the center to accomodate the grease fitting and the grease, but the Delrin would just rub on the fitting as it's not anchored in place.
OK, I had the decision made for me (I think).
I accidentally dropped both the Delrin bushing and the poly bushing at the same time. I was concerned there wouldn't really be a noticeable difference between the 2 because the poly felt so hard.
The Delrin bushing just dropped and kind of sat there, but the poly bushing bounced all over the place. I repeated the experiment several times and the poly won by a pain in the butt. Because that's what I think the Delrin will be.
But I'm still not going to drill & install the grease fittings till the very end because once I do that I am committed.
If I were building a locost, and welding up the suspension arms myself, I'd size the bushing tubes to take stock rubber bushings. Miata ones would probably be in play, just because they're easy to find.
In reply to DeadSkunk :
And there’s also the stiffer rubber bushings that FM sells.
In reply to Pete Gossett :
I put a complete set of those in the Miata I just sold. Good in the Miata, but the extra stiffness would be pretty noticeable in a lightweight Locost.
In reply to DeadSkunk :
Good to know, I’m considering them for mine too.
Heres something from the tech tips forum on how to keep em quiet.
DeadSkunk said:If I were building a locost, and welding up the suspension arms myself, I'd size the bushing tubes to take stock rubber bushings. Miata ones would probably be in play, just because they're easy to find.
If I were building a Locost I'd use rod ends, because I don't think it's going to make any difference in the amount of NVH. The one I owned for a while had them (I bought it from the guy who built it), and the additional ride harshness from the heim joints was completely drowned out in terms of ride discomfort by everything else. A Locost is never going to be a comfortable car.
As for other choices, the problem with delrin is that it has essentially no give, so the pivot point can only rotate on one axis. This is fine for a suspension arm such as the front upper inners on a Miata, where the two pivot bolts are colinear (in fact, on the Miata it's a single long bolt that goes through both of them). It does *not* work on a suspension arm like the front lower inners on that same Miata, where you need to be able to move the two bushings independently of each other to align the car. You can use delrin in one of those bushings, but if you put it in both then the suspension will bind badly and the handling will be terrible.
Poly will deflect enough to solve that problem, but it's got a bunch of problems all its own. It's not just that they squeak when they're improperly lubricated, they also start to bind. You get stiction in the suspension, meaning that it's effectively acting as a variable rate spring. It takes additional force to get the suspension to start moving, then it drops to the normal spring rate. Poly is great when you first put it in, but after a month or so it's squeezed the lube out and it starts binding. You can put in zerks to try to re-grease them, but IME that doesn't work very well. It's better than nothing, but there's no way to get that initial buttery smooth motion back without completely disassembling it and manually re-greasing everything.
What I have on my Miata right now is a new set of polys with custom 2-piece oilite sleeves. That eliminates the need for something to bear against the poly and theoretically removes the stiction problem. I haven't had enough opportunity to drive the car since installing them to come to a conclusion on it yet, though.
codrus said:If I were building a Locost I'd use rod ends, because I don't think it's going to make any difference in the amount of NVH.
^This. A lightweight/limited-use Locost won't beat up rod ends like a frequently driven street car will. Spherical bearings allow full range of motion without binding or unwanted deflection. NVH and limited service life are the drawbacks but that's not applicable in a Locost, so you don't have to compromise with a stock-type bushing.
Actually NVH is a factor on a Locost, maybe moreso than that factory car that has all kinds of other ways to lessen the NVH.
With a Locost you can quickly get yourself a car that is miserable to drive on the street for more than getting groceries. Oh, it's fine on the track or autocross but soon you find yourself trailering it instead of driving it to the track.
I've had multiple of these cars which is why I'm looking to tame it a little.
carguy123 said:With a Locost you can quickly get yourself a car that is miserable to drive on the street for more than getting groceries. Oh, it's fine on the track or autocross but soon you find yourself trailering it instead of driving it to the track.
IMHO pretty much all Locosts fall into that category, rod ends or not. :)
I find the wind to be much more fatiguing than the suspension NVH, and with a small, flat windshield and nothing else above mid-torso, a Locost has a lot more wind than something like a Miata.
Any time a bush is clamped in an 'eye' and turns against the pivot or the eye, you get wear. You can minimize it with lube, but it will wear out, and given the average person's attention to proper maintenance they will probably end up damaging something if left alone long enugh.
I always prefer a bush that doesn't turn in the eye or on the pivot. A Metelastic rubber bush bonded to a steel inner will be clamped in place and all the motion is flex, with no motion in either the eye or on the pivot, so zero wear. Just be sure to have the suspension loaded before tightening them in there, lest you preload them and get shortened service life as a result.
In reply to wspohn :
But the rubber wears, tears and generally breaks down
carguy123 said:In reply to wspohn :
But the rubber wears, tears and generally breaks down
It's also a part that's much more expensive to manufacture in small volumes, so you're usually stuck with OEM stiffness levels which may or may not meet your needs.
This might help in your search:
http://polybushings.com/pages/bushingsbysize.html
I believe that Delrin will eventually cold-flow and become loose, luckily they are cheap and relatively easy to make.
I've got Delrin in a few places and rod ends in a few others in my daily/track Fairmont. I started with stock, progressed to graphite impregnated poly, then to the current setup. The ride is much more pleasant with the Delrin front LCA bushings, because there is very low friction in the bushings. The rod ends in the rear click a lot on and off power, and they transmit gear whine/hiss to the cabin. I only hear it up to about 40 or so, though, because the wind noise/transmission/lack of sound deadening takes over at that point.
I pretty much love my Delrin bushings.
P. S.: Whatever you do, make *sure* the inner sleeve (that the bolt goes through) is long enough that the chassis clamps it before it squeezes the bushing material. Otherwise, E36 M3 gets really weird, really quickly.
In reply to Stefan :
Oh sure, NOW YOU SHOW ME THAT PAGE!! After spending hours inside Summit and waiting a week for parts to arrive from all over and all of them need to be trimmed to length.
Stefan said:I believe that polyurethane will eventually cold-flow and become loose, luckily they are cheap and relatively easy to make.
FTFY. Delrin is vastly superior to polyurethane in both lubricity and cold flow properties. The only technical advantage to poly is that it will tolerate at least a small amount of misalignment, due to its softer nature.
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