Lotus Elan

Rack height for cranked bones

PostPost by: cabc26b » Thu Sep 10, 2009 1:49 pm

Hi Russ,

Apologies , but I don't see how the marking and or compensating for frame variance standardizes the dimensions of the 3 different rack mounts I used on an elan.
Unless of course you bought the reference rack mounts at the same time, then it make's sense. It would be better still if you got the correct stand off dimension then you could machine a set of proper solid mounts out of aluminum block.

George
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PostPost by: CBUEB1771 » Thu Sep 10, 2009 3:42 pm

cabc26b wrote:Hi Russ,

Apologies , but I don't see how the marking and or compensating for frame variance standardizes the dimensions of the 3 different rack mounts I used on an elan.
Unless of course you bought the reference rack mounts at the same time, then it make's sense. It would be better still if you got the correct stand off dimension then you could machine a set of proper solid mounts out of aluminum block.

George


George - I should clarify my position. I was responding to the enquiries as to whether Lotus marked their chassis with the required shim thicknesses to set the rack height. The service parts lists for the Elan and +2 show one rack clamp and bushing configuration for all series and years. This is what Lotus would consider the reference rack mount. Lotus would only care about what they supplied and the means for accommodating for the inevitable variation in rack platform height with respect to wishbone pivots on a welded sheet metal chassis. There are many aftermarket rack clamps and the buyer is really on his/her own when buying non-Lotus parts. (OK, I'll relent, you are still on your own even if you buy genuine Lotus parts. :shock: )
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PostPost by: miked » Sun Sep 13, 2009 10:19 am

I, personally, am convinced that proper checking is the only way to find out what is happening over the range with the diference in manufacturing and the different height rack clamps avialable.

A further question, on this. The article in the club Lotus mag talks about eliminating all bump steer. I understand that balance from "side to side" is critical (and amount) but what about the 26r bones and set up, should some bump be left in? I was looking in the archive and came across this statement.

Quote from Roy Jewell in Dec' 2000

Whoops, missed a bit, which is pertinent to previous string on bump
steer. I quote; '1/8"more toe in on rebound, than bump, is correct.
To alter, change spacers under rack. Raising 1/16" on one side will
produce 3/32" more toe in on rebound than bump, on that side'.
Err, don't just do that, though. Check the results as I don't want
to be responsible for a spate of Lotus in ditches!



Sorry for my ignorance to those who know the "in and outs" on this. Do I attempt to get rid of all bump or should there be some left in?

Mike :D
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PostPost by: 69S4 » Sun Sep 13, 2009 11:00 am

types26/36/74 wrote:I thought that Lotus chassis's were supposed to have the amount needed (by shims) scribed on the rack mounting, I have never seen a chassis with such markings.......has anyone seen a chassis with this measurement on it?


My Lotus replacement chassis from the late 80's did come with the shim thicknesses scribed into the galavanising - 70 thou if I remember correctly.
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PostPost by: miked » Wed Sep 16, 2009 7:41 pm

After some shim adjustments, I got rid of the bump steer. I have built back in 0.5mm (each side) of "toe in" on bump over the total travel. This was advice from a mechanic that looks after track cars.

A point of note. With those small alloy "U" bolt type rack mounts, I needed 0.4 inch of shim to acheive this. A lot! :o Hence my original question about the race chassis and the cranked bones. I will make up a block of .370 and then use small shims to allow for and further future up and down adjustments. At least I am there or there abouts. Known quantity! :)

I was amazed at the subtlety of adding and subtracting the shims and the amount of effect. This car is to be for track days and hill climbs, I hope, in the future.

PS Re: appreciation, I do appreciate the help I have had on here over the years. In particular, Rohan H, Gary A, John P, Steve WW, Ed and many other. Also the archive, I use lots. So guys, please carry on. It is a great forum and like a family with the different type of people.

My confession. I am guilty of not posting enough help. Work pressure etc. I write stuff and delete for fear of not knowing enough. :? I only tend to help, if I am really sure. I tend to PM and talk on the phone if I can help when I have suffered the problems. Saying that, I am only a dabbler and some of the stuff on here is beyond me.

Also, I have made some good friends . Good forum!

Mike :D Theres my two pennies worth!
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