Lotus Elan

Removing hub housing from strut

PostPost by: CBUEB1771 » Thu Feb 23, 2017 6:41 pm

Bill,
When I last did this I took an entirely empirical approach. I used an oxy-fuel torch with a "rosebud" heating tip to heat the hub carrier. I did not bother to cool the strut tube. Eventually the hub carrier slipped off of the strut tube under its own weight with no damage to either part. I 'll wager I got the hub carrier up to at least 500 F.
Russ Newton
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PostPost by: bill308 » Fri Feb 24, 2017 2:13 pm

Hi Russ.

Thanks for that data point.

For reference, heating from 65F to 500F results in a change in diameter, different for the two materials. My calculation shows a 0.0044 inch change in diameters for the 500F heating condition, resulting in a clearance between the tube and casting of:

If one subtracts the interference fit (0.002 inches) from the change in diameters, the clearance will be 0.0044-0.0020=0.0024 inches between the tube and casting, at 500F.

Your method probably works even better then I assume, because you are heating the cast aluminum. The casting temperature will always lead the lagging temperature of the steel tube, resulting in a larger gap than predicted..

Was there corrosion between the tube and casting?

My concern was that I really didn't want to go above about 300F as I don't really know all that much about the casting material. Generally, aluminum softens when exposed to high temperature and this softening may also be time dependent. Rohan speaks often about heads that have lost their temper, resulting in plastic deformation, and loosening of head bolt tension and ultimately loss of a head. Still, heads routinely run at a coolant temperature of 230F, but a loss of coolant condition could bump this up quite a bit more.

How hot do hubs run? I would think the biggest concern would be heat from the rear brakes (both discs and calipers) or a failed bearing?

I guess if a wheel bearing loosens up, it will spin in its hub bore, ruining the fit.

Bill
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PostPost by: CBUEB1771 » Fri Feb 24, 2017 5:24 pm

Bill,
It has been years since I last extracted the strut tubes but I recall that the areas of the strut tubes that had been gripped by the hub carriers were fairly free of corrosion. This is the most vexing part of the mathematical model, what is the bulk coefficient of heat transfer between the hub carrier and the strut tube? In my case I would say that the the coefficient was pretty high and that the temperature of the lower end of the tube was close that of the hub carrier when the two pieces slipped apart. The strut tube has a thin wall in the section within the hub carrier, hence low thermal mass. I think it is always safest to assume that the two parts will be at the same temperature and the we have to rely on the difference in coefficients of expansion. This is especially true with assembly operations when you don't want parts to tighten together much when your are only halfway to the fully seated state.
Russ Newton
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PostPost by: jono » Mon Feb 27, 2017 9:39 am

...as always, it's a question of having the right kit!

I used my pal's hydraulic press and after heating the ends of the hub housing with an oxy torch it came out relatively easily.

I also removed the existing strut tube in the same way and it came out intact and re usable.

Just need to refit now - will be using the freezer and oven method

Jon
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PostPost by: Certified Lotus » Tue Feb 28, 2017 12:30 am

bill308 wrote:Hi Glen.

It is possible to figure this stuff out, but there are frequently unknowns like how much clearance is required to separate the assemble?.

The danger of the brute force method is that the shrink fit you are trying to overcome, could be compromised for later use. The other thing is the interference fit of the wheel bearings. Who heats the hub carrier when fitting/replacing them?

I have a new set of adjustable spring perches if anyone is interested.

How's the chassis powder coating holding up?

Bill

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Hi Bill, chassis is in like new condition. I only drive my S1 in dry weather ;-) The S1 just accelerates with my torquey engine. I'm very happy the way the car turned out. Now I'm rebuilding a Europa to my specs ;-))
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PostPost by: gus » Tue Feb 28, 2017 12:55 pm

Bill, I think the failure was do to your setup with the engine crane

an engine crane is good for half a ton, a small press is 5 ton or more

in addition hydraulic power is absolute, fluid does not compress, where your setup is flexible.

repeated with a proper press and I think you will have success
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