Lotus Elan

Removing hub housing from strut

PostPost by: jono » Fri Feb 17, 2017 7:46 am

I need to swap a rear hub housing and re use the original strut tube.

Can anyone advise how to do this? I am guessing a hydraulic press is required?

I've tried all ways to remove the old tube from the donor housing but it's stuck fast.

Cheers

Jon
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PostPost by: john.p.clegg » Fri Feb 17, 2017 8:23 am

If the housing is scrap,grind a couple of cuts down its length and chisel it apart?

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PostPost by: elanman999 » Fri Feb 17, 2017 9:53 am

Jon,
Heat the alloy housing with a blow torch and it can be knocked off the tube. Stick the tube in the freezer for a day then heat the new housing up (till it sizzles when you spit on it) and pop the tube into the housing.
Cheers
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PostPost by: CBUEB1771 » Mon Feb 20, 2017 3:30 am

elanman999 wrote:Heat the alloy housing with a blow torch and it can be knocked off the tube.


This technique works well but it also helps to clean off any rust on the outside surface of the strut tube which is inside the hub carrier. With the outboard drive shaft and bearings removed you will have reasonable access to this section of the strut tube. If you don't clean this section of the tube off you will score the bore of the hub carrier when you try to remove the tube.
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PostPost by: Certified Lotus » Mon Feb 20, 2017 12:08 pm

I put the housing on the outdoor grill to heat it up uniformly and froze the tube. Had the hydraulic press all set up for quick pressing. Worked like a charm. DONT hammer the tube, you must use a press.
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PostPost by: bill308 » Mon Feb 20, 2017 4:04 pm

Hi Guys.

I was unsuccessful in my attempt to replace the tubes on my set of issue 18 struts.

TTR told me the tube to casting is a 0.002 inch interference fit. Also, the bearing to casting joint is an 0.001 inch interference fit, so the question whether refurbishment is the best choice, should be evaluated. I elected to go with new TTR assemblies, with adjustable perches rather than replace the tubes in my Issue 18's with adjustable perch tubes. The adjustable tubes make for a very clean installation.

In my attempt to remove a tube, I first degreased the bare strut then submerged the steel portion in Envirorust, de-rusting liquid for 3-days. The tubes were exhibited only a light to moderate amount of surface rust inside the casting. After the soaking, the rust was gone with a bit of a dull appearance as if they had been phosphoric acid cleaned. There was no apparent loss of good steel or aluminum. The tubes felt and looked clean of all rust.

What was not apparent was any corrosion between the aluminum casting and the steel tube after 45-years.

In my attempt I ran the numbers and came to the conclusion that the only way to be sure the heating/cooling processes worked was to go to extremes.

On the high end, I limited temperature to 300 F with a thermocouple mounted on the back side of the casting with high temperature tape. The temperature could be read with a Fluke DVM set read temperature (type-k or copper/constantan, yellow connector) thermocouple. Aluminum, even in cast form, is a very good heat conductor, so with gentle, extended heating, temperature gradients throughout the casting will be modest (not so big). The outside of the casting was insulated with some fiberglass insulation and the casting was heated with a couple of heat guns. It took about 10-minutes to get up to temperature, as measured by the thermocouple on the back side of the casting.

The casting was heated while under about 2000 lb tension on an engine crane. The casting was attached to the crane at the base of the hydraulic ram and the top of the tube was attached to a minimal length boom.

So the idea was to heat the casting to 300 F, and shock/cool the tube, but how?

Solid CO2 or dry ice will get you down to about -75F but imperfect contact with the id of the steel tube mean cooling takes place slowly and if a crack cannot be formed between the cold tube od and the casting id, then heat will just flow from the heat guns to the dry ice, so separation is doubtful. Indeed I could not make it work.

I originally tried to get liquid N2 (very cold), available locally for pickup under strict rules. One needed an open truck and a cryogenic rated dewer (thermos bottle). I couldn't find anyone to borrow a (3-liter) dewer from and new ones for purchase started at about $200.

The third possibility was to use liquid CO2 as a spray. This would have solved the chilling rate problem, but still may not have been enough to crack any corrosion between the tube and casting.

The calculations:

The relevant diameter (d) is 2-inches.

Change in length due to temperature change:

s=a*d*(T2-T1)

where:

a=coefficient of thermal expansion=8.30E-6 for mild steel=13.4E-6 for cast aluminum in units of in/in/F.

d=tube od or casting id=2 (inches)

For the heating condition, T1=65F, T2=300F; diameter expansion 0.00643 inches
For the cooling condition, lets assume the coolant is liquid N2, T1=65F, T2=-300F; diameter expansion=-0.00598 inches

My information says, liquid C02 boils at -70F, dry ice sublimates at -109F, both a atmospheric pressure.

So, for this case, we should have a total diameter change due to temperature of 0.01241 inches. Subtract the 0.002 interference fit and one gets a potential 0.01041 clearance between the tube and casting.

Bill
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dsc01472d.jpg and
General setup and tools used; not tensionsed in this picture
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PostPost by: Certified Lotus » Mon Feb 20, 2017 5:05 pm

Bill, a lot of science for removing the shock tubes :) I also went with the TTR adjustable tubes. For removal of the old tubes I sprayed WD40 down the sides overnight, used a torch to heat the uprights (which were in a large vice) and took a very large pipe wrench to the tubes to get them off. It was a bear, but they came off.
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PostPost by: elj221c » Mon Feb 20, 2017 7:07 pm

If it were me, I would push them out with a press.

IF the tube manages to break free it could go anywhere.

It's always best to use the correct tool for the job....

'Lash-up' and Heath Robinson come to mind!
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PostPost by: bill308 » Mon Feb 20, 2017 9:38 pm

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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PostPost by: englishmaninwales » Tue Feb 21, 2017 9:34 am

I found this is the best method:

Send wife out to the supermarket for gin, beer and food, for time = y, where y is > 2 but < 4 hours

Place strut in Aga, on max roast temperature, for time = x, where x = time for coffee, including bean grinding

Weigh Birmingham screwdriver, for weight W = w, where w is expressed in lots of non EU pounds

Hold strut firmly in best oven gloves to prevent burns.

Hit strut with Birmingham screwdriver with force F = F, where F is expressed in fcuk hard units

Once separated, allow to cool, and place in dishwasher to deep clean.

Ensure total time is less than 4 hours.

Job done.
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PostPost by: john.p.clegg » Tue Feb 21, 2017 11:27 am

:lol:

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PostPost by: nmauduit » Tue Feb 21, 2017 1:51 pm

As a continuation topic : I have these bare hubs that I'd like to save, I'm considering not having such a strong interference fit so as to hold the car, and was thinking to weld a circular stop where the tube is supposed to line up with the hub. That way, a close fit plus rest on the top part of the hub would share the support of the car weight. Any thought on that approach ?

ps: these are magnesium 26R parts (so issue 16 I understand), and the tube diameter at first sight (hand caliper) is a lot more 50.0mm than 2", so fitting a 2" OD would be a rather tight fit indeed (32 thou rather than 2)...
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PostPost by: jono » Wed Feb 22, 2017 3:28 pm

Thanks for the comments guys,

Story is I converted my car to narrow springs when I restored it 5 years ago and left the existing struts on the hubs when I did this. I've always had an issue 16 on one side and an 18 on the other (part of the cars history I imagine - an old accident?).

I'm fitting new TTR hub shafts so I decided to correct the issue 16 hub at the same time since I have everything apart, new hub shafts, bearings etc. - got a second hand one with a butchered tube on it. I need to remove that in any way possible but of course taking care not to damage the housing.

I then need to remove the narrow spring tube from my existing hub without damaging it and fit it to the issue 18 hub.

I've tried heat (lots), then iced water in the tube and all sorts of other tricks but to no avail. The tube in the donor hub is stuck fast. I'm going to go to somewhere with a hydraulic press and try to get it out that way.

I've tried to carefully split the remains of the tube with a hacksaw and then peel it out but it proved impractical and I was bothered about inadvertently sawing into the hub tube.
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PostPost by: Craven » Wed Feb 22, 2017 4:29 pm

Hi,
If the only difference between an issue 18 & 16 is the depth of the bearing recess then perhaps a competent machine shop could bore to size with tube attached.
BTW, to best of my knowledge the actual bearing i.e. size of track, number & size of balls etc. is the same for both wide & narrow bearing. Ford introduced the wide bearing into its live rear axle to stop ingress of oil on to the brake, so the wide bearing is effectively a narrow bearing with integral oil seal. I believe Lotus change over as they had trouble with inner bearing frailer due to water/dirt contamination, not sure if the metal shield was added to protect the oil seal or as extra bearing protection.
FWIW
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PostPost by: bill308 » Thu Feb 23, 2017 2:06 pm

Hi nmauduit,

I now have a set of issue 18's with good tubes, but I'd still like to replace the OEM tubes, just not for my uprated car. Maybe use on my S2 SE?

The new adjustable tubes have a 2-inch bore, then a step up in diameter where it meets the top edge of the casting. So there is an OEM press fit stop feature. I'm pretty sure the OEM tubes are built the same way. You can check by comparing the OD of the tube emerging from the top of the casting, with the bit of tube protruding from the bottom of the casting. This end should be a nominal 2-inch OD.

Bill
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