Lotus Elan

Release bearing carrier

PostPost by: hansaxl » Tue Oct 23, 2012 8:39 pm

Hi all,

I am about to re-fit the engine and want to make it right concerning the clutch (well, not only). So, beside this and that, I bought a new release bearing carrier (right, the one that has the clips attached to it). It is a re-manufactured part, and now it turns out that its inner diameter is too small. It will not fit onto the iron tube at all. My dealer was nice enough, measured the entire batch he had recently bought, but they are all wrong... So, what can he do... No problem, I have access to a lathe.

Finally the question: What clearance is suggested between the carrier and the iron part/tube/ transmission main shaft cover (sorry, my English...). You get it, I suppose, the part the carrier slides forward and backward on? The workshop manual does not have any data. Should it barely move, or rattle like hell..?

Thanks for any reply, Cheers,

Hans
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PostPost by: Chancer » Tue Oct 23, 2012 10:18 pm

A reasonable loose clearance fit, not a transition fit which may bind with heat expansion and not too loose a fit that may rattle or rotate and gall.

Not knowing what tolerance the gearbox spigot was machined to I would go for an H8 tolerance on the hole in the bearing carrier which according to BS4500a represents machining the hole to a minimum of the nominal spigot size (which will almost certainly be an imperial dimension) and 0.039mm above that.

To give a bit more detail I have assumed that the diameter we are talking about falls in the 30 to 50mm range, the shaft will already have been machined to limits that fall just under the nominal size which for the sake of this I am going to call 40mm although it would probably be something like 31.75 (1 1/4") so you machine your bearing carrier out to between the limits of 40.00 and 40.039mm.

Google BS4500a for more info, been years since I did this stuff every day but I still recalled the BS number and the correct tolerance.
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PostPost by: gjz30075 » Wed Oct 24, 2012 11:16 am

Hans, is it possible that your gearbox has the wrong nose piece on it? I don't know if there were differences amongst the different applications but give your outside diameter measurement of your nose piece tube and we can tell you if its correct.
That way you know if the bearing is incorrect or not.

Greg Z
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PostPost by: garyeanderson » Wed Oct 24, 2012 1:56 pm

I don't know about BS4500a, to me it sounds like a lot of Texas cows at work working on an alternate :) . Here in Massachusetts, I work under the hoakey wolf method of measurement :shock: . As usual I couldn't find the feeler gauge set I used to set the valve clearances a month or so back so I grabbed a release bearing carrier and the nose piece from a gearbox and slid it on, rocked it back and forth a bit and then thought "how the hell am I going to measure this?". I saw a sheet of paper and said "about .003 inch" per and tore off a length to wrap the nose piece with, the release bearing carrier slid right on. So I took another sheet and did 2 wraps and I had to force the nose into the bearing carrier but it went on all the way, I then miked the two sheets (times 2 as it was 4 thicknesses of paper, two on each side) and it measured out at 11 and a half thousandths of an inch. Taking in to account the fudge factor of both parts are used and a bit worn, I would set the clearance to .010 inch and see what it feels like.

Gary

two sheets to the wind.JPG and


eleven and a half thou.JPG and
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PostPost by: Chancer » Wed Oct 24, 2012 8:50 pm

Nice to see a man that knows how to hold a micrometer Gary even if he is left handed!

I remember one apprentice using one as an adjustable spanner on the toolpost of his lathe :(
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PostPost by: garyeanderson » Wed Oct 24, 2012 9:10 pm

Chancer wrote:Nice to see a man that knows how to hold a micrometer Gary even if he is left handed!

I remember one apprentice using one as an adjustable spanner on the toolpost of his lathe :(


The camera was in the right hand :) . I found the feeler gauges and I got a .010 inserted between the nose and the bearing carrier. An .011 wouldn't go, too stiff I guess, so I used a .002, .0025, .003, and a .004 and I was just able to slide the bearing on. It didn't go on far (I didn't want to break or damage anything) but it went on.
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PostPost by: hansaxl » Thu Oct 25, 2012 8:27 pm

Great. I have an idea now and will get that done soon. Thanks for all your comments!
Keep rolling, Cheers, and keep up the good work!

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