Lotus Elan

Gearbox dimensions

PostPost by: garyeanderson » Sat Jan 07, 2012 5:25 pm

The third photo is with all parts pushed together as far as physically possible. To leave a gap would add another variable. Its tough to hold the camera, hit the shutter and line up the heights when your half blind looking at a 65 mm viewfinder from a bad angle. Its point and shoot 10 photos and then go and see what you caught on the monitor screen.

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PostPost by: worzel » Sun Jan 08, 2012 11:45 am

Hi- yet again I'm afraid.

Now I know I've sometimes been accused of "slowing up" but after much pondering I still can't figure out something.
Given the following dimensions of a std 4 speed elan-

173mm bellhousing depthI
Input shaft of 160mm overall length with a splined section of 43mm starting 85mm from the gearbox
Flywheel outer face (ie the face against which the friction disdc sits) of 54mm from the engine block.

These numbers surely mean that the friction disc sits at a point 34mm along the splined section of the input shaft leaving only 9mm of splines facing towards the block. I'm sure from memory that the flywheel marked side of the friction disc has more than 9mm of splined section protruding- does this not mean that in effect the splines of the disc overhang the splines on the shaft?

Apologies for being pedantic/confused/irrational/whatever.

One other point- I'm pretty sure that I was given the measurement of 66mm as being the distance of the flywheel face from the block. This figure would bring the friction disc position virtually central on the shaft splines. I believe 4 and 6 bolt flywheels were fitted during production- is there a difference in their dimensions allied to different types of input shaft?

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John
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PostPost by: garyeanderson » Sun Jan 08, 2012 12:52 pm

more! It would be helpful to draw this out with the questioned dimensions you need highlighted. I barely got out of high school with middle school comprehension skills. If it doesn't have a picture, you are not going to get much other than added confusion from me as I really am not sure what it is you need.

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PostPost by: worzel » Sun Jan 08, 2012 3:35 pm

Hi Gary

Thanks for your patience!

Right- in a nutshell- if you were to hold a std input shaft 173mm away from a std flywheel (mimicking its fully assembled state) with the clutch pressure plate removed but with the friction disc held against the flywheel face exactly where do the splines of the input shaft end up relative to the splines on the friction disc. I'm assuming the input shaft is 160mm overall length with a 43mm splined section that begins 85mm from the gearbox.

Based on 54mm being the distance from the flywheel outer face to the block I reckon the splines of the friction plate overhang the input shaft splines.

As I said I seem to recall a figure of 66mm instead of 54mm as the distance in question- this fiure would put the splines of the disc dead central on the shaft which is how I imagined Ford designed it. There do appear to be gearboxes with differing input shaft lengths and spline positionings so this might be the answer. Quite clearly your picture shows a 54mm distance so I can't argue with that.

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PostPost by: worzel » Sun Jan 08, 2012 3:46 pm

Hi Gary

Just an addition. I know you mentioned the difficulty of obtaining good pictures but looking at the top one of the 3 you 1st posted the numbers seem to indicate that the splines start at around 78/80mm, extend to around 133/4mm and the overall length is around 172mm. Assuming I'm seeing these correctly that means that shaft has a spline length of around 54mm rather than 43mm. This would bring the splines into the correct position I guess given the 54mm flywheel measurement.

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PostPost by: garyeanderson » Sun Jan 08, 2012 4:08 pm

I don't know if this helps, the bell is positioned without the spacer but there is a similar gap, if you look at the front gearbox bearing seal retainer in this photo, its about 8 to 10 mm forward (the input shaft pushed tight into the pilot bush) of the back of the bell. Now look at the previous photo and you will see the the splines would be fully engaged with the bearing retainer moved rearward that 8 to 10 mm.

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PostPost by: worzel » Tue Jan 10, 2012 6:34 pm

Hi

Back again!

Right- I've eliminated all extraneous info.

On the drawing A = Gearbox, B = Engine Block.

Here's my point- if you draw a line 54mm from the block (representing the flywheel outer face)
DSC00535.JPG and
that must leave 119mm on the left hand side of that line.
Since 85mm of that 119mm is the plain part of the shaft that MUST mean that the line drawn passes thru the 43mm splined section 34mm along the splined length.

This leaves 9mm of spline rightward of the line.

Therefore, either the end of the splines on the friction plate (flywheel side) end up at the end of the splines on the shaft or they overhang them (here I'm assuming the friction plate splines are roughly 1.25-1.5 inches in length)

I'd have expected Ford to so design the whole assembly so that the friction plate splines are located centrally on the input shaft ie with an equal amount of exposed shaft splines each end
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PostPost by: garyeanderson » Tue Jan 10, 2012 8:11 pm

The tape reads 120mm at the face of the flywheel, I didn't want to look for a spacer that would bring it down to your 119mm or 4 11/16 inch.
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PostPost by: worzel » Wed Jan 11, 2012 9:22 am

Hi Gary

Brilliant!

That answers my doubts about the relative positions of the splines on the shaft/clutch.. I'm making a visual calculation- would I right in saying that there's about 4mm of input shaft spline protruding above the friction plate?

As I said I'm going to use a bellhousing 5mm deeper than the std 4 speed one so had to be 100% certain that this extra depth wouldn't cause problems with the clutch operation.

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