Project Coalnotdole's Scimitar - Machining work: Speedometer Drive Unit 12/4/19

[coalnotdole]

Cor, the state of that black fluid.

 

Are you able to see it noticeably "looking cleaner" inside

 

It looks a bit clearer in there, but as its a cast iron block I want really expecting it to look like new....

 

 

Is there no area of restoration that you struggle with?!

I think between Dave and myself we're quite well covered skills wise. (He's more ninja than I am at most of the practical stuff though it has to be said.)

 

I'd not done anything on an old car before I bought this one in 2010. Before then I think the most technical thing I'd done on a car was change a set of glow plugs! I'm still learning on every job I do and pushing the limits of what I can do from a single lockup garage.

 

The scope of what can be done has increased as the faclites have improved. For example jobs I would once have got done locally by an engineer are now being done by Dave on the IOW. Having that availavble as an option has probably increased the feasbility of doing something like creating the TVR / Cosworth bastard gearbox. The sensible thing would have been to flog the TVR gearbox on and get the Cosworth one refubished!

 

Speaking personally there are loads of areas where I really could do with improving my skillz. I need to practice my welding and I'd like to get more involved in the machining work too at some point.

 

Cheers

Joe

[tooSavvy]

When you showed the movable collar for the speedo drive - being a USA widget - I had thought of those taper sleeve collars [with the castle ringnut to wind them tight] used everywhere for gears & pulleys.

 

https://www.bearingboys.co.uk/Bearing-Adaptor-Sleeves-/HE309-HMEC-Bearing-Adaptor-Sleeve-143491-p?gclid=CjwKCAjwhbHlBRAMEiwAoDA34_9ANYDTWHecEykBPJqgrWy1rF4g1LTuHQ_sjscgc_tY7LFxDcWVMxoCm9oQAvD_BwE#

 

Must be a catalogue with really small ones ??

[coalnotdole]

Bet that core plug would have ruined your day if you hadn't found it!

 

I'm hoping removing that stray core plug might cure the strange 'squelching' noise that could sometimes be heard when the engine was switched off... It sounded a bit like the noise you get when you walk with water in your wellies! It only did it for a second or too but it was a bit strange!

 

Parcel tape for mould release.

 

Brilliant. This bit of priceles information has been added to my toolbox!

 

This was the first time I'd tried doing this. It does't give quite as good a finish as filling and sanding the mould would have done, but on jobs where the finish hasn't got to be perfect, it can save a load of time.

 

When you showed the movable collar for the speedo drive - being a USA widget - I had thought of those taper sleeve collars [with the castle ringnut to wind them tight] used everywhere for gears & pulleys.

 

https://www.bearingboys.co.uk/Bearing-Adaptor-Sleeves-/HE309-HMEC-Bearing-Adaptor-Sleeve-143491-p?gclid=CjwKCAjwhbHlBRAMEiwAoDA34_9ANYDTWHecEykBPJqgrWy1rF4g1LTuHQ_sjscgc_tY7LFxDcWVMxoCm9oQAvD_BwE#

 

Must be a catalogue with really small ones ??

 

I've never seen one of those before! They do look like they may well have done the job. I'll try and sort the photos out for the next update in a bit.

 

Cheers

Joe

[coalnotdole]

Making a TVR T5 work with a mechanical speedometer drive

Last month the TVR T5 gearbox went off to Dave on the island. The plan was for him to have a look at machining the mainshaft to allow us to mount the speedo drive gear in the right place for the Cosworth tailshaft. As well as turning up a new speedo drive body which would work with that gear...

A TVR T5 Gearbox, now leeching ATF on the IOW:



Its Dave's busiest time of year as the boatyard prepares for the spring lift in, On top of that he's just moved into an new (huge) workshop and is still in the process of trying to get the workplace setup.

He also had a pretty severe case of pneumonia last month too so its amazing he's found any time to do this work!

Anyone else got workshop envy?






First step was making a section of aluminium tube for the speedo drive gear to run on. The Tube has been split allow it to stretch to fit over the splines at the end of the mainshaft.





Here it is with the gear trial fitted.



In order to retain the gear and the sleeve, the mainshaft needed to have a 4mm hole machined in the correct place. As the mainshaft is hardened steel this turned out to be quite hard. The first attempt broke the carbide end mill barely making a mark on the mainshaft...



Second attempt was made with A Dremel sharpening bit...



Two broken bits later and a small hole had been achieved...



Finally some new shorter carbide end mills were ordered and they finally managed to do the job:





Testing the depth with the retaining clip.



Heres the gear, collar and clip trial fitted.





With the tailshaft on the gear is in the right place!



With that sorted Dave then turned up a new body for the speedometer drive, Its based on the dimensions of the Cosworth one but is slightly shorter to accommodate the GM driven gear.



The inside has been counterbored to suit take an oil seal that came with one of the American kits, This means that most of the component parts should be standard GM / T5. Which should help with future serviceability and should mean its easy to adjust the gear ratios in the future if needed.



Trial fitted:



To fit the speedometer drive cable a groove was needed for a circlip. The proper tooling to do this would cost around £200 so instead Dave cut this tool down with some careful angle grinding and an extra thin zippy disc. Should be ok to use on ally...



The new drive unit with seal and circlip groove (which is a bit hard to see in this pic):



Trial fitted with a speedo cable:



Heres the complete unit, A 9/64th’s end mill was used to machine the slot. A steel tab sits against this to retain the unit in the gearbox.



The last step was to fit a small stainless rod to the end of the driven gear, this will stop the gear dropping when reverse is engaged.





Its all been tested together on the bench and it all looks like it should work. The cable moves when the mainshaft turns so thats a good sign! We'll see how it holds up once its on the car!



Cheers

Joe

[320touring]

There's more engineering on that Speedo drive than in my fleet of 10 cars combined. Top work, and sensible re servicing/ratio changes too.

[somewhatfoolish]

The hole in the mainshaft is giving me teh fearz; how many horses will it be transmitting? I'd have been tempted to glue the gear on.

[coalnotdole]

The hole in the mainshaft is giving me teh fearz; how many horses will it be transmitting? I'd have been tempted to glue the gear on.

 

The gearbox will take around 200 bhp ish in the Scimitar. In a TVR apprication this gearbox might be expected to deal with 400+. So its very under stressed in my application.

 

This picture shows the hole on the left made by the factory to do exactly the same job as the one we've made:

 

 

Its only 3-4mm deep so I doubt its caused any significant weakness...!

[mercedade]

I can't express just how much I want to see this flourish, post-COVID.