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SP250 gearbox overhaul

Vortex O'Plinth
Extra-Wise Man
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Posts: 1065
Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: SP250 gearbox overhaul

Post by Vortex O'Plinth »

The cross shaft bushes in the bell housing are simple to replace Ian - as the manual states, just press them out and the new ones in. They are pre-sized and don't require reaming after fitting. A word of caution when fitting them though; make sure the right hand bush is an adequate press fit in the housing. If you can push it in by hand it is too loose and could potentially creep along the actuating shaft in use. It could only move one way and that's inwards, so if it happens it's a gearbox out job again to sort it. If at all in doubt about the fit I'd suggest either securing the bush with Loctite or lightly peening the inside of the bell housing to prevent any possible movement.

The only way to asses whether the crankshaft bush needs replacing is to check its fit with the gearbox first motion shaft. If you 'hydraulic' it out à la manual you can compare the fit easily with the shaft. If it's OK, the downside is you needn't have taken it out in the first place, and you've now got to put it back. Other than using internal and external micrometers, an old first motion shaft or a bar turned to the same diameter is probably the easiest way to check if it needs replacing first. Alternatively just replace it anyway as a precaution.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

Falcon
Posts: 31
Joined: Sun Feb 14, 2016 9:37 am
Location: Sherborne

Re: SP250 gearbox overhaul

Post by Falcon »

Hi all, thanks for all your good inputs

Just a brief update and a further question

Box is going away to overdrive service ltd for attention.

I am fitting the diaphragm clutch cover and thanks to Barry Thorne, who is supplying me a new release bearing, cross shaft, bushes and tapered bolt, also suppling the input shaft bush for the end of the crankshaft. As always Barry has been extremely helpful and provides a first rate service.

I am going to reuse the operating fork as they are difficult to find, also the clutch driven plate which has only slight wear. This leads me to my latest question

My clutch driven plate, as I said, has minimal wear and I did show it to a local clutch specialist for surface condition, who said it looked fine. He and his clutch assembly man both independently said the clutch lining material was very hard compared to modern clutches. They said the friction material could be replaced if I wanted it done for not much money. As background to the Company not only do they do modern clutch stuff they cover all forms of classics back prewar as well.

Now my question for your views.

Should I get the driven plate refaced

On the side not to change it, the current material will last and provide a degrees of slip, I guess this would take some of the shock from the rest of the transmission down the line from the clutch. The upside to change the clutch material to modern (I know not always a good thing!) would be the counter of the above i.e. it will be I think a clutch with less slip and a more positive engagement and less life, but most of us don't use our Darts that much so would still last years. hence the question to reface it or leave it as is?

Thanks as always for your valued views

Ian

Fossil
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Posts: 516
Joined: Sat Feb 13, 2016 5:08 pm
Location: Helensburgh, Argyll

Re: SP250 gearbox overhaul

Post by Fossil »

My personal decision FWIW, if I was in your situation, would be leave it alone; especially if that is the professional's advice also.

Regards

Geoff

Falcon
Posts: 31
Joined: Sun Feb 14, 2016 9:37 am
Location: Sherborne

Re: SP250 gearbox overhaul

Post by Falcon »

Hi Geoff

I agree I am leaving the driven plate as is, but the professional advice was different depending who I spoke to!

Just an update,

Wilf your method of a tap to remove spigot bush worked perfectly.

For others who come across this thread (excuse the pun) I used a 7/8 BSF taper tap, bought at the Autojumble at the weekend for £1, perfect result.

So back to work putting in the new spigot bush and the new clutch parts that all arrived from Barry T this morning


Ian

Falcon
Posts: 31
Joined: Sun Feb 14, 2016 9:37 am
Location: Sherborne

Re: SP250 gearbox overhaul

Post by Falcon »

Hi all

An update gearbox and clutch in.

excellent work from Overdrive Services Ltd they returned my box within a week of having it. Came back well rebuilt and immaculate

I installed the diaphragm type clutch using a Barry T mandrel ( see other thread)

Took her out for a test drive, gearbox is perfect, clutch is lighter (subjectively) in operation, and new actuating shaft bolt has lever in the vertical position so all generally ok, I do have a further question on the clutch slave cylinder shaft play which I will start a new thread as it may be of use to others if they search for the specific question.

But for this thread, thanks for all your help in identifying solutions to get my Dart back together

Ian

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