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4 synchro into all alloy 3 synchro box


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Hiya guys,

Would anyone happen to know if it is possible to rebuild a 4 synchro 3 rail into one of the very early all alloy boxes with the integral bellhousing?

I expect it probably is, but does anyone know what it entails before I dive in?

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Like you, I expect it is, though I suspect there might be a bit of machining involved.

The other thing though is that I’m pretty sure that I’ve seen them described as too weak even for a 1200?

What are you planning?

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Posted (edited)

I agree with Nick, I've heard whispers of it being done... But also heard people warn against it as the casing was designed for a 30hp Standard 8/10.

Main question would be around the clutch, as Bill Davies comments here:

https://www.triumphexp.com/forum/spitfires-list-archive.16/spitfire-transmission-with-aluminum.970889/

But if anything the diaphragm clutch is more compact, so I'm not convinced it will be an issue?

Also perhaps modification to the front cover to accept a lip type seal for the input shaft? Depending on your donor gearbox.

But very interested to hear how you get on if you do decide to try it!

Edited by JumpingFrog
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Posted (edited)
3 hours ago, JumpingFrog said:

I agree with Nick, I've heard whispers of it being done... But also heard people warn against it as the casing was designed for a 30hp Standard 8/10.

This...

3 hours ago, JumpingFrog said:

Main question would be around the clutch, as Bill Davies comments here:

https://www.triumphexp.com/forum/spitfires-list-archive.16/spitfire-transmission-with-aluminum.970889/

But if anything the diaphragm clutch is more compact, so I'm not convinced it will be an issue?

Also perhaps modification to the front cover to accept a lip type seal for the input shaft? Depending on your donor gearbox.

I have one of the original alloy bellhousings on my Spit.  I can confirm that the 3 synchro 6 1/2 inch diaphragm clutch and the larger 7 1/4" Ford clutch both fit fine on the 1300 type flywheel. I haven't tried with the 1500 Spitfire 'pot' type clutch and flywheel combo.

The alloy bellhousing takes the same scroll seal /release bearing sleeve casting as the cast iron bellhousing and swapping over is a case of tapping one out and tapping the other in. The scroll seal for the 3 synchro box fits the early 3 rail 4 synchro input shaft without modification.

The single rail input shaft requires the later oil seal/release bearing sleeve. Again this is a straight swap in the bellhousing.

You can also use the oil seal/release bearing sleeve from the GT6 by turning it down to fit although the Spitfire parts are available new.

 

Edited by Escadrille Ecosse
flywheel detail
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Confirm the sleeve swap.  We have an alloy bell housing on our Spit with a 4 synchros box abd lip seal.  Only thing to add (not really relevant to the OP) is that there are three styles of original alloy bell housings with varying degrees of "ribbiness".  The oldest are the lightest I think but so light I'd hesitate to use with a powerful engine.  Ours is the middle one I think.

There is also an aftermarket (Bastuck?) version which can also be used with single rail (and boy does a a 1500 Spitty OD box need the lightening) which is chunkier again - looks like the iron one but in ally.

 

What's the plan Arlo?  I'm racking my brains to think what the differences might be that could cause you problems, but the truth is I've done very little with 3 synchro boxes

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I think I'll give it a punt. 

Years ago I built up a 1300 that should be quite quick- but then I shelved it as I turned to the mazda engine. I'd used lots of fancy Canley alloy bits on it as I was, and still am, heavy on lightness. I've always used alloy bellhousings where possible- but these boxes are in another league altogether. 

I've a mate with a snagged mk2 spit, and as I've no use for the 1300 or synchro box I have sitting there, figure I may as well fit it for him and see how it goes. 

Not being able to use the diaphragm clutch may be a bit of a pain- but I'll look harder at it and see whether it's possible to cut, mill and tap the case for a later alloy bellhousing 

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38 minutes ago, rustbuckit2011 said:

I'll look harder at it and see whether it's possible to cut, mill and tap the case for a later alloy bellhousing 

I wouldn’t have thought you’ll need to go to these lengths. It was years ago now, but I swapped my ‘64 1200 Herald to diaphragm clutch in the late 80s. As I recall it was straight forward with not many parts involved.

This may help

https://www.triumphexp.com/forum/spitfire-and-gt6-forum.8/parts-list-to-convert-from-spring-to.1551416/

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1 hour ago, Nick Jones said:

I wouldn’t have thought you’ll need to go to these lengths. It was years ago now, but I swapped my ‘64 1200 Herald to diaphragm clutch in the late 80s. As I recall it was straight forward with not many parts involved.

This may help

https://www.triumphexp.com/forum/spitfire-and-gt6-forum.8/parts-list-to-convert-from-spring-to.1551416/

Yes, and as I said, I've currently got a 7 1/4 inch clutch in mine without mods to the bellhousing.

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Posted (edited)

I would try the clutch before making any drastic modifications, 99% sure it will be fine and Bill is mistaken. I really also don't think its a good idea to use the coil spring clutch with a 1300 engine...

Some more anecdotal evidence it's possible:

https://www.triumphexp.com/forum/spitfire-and-gt6-forum.8/70-gearbox-in-a-box.1428752.1428785/#msg-1428785

The reason I mention the input shaft sleeve, is because the integral bell housing gearbox is more similar to a big saloon box here, and I don't think the sleeve is a separate part from the front cover plate in this instance.

Parts diagram shamelessly stolen from Canley's:


herald948_plate_l.jpg.daebe8b7530e6531bb417b50854732e5.jpg

Edited by JumpingFrog
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