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Six cylinder gearbox / engine compatibility


Roger
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Good morning Gentlemen,

I have spent several evenings in my garage lately (loosing lots of sweat and blood) trying to mate a gearbox from an early 1966 2-Litre Vitesse with an engine from a 2000 Mk I Saloon without success. First I thought that the clutch was not centered properly so I repeated this process several times trying to improve accuracy of the alignment, but still no joy. I can get the splines to connect, but then I always have about 10 mm distance between gearbox and back plate no matter how much I try to push it forward. Then I made a test and removed both clutch and flywheel (which is from a Vitesse Mk II) and then the gearbox fits properly! No gap between gearbox and back plate any more! ("long" spigot bush still in the crank shaft though).

I have measured and compared flywheels between my early HC angine and the Vitesse Mk II flywheel but I find no other difference than the bolt size. The only reason for this problem that I can think of now is the crank shaft? Is it a fact that my early 1966 Vitesse gearbox (HC585) is not compatible with my Mk I 2000 Saloon engine crank shaft? Regardless of which flywheel I use? The engine number has been almost completely “erased” by PO but I think I can read MB78380HE with much magnification and imagination.

Any advice how to proceed or an explanation why I have this problem would be much appreciated.

 

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In the photo it does look like the gearbox splines have been in contact with the Vitesse flywheel around its central hole. I think if you put just the flywheel back on and try it again the problem will return so either theres a difference between Mk1 and 2 Vitesse/GT6 flywheels or, as you say, your crank rear face protrudes further...

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Thanks for your quick response Johny and NM. I should have the cranshaft from the HC engine lying around somewhere, I will see if I can find it and do some measurements. The frustrating thing is that I have several engine blocks / crankshafts but only one decent gearbox, HC585. I have a gearbox from a 2000 Saloon MK II in unknown ukondition, but that will definitely not fit this MB engine unless I can switch gearbox shafts between those gearboxes to make either one of them fit (?). Unlikely I guess...

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I think I might have found the problem. A bit difficult to see on the pictures, but the HC crankshaft (blue block) seems to be shorter than the MB version. Bugger! This was my last chance to get my Vitesse on the road in 2021 😣😢

 

 

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Let me know if you find the reason. My Mk1 GT6 had a saloon engine when purchased, retaining the saloon flywheel plus a non-O/D GT6 Mk1 gearbox, and when I tried to fit an overdrive gearbox it wouldn't fit - same gap as in the photo Roger has posted. The friend who was helping me insisted that tightening the bellhousing bolts would pull it into place, with the result that on startup the engine ate the thrust washers then seized completely. On inspecting both gearboxes I found that someone had done a little bit of surgery on the original input shaft to close the gap.

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I purchased a completely refurbished GT6 engine from a supplier but on fitting, same problem, even with the GT6 flywheel. I ended up removing the replacement gearbox shaft and reusing the old one (which has lasted twenty years so far!) and it fitted first time. The replacement gearbox shaft will not fit at all, despite numerous attempts with varying sizes of bronze bush etc. This is the replacement shaft, about half an inch longer...

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So: if you find out why I'll be interested!

 

 

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10 minutes ago, Colin Lindsay said:

On inspecting both gearboxes I found that someone had done a little bit of surgery on the original input shaft to close the gap.

I fully understand the PO's efforts. At this point I'm desperate and I would use any bodge you can recommend no matter how drastic as long as I get my Vitesse back on the road in 2021 using the bits I have...

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10 minutes ago, johny said:

Trouble is, with the long crank isnt the clutch also out of its correct place so altering its thrust bearing and operating arm position?

Petes talking about shortening the gearbox input shaft spigot as was done in Colins case...

Dont forget the flywheel position as well - will the starter still work correctly with the ring teeth being 15mm further back?

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7 minutes ago, johny said:

Dont forget the flywheel position as well - will the starter still work correctly with the ring teeth being 15mm further back?

Thanks, I think my only option now is to either find an MB gearbox or use my Mk II PI engine with the above mentioned MK II Saloon gearbox. But the MB engine I have is in really good condition so finding a new gearbox is definitely my first option. I thought I finally had the parts needed to get my car back on the road. Will it never end... 😞

Edited by Roger
Corrected link to earlier PI post
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Surely if the only difference is the length of the spigot shaft? Shortening it is the way forward. The one in Colin's photo is a bit "rough" to say the least but i bet it worked..... How long for i don't know, but will it be a daily driver and you have lots of hurdles to jump to get it perfect.

Tony.

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44 minutes ago, Roger said:

"stem wheel" spigot?

sorry from my past the input shaft was always known as a stem wheel    all down  to terminology 

the clutch position could be assisted by using a frequenlty supplied throwout of 15mm thick not as orig at 19mm thick  but thats only 4mm in the right direction   fitting a saloon gearbox needs   some of chassis chopping to make it fit 

any other realignment of the throwout  would be a cut down spherical post 

the starter is also a challenge   you dont want a saloon flywheel  weighs a ton 

Pete

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10 minutes ago, poppyman said:

Shortening it is the way forward

It might be! But I'm confused since the gearbox fits perfect with no gap to the back plate if I remove both flywheel and clutch and attach only the gearbox to the engine. But when I put the flywheel back then I get that 10 mm gap again. Hence, it must be something with the gearbox / flywheel interfering and not the length of the input shaft??

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33 minutes ago, Pete Lewis said:

it will be the clutch splines hitting the flywheel / bearing bush as said they would need a careful look and grinding some off .

Pete

I see what you mean Pete difficult without actually being there, a bit a careful measuring should tell if it will work or not, or simply blob paint on each end of the splines will tell you if it is the splines. 

Tony.  

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Thanks a lot for all your feedback! This is a complex matter so I think I will have to measure all the parts I have and sit down with pen and paper and do some calculations. Paint on splines was a good tip, will try. I guess the best solution would be to find a later KC-gearbox from a GT6 Mk I or a later Vitesse HC-gearbox (made after HC4500). One of those should hopefully fit without any modifications. An MB-gearbox from a Mk I Saloon could also work, but then I would probably have to cut away parts from the chassie (?). If shortening the shaft (in a lathe) would solve my problems then it is definitely an option. But there are many parameters and dimensions to consider and I want to be 100% sure it works before I take the shaft to a machine shop. Measure twice, cut once...

I know there are quite a few Vitesses on the road with both engine and gearbox from a Saloon and that it requires some modification of the chassie to make the gearbox fit (I have the parts, so also an option). I have searched here on the forum and some describe that chassie modification as "major modifications" and others make it seem quite simple. Might be a subject for a new topic, I appreciate if someone have pictures of such a modification.

Thanks! /Roger

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2 hours ago, Colin Lindsay said:

I purchased a completely refurbished GT6 engine from a supplier but on fitting, same problem, even with the GT6 flywheel. I ended up removing the replacement gearbox shaft and reusing the old one (which has lasted twenty years so far!) and it fitted first time. The replacement gearbox shaft will not fit at all, despite numerous attempts with varying sizes of bronze bush etc. This is the replacement shaft, about half an inch longer...

Sorry Colin, daft question: I have been reading your post again and I try to figure out exactly what combination that has lasted 20+ years for you. Did you use an early gearbox "made before HC4500" + large crankshaft (after HC4500) engine + shortened input shaft? Any engine / gearbox numbers you could share from that successful combination? Thanks in advance.

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Lets recap:

The bigger gearbox will fit your engine no problem and can be fitted to your Vitesse. The fitting will be much easier if its a non OD box however the ratios of any saloon/TR6/Dolomite Sprint unit are different so 1st gear will be pretty useless without changing the diff (the 3.27 ratio would be good but is difficult to find).

All GT6/Vitesse gearboxes have the same dimension input shafts so none will work with your engine without modification. Interestingly the Spitfire/Herald shaft is very similar but shorter however this would need further careful investigation.

It sounds from Colins experience that the Vitesse gearbox shaft could be modified to fit. Certainly as Pete says I think the clutch will work and the starter also (possibly by leaving out the spacer its fitted with?) however looking at the drawing in the workshop manual both the clutch and flywheel will end up very close to the inside of the bell housing....

Of course the neatest solution would be a thicker backplate but thats not practical if it needs to be an additional 15mm😵

  

 

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The GT6 gearbox was an original GT6 MK1 gearbox from 1968; the reconditioned engine and block is an HC block originally, so Vitesse 2.0 litre. The gearbox shaft had already been crudely trimmed for the saloon (MB) engine that was fitted, and it used the saloon flywheel. We could not get the bellhousing to mate with the block at all and when tightened up it simply pushed the crank forward so far that it ate the washers and seized the engine. Once the gearbox was removed a whack on the crank pulley with a block of wood freed it up again. If I remember correctly the input shaft from the replacement overdrive gearbox, which was a Dolomite 1850, also would not fit so my mate took a spare shaft and we had it turned down on a lathe (don't ask what that did to the original hardening etc!) but the shortened shaft fitted first time and has been in use ever since. I tried quite a few different bronze spigot bushes, still have a selection of them in the drawer and nothing worked.

By the time I fitted a proper GT6 flywheel, two, maybe three years later, I was still using the same input shaft so I've no idea if the longer one would have made any difference with the replacement flywheel. Every year I expect the tip to start complaining and was actually looking for a replacement quite recently, but it's given no bother that I'm aware of despite the butchering it got.

 

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