1974 MGB GT V8 - the homework continues...

[Deleted]

So a brief hijack of Sam's 'V8 B' thread - why do I need MGB overdrive gearboxes when I don't own a B ? - well I don't need the boxes either but I do need the overdrives - you see I have a few of these to restore / rebuild over the next few years (I think I am up to 4 number currently)



Jowett Jupiter - they are great cars but the little 1500cc boxer engine starts to scream at 65 MPH - the solution is to fit a overdrive and it makes for much better cruising speeds



This is the Jowett gearbox



This is a overdrive conversion being tested on a lathe bed - the red sections to the rear of the box being the overdrive adaptor housing (owner / engineer fabricated and not a off the shelf part) and the overdrive these take up the same length in space has the removed tailshaft from the original Jowett box - hence there is no requirement to modify the propshaft and the car can be returned to original specification if required by simply bolting a standard Jowett gearbox back in

It just so happens that the Laycock GKN LH overdrive (has fitted to the MGB) is the most easily sourced overdrive unit available - its also the strongest whilst also being the cheapest to rebuild when compared to other units in the market



What I need is a very talented & inventive engineer whom operates on a not a problem & can do basis (Enter 'Sir' @johnnybravo) to machine the main output shaft on the Jowett box



And manufacture the overdrive adaptor housing for me - once fitted & tested in the forthcoming builds I then hope to offer the overdrive conversion has a turnkey package for Jowett Jupiter & Javelin owners

With apologies to Sam for the thread hijack - I shall cover the conversions when they happen in my Jowett threads

[Deleted]

You can drop the “sir” part as soon as you like 😂😂
Looks like an interesting project and should make the cars more driveable. Also will be long term beneficial in that even if you don’t want to cruise at 80mph, the engine isn’t going to be revving it’s nuts off all the time.

I see Samta22 found the other gearbox and overdrive unit 😊

Weren’t there two different versions of these over drives? The one with the very shiny aluminium casing and the less than desirable one that had a more Matt finish and a slight casting mark and two dimples from the ejector pins in the diecasting tool? Think Sam would need to clean the second one,just to make sure it’s the right one.....🤔😉

[samta22]

You beat me to it...

Seeing as you won't do sir, as 'Lord' or perhaps 'Baron' Bravo has mentioned 😂😂, the second gearbox was duly found (I knew where it was honest!) and is being cleaned up as I type (not slave labour, she offered your honour...). It's a bit more... errr, 'protected' than the first but should clean up nicely.



I did manage to remove the support bracket and gave the overdrive ID tag a wipe to confirm which type it is


So that's two of the LH types for you Chris, hopefully they will fit the bill. Oh and feel free to thread hijack away, all interesting stuff and is amazing what B parts end up in, Cobra kit cars are another popular home that many don't realise.

In other news, as I'd not been to the workshop for some considerable time (I know, I know all rather shameful  ), it appears that the spiders have moved in and are seeking to reclaim the Celica parts



I'm hoping to rectify that situation next weekend if I'm allowed and the back passes inspection - it's been rather too long. On reflection I think I was suffering from spending too much time on it ahead of the NEC show so the break has definitely been good for perspective. Anyway more on that in the Celica thread soon. I might even treat myself to that new R-Tech welder I've been toying with to celebrate.

Back to MG, and the reason I went ferreting in the workshop was to pull this out



Primarily to have a look at the ID tag, as although I know it's a 3.9, I can then find out exactly what version, how old etc. ready for some parts ordering


Plenty of work to be done, but on the whole it's not in bad shape and still turns nice and freely. It's been added to the clean up list and will then decide how best to proceed. petervdv 's rover thread may prove rather helpful however... that is if I can get it somewhere where it can be worked on in clean surroundings... say for example where there currently appears to be a collection of saddles...

The same is true for the rear axle, as although I've rebuilt it previously, in order for it to work best with the V8 I need to fit a different CROWN wheel and pinion... which in turn also means that the carrier needs to be machined. However details on exactly what is needed is proving tricky to find so more research required on that one. It seems that although this is a commonly swap, seemingly the permutations are plentiful and everyone does things slightly differently. 

Lastly, another piece of the puzzle required for testing some of my planned 'tweaks' turned up on Friday night, however that can stay wrapped for now as will have to wait until it meets the shell to see what, if anything, is required for it to be fitted.


As the gearbox plea worked so well... anyone need/want any of this lot before I move it to my parts store and start to sell off? the M.I.L is loving me right now 😂😂

[petervdv]

It is a 3.9 from a RR- Discovery auto EFI 1988 onwards as you can see at www.v8register.net/FilesV8/V8%20engine%20number%20reference%20R7%2030.11.07.pdf

[scimjim]

Nice conversion - the Scimitar SE5 and early SE5a also use the LH overdrive. They moved to the J type after that.

[swissjav]

Aug 5, 2019 5:02:37 GMT @grumpynorthener said:

So a brief hijack of Sam's 'V8 B' thread - why do I need MGB overdrive gearboxes when I don't own a B ? - well I don't need the boxes either but I do need the overdrives - you see I have a few of these to restore / rebuild over the next few years (I think I am up to 4 number currently)



Jowett Jupiter - they are great cars but the little 1500cc boxer engine starts to scream at 65 MPH - the solution is to fit a overdrive and it makes for much better cruising speeds



This is the Jowett gearbox



This is a overdrive conversion being tested on a lathe bed - the red sections to the rear of the box being the overdrive adaptor housing (owner / engineer fabricated and not a off the shelf part) and the overdrive these take up the same length in space has the removed tailshaft from the original Jowett box - hence there is no requirement to modify the propshaft and the car can be returned to original specification if required by simply bolting a standard Jowett gearbox back in

It just so happens that the Laycock GKN LH overdrive (has fitted to the MGB) is the most easily sourced overdrive unit available - its also the strongest whilst also being the cheapest to rebuild when compared to other units in the market



What I need is a very talented & inventive engineer whom operates on a not a problem & can do basis (Enter 'Sir' @johnnybravo ) to machine the main output shaft on the Jowett box



And manufacture the overdrive adaptor housing for me - once fitted & tested in the forthcoming builds I then hope to offer the overdrive conversion has a turnkey package for Jowett Jupiter & Javelin owners

With apologies to Sam for the thread hijack - I shall cover the conversions when they happen in my Jowett threads

[Deleted]

Aug 5, 2019 11:32:20 GMT swissjav said:

Aug 5, 2019 5:02:37 GMT @grumpynorthener said:

So a brief hijack of Sam's 'V8 B' thread - why do I need MGB overdrive gearboxes when I don't own a B ? - well I don't need the boxes either but I do need the overdrives - you see I have a few of these to restore / rebuild over the next few years (I think I am up to 4 number currently)



Jowett Jupiter - they are great cars but the little 1500cc boxer engine starts to scream at 65 MPH - the solution is to fit a overdrive and it makes for much better cruising speeds



This is the Jowett gearbox



This is a overdrive conversion being tested on a lathe bed - the red sections to the rear of the box being the overdrive adaptor housing (owner / engineer fabricated and not a off the shelf part) and the overdrive these take up the same length in space has the removed tailshaft from the original Jowett box - hence there is no requirement to modify the propshaft and the car can be returned to original specification if required by simply bolting a standard Jowett gearbox back in

It just so happens that the Laycock GKN LH overdrive (has fitted to the MGB) is the most easily sourced overdrive unit available - its also the strongest whilst also being the cheapest to rebuild when compared to other units in the market



What I need is a very talented & inventive engineer whom operates on a not a problem & can do basis (Enter 'Sir' @johnnybravo ) to machine the main output shaft on the Jowett box



And manufacture the overdrive adaptor housing for me - once fitted & tested in the forthcoming builds I then hope to offer the overdrive conversion has a turnkey package for Jowett Jupiter & Javelin owners

With apologies to Sam for the thread hijack - I shall cover the conversions when they happen in my Jowett threads

So this is a fellow Jowett owners way of indicating to me that he wants to be first on the list for the said overdrive conversion by quoting the overdrive topic



Which he would like fitted to his Javelin - looks like myself & JB are going to be busy for some time to come

[Darkspeed]

It looks like the RV8 has 10 bolt heads - If its a 3.9 doe is have the cross bolt bosses along the bottom of the block above the sump line. If it does - spin it over and whip the sump off and see if it have the cross bolt main caps. as its going in a B it would good to have a lightweight flywheel on the parts wish list.

What front cover does it have?

[samta22]

Aug 5, 2019 16:36:42 GMT Darkspeed said:

It looks like the RV8 has 10 bolt heads - If its a 3.9 doe is have the cross bolt bosses along the bottom of the block above the sump line. If it does - spin it over and whip the sump off and see if it have the cross bolt main caps. as its going in a B it would good to have a lightweight flywheel on the parts wish list.

What front cover does it have?

Not sure is the answer, will clean it up and have a closer look next time I'm over at the workshop.

[Phil H]

Aug 5, 2019 11:31:55 GMT scimjim said:

Nice conversion - the Scimitar SE5 and early SE5a also use the LH overdrive. They moved to the J type after that.

I was about to pick up on this, Chris (apologies), but when you mentioned the LH is the strongest out there, is that relative to all the Laycock variants (A/D/J)? Curious as we are intending to give one a very hard time...

Sorry for the intrusion, Sam - there’s Scimitar content here..😉

[glenanderson]

Overdrives are nice bits of kit. I had a factory fit one on my Rover P4, which had a very interesting set of inhibitor and actuation switches and relays which prevented you from engaging it under hard acceleration, or disengaging it on a closed throttle, which made it very smooth in use. It also allowed you to “kick down” out of overdrive by flooring the throttle and to drop back in when you eased off. It made motorway overtaking very easy. Most setups use some kind of interlock to only allow engagement in top, or third and top, but I understand the most important thing is to make it impossible to engage in reverse (usually with a simple cutout relay linked to the reversing light switch), because the oil pump doesn’t work when the unit is working backwards.

[peteh1969]

I had one in a Septre turns a lowly 4 speed into a 6 speed weapon and helps spread the load especially with a tuned Hollbay 1725 engine.

[Deleted]

Aug 5, 2019 20:44:57 GMT Phil H said:

Aug 5, 2019 11:31:55 GMT scimjim said:

Nice conversion - the Scimitar SE5 and early SE5a also use the LH overdrive. They moved to the J type after that.

I was about to pick up on this, Chris (apologies), but when you mentioned the LH is the strongest out there, is that relative to all the Laycock variants (A/D/J)? Curious as we are intending to give one a very hard time...

Sorry for the intrusion, Sam - there’s Scimitar content here..😉

Phil - There are quite a few Jupiter owners that have undertaken the overdrive conversion on their cars using various OD units (it was never an original option on the cars) in order lower engine speeds and increase cursing speeds - although only 1500cc the Jowett engine carries a lot of torque at the flywheel with it being a boxer engine - some overdrives have failed prematurely whilst the LH has stood up to no end work being transmitted through it - so certainly in the case of the Jowett's we have found them to be most durable unit - I have a fellow Jowett owner with one on his Jupiter race car and that gets the very thick end of a hard time without it giving issues - Chris


PS Given the interest maybe we ought to have a 'Overdrive' thread in the tech section of the forum

[npp]

and, to go even further off topic, Laycock overdrives were built just a few hundred meters from where I now live

[legend]

mate of mine worked at Laycock many many years ago and did a lot of testing of experimental viscous couplings for the Ferguson formula Capris

[Phil H]

Aug 6, 2019 8:41:47 GMT @grumpynorthener said:

Aug 5, 2019 20:44:57 GMT Phil H said:

I was about to pick up on this, Chris (apologies), but when you mentioned the LH is the strongest out there, is that relative to all the Laycock variants (A/D/J)? Curious as we are intending to give one a very hard time...

Sorry for the intrusion, Sam - there’s Scimitar content here..😉

Phil - There are quite a few Jupiter owners that have undertaken the overdrive conversion on their cars using various OD units (it was never an original option on the cars) in order lower engine speeds and increase cursing speeds - although only 1500cc the Jowett engine carries a lot of torque at the flywheel with it being a boxer engine - some overdrives have failed prematurely whilst the LH has stood up to no end work being transmitted through it - so certainly in the case of the Jowett's we have found them to be most durable unit - I have a fellow Jowett owner with one on his Jupiter race car and that gets the very thick end of a hard time without it giving issues - Chris


PS Given the interest maybe we ought to have a 'Overdrive' thread in the tech section of the forum

Probably right with a new section - I’ll post there to save clogging up Sam’s thread..

[samta22]

I was quite enjoying the discussion to be honest... not sure one of my threads has ever been so busy! 😂😂

and Phil as you said there was Scimitar content, so there is a tenuous family link... although not one that anyone else would get asides Jim!

Looking forward to hearing what you chaps are up to...

[Phil H]

Blame Ian..and several pints of Cisk..

[peteh1969]

Phil H has started a new thread in the Technical section.

Nice

[samta22]

Aug 5, 2019 10:38:10 GMT petervdv said:

It is a 3.9 from a RR- Discovery auto EFI 1988 onwards as you can see at www.v8register.net/FilesV8/V8%20engine%20number%20reference%20R7%2030.11.07.pdf

Peter,

Thanks for the pointer, some useful information on there.

I've been doing some reading up on the benefits of the 3.3:1 ratio for the rear axle versus the usual approach of 3.07:1, which did you choose when doing your conversion? am I right in thinking you went to Heathrow transmissions to get the work done?