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1966 MGB roadster project

Posted: Mon Feb 17, 2020 7:07 pm
by John1956
A moment of madness resulted in me buying a 66 roadster which has been restored to the point where the engine and gearbox need putting in. I was told everything was ready or in the multitude of boxes. The crossmember assembly is there as is the engine mounting bracket which has been put together but no sign of the stay rod or bracket. A few questions where is the best place to find out how all these brackets come together. The stay rod appears to be not required in some models. I am confused by the various articles i have read in the manuals and on the internet.As you can probably guess this is all fairly new to me.Help!

Re: 1966 MGB roadster project

Posted: Mon Feb 17, 2020 10:54 pm
by Vic Butler
John, I've had a look in my genuine BMC parts list and there are 2 different cross members. One with the stay rod is for all GHN3/GHD3 chassis numbers to 138400. The one without the stay rod is for GHN4/GHD4 138401 onwards.As yours is 1966 it'll be GHN3 and will have the crossmember fitted for the stay rod. There are numerous brackets, spacers etc for the stay rod. The rod itself has a thread cut part way along its shank and a bracket with one hole larger than the other welded on the other end. You can see the set up on the parts list.
If you can't get the list I may be able to photocopy the relevant pages.

Re: 1966 MGB roadster project

Posted: Tue Feb 18, 2020 11:10 am
by Paul Hollingworth
The tie rod and all the brackets are shown in the Moss catalogue on the engine mountings page. Their exploded diagrams are invaluable if you are confronted with a box of bits. My B being a GHN5 doesn't have the tie rod. Is it really necessary ?

Re: 1966 MGB roadster project

Posted: Tue Feb 18, 2020 12:51 pm
by Vic Butler
With the introduction of the all synchro box on GHN/D4 cars, the rear cross member was changed to accommodate the different gearbox and the tie rod deemed unnecessary. I don't know what leaving it off on earlier cars would cause. There must have been a reason for it.

Re: 1966 MGB roadster project

Posted: Tue Feb 18, 2020 4:58 pm
by John1956
Thanks to all of you for your comments. I will look at the moss catalogue.as mentioned being a 66 mine is a HN3. So i must need the stay rod. I am going to have another look through the boxes to see if i have missed anything.

Re: 1966 MGB roadster project

Posted: Thu Feb 20, 2020 1:59 pm
by Peter Cresswell
Paul Hollingworth wrote:
> The tie rod and all the brackets are shown in the Moss catalogue on the
> engine mountings page. Their exploded diagrams are invaluable if you are
> confronted with a box of bits. My B being a GHN5 doesn't have the tie rod.
> Is it really necessary ?

Paul and John
The purpose of the tie rod is to restrict the forward movement of the engine/gearbox under heavy breaking or in an accident. If the engine and gearbox are only restrained by the rubber mounting blocks, it can move sufficiently forwards to put the fan through the radiator. There are two parts to the restraint system - the tie rod from the gearbox to the gearbox crossmember, and the restraint plate that is fitted to the left hand (nearside/carb side ) side engine mounting. This however doesn't explain why the tie rod arrangement was fitted to the 'rubber' bumper cars which used an electric fan and the radiator was moved some way forwards. The second reason for the restraint system is to stop the crankshaft front pulley from hitting the steering rack.
As you say, Paul, there are several different arrangements , which can be clearly seen in the Moss catalogue here:
https://www.moss-europe.co.uk/shop-by-m ... 62-80.html
There is a mistake (?) in this diagram. The first crossmember arrangement shown in the picture is titled 'Type 2 1965 - 67, 3 Synchro GT' , should read (I think) 'Type 1 1962 - 67, 3 Synchro Roadster'. This is what the labelling reads in the paper book catalogue.

So the Type 1 used a tie rod, the front of which mounted onto a boss cast onto the bottom of the remote control housing attached to the back of the gearbox. This is the type that John should have unless the gearbox crossmember has been changed to the 3 Synchro GT type at sometime in the cars life. The GT used the type 2 arrangement, which is similar to the Type 3 used on 1967 - 74 4 Synchro Roadsters and GT with one very important difference. The Type 3 has two holes for the rubber mounting blocks to attach to the crossmember. On the Type 2 and Type 3 the forward movement is controlled by the vertical pin (instead of the tie rod) and it is essential that the rubber mounting for the pin are in good condition. These are very difficult to replace as they are much bigger than the hole they have to go into!
Type 4 was used on all Rubber Bumper Roadsters and GTs and the tie rod is needed because there was no additional restraint on the engine mounting which changed to a large circular type from the rectangular type previously fitted.

There are many permutations for fitting the various parts of the crossmember together. The Type 1 and Type 2 have 16 combinations, but the Type 3 with the 2 mounting holes for the mounting rubbers increased this to 32 combinations. You can't work out which is correct with the engine and gearbox out of the car. You have to fiddle with it underneath the car as you fit the gearbox and engine together. This is why it is recommended that the various parts of the of the crossmember are marked so you know which way they fitted before removing the crossmember from the gearbox to remove the engine and gearbox together from the car. It is worth John noting that the gearbox crossmember is too wide to pass between the chassis rails so it has to be removed (and dismantled) before the engine/gearbox can be taken out of the car, and conversely has to be reassemble and fitted after the engine is sitting on the front engine mounts. I know all this because I failed to mark the relative positions of the crossmember components when I took my engine and gearbox out. I then had to spend 5 hours on my back underneath the car trying to get the crossmember refitted.

There is a mod you can do to the crossmember which makes refitting easier and that is detailed here:
https://www.mgexp.com/article/crossmemb ... ation.html
This well worth doing as it saves a quite a bit of time, effort and exasperation! I did the mod and it still took 5 hours to work out how the crossmember went back together!!!!!!!!!!!!

Refitting the gearbox crossmember is one of the most frustrating jobs you have on an MGB. Why they didn't adopt the gearbox crossmember system used on the MGC is beyond me as this bolts to the floor of the car either side of the transmission tunnel and so is much narrower and doesn't need to be taken apart to take the engine and gearbox out.

Re: 1966 MGB roadster project

Posted: Thu Feb 20, 2020 5:18 pm
by Paul Hollingworth
Couldn't John go to the mounting set up that's on my GHN5 car with no tie rod. Is the gearbox mount or cross member different on the 3 synchro car from mine.

Re: 1966 MGB roadster project

Posted: Thu Feb 20, 2020 9:17 pm
by Peter Cresswell
Paul and John
I don't know why MG used a different mounting arrangement for the 3 Synchro GT over the 3 Synchro Roadster, but I would think they discovered a harshness in the more rigid GT bodyshell created by the rigid fixing of the tie rod at the gearbox end and decided to eliminate it. I make this assumption from the different audience brochures the GT was aimed at, over the Roadster.
(Please read the rest in conjunction with my post above).

Having said that I don't think there was any difference between the Roadster gearbox castings and the GT castings, so this leads me to think the Type 1 and Type 2 crossmember assemblies are interchangable as complete units. The crossmember itself has the same Part No. (AHH6134) but the mounting blocks have a different part No (GEX7453 for the Type 1 and GEX7422 for the Type 2), which is why I suggest if the GT crossmember is fitted to the Roadster then the whole assembly should be used. However the Moss catalogue also specifies that the Mounting GEX7453 is a replacement for GEX7422 so maybe a crossmember can be made up from parts from both the Type 1 and Type 2 crossmembers. You would have to try it and see!

The Crossmember for the 4 Synchro cars has a different part number AHH8430 because of the 2 holes for the mounting blocks on each side I suspect. This is also listed in the Moss catalogue as being a replacement for AHH7422, so should fit a 3 Synchro Roadster or GT. However I don't see any advantage to this as it just adds the complication of doubling the number of combinations that the various parts can be assembled together.
However if John finds he has a dismantled crossmember in the boxes of parts he has, it would save a lot of time if he sourced another complete assembled crossmember that is a Type 2 or Type 3 (in the pictures from the Moss Catalogue). Remember though that the crossmember has to be dismantled to remove the engine and gearbox from the car as a unit. If it happened to be a Type 3 and he had parts in the boxes from his original then he should be able to overcome any issues he came across - albeit this would be time consuming in itself.

Re: 1966 MGB roadster project

Posted: Tue Feb 25, 2020 4:15 pm
by John1956
Peter
Thanks for your moet comprehensive comments .I was also confused by the typo error. It would appear that my boxes just contain the cross member and the brackets in fig 2 .So the previous owner of the project has bought the brackets assuming it was ok to use the GT brackets on the roadster. I just need to get my head around your other comments. Once again thanks.John

Re: 1966 MGB roadster project

Posted: Tue Feb 25, 2020 4:49 pm
by Peter Cresswell
Hi John
Should you need more info please let us know on here. I'm sure between us we can help you to sort out any problems you encounter.
In the meantime you might find the following Youtube videos useful:
https://www.youtube.com/watch?v=gUJE0AkWh1E
https://www.youtube.com/watch?v=izuDRlaxf5Y
https://www.youtube.com/watch?v=ATJRTtRRKl8
Good luck!
Pete