GT6 Mk3 Chassis front cross member

[Alex Lowe]

Hi All

Im about to start the replacement of my front cross member and bonnet hinge boxes, is there any advice on how to align everything back to how it should be.

Thanks in advance guys 

[Paulfc]

Hi Alex,

I’ll send you a private message with details of a process I successfully used to rebuild the front end.

Paul

[Graham C]

When I replaced my front chassis member I used the diagram in the works manual for the correct measurements.

Graham

[Blakes73]

On 20/02/2020 at 19:42, Paulfc said:

Hi Alex,

I’ll send you a private message with details of a process I successfully used to rebuild the front end.

Paul

Hi Paul, I appreciate that this was some time ago but if you wouldn't mind I could do with some pointers on this subject. I need to replace the bonnet hinge boxes on my MK3, the previous owner has replaced them and had the chassis powder coated but clearly hadn't checked the bonnet fit (I purchased the car with a new heritage bonnet not fitted, I'm starting to understand why now). The bonnet boxes are new but looking at the fit and some dimensions I found, they're about 35mm low. Any information you could provide would be gretly appreciated.

Regards~

[Paulfc]

Hi,

Happy to help but can’t immediately get to the car. Any chance you can send me a couple of images? When you say too low - measured from where?

Paul

[Blakes73]

On 27/04/2023 at 17:42, Paulfc said:

Hi,

Happy to help but can’t immediately get to the car. Any chance you can send me a couple of images? When you say too low - measured from where?

Paul

Hi Paul, sorry I didn't get straight back to you, I been busy with work. I've found a tech drawing of a late spitfire that has the bonnet hinge boxes so I'm assuming this will be the same as the GT6 Mk3. I've taken a measurement from the underside of the front crossmember to the top of the bonnet box. This measures 145mm, looking at the chassis drawing this should be 185mm if the drawing is relevant. I've attached images, hopefully you'll see what I mean. I've currently got the bonnet propped at the front and the gaps at the scuttle and sills are somewhere close so I'm thinking it must be the bonnet boxes? The bonnet arms currently sit way too high and too far back towards the engine.

[Blakes73]

Apologies, I meant to attach the tech drawing of the Spitfire chassis. Its measurement No. 46 on the drawing that has me confused.  

[Paulfc]

Hi,

I’ll take a look as soon as I can at my car and take some measurements, tomorrow hopefully. The chassis diagram you say is a Spitfire and certainly is significantly different to GT6 dimensions in the WSM. Not meaning to be pretentious, but are you sure the boxes are mounted to the cross member correctly? Also, are they GT6 III boxes?

[Blakes73]

1 hour ago, Paulfc said:

Hi,

I’ll take a look as soon as I can at my car and take some measurements, tomorrow hopefully. The chassis diagram you say is a Spitfire and certainly is significantly different to GT6 dimensions in the WSM. Not meaning to be pretentious, but are you sure the boxes are mounted to the cross member correctly? Also, are they GT6 III boxes?

Hi Paul,

That's my quandary I'm not sure if they're the correct MK3 boxes or they've just been fitted badly. That's the only diagram I could find of a chasis with hinge boxes. All the others seem to be the more conventional hinge type 

[Paulfc]

Hi,

The attached are the correct dimensions for the GT6 MkIII. These are what I used to set my new cross member and position the hinge boxes. I still haven’t been able to get an hour in the garage but will try again tomorrow and get some dimensions and pics. Any issues with the attached let me know and I’ll resend.

Paul

 

 

[Blakes73]

Thanks so much for your help and your time.

Steve 

[Blakes73]

The bonnet hinge boxes on the crossmember look completely different from the ones on mine. A photo with dims as you suggest would be a great help when you get a moment.

Thanks again, Steve 

[Paulfc]

Steve,

I got out and have taken some pics. What I can’t see on your pics are the bracketry that connects to the inner wings and goes into the hinge boxes to provide the pivot points. It’s made up of parts 911108/7 and 911150 as shown on parts diagram.

Assuming your boxes are set equidistant from the centre of the cross member the distance between bolt centres is 690mm. The distance between the outside edges of the boxes is 760mm.

The gap tween the bottom from edge of the bonnet and the horizontal top of the box is 90mm,

The outer edges of the boxes extend out from the cross member 190mm.

Does any of this help? If not and you additional images/dimensions please let me know.

Paul

[KevinR]

23 hours ago, Paulfc said:

Hi,

The attached are the correct dimensions for the GT6 MkIII. These are what I used to set my new cross member and position the hinge boxes. I still haven’t been able to get an hour in the garage but will try again tomorrow and get some dimensions and pics. Any issues with the attached let me know and I’ll resend.

Paul

 

 

I believe that the attached diagram is NOT for the MK3 GT6.  
The bonnet hinge box dimensions for the MK3 GT6 is identical to the MKIV and 1500 spitfire.

[Paulfc]

Ouch!!

Hi Kevin,
The diagram is from the WSM (purchased from the Club many years ago) page 5.104. Page 5.106 details the differences with Mk I and II. These were certainly the dimensions used by myself as I have no other reference. As you can see from the images it all goes together as it should. Clearly dimension 2 is incorrect while 3 is correct.

Steve,

My sincere apologies for apparently misleading you! Should you want to continue I’m happy to supply dimensions from my car but I’m the first to admit there are many more experienced than I on here who, I’m sure, will happily guide you.

Paul

[KevinR]

14 minutes ago, Paulfc said:

Ouch!!

Hi Kevin,
The diagram is from the WSM (purchased from the Club many years ago) page 5.104. Page 5.106 details the differences with Mk I and II. These were certainly the dimensions used by myself as I have no other reference. As you can see from the images it all goes together as it should. Clearly dimension 2 is incorrect while 3 is correct.

Paul,

the problem with the GT6 diagrams is that they are prepared for the MK1 and Mk2, with some vague details about the MK3, which can easily mislead.  I completely agree that dimension 3 is correct.  My comment concerns the pictorial representation that is not correct for the MK3- even if many of the dimensions are correct.

 When working on the front end of a MK3 GT6 chassis, I always work from the Spitfire mkiv /1500 chassis diagram (except radiator mounts) as it is pictorially correct.

it would be nice if someone could draw up a pictorially correct MK3 GT6 chassis as a complete item.

[Paulfc]

Kevin,

Thanks for clarifying. It just goes to show, you never stop learning.

Paul

[Blakes73]

Paul and Kevin, thanks so much for your input and thanks once again Paul, for taking the time to take the photographs and put together the detailed responses.

I've come to the conclusion that someone has mounted the bonnet hinge boxes incorrectly onto the chassis cross member. I'm going to remove the boxes and tidy up the cross member. Once that's done (noting the lateral spacing measurements) I'll sit the bonnet (new heritage bonnet with 911150, 911107 & 08 attached) and line the scuttle, sills and door gaps up and then prop the bonnet in place. I'll then attach (probably new) bolt boxes to the bonnet vis 911107 7 08 and tack in place, I'll also make sure the lower valances, lower panel and bumper all line up too. 

All sounds simple in theory, the practice may be another matter.

 

Regards~

Steve

[Blakes73]

I still wouldn't mind a measurement level off the underside of the crossmember to the horizontal section of the pivot box. If you have a look at my photo above you'll see mine measures 145mm and the chasis diagram I posted  shows 184 to 187mm, it would be nice with a reference of an actual vehicle.

 Regards~ 

Steve 

[KevinR]

17 hours ago, Blakes73 said:

I still wouldn't mind a measurement level off the underside of the crossmember to the horizontal section of the pivot box. If you have a look at my photo above you'll see mine measures 145mm and the chasis diagram I posted  shows 184 to 187mm, it would be nice with a reference of an actual vehicle.

I assume you are referring to the measurements shown for dimension 46 on the Spitfire drawing several posts above.

I'm not convinced that the reference line "YY" is the bottom of the front cross member.

On the segment of chassis I've just measured, the distance from the bottom of the cross member to the horizontal section of the pivot box is about 158mm

The bit of chassis is original.

[Blakes73]

Thanks for taking the time to do this. It's interesting to see the difference in apertures in terms of both shape and elongation. There must have been a few variants, either that or variants of aftermarket parts.

Regards ~

Steve 

[Paulfc]

Steve,

I measured mine and it’s ~ 184mm. I then dug out from deepest recesses of my garage the original box that’s still attached to a section of original cross member and it’s the same - see image.

You may like to try this technique to align the boxes on the cross member. I was taught this by a a guy who has restored many small chassis Triumphs and is still doing so. If you’re familiar with it my apologies.

Get a piece of straight timber no less than 18mm thick and about 140mm deep and about 900mm long. Mark the centre point of the length. From there mark either side at approx. 349mm, this being the centres for the bolts that the bonnet hinges on. Drill two holes in the timber for each box and bolt the boxes to the timber.  Test, measure and adjust until you’re happy the two boxes are aligned the same on the timber. You’ve then got them laterally positioned and can position them on the cross member both at the same time and adjust etc. Providing the cross member is straight and at the correct height you should be able to get them within the stated tolerances. Obviously you can clamp and tack weld them before removing the timber. 
 

Hope this helps and let’s know how you get on.

If this doesn’t make sense please let me know and I’ll try and clarify.

Paul

Edited May 7, 2023 by Paulfc

[Blakes73]

25 minutes ago, Paulfc said:

Steve,

I measured mine and it’s ~ 184mm. I then dug out from deepest recesses of my garage the original box that’s still attached to a section of original cross member and it’s the same - see image.

You may like to try this technique to align the boxes on the cross member. I was taught this by a a guy who has restored many small chassis Triumphs and is still doing so. If you’re familiar with it my apologies.

Get a piece of straight timber no less than 18mm thick and about 140mm deep and about 900mm long. Mark the centre point of the length. From there mark either side at approx. 349mm, this being the centres for the bolts that the bonnet hinges on. Drill two holes in the timber for each box and bolt the boxes to the timber.  Test, measure and adjust until you’re happy the two boxes are aligned the same on the timber. You’ve then got them laterally positioned and can position them on the cross member both at the same time and adjust etc. Providing the cross member is straight and at the correct height you should be able to get them within the stated tolerances. Obviously you can clamp and tack weld them before removing the timber. 
 

Hope this helps and let’s know how you get on.

If this doesn’t make sense please let me know and I’ll try and clarify.

Paul

Paul, That's a great idea reference lateral alignment. It's also good to know that your hinge boxes match the dimensions on the diagram I posted, it puts the issue to bed, I'm now confident that the aftermarket hinge boxes have just been poorly mounted (approximately 40mm too low). Shouldn't be too much of a problem with the jig you described keeping things right laterally and a bonnet laid in place for vertical reference. Thanks once again, I'll let you know how I get on.

Regards~

Steve 

[Blakes73]

Just a quick update. I went back to the previous owner who had a spare chasis. This was included in the original deal but I didn't have space on the car trailer. I brought the chassis home for reference and had a friend make me some hinge pivot boxes. Next steps is to offer up and fit this weekend.

I also bolted on the body, this fitted perfectly everywhere but the front out riggers. These have been replaced but clearly without properly measuring, they bite currently sat approximately 20mm too far forward. These are going to have to come off so I've purchased replacements from the club shop. So it's body off and engine out, body back on bolt up out riggers, tack in place, body back off and seam weld. These things are sent to try us !! 

[Paulfc]

Steve,

Glad you’re on your way to sorting it. Life’s never dull with a Triumph!
 

Paul