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Lengthening Herald Wheelbase


Adrian Girling
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With apologies to the purists I'm looking at using a Triumph Herald chassis and drivetrain as a donor for a replica of a 1936 BMW 328.  See https://en.wikipedia.org/wiki/BMW_328  I have a GRP body made by someone who restored an original car from wich he made a GRP buck.

By using the chassis, motor, drivetrain etc, I believe I can avoid the full IVA test.

Ideally, I need to extend the wheelbase from 2311 to 2400mm - i.e. 89mm.  My first question is whether it is possible to move the front suspension turrets forward by this amount - I understand they are bolted to the chassis and photos of the chassis suggest that tubes at the front run parallel so maybe extra holes and a little welding would allow?

Secondly, is there room to move the engine/gearbox backwards a bit without it meeting the "hourglass" shape of the chassis.  I'm going to have to cut into the front bulkhead anyway, but really don't want to cut the chassis.  I would need to do this if possible as the replica front wheels are set far forward with the nose of the car already sloping down from the centre of the front wheels whereas the Herald engine looks as if it sits roughly equally spaced either side of the front axle.  Every mm counts.

Ideally, someone with a Herald who lives near TW20 postcode would let me take a look and make measurements....

Most grateful for any thoughts/suggestions.

Adrian

 

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I can't see why you couldn't move the turrets forwards. But there are strengtheners inside the chassis rails, so be aware there may be more to it than just drilling and bolting. I had to repair my chassis aftr I got some cracks, and found 50x75 box section fits just inside the original rails, worth a thought. Remember that you need to keep teh steering geometry identical, do not vary it, even by a couple of mm forward or back in relation to the suspension position.

Yes, you can move the engne back. How much will depend on "stuff" like if you itend to use an overdrive gearbox, and if you are prepared to have the engine/box sit a bit higher. To give you an idea, 6 cylinder engines are sometmes moved back 6" in a spitfire chassis. 

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Thanks Clive, that is extremely helpful.  I did wonder about the Vitesse where the six cylinder has to fit in a chassis which is only 13mm longer wheelbase and it does look like a tight fit.  And the spitfire wheelbase is only 3mm shorter than the Herald.

And thanks for the reminder about the steering.  Presumably the steering rack needs to move forward by about the same amount - although not quite, if I'm to keep the correct ackerman angle - can't get my head around whether it moves more or less forward without a sketch...

Now I need a donor!  Good chassis, body and interior ideally a mess so I don't feel too guilty using it.

Cheers
Adrian

 

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20 hours ago, Adrian Girling said:

Now I need a donor!  Good chassis, body and interior ideally a mess so I don't feel too guilty using it.

Adrian,

Have you looked on eBay; there's a 13/60 "for spares/repair" at Swindon with the auction ending on Saturday 30th.  See eBay item no: 265658318214

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4 minutes ago, Adrian Girling said:

Hi Steve,
That would be great!  I'm a newbie - does this site allow exchange of email addresses or is there a private messaging system, so we don't share details with everyone?
Cheers
Adrian

Click on Steve's big green circle/S, that will take you to his profile and from there you can send him a message. All very civilised.

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On 25/04/2022 at 15:55, Adrian Girling said:

Thanks Pete, good spot!  I'll contact the seller and try to arrange a viewing 😀

Just to say, I went to see this Herald and it was better than I had expected - the owner is a professional welder and had done some really neat chassis and body restoration.  I'm now the proud owner of ARK 880H - "'Ark the Herald"

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26 minutes ago, Adrian Girling said:

Just to say, I went to see this Herald and it was better than I had expected - the owner is a professional welder and had done some really neat chassis and body restoration.  I'm now the proud owner of ARK 880H - "'Ark the Herald"

Well done, Adrian - Swindon must be a lucky place for eBay buyers!  I bought a ride-on mower there 4 years ago and it's still going well!!

Good luck with your project.

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Adrian,

Why so against lengthening the  chassis?  As said above,  the angles that the turrets must be set at are critical.     The chassis rails are two simple pressings, spot welded together.     Fabricating a sleeve to go inside a cut rail and extend it would be simple for someone like you!  I would suggest between the front outriggers and the turret mounts, which would give you more length behind the engine too.   Like this (red circles):

image.png.6cd5802ace8e0c1ae14d096390177b4c.png

Some pictures if only of an original BMW would be great!  Like this?

BMW 328 (16.06.2007).jpg

Good luck!  Please keep us informed!

John

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1 hour ago, Pete Arnold said:

Well done, Adrian - Swindon must be a lucky place for eBay buyers!  I bought a ride-on mower there 4 years ago and it's still going well!!

Good luck with your project.

Thanks Pete.  I'm enjoying the first rush of excitement, before the truth of the task ahead of me sinks in.  Probably a ride on mower would have been a more practical investtment...

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56 minutes ago, JohnD said:

Why so against lengthening the  chassis? 

Hi John, just a bit nervous of chopping the chassis about, once done, hard to go back, but your input encourages me.  Your picture is a good one, you can see how far forward the front wheels are, with the nose sloping down only just in front of the axle.

I'm picking up my herald next Wednesday, so will be able to do some serious planning, and Steve P who lives just round the corner from me is happy to show me his Herald which is great.

So far, only a couple of pictures of my bodyshell, actually sitting on a "locost" chassis but I favour the herald where the only serious work I need to do is lengthen the wheelbase.  The good pictures are what a real one looks like

Strictly, I should have 16" wheels and overall tyre diameter of 680mm which might be a big ask for the engine/drivetrain.  Reminds me to ask, were there different ratio diffs?  I expect I will need a spacer to lift the centre of the rear transverse spring as the weight on it will be significantly less, so changing the diff at the same time would make sense...

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Standard Herald, 4.11:1, others in same series, 3.81, 3.69 and I think a 3.4 (some guru will correct me!)

The problem with the big wheels is that Triumph suspension imposes quite large camber changes from bump to droop.   Those old BMW wheels will have worn crossplys that are tolerant of such change.  Modern radials are not.   You need to lower the rear spring, which is good as this puts the wheels at rest in some negative camber, so further to go to get into positive (bad).   Diff to spring spacers are available!

Camber change least with Rotaflex suspension - not used in any Herald, I'm afraid!  Only GT6/Vitesse.

John

 

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16 hours ago, JohnD said:

Standard Herald, 4.11:1, others in same series, 3.81, 3.69 and I think a 3.4 (some guru will correct me!)

You need to lower the rear spring, which is good as this puts the wheels at rest in some negative camber, so further to go to get into positive (bad).   Diff to spring spacers are available!

 

Many thanks for the info and tips John.  I had thought of looking for narrow 16" wheels and using crossply tires might be a good idea.  With the lower weight at the back the ride height would tend to be higher so I certainly need to install a diff to spring spacer anyway.  But I see your point, the bigger diameter will create a bigger "jacking" moment for the same cornering force.  I think classic car tires are available but expensive, and I've get to find a 16" wheel narrower than 6.5J.  I'm sure I read somewhere about an anti jacking solution using a rod connecting the the LH and RH lower rear wishbones?  And has anyone lowered the inside pivot point of those wishbones?  Apologies, so many questions...

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31 minutes ago, Adrian Girling said:

Many thanks for the info and tips John.  I had thought of looking for narrow 16" wheels and using crossply tires might be a good idea.  With the lower weight at the back the ride height would tend to be higher so I certainly need to install a diff to spring spacer anyway.  But I see your point, the bigger diameter will create a bigger "jacking" moment for the same cornering force.  I think classic car tires are available but expensive, and I've get to find a 16" wheel narrower than 6.5J.  I'm sure I read somewhere about an anti jacking solution using a rod connecting the the LH and RH lower rear wishbones?  And has anyone lowered the inside pivot point of those wishbones?  Apologies, so many questions...

You will want a softer spring, easy if you use the herald one as you can just remove a few leaves. 

You need to search "camber compensator" as the solution to "jacking"

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On 01/05/2022 at 00:17, JohnD said:

and I think a 3.4 (some guru will correct me!)

Not 3.4 but 3.27 on non-OD GT6s. Possibly also some automatic Dolomites? Although it's a different axle the diff nose and internals are very similar.

There was a 3.45 diff on the 2500 saloon but it's a very different unit.

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15 hours ago, Clive said:

You will want a softer spring, easy if you use the herald one as you can just remove a few leaves. 

You need to search "camber compensator" as the solution to "jacking"

Softer spring, remove leaves, genius!
I'm off to google to search....

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11 hours ago, Craig said:

or just use a later Spitfire swing spring?

I'm going to have to google that.  It did occur to me that the rear spring could be replaced with a frame to which one could attach upper wishbones at the correct angle and of the correct length.  I doubt anyone has done this (except perhaps for racing), but with my replica there will be lots of room behind the seats

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24 minutes ago, RobPearce said:

Not 3.4 but 3.27 on non-OD GT6s. Possibly also some automatic Dolomites? Although it's a different axle the diff nose and internals are very similar.

There was a 3.45 diff on the 2500 saloon but it's a very different unit.

Thanks.  4.11 to 3.27 is a big difference.  I've read that the herald classis tyre OD is 582mm and if I want to go to the full 680mm for my replica then 3.52 would be the exact number.  In this case, 3.69 would be within 5%

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Adrian,

If you persist with the transverse spring, then softer will make it more likely that you will get compression, positive camber and Jack up.  It's built into the swing axle!

And a transverse spring is not suited to wishbones, unless there is provision for the spring to move on the upright, or as Triumph did with Rotaflex, a variable length drive shaft.

There have been many attempts to convert to coil over rear suspension, none AFAIK successful!  You might be the man!

John

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46 minutes ago, JohnD said:

Adrian,

If you persist with the transverse spring, then softer will make it more likely that you will get compression, positive camber and Jack up.  It's built into the swing axle!

I was thinking the new body would be more akin to that of a spitfire in terms of weight, so reducing the spring to something spitfire strength would be ideal. That, with a camber compensator woud work well, but as Craig suggested, a later spitfire swing spring is the simpler solution. 

I have been trying to think of wheel ideas. There are 16" steel wheels about, but anything modernish will be wide. I was thinking if any 60s cars had big wheels? Saab 96 were 15" and 4.5j I think. French cars??  Hub adapters are available to convert the PCD as required.The Saab PCD is huge though, so may be a problem.

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