Build progress

[peterux]

Front steering and suspension defeats my logic. I've got this great book called "How to build & modify sportscar and Kitcar Suspension and Brakes" by Des Hammell, but despite reading it about 6 times i still don't understand it!

When you go round a corner at extreme steering angles, the wheels have to turn at a different angles to account for the diffrent radius circles. (Patrick, take a look at your Alfa model and you can see it). This is called Ackerman steering and is realised by the steering rack and the offset steering arms.

My normal logic says, increasing the caster angle should improve the self centering (like supermarket trolly wheels) but the book says this also causes "dynamic negative camber" i.e. lots of negative camber on full lock on the inside wheeel, which may not help? I know my Sportster does something strange at full lock.

Increasing the tyre pressure should reduce friction and make it easier to self centre.

The book says that self centering on rear wheel drive cars is achieved by the addition of toe-in, but that can cause understeer at speed.

So...

I think the plan should be to set maximum caster angle with the washers, pump up the tyres and keep increasing the toe-in equally each side until it self centres from full lock.
If that doesn't work you could try Robin's suggestion of positive camber to off-set the dynamic negative camber.
Another option might be to reduce the range of the steering rack with your hose clip end stops. The book says..." In the normal course of events, the front wheels do not turn (angularly) all that much from the staight ahead position (often not more than 20 degrees)." That's if you can get it to self centre from less than full lock.

Good luck with the trials and it's nice to see the real friendly helpful advice from Marlin hasn't changed. But we wouldn't enjoy the challenge if they told us exactly how to do it, would we?
Oh and just to repeat, I'm no expert on this stuff so all of the above is just ideas!

[Patrick]

Thanks Peter Paul posted this on the MOC forum so between all those post I hope we can get something setup at the weekend:

Re: SVA fail - but its not too bad.
Posted by Paul Carey (Hampshire) on 9th Oct 07, 12:57 MOC Member: Yes
Most modern cars the various steering geometry angles are set so it is not easy to get hold of the information. I know that Millie’s Sierra based geometry is all to cock and I should do something to set it up correctly but it generally does not affect the driving experience most of which only requires the steering to move a few degrees. That said the tyres do squeal quite a bit in multi-storey car parks. Not a bad thing as it scatters pedestrians without actually endangering them.

My somewhat older Haynes manual for the Granada does give dimensions and I have included those for you to look at. I give them all as it shows there is quite a range. Depending on the options, and given a tolerance of 1 degree, the castor angle can be from slightly less than a degree to almost 4 degrees. One source gives angles of 3.5 to 4.5 degrees for BMWs.

I guess that given a short journey to the test centre and the fact that you are a fit young man and not a weedy little old lady in a Granada a castor angle of 4 degrees or more would be good enough. It might make it a little stiff when parking but should be fine on the open road. It should guarantee self-centring.

Measurement is another problem. The only way I found to do it is using a steel tape measure. This I attach to something near the rear wheels. The Sierra has a small hole in the axle and I put a pin into it and sticky tape the tape measure to it. Then I measure as best I can to the top and bottom of the kingpins. I know the Sierra has ball joints but they form a virtual kingpin. Given that the nuts of the ball joint are about 150mm apart 4 degrees will give a difference of about 10 mm. Roughly 2.5 mm per degree. So to be within +/- 1 degree you should measure between 7.5 to 12.5 mm. Fairly easy to do with a steel rule. The Camber angle will also affect the caster. For Millie the camber is close to zero.

I think you can check your set up by eyeball. The top of the wheels should have a pronounced lean towards the back on full lock. Compare it with a production car. Sportier cars tend to have more to compensate for hard cornering. Both locks should look the same (Millie’s doesn’t).

One other tip I read is to inflate your tyres a little harder than usual. This helps reduce steering resistance.

Once you are through the test road testing should allow you to experiment to optimise your geometry.

Good luck wit the retest,
Paul


Front wheel alignment

Toe:
Setting value . 2 ± 1 mm (0.08 ± 0.04 in) toe-in
Tolerance in service . 0.5 mm (0.02 in) toe-out to 4.5 mm (0.18 in) toe-in

Castor :
SOHC and 2.8 litre models:
Standard, without ride height control . . . + 1°51’ ± 1°00’
Standard, with ride height control . . . . + 1°58’ ± 1°00’
Heavy duty . . . . . . . . . . . . . . . . + 1°46’ ± 1°00’
DOHC carburettor and low series fuel-injection models .
+ 2°27’ ± 1°00’
DOHC high series models . . . . . . . . . . + 2°26’± 1°00’
2.4 litre:
low series models . . . . . . . . . . . . . + 2°17’ ± 1°00’
high series models . . . . . . . . . . . . + 2°50’ ± 1°00’
2.9 litre models . . . . . . . . . . . . . + 2°22’ ± 1°00’

Camber :
SOHC and 2.8 litre models:
Standard . . . . . . . . . . . . . . . . . . 0°23’ ± 1°00’
Heavy duty . . . . . . . . . . . . . . . . . 0°00’ ± 1°00’
DOHC models . . . . . . . . . . . . . . . .-0°17’
2.4 litre low series models..... . . . . . .-0°27’
2.4 litre high series and 2.9 litre models .-0°21’

Tolerance:
DOHC, 2.4 and 2.9 litre models: 1°00’ to + 0°60’

Difference between left-hand and right-hand sides:
SOHC and 2.8 litre models:
Castor . . 1°00’ maximum
Camber . . 1°15’ maximum
DOHC, 2.4 and 2.9 litre models:
Castor . . 1°00’
Camber . . 1°15’


I bet this forum will mangle the special characters I have used so here is a translation:
+ Plus
- Minus
± Plus or Minus
° Degree
’ Minute

[MartinClan]

Originally Posted by MartinClan

However I think it's a bit extreme expecting it to do it on full lock Robin

I tried an experiment this morning with the donor vehicle (not the real one but my 318is daily driver). It self centers from full lock without much apparent difficulty. So - it should be possible to achieve on the Sportster unless Marlin have messed with the front suspension geometry too much.

Best

Robin

[peterux]

Originally Posted by MartinClan

It self centers from full lock without much apparent difficulty. So - it should be possible to achieve on the Sportster unless Marlin have messed with the front suspension geometry too much.

Best

Robin

There you go again, Robin, making those sweeping assumptions!


But seriously, I agree, with the right settings, it should be possible........
(we can let Patrick figure it out and then copy him )

If I get time, I might have a play with mine at the weekend and see what I can achieve...

[Patrick]

Originally Posted by peterux

(we can let Patrick figure it out and then copy him )

..the world is doomed

[Patrick]

I've booked a re-test next Friday, which will hopefully give the postal server time to deliver Marlin's letter and this weekend to finish up all the changes!

[Patrick]

Lets get the mundane stuff out the way first:

Edge trim now firmly attached to the bonnet and surround

Holes in the tub for the belts to clear

Edge radius on the fibreglass

More stronger clips added to the brake pipes. Zip ties replaced with P clips

Ok I'm officially an idiot. After spending many ours buggering about with a camber/caster gauge make lots of adjustments and getting nowhere. Also measured up my Coupe as a reference. The front wheels have always looked a bit off to me. Turns out I was right. The wish bones are correct left and right, but they 180 degrees up the wrong was. DOH!!! Flipped the wishbone over, now the car auto centres no problem at all!
Note to all builders - make sure the more curvy part of the wish bone is at the front as in these pictures! Now in this situation a build manual would have been useful, unfortunately with a Marlin you don't get that!

The cycle wings now sit very much further back! Looks a bit odd. Might need to adjust those, but SVA first!

[peterux]

Originally Posted by Patrick

The wish bones are correct left and right, but they 180 degrees up the wrong was. DOH!!! Flipped the wishbone over, now the car auto centres no problem at all!
Note to all builders - make sure the more curvy part of the wish bone is at the front as in these pictures! Now in this situation a build manual would have been useful, unfortunately with a Marlin you don't get that!

The cycle wings now sit very much further back! Looks a bit odd. Might need to adjust those, but SVA first!

Wow, what a breakthrough.
What was the result of having them upside down? Less caster angle, I presume? I will need to check mine down the garage but looking at my photo's, looks like I am Ok.
So what Camber, caster and toe did you end up with?

[Patrick]

camber was -0.75, didn't measure the caster after flipping the wish bone but 2 washers at the front and 3 at the back is what I went with. Toe is slightly in ward but I don't have a way to measure it.

I will do more measuring and experimenting but its now set so I can pass SVA. I think it has quite a lot of caster as the steering really weights up as I turn in.

[Alfie]

As I recall, it took me a while and a lot of head scratching to decide which way was right for wishbones. What swayed it for me was the angle of the upright. As you say, it would be a lot easier with a build manual but you can't have everything!
Good luck again on Friday. Your car looks great.
Alfie.

[Patrick]

Richard did a bit of experimenting with the settings yesterday. The toe was slightly outwards to start with - auto centred fine. Changed it to toe in no longer auto centred so it looks like straight or slight toe out might be a good place for it.

Its good enough now to pass the test more measuring / testing / driving once its on the road properly

[Patrick]

Well I drove it about yesterday, car is really transformed with the geometry correct (shock horror!) steering pretty heavy the way its set so I will need some adjustment.

Took more tub out for the belts to clear, think this will need a better solution in future, especially with a spare slapped on the back without the cover.

I think we're all set now, more pictures here: http://www.msportster.co.uk/detail.asp?cat=20&offset=24

Not done a news item yet.

[Rich]

With the belts repositioned the boot floor needed to be modified so they clear.

Smoother out the edges around the holes for the belts.

Belt holes all done and cleaned up

All done


Sportster through the looking glass

[Patrick]

It passed

It was a chilly drive this morning with the frost still on the ground, but nice and sunny on the way back, almost warm!

I just got back from the DVLA, all the forms are filled in and I have an inspection on the 30th. I've had to arrange to trailer it there as they won't let me drive it.

[MartinClan]

Great news - well done!

Robin

[Simon]

Congratulations chaps - the car looks superb

What are your plans now about getting it painted?

Simon

[peterux]

Originally Posted by Patrick

It passed

It was a chilly drive this morning with the frost still on the ground, but nice and sunny on the way back, almost warm!

I just got back from the DVLA, all the forms are filled in and I have an inspection on the 30th. I've had to arrange to trailer it there as they won't let me drive it.

Well done chaps, that's terrific news!

The government department logic beats me. You can drive it the SVA before it's even been tested. You can drive it home after it's failed, but you can't drive it to the DVLA office after it's passed the SVA?

As my son says...............der............

[Patrick]

Originally Posted by MartinClan

Great news - well done!

Robin

Thanks

Originally Posted by Simon

Congratulations chaps - the car looks superb

What are your plans now about getting it painted?

Simon

Going to fit the screen, switch the fog/reverse lamps, change the side repeats and front indicators, make an air scoop for the side and then take it on some shake down runs - its done 80miles already now

After some shake down I'll take it to a few paint shops for quotes. There's a place in Newbury that didn't the paint on the Cobra that was in Total Kit car last year (or year before) pricey but very good.

As for colour BMW Le Mans blue is still our fav, http://www.pfyc.com/m5/ not too many in the light shots on the site but its nice and bright with run reflecting off it and very dark in the shade.

Originally Posted by peterux

Well done chaps, that's terrific news!

The government department logic beats me. You can drive it the SVA before it's even been tested. You can drive it home after it's failed, but you can't drive it to the DVLA office after it's passed the SVA?

As my son says...............der............

Does not compute - indeed! Now its declared safe for the road but you can't drive it to the inspection, but that's bureaucracy for you I guess. The woman at the DVLA didn't seem to know the answers to many questions, she just said I just check the forms. So I don't know for sure that it's all filled out correctly.

[peterux]

Originally Posted by Patrick

8) Design weights were wrong on the form. Car is heaver at the back that expected - probably due to the exhaust. So need a letter from Marlin with new weights. The rear needed to be at least 563 (and the gross put up to cover this)

Patrick,
Now you've passed, can you tell us what the correct design weights are on the Marlin letter?

thanks

Peter

[Patrick]

The original design weights were not wrong as such, due to the layout of our car there was more weight at the back than expected. Terry said that this happens sometimes. I'm guessing its the heavy exhaust hanging out the back (and the birch ply floor) that's pushed the weight up.

The correct design weight for ours was:
500 axle 1
563 or above axle 2
1063 or above gross weight

Mark the tester said put 563 or more for the rear design weight which is what came out processing on the scales. I asked Terry to put:

500 1
565 2
1065 Gross

In the letter which was fine with Mark - 65 was a nicer number than 63 to go on the form

Basically the design weights needs to be higher than the actual weight of the car as it should take into account luggage / passengers / fuel.