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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin 5exi builds

Marlin 5exi builds Calling all you sexi builders....sorry 5exi builders, show us your progress.

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  #1  
Old 29th March 2008, 18:07
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Default Road legal... exceptionally twitchy.... and now it's time to make it handle / grip...

Hi all,

I thought I'd start a thread, and update it as I make a bid to resolve the handling woes of my car.

When I first put my car (2006 chassis) on the road I was quite happy with the go, but somewhat dissapointed with the handling and grip. The car wallowed, the back end bump-steered an astonishing amount, and generally it was a nasty dissapointment. Yes it was great to be on the road, but the feeling wasn't as good as it could (should?) have been.

I did have Marlin's latest rear suspension on order, but cancelled that owing to delivery issues.

With no updated rear suspension, I've decided the best way forward is to bite the bullet and pay someone to ammend the car, and make it work.....

... and today that process started, with a "consultation" at Track Developments.

I'll keep adding to the thread as things progress, as I'm sure others will be interested to learn what modifications are made to my car.

The first set of photos (fairly uninspiring), can be found here:

http://www.johndry.com/gallery/main.php?g2_itemId=12089
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  #2  
Old 30th March 2008, 07:17
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Hi John.

I have not got the driving skills you have to find the woes of the car. Will be good once your car is done, for you to compare with mine (the later setup) to see how they feel side by side while your driving.
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  #3  
Old 30th March 2008, 09:40
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John - I don't have the skills to drive around the woes, which is why I'm trying to get the car corrected, and made more docile. I've spent too much time driving idiot proof FWD cars to be especially able with a mid-engine RWD car, with a fairly low moment of inertia.

Presently, there's no denying the car is a ditchfinder - reasonable in a straight line, but throw in some corners and a broken surface, and the car gets very unsettled! A typical modern diesel hatchback is far more capable on b-roads, and that my daily driver bettered Ric H's lap times around Llandow, goes to show the lack of confidence the car inspires. I don't think the lap times at Llandow have anything to do with driver ability, as I think I'd be faster on track at present in my hatchback, than in the 5EXI.

Yesterday there was a lot of rain, with standing water lurking on many of the single-carriageway a-roads. I'm pretty sure the instability of the rear geometry caused by the closely spaced top pick up points on the rear uprights, means the rear end grip under drive is considerably lower than it could quite easily be. Whatever the cause, when it's like it was yesterday, the ease with which the rear wil step out, excites one to exercise appreciable caution, and drive as smoothly as possible.

A few figures from yesterday's exercise:

Front / rear weight distribution: 44% / 56%

Axle split left to right - just under 1% on both the front and rear.

Front roll centre approx 115mm above ground.

Rear roll centre approx 145 mm above ground.

For comparison, Jon Coombes' car has a roll centre about 25mm off the ground, which is generally regarded as good practice.

The front suspension has an element of pro-dive, which is slightly unorthodox, and generally translates to needing a higher spring rate to counter the dive, which compromises the braking ability.

The rear suspension has a small amount of anti-squat, which is common practice, and generally considered appropriate for a road car. Dragsters, and hill climb cars, are typically the exceptions, and I understand sometime have pro-squat.
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Old 30th March 2008, 22:48
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Will be interested to see what happens. Did they give any clues as to what they are thinking off to correct some of the things they have found, or will it require further analysis.

Have been playing with my suspension today, a bit of a dry fit to try and work out where things go when in my own garage rather than the 5 mins description when collecting. (will upload some photos in a few days time and link to them here). I have also found I'm missing a few bits I thought I had but will probably find Mark and Terry knew they hadn't supplied. Have also been comparing my suspension with others pictures to understand how it differs from the previous suspension setup. One thing that is clear is that they have space apart much further the rear two top ball joints which I can see will result in a lot less rear steer hopefully.

BTW does anyone with a rover front hub setup have pictures of where the steering arm connects to the front hub assembly as amazingly I cant find it in the build manual ;-) and its not at all obvious to me at the moment as cant see anywhere logical it would connect to which is puzzling. Mind I dont yet have the steering rack and its trackrod ends.
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  #5  
Old 30th March 2008, 23:15
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David, the rear steer is caused by two things, the first being the lack of stiffness, and the second being different balls joint types. Your design of suspension should not suffer from either issue. The main problem, as I understand it, is that the rear inboard pickup points are in the wrong place - the lower arms should pivot *under* the chassis tube, and the top should also be moved slightly, I believe. The effect of the pick up points being where they are, I don't fully understand, but I believe it causes a jacking effect, which ultimately makes the car display rather undesireable tendancies.

As for the front, assuming you have the same setup as me, you bolt the steering arm to the rover stub axle, using two of the bolt holes that were originally used to hold the stub axle to the rover rear beam.
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Old 31st March 2008, 11:35
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Default Dynamically

Two points here,

The difference in the rear ball joints size means that the relative heights of the suspension pick-up's at the wheels are at a different height to each other. Its this difference in height that dynamically, can be modelled to show, the reasons for the way the rear performs.

Second one for David, as you are dry running the front assembly itís now (without the springs and damper in place) that you can easily set up to avoid the front bump steer. Once you have worked out how to fit it all together and I am sure you have picís to help you by now, bump steer is cause by the tracking changing as the suspension raises and lowers. Marlin have provided adjustment on the steering knuckle pickup bracket (ie back of the hub) to adjust the way the dynamic steering movement is affected by the suspension movement. So with no damper and spring in place set up and lock the steering movement and raise and lower to the suspention to its extremities and adjust the bracket at the back of the hub to reduce the tracking changes as best you can.
I bolt a length of aluminium angle iron to the wheel hub to exaggerate the movement and measure between the end and a fixed poit. All you have to do is adjust to reduce the movement to a minimum you will not eliminate it.

Hope that helps.
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Old 1st April 2008, 22:00
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Ah hadn't put the hub in during the dry run so didnt think of teh steering bolting to the back that makes sense now I think about it.

Thanks will try that adjustment when my steering rack arrives. looks like that will be 3 weeks or so away due to hol's and move at Marlin.

I'd heard rumours that the steering rack was just a rover 100 one but seems its bespoke so am getting it from Marlin.
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Old 1st April 2008, 22:39
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I think the only bespoke aspect of the rack, is the fitment of approx 20mm collars to limit the rack movement. It's a standard QH component.

You'll want to hack off and bin the lock limiters once through the SVA, as the car has an horrendously large turning circle with the limiters fitted - the SVA guy was laughing at the turning circle when I put my car through.

On the story of the mods to my car - the "software" (I think it's more of an elaborate excel sheet to be honest) analysis of my car has revealed the mods required to get the car to handle, and stop being a ditchseeker.

1) fabricate and weld on new suspension hard points on the front and rear of the chassis.
2) modify the rear uprights to remove bump-steer
3) make new front upper suspension wishbones to separate the castor and camber
4) make spacers to reposition the steering rack and eliminate front bump-steer
5) fit front and rear anti-roll bars to counter the increased roll moment, caused by lowering the roll centre.
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  #9  
Old 13th April 2008, 19:52
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Some times you have to go backwards to go forwards.....?

http://www.johndry.com/gallery/main....serialNumber=2
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  #10  
Old 13th April 2008, 22:07
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wow looks a little drastic but am sure it will be worth it, hey half the fun is playing with the car when you've built it.
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  #11  
Old 19th April 2008, 20:50
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after a "fun" afternoon, the car is almost ready to be karted off....



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Old 19th April 2008, 21:21
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Been a busy bunny!
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  #13  
Old 24th May 2008, 18:53
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I popped up to Track Developments this morning, taking with me my car's gearbox to chock into place and check clearances.

A couple of pics to keep this thread ticking over....



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Old 4th June 2008, 17:27
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Old 6th June 2008, 19:53
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Idle hands.... result in a clean engine....(those with super keen eyesight might spot the Hondata inlet gasket).



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Old 7th June 2008, 07:29
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John thats so much better! What did you use for the cam cover?

The hondata gasket looks thicker?

Craig
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  #17  
Old 7th June 2008, 15:39
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I used Halfords rattle cans. It remains to be seen how durable it is.

The hondata gasket is approx 5mm thick, and plastic, like most cars with aluminium manifolds. The standard Honda gasket is thin steel.
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Old 19th June 2008, 16:12
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Offside rear:


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Old 25th June 2008, 22:53
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Hopefully there are no potential issues, with the following being posted.

Abridged version of comments on my car's geometry:

".....Your car mainly had the roll-centres too high. This leads to a condition called suspension jacking - this has been discribed as "a general leaping about like a demented mountain goat".

It's potentially quite dangerous....A secondary affect is an oscillation of the roll axis, especially if the spring frequencies are out as well. Mix in some bump-steer and upright flexing, with a not-very-well-triangulated chassis, and you've a problem. Your car also had some pro-squat and dive, and the king-pin offset was a bit high - leads to instability under braking...etc - by altering the chassis suspension pick-up points, and fabricating the upright mod's we were able to get the roll-centres down, the VSAL's more equalised and the deflections and camber changes to the point where both ends of the car are working in harmony instead of fighting each other ! "
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Old 27th June 2008, 19:08
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Getting closer.........




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