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420R (S3) Radiator design issue, regular failures???


CtrMint

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Hi All, 

As per my post on 7Up's thread my radiator has also failed, this is the 2nd in a total of 4500 miles, they seem to be doing approximately 2000 miles between failures.  Although that's a sample of 2, my original replacement rad from the build was also dodgy, so possibly 3.

I've checked the radiator this morning and it's failed in the same position very top passenger side vane in against the end tank. There is a pattern here, and I'm wondering if there is a design flaw which goes back to my original kit etc.

When I was sent my kit what I understand is the revised radiator wouldn't fit under my nose cone, not by millimeters, but by centimeters.  Caterham eventually stated they'd switched radiator designs and sent me a new rad and additional hanger (see image).  The new radiator design is still mounted using bobbins, but the hanger for the top bobbin is solidly mounted, and well look at the images for proximity to the top hose and the point of failure.  There is actual contact between the hanger and top hose.

Based on comments from the 7Up's thread, I checked for vibration, and yes there's a notable resonance in the rad at tick over which disappears once the engine spins up.  So I'm left considering if CC inadvertently missed something with the new hangers?  I'm no mechanical engineer, but surely this is a smoking gun?  The point of the solid mount, is the point of repeated failures.

Has anyone else got a 420R S3 late 2018, which has similar hangers? 

I'm trying to attend the Taffia so will need to source a replacement radiator, but at £600 (CC Parts) per 2000 miles this is just silly.  I need to come up with a solution/improvement to resolve this interference while maintaining fitment under the nose.  The club has always been an invaluable source of information and support, hope you can all assist.

Thanks

Mark

IMG_1683.thumb.jpeg.64a33dfe004453c3bef7c4f13910cd04.jpeg IMG_1684.thumb.jpeg.50c601c52f5b8b95652aeb5123d29b2b.jpeg

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Can you see a reason why the end of the hanger bends up (and contacts the radiator) rather than down to the bobbin? Was that design introduced for a different type of radiator, and then for your type they added the extra piece that connects the hanger to the bobbin?

And regardless of the history and what the factory offers how about cutting off the upturned end of the hanger, inverting it and welding or bolting it back so that it engages the bobbin directly?

Jonathan

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I understand the design is used to pull the rad closer to the chassis or rather further up the nose cone, given the nose cone narrows the closer it gets to the grill.  If I were to rotate the hanger, I'd be pushing the radiator further down the nose cone, I guess by the length of the horizontal offset in the hanger.

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I think there's more to it than that, JK. I've never seen a rational explanation of why CC changed the design of the rad/cooler from that which had been fine (quality issues excepted) for years, to one that didn't fit at all well and needed the sort of cobbling together we see above. 

The most likely explanation I've heard is that they had a supply issue with one or more of the earlier design parts so started to put parts designed for something else (race cars) into kits.

I wonder if more recent models have been redesigned to avoid the issues Mark had and perhaps now include the suggestion you offer?

If that mount is a solid connection to the radiator, it could well be the source of Marks problem; but what's the bobbin doing there? At first I thought it was just and odd arrangement to connect the bobbin to the chassis but now see it's a solid connection.

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"If that mount is a solid connection to the radiator, it could well be the source of Marks problem; but what's the bobbin doing there? At first I thought it was just and odd arrangement to connect the bobbin to the chassis but now see it's a solid connection."

I'm suggesting losing the solid connection and only having the connection through the bobbin...

Jonathan

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I can't understand why your chassis mounting bracket is touching the radiator inlet.  I had no issues with that mounting.  The original top hose was to inflexible and put a lot of strain on the radiator inlet, thankfully I found that out when I cut it to short, ordered a replacement which was much more flexible and removed strain on the rad.

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Thanks Chris, the fact you don't have any interference is certainly helpful and likely supportive of why I'm experiencing repeated failures.

There's no adjustment possible, due to the alignment of the 90 degree elbow and bolt holes.  I'm back to the frustration of my original build.  *smash*.  

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Sorry I don't,  i Ironically at the moment I am also struggling with a problem and have the whole backend of the car disassembled, so have no space in the garage to remove the nose and bonnet.  I am killing rear wheel bearings and driveshafts every 1000 miles. 

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IIRC, Mark's original build problem was that the top of the rad butted up against the nosecone.  The basic cause was that the "new" composite rad+cooler wasn't a good fit within the old nosecone -- they didn't match.  That hanger extension in #1 was CC's fix for lowering the rad and moving it further back.  The rad is still mounted on bobbins in the usual way.

Do current kits have the same "fix"?  I'd hope not as I'd like to think that CC have (a) rejigged the bracket or (b) reintroduced the earlier rad version (which, IME, did the job perfectly), or © redesigned the nosecone to increase clearance.

JV

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Yes John you are correct.  I was originally shipped the 'newer' radiator without the drop hangers, which ended up with zero chance of fitting the nose.

My original blog with an image is here.

https://www.caterham7diaries.com/post/what-a-load-of-bobbins

Though curiously I now think I still have an interference between the inlet and the hanger, which is increasing vibration and resulting in premature failure.

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Looking at the bottom photo in #1 there appears to be an interference fit with the top fastener bracket(s)? This indicates to me that the bobbin is actually not doing anything as the complete mounting system is solid & not flexible.

There needs to be some shimming with a penny washer or two to provide clear space for the bobbins to do their job. But is there space to do this & accommodate the nose cone?

No wonder radiators are failing. 

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My chassis mounting bracket touches the top hose.  Only just, but it does touch. I can lift the rad to gain clearance, but it settles touching.  I am sure there would be a witness mark on the top hose.  Don't forget this top hose had a slimmer side wall to my original so that would have been even tighter (and less flexible)

5FBA7988-F090-449E-B5E4-B06A4D016420.jpeg.f22df02c648c5467eff43bc162eb62d3.jpeg

DEE03180-A444-4DE6-BBF3-B5256CB1F722.jpeg.34f684cbb0680fa8afe77f94203d2aef.jpeg

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I been in a slackened everything, I can get maybe an additional 1mm of movement, you can just see light between the bracket and top port, but not much, and there is nowhere near enough to get the hose on.

I've also had a play with looking at ways to space out things to try and buy enough clearance, I just can't see a solution that works.  

If the holes in the radiator ali bracket are moved lower, it would lift the radiator up, and gain clearance but I suspect risk hitting the nose.

Spacing the bobbins or hanger forward doesn't work either.  

As far as I can see the only way to resolve it is to grind the hanger down and increase the gap  *nono*

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I am inclined to agree about grinding the hanger down but one thing I have noticed is that looking at the two photos, yours and #14, the chassis bracket in #14 is narrower than your chassis bracket and therefore has more clearance with / from the radiator outlet.  Here is a photo of the two brackets for comparison

Radbracket.jpg.a1ea1bae735ff94952dee8faf9d6b118.jpg

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It looks wider than 20mm more like 25-30mm but photos can be deceiving.  Regardless, I think I would file down the area I have outlined in red to eliminate any contact with top hose or radiator outlet.   It seems ridiculous that you should have to do this but I had to shave a good bit off oil filler cap and Cosworth coil cover badge to eliminate contact with the bonnet, so very Caterhamesque 

Radbracket2.jpg.dfe6ac0632edf168c9064acf0b134e25.jpg

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