DIY Guide: Sump Guard for CSR (and possibly other metric Series 3 cars)

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James B
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DIY Guide: Sump Guard for CSR (and possibly other metric Series 3 cars)
 

I recently started a thread eleswhere in TechTalk asking if anyone had developed a sump guard to protect the very exposed Cosworth dry-sump pan on CSRs.  Some kind members (thank you!) were good enough to provide some ideas and even photos of what they had tried, but I felt a different approach could be worthwhile. 

I thought that a wedge shaped affair, mounted securely ahead of the engine and the sump, would be a good approach - allowing the car, hopefully, to 'rise and glide' over any significant middle-of-road obstacles, without further reducing the already very limited ground clearance by fitting a shield running under the engine.  After a lot of head scratching, I decided that a good approach would be to rigidly mount a solid, horizontal plate to the chassis cruciform area - a very strong and stiff area of the car, particularly on a CSR - and then mount the wedge securely to that.  I explained the concept and a few members expressed interest, hence this thread to report back on what I have done.

Interestingly, some members asked whether the same approach would work on other Caterham derivatives, including later Series 3 cars with low-hanging wet sumps.  My view is that, in principle, the answer is "yes" (the concept of strongly mounting to the cruciform appears to be a good starting point) BUT with two reservations:

  • Firstly, I understand that the cruciform structure was considerably reinforced at the change to metric chassis, but earlier cars are known to be weaker in this area (tales of bent cross members when jacking under the cruciform on Imperial cars) so I'd suggest that the concept should be tried only on metric chassis.
  • Secondly, having compared my own Series 3 car to the CSR, it's clear that there is a lot more bracing (vertical bracing at that) on the CSR than on the S3 so it feels to me that there is greater risk if adopting this idea to a S3 car.  That said, the metric S3 cruciform looks to be both stiff and strong so I wouldn't rule it out - just weigh up the pros and cons carefully,

Anyway, I'll write a number of posts here to show the DIY design I developed - so give me a bit of time to write the words and post the images before wading in with too many comments, please.  And it goes without saying, of course, that I offer no guarantees and accept no liabilities as to outcomes if you copy this idea!

But, in time-honoured Blue Peter style, I'll start here with an image of the finished article and then I'll provide more detail in subsequent posts.

James


 

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A good place to start is to summarise the materials I used and the approximate cost.  I should add that I set out to deliver a design that nearly anyone else could copy without difficulty using tools likely to be found in most domestic tool boxes, and without needing any permanent changes (for instance, cutting and/or welding) to the car.  This is a fully reversible, bolt-on/bolt-off concept.

  • Base platform plate - 6mm aluminium sheet sized 350mm x 200mm.  I bought mine from 'alum-droitwich' on eBay (I have found them always to be excellent) and it cost £25.  The plate can be left rectangular or shaped a bit into a trapezoid or even a variant on that with some nice curved edges (for those who think under-car aesthetics are important...).  I shaped my plate using a cheapo-bandsaw and the final weight was just under 800g.  After shaping, the plate measured 330mm width across the back edge and 250mm across the front (retaining the 200mm front to back dimension), with some gratuitous curved shaping to the side profile. 
  • Mounting blocks - I used four of these to clamp around four of the cruciform members.  The principle is that these clamping blocks kind-of interlock, due to their positioning around the X-shaped cruciform, to provide a strong mounting mechanism - one that should withstand a typical under-car impact and distribute those forces into and around the cruciform area without excessively loading any single point.  I looked and looked for clamp blocks that would be strong enough and eventually found them described as 'Hydraulic Pipe Clamps, Stauff Style - size 20mm'.  They cost me £16 from 'parquiphoseandhydraulicsltd' on eBay.  Weight for the four is 360g.
  • Wedge block - I ended up shaping and using an off-cut of reasonably hard timber for this part, which I painted black to make it look more technical!  It's just over 47mm maximum 'height' in my installation (the Cosworth dry-sump hangs below the cruciform 'surface' by more than 60 mm).  I actually think that wood is a good engineering material for this application - but the downside is weight at 440g.  It's easy to work with (saw and plane, etc) and I shaped the block to cover the full width of the sump face with an appropriate 'slope' to the lower surface to provide the wedge effect.  For reference, in plan view the wedge measured 225mm along the rear width tapering to 160mm wide at the leading edge.  In side view, the rear of the wedge was 47mm deep and reduced down to 13mm, or thereabouts, at the front.  (Interestingly, I also made a second wedge from a lightweight structural foam material that would have saved 320g, but whilst it looked 'more engineered' I had some doubts as to its ability to withstand likely impact forces so stuck with the wood piece).
  • Impact plate - I happened to have some 2mm aluminium chequer plate in the garage so I cut and formed (bent by hand, using a vice and some elbow grease) a piece of that to conform to the shape of the wedge and to allow for secure attachment to the base platform.  I guess that this might have cost around £5 or so to purchase.  It ended up somewhat trapezoidal in shape and measured 230mm at the rear, (a tad wider than the wedge it covers) tapering down to 170 across the leading edge.  The dimension from front to rear was 190mm and the shaped peice weighed 150g.
  • Fixings - I found I needed a variety of M6 allen key headed bolts, mushroom headed bolts and countersunk bolts in the range 50mm to 60mm length and a few M6 self-locking nuts.  The collection weighed in at 120g and cost around £6 for the quantities I used.

So, in summary, total costs of just over £50 and a weight effect of 1.75kg in the wrong direction.  I worried more about the weight than the cost but in the end I decided I'd eat a few pies less and just take the hit.  Life's too short (and my CSR is for road use, anyway, and is not a track car where the added weight might - in theory - be of greater consequence).

Some images below which, hopefully, will be self explanatory.

James

 

 

James B
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Assembly on to the car was a bit fiddly, but quite straightforward.  I started by mounting the base platform using the clamping blocks.  I carried out a number of dry-fits to make sure everything was in the right place (in fact, I made an MDF version of the base platform plate first, which helped immensely with the measuring and marking up of the various holes that would be needed in the base platform itself).  It was then straightforward to drill the various holes through the base platform - not only to secure the mounting blocks/clamps but also to allow attachment of the wedge block and, eventually, the impact plate. 

I found I needed to shorten several fixings to make sure there was no danger of protruding bolt-ends interfering with the engine v-belt and a few corners also had to be radiused on the mounting blocks to ensure adequate clearance to parts of the engine and the CSR inboard damper mounts.  As I say, quite fiddly to get right (taking the plate on and off the car a number of times) but quite satisfying to see it all come together and to know that the detail had been taken care of as well.

With the base platform secured I then mounted the wedge block to it, bolting up and and through the block, being mindful of the likely impact forces that the block might be expected to transfer into the base platform plate.

And finally, the impact plate which was secured by two fixings at the front and a further two along the rear edge of the wedge block.

James B
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And then it was finished...

Some final observations.

I decided to leave a nominal gap of around 10mm between the rear edge of the wedge/impact plate and the front of engine to allow for a bit of engine movement (though I can't believe it ever moves more than a fraction of that, fore and aft, on its mounts) and also because it sort-of looked about right. 

In terms of height, with the car at normal ride height and rake, the radiused front edges of the Cosworth dry sump cooling fins now extend maybe 1mm or 2mm below the trailing edge of the wedge and impact plate.  I'm pretty sure that will provide the 'lift and glide' functionality I am after (grazing the sump fins, rather than taking the whole sump pan out in one blow).  The danger of having the sump guard lower than the sump is one of catching it (the guard) on obstacles when reversing, and ripping it off...  Although it would be easy to adjust this to achive an exact match to sump depth (through shims, or a revised wedge piece, or even a thicker impact (chequer) plate) on balance I think it's better to be slightly under-flush.  Approach angles (hardly an issue on a Seven) are unaffected.

I know that the guard will have an adverse effect on airflow through and around the sump, and therefore on sump and oil cooling.  But I expect this to be minimal in extent in most European climes.  If I was tracking the car in Dubia I might remove the wedge before trying too hard but, for general road use - even at high speed and on the hottest of our typical summer days - I don't expect this to be a factor.

As I said at the start, I think the approach here has applicability to other Caterham derivatives where the front of sump is both exposed to road detritus and is the low-point on the car.  The principle of having the strong, flat base platform securely mounted to the rigid cruciform area is the key factor here; it allows wedges to be shaped and adapted individually to suit whatever is necessary to protect different engine and sump installations. And whilst the CSR cruciform looks (by virtue of its additional vertical bracing) to be more than strong enough for this application, the single-plane cruciform on the metric S3 chassis also appears to be quite strong - but please be careful and check for yourself if you do go ahead with a metric S3 installation.

I hope that others might be encouraged to make copy-cat versions; it would be great to see replicas on other cars, if anyone feels so inclined!

To finish - some images of the final guard, mounted and ready for action...

James

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DJ.
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That looks nicely engineered. I like the way you have avoided welding or damaging the chassis as far as I can see. It also maintains your ground clearance as you said.

It's always difficult to decide which is better to sacrifice, the chassis or sump. My Sigma 125 is pretty much standard Ford, so I'll take my chances with the sump.

Reducing ground clearance by completely covering the sump isn't a great idea, I have a friend who added a substantial guard below his very low sump. He went over a badger corpse, the sump guard lifted the front as planned, but at the crucial moment he couldn't turn into a corner and went off the road!

Duncan

Mark w
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Neat install James .*thumbs_up_thumb*

Will the Mk2 version extend the checker plate a tad over the front ribs on the sump ?

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I think leaving the chequer at the same level is preferable, as lipping it over reduces clearance still further - and there's not much to start with !, it might also get snagged if your reserving over something too.

James B
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Replying to #7 - you were too quick, Mark, and asked the question whilst I was still writing a later part and providing the answer. 

As Neil says (in #8), avoiding any further reduction in ground clearance is key - as is avoiding it being ripped-off in reverse.

James

Mark w
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Understood but i was just thinking it might protect the front fins a bit more .

If you are reversing and an extra 2mm thick plate represents a risk of snagging then the whole ride height might need a rethink given the speed most Caterhams are reversed at.

Anyway , as said above,  a lot of thought and care has gone into the design .It looks good . 

 

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well its 2mm plate plus the chequer nigh on another 2mm plus clearance to the fins say another 2mm so thats a 6mm overall reduction.

The reversing was aimed mainly at parking, (unless of course your in the habit of high speed reversing into the scenery or kitty litter) some coastal car parks have you on slightly raised kerbs or as a friend found out the 'kink' in a ferry deck, he got firmly stuck on just such a plate.

A few dozen 44 tonners were not overly impressed !