Replacing entire front end of Caterham and need some guidance

[Jonathan Cort]

About 13 years ago we put our Caterham into a rock during a Hillclimb in Wester North Carolina.  We are planning to cut off the front end. We have purchase a replacement frame from Caterham that extends form the foot wells forward. Any advice on peeling aluminum back and where to cut and reinforce the frame tube connections?

 

Cheers,

Jonathan Cort

[S1Steve]

I’d like to see a few photos of your new front frame you bought from Caterham.. Good luck with your replacement..

[wemtd]

I think some folks on OzClubbies have been through this before (probably BlatChat too).

just in case you haven’t looked there yet..
 

[Jonathan Cort]

[MV8]

Lovely Seven. It would be better to reskin the whole side and weld at the original narrow section near the rear wheel arch since the welded area may be different from the rest of the panel as far as polishing is concerned. Maybe you have a Wicks or Aircraft Spruce nearby to pick up the 3003.

Proper welds do not need extra reinforcement. If the welds will be mid-span on a tube, it would be better to fill a narrow gap if the tube will be ground level after welding, removing part of the weld bead. Align tube sections with strips of angle iron the same size or a little smaller than the tube and that are as long as the available space along the tubes. Use four vice grips clamping lightly and spaced as far apart as practical. Tack it all, remeasure, and recheck body panel fit before fully welding anything. Go back and forth (like when torqueing lug nuts or head gaskets) and don't weld more than a half inch at one time.

I see it came in three sections. I would not install everything they sent if it isn't needed. It depends on the actual damage.

I expect there is no repair data made available with chassis dims from each point in three dimensions. Measuring another car might help but is no guarantee it will be right for your panel fitment. Can't assume the chassis dims on the opposite side are correct either. You could compare the published wheelbase then adjust the caster to the typical spec to measure on the "good" side and use a straight edge carpenter square or level to see if the tubes are straight in two dimensions. If that's good enough and the bonnet edge to the scuttle and nose fit well, you could use the good side to base the new front end off of. You can also see how bad the bent side is.

Care to share a pic of the damage?

It could be a minor pull to correct without all this work.

Are you doing the repair work yourself or just want to strip the car as much as possible before it goes to an frame shop?

Edited January 17, 2023 by MV8

[Croc]

I don't think you will find anyone on USA7s who has done a long front chassis replacement.  Its been 35+ years since I worked with Dad to do one on his S2.

 

There is a modern Caterham long front replacement thread running on OzClubbies that @wemtd refers to.  Definitely worth reading.  

 

All Blatchat threads seem to involve delivering the crashed mess to a professional to be fixed.  Not seen one that was self-done.  The UK has it easier for these repairs than we do in the USA.

 

To start with you want to strip the chassis back - engine out, radiator out, all ancilliaries, plumbing, steering rack, etc. out.   Front suspension out.  You want a clear front chassis.

 

Your side skin join is a vertical at the rear wheel arch both sides - it hides under the rear wing.  A side skin forward of that is removed and will be replaced.   Removal is drill out all rivets and remove.  Lots of bits will go inside the horizontal chassis tubes but you will cut those tubes and that is an opportunity to try to get the bits out.  I suspect the ali skin is already damaged and non-salvageable but the removal process is usually going to cause damage that you will want it new anyway.  This is more than you think you will want to remove but anything else is going to leave an unsightly side skin join that is visible.  The rear basket skin panel will stay in place.

 

Scuttle is removed and saved.  Rear suspension and rear wing come off.  

 

You will want to jig the existing chassis on a table or something to ensure it is square before you start.  You also want to mark up key location points on existing chassis to give you reference points before you cut.

 

The use of a jig and firmly securing the chassis is intended to make sure nothing warps in the re-weld.  It would not surprise me to see the rear of the chassis warp as you cut off the old broken bits - its been under torsional stress from the accident damage for a long time.  

 

One question:  Was there enough accident damage to justify a long front replacement?  Could you have got away with just a short front (i.e. stops as second vertical chassis bar back from front)?  Reason I pose the question is the major concern I would have about chassis warp during this process.  I have never faced a seven chassis warp issue to be cured - anyone else on here able to talk to it?

 

Second question:  Did Caterham supply the right long front for a 1993 S3?  They have had a lot of chassis configurations over the years?  Your car is around the changeover point for long footwell too.   

 

Next question:  I think this is an Arch constructed chassis - was it brazed or welded originally?  Can you mix braze and weld at long front joint points?  

 

Then it is a case of measure a lot of times and then measure again before cut and weld.  You are not trying to lengthen or shorten the chassis so what you remove of the chassis is what you will be replacing.  No special gusseting or join strengthening is done - just a straight re-weld covering the entirety of the join.  You will want to protect the weld with some suitable chassis paint.  Side skins should be installed.  You used to be able to buy them in the UK but I think it will be cheaper to just get a local professional to do it from scratch as shipment is prohibitive.  Josh at Rocky Mountain Caterham may have some or a supplier as they have a good knowledge of the older model Caterhams.  

 

Are you going to do the work or get a professional shop do it for you?  

[fastg]

Croc is right, this is a major project. Even I would think twice about this and look at local repair before going this far. But I would strip it down to as close as I could to a bare chassis. Build a table, jig it up to get as many reference points as possible before cutting and welding in the new sections. I bet this chassis is not straight to start with, so it's going to be a real can on worms rebuilding it.  The LocostUSA.com site has lots of good posts on build tables. 

 

Graham 

[MV8]

3 hours ago, fastg said:

Even I would think twice 

 

Graham 

Curious as to what you mean by this. You bought the cmc turn-key.

 

 

[fotsyr]

I did a similar repair about 25 years ago. Carefully pulled out the side skin, installed new front end and use the side skin as a jig. Used a chassis plate to ensure all even. 

[ianashdown]

You will need to explore the type of welds on the original chassis and the repair section.  If either part are Arch built it will be Nickel Bronze Brazed.  You will not be able to TIG close to any Brazed joint.  Nickel Bronze is a low temperature repair, and in my opinion ideal for this type of repair, but there are relatively few in the US who can do it in the way Arch does.  
 

I did a similar repair to a Formula Ford many years ago and it is quite difficult, given the hand built nature of these chassis.  There are small dimensional variations.  Be very thorough checking, measuring, etc before you cut. A basic jig or fixture would be a very good idea.

 

Good luck!

 

Ian