620 S Build

[CBuff]

Left side tunnel clearance seems to be a thing. (Since I was inept I don’t have first hand knowledge of this).  But some of the other build blogs discuss. Leaving engine mounts loose to adjust. 
 

https://caterham420detailedbuildblog.co.uk/2019/10/28/engine-install/

 

https://purplemeanie.co.uk/index.php/2017/09/02/build-session-12-bonnet-delivery-gearbox-move-and-engine-bay-first-fix/
 

https://www.caterham7diaries.com/post/look-back-at-the-engine-install
 

some discussions about vertical clearance to the chassis rail. Some have added a caterham spacer to trans mount. But not super clear of its effect. 
 

https://www.caterhamlotus7.club/forums/topic/275387-nvh-placement-of-gearbox-in-transmission-tunnel/

https://caterhamparts.co.uk/fittings/7111-gearbox-mount-spacer.html

 

[CarYenta]

1 hour ago, CBuff said:

Left side tunnel clearance seems to be a thing. (Since I was inept I don’t have first hand knowledge of this).  But some of the other build blogs discuss. Leaving engine mounts loose to adjust. 
 

https://caterham420detailedbuildblog.co.uk/2019/10/28/engine-install/

 

https://purplemeanie.co.uk/index.php/2017/09/02/build-session-12-bonnet-delivery-gearbox-move-and-engine-bay-first-fix/
 

https://www.caterham7diaries.com/post/look-back-at-the-engine-install
 

some discussions about vertical clearance to the chassis rail. Some have added a caterham spacer to trans mount. But not super clear of its effect. 
 

https://www.caterhamlotus7.club/forums/topic/275387-nvh-placement-of-gearbox-in-transmission-tunnel/

https://caterhamparts.co.uk/fittings/7111-gearbox-mount-spacer.html

 

Thanks for the links!

My kit has the transmission mount spacer which I used. It sounds like if I can't move the left side of the transmission in the tunnel away for more clearance, I should only worry about it if the transmission is up against a hard thing/rail and not so much if it's against the padding?

[CBuff]

That seems to be my understanding. Again limited first hand knowledge.  I actually bought the spacer but haven’t installed it (or know if there is one currently installed ).caterham =  Keeping the mystery alive. 

[wdb]

Good progress! Be sure to loosen all of the motor mount hardware while adjusting the transmission location. Get everything centered up, then tighten.

[CarYenta]

23 minutes ago, wdb said:

Good progress! Be sure to loosen all of the motor mount hardware while adjusting the transmission location. Get everything centered up, then tighten.

That is the plan, if it works, I do not know haha. I think I'll be using a breaker bar and a wedge to get it straight.

 

One more thing to do, my seat when the slider is all the way forward is still to far from the pedals for me. I'm thinking of making a new set of floor pan holes a few inches forward of the existing holes with a step drill bit. Any problems doing that? I'm going to bend the seat slider adjustment rod 90 degrees so it doesn't hit the footwell cross member.

 

[Nocturnal005]

On 6/9/2025 at 4:30 AM, CarYenta said:

Thanks for the links!

My kit has the transmission mount spacer which I used. It sounds like if I can't move the left side of the transmission in the tunnel away for more clearance, I should only worry about it if the transmission is up against a hard thing/rail and not so much if it's against the padding?

 

There's just zero clearance for the trans in some spots, particularly near the bellhousing. My bell housing is touching the insulation foam particularly on the left side (it was hard to remove the thin cardboard I used for tunnel protection at some points). No amount of pry bar, loosening bolts, etc seemed to help. Glad to report that there seem to be no ill effects after ~1000 miles. There seems to be no metal to metal contact in my case, but the padding definitely is compressed in spots.

[CarYenta]

1 hour ago, Nocturnal005 said:

 

There's just zero clearance for the trans in some spots, particularly near the bellhousing. My bell housing is touching the insulation foam particularly on the left side (it was hard to remove the thin cardboard I used for tunnel protection at some points). No amount of pry bar, loosening bolts, etc seemed to help. Glad to report that there seem to be no ill effects after ~1000 miles. There seems to be no metal to metal contact in my case, but the padding definitely is compressed in spots.

Good to know! I assume at some point the heat shielding will wear away at the contact point, but I can deal with that if/when it happens. 

[CarYenta]

It has been an incredibly busy summer! Since I'm too short for the stock shoulder belts (metal strap hits the top of my shoulder with the seat scooter forward), I installed some Schroth Flexi 2x2's. For the sub belts, I had to source my own hardware.

From Grainger, I ordered four 7/16-14 x 3 in hex head bolts (not the most aero, but whatever) that are inserted in from underneath the floor pan (drill new holes) into a bolt-in harness bracket, into a thick walled 7/16" hole by 1-1/2" long spacer (https://www.grainger.com/product/Spacer-For-7-16-in-Screw-Size-4GVD9), then through the pre-existing sub mount tabs, and then a washer and 7/16-14 nylon nuts.

 

Interestingly, the bolt in brackets on the passenger side, which has fixed rails, interferes with the bolt in harness brackets. I also tried putting the harness brackets above the spacer instead of below, but it would interfere with the seat back instead. I then elongated holes in the floor to get it to fit. I measured wrong! AHHH. I ended up flipping the seat rails 180 degrees from the picture shown to get it to fit and mounted in the original holes. This means, however, that the passenger seat is scooted quite a bit forward instead of slammed back against the back wall. I will need to search for some aftermarket seats rails.

 

 

I also bought some 40 mm wide nylon washers to cover up the elongated portion of the holes as they were now wider than the stock aero washers (https://www.amazon.com/gp/aw/d/B0DHH73CC3?psc=1&ref=ppx_pop_mob_b_asin_title). 

 

Finally, I raised the driver's seat up slightly using Tillet brand nylon seat spacers. They seem near identical to the cheap Amazon ones, but do come in thicker sizing. I also got some longer M8-55 mm hex bolts to attach the sliding seat rail to the seat since the stock ones (M8-40 mm I think?) no longer poked through the washer stack at all. There is considerable thread in the seat, so could have gotten longer ones even, maybe M8-70 mm or so. I added height of an additional three of the 40mm OD washers x 4mm thick for a whopping half inch height increase. I can see so much now. 

 

Also, I attached all the coolant hoses and supercharger piping finally. In another thread, Pickles kindly layed out how to get around multiple issues which made my life considerably easier and with -1 broken knuckles. Thanks! Fascinatingly, and perhaps unsurprisingly for Caterham, my builder had dibs on the ruler that day and cut my coolant hoses to the correct length from the get-go, so I had no trouble fitting the lower radiator hose with no interference from the supercharger exit pipe.

 

Next up are manifolds woohoo 🎉 

 

Edited September 3 by CarYenta

[CarYenta]

Another pro tip from Pickles, I had my intake side engine mount spacers on the exterior of the mount, acting like washers and not as spacers. I moved them in between the engine block and mount hoping it would give more transmission clearance. Loosened all parts, engine on jack, didn't really move much, hard to tell.

 

Wow, the 4 into 1 exhaust springs really were a pain! Much much struggle but got these on.

 

My kit was missing the 4x m10x20 mm differential to driveshaft bolts as well as the throttle body to intercooler exit "reducing elbow for intercooler". The fit is going to be extremely tight, I'm concerned! I can wiggle the intercooler around to install, but these photos are with the intercooler exit pipe jammed as far is as possible into the intercooler and the intercooler bolt aligned.

 

I will finish the exhaust, tidy up a bunch of wiring with rivnuts, start putting in the fluids, and hook up the shifter while I wait for the elbow and diff bolts to show up. 🎉 

Edited September 6 by CarYenta

[KnifeySpoony]

Interesting. No spacers on engine mounts on my 420 build. 

[CarYenta]

Exhaust is on. Pro tip, the rubber pieces for the exhaust hangers go on top, not on bottom of the mounts 😂 Exhaust was on, hanging waaayyy down, doh!

 

If I were to do it again, I'd try bolting on the exhaust hangers, connecting the rear silencer and connector pipe together, then sliding in the hangers while attaching to the side pipe.

 

I see why people complain about scraping these, even with the hangers on top of the rails, it's pretty low.

 

Anyone know how loud it is if you just modify the side pipe exit to stick outwards? I believe the cat is in the side pipe,band no cat in the rear silencer, right?

 

Edited September 7 by CarYenta

[pickles]

On 9/6/2025 at 3:03 AM, KnifeySpoony said:

Interesting. No spacers on engine mounts on my 420 build. 

I think the spacers are only for RHD cars.

[pickles]

On 9/7/2025 at 3:45 PM, CarYenta said:

Exhaust is on. Pro tip, the rubber pieces for the exhaust hangers go on top, not on bottom of the mounts 😂 Exhaust was on, hanging waaayyy down, doh!

 

If I were to do it again, I'd try bolting on the exhaust hangers, connecting the rear silencer and connector pipe together, then sliding in the hangers while attaching to the side pipe.

 

I see why people complain about scraping these, even with the hangers on top of the rails, it's pretty low.

 

Anyone know how loud it is if you just modify the side pipe exit to stick outwards? I believe the cat is in the side pipe,band no cat in the rear silencer, right?

 

I'll let you know ... I thought the rear silencer the ugliest thing I have seen ... I ordered mine with just the side silencer ... If I ever get it running I'll let ya know how loud it is :-)

[CarYenta]

Once again, Pickles to the rescue! I've spent probably 16+ hours trying to get the intake manifold to intercooler pipe installed without pinching the thermostat coolant tube too much. Turns out I didn't read Pickle's other article well enough which had the answer right in it. So for others like myself - zip tie the darned coolant pipe to the supercharger outlet pipe, and place the aluminum tube on top of it not under nor on the side. I had to loosen all my upstream barb fitting to get enough slack but then it was very simple to do so:

Note that the supercharger to air filter tube is out to do this.

 

Fix the elbow to the tube, with your O clasps readied but not tight

 

With the intercooler either locked down or loose, you can put the pipe right into it first and slide the other end right in from the side:

 

Now, with liberal use of silicone spray on both ends of the elbow and the intercooler connection, pivot the tube and elbow clockwise (up) towards the butterfly valve and get one side of the lip over the edge, making sure to remember the large O clasp:

 

Now, pivot pivot pivot. Takes some convincing, so more silicone spray the easier it is:

 

Fiddle around twisting the tube a little, the elbow a little, and it will pop right on. I had previously added so much silicone spray from prior methods that I had to hold the elbow in place to prevent it from sliding a bit while tightening.

 

 

Done! Look at all those bottle scars.

 

Edited October 7 by CarYenta

[CarYenta]

Alcantara 1-24 momo steering wheel showed up from Caterham as they mistakenly gave me a leather 1-21. 

Attached is a drill template Bruce graciously created for me.

 

All I can say is, drill from the back onto a piece of wood, and expect the bit to slip if your initial tap isn't quite deep enough. Really give it a thwack and start with the tiniest of drill bits. I ALMOST was off by about 2 mm on the top center but caught myself before making it all the way through and made a second start. Whew. Bolts fit perfectly snug with a 1/4" bit.

 

Now everything is fuzzy

 

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