RMC #36 420R in PA

[JohnCh]

  On 3/25/2025 at 1:41 AM, Legs said:

It's one of the best! Something I've found immensely helpful is https://www.tiggercaterham.co.uk/tiggers420rbuildmanual who actually took the time to go through several of the detailed build blogs and pull our the helpful tidbits and not only list them out at the start of each section, but also provide the link to turn! It's a gold mine haha

Expand  

 

I forgot about this one.  I just added it to the Build Blog links thread:  

 

[Legs]

Diff Day 1: diff wins 

 

Bottoms weren't too bad. I put one in to pull the diff to one side to them determine the total washers/shims needed in total. Split those in half and have an equal amount for each side, back the bolt out, then add washers and bolts.

 

Top bolt, as expected, is going to need some finagling. Top left has a small gap, I can get one thick and one medium washer in while jostling the diff to make space, so that's tight. Top right has enough space for two thick and probably can squeeze a smaller one in. The bigger issue is simple getting the diff in line with the holes, it seems like it needs to go another 1/8" further into the car, but the front bolts naturally won't allow that. Possibly swinging the rear towards the right wheel well is what's needed, given the left side is tighter than the right, but again, the front bolts will keep it from moving off it's current line AFAIK. Not sure!

[Timberline]

Sounds about right. The shapes are not the same as fabricated.

 

 Putting a big taper on the bolt and/or using pin punches are the tools for the job. That and a big mallet

[JohnCh]

  On 3/26/2025 at 12:00 AM, Legs said:

Bottoms weren't too bad. I put one in to pull the diff to one side to them determine the total washers/shims needed in total. Split those in half and have an equal amount for each side, back the bolt out, then add washers and bolts.

Expand  

 

In case you split the washers evenly because that is implied in the build manual, that is not necessarily correct.  When Caterham introduced the Ikea-style build manual in an attempt to make assembly appear easy, they left out information from the earlier, and more thorough written manual.  In the case of the washers, the Ikea diagram shows the same number washers on either side, implying they should always be equally split.  However, from page 129:

 

"Measure from either side of the differential carrier to the outboard side of the chassis (outboard of rear ARB mount – 1” BOX) to centralise. During this process there will be a need to pull the bottom bolts out and use shim washers (item 21 in pack 30Z1067A) inserted in between the metalastic bush and carrier as necessary. You may now use the ½ x 11” top bolt (schnorr washer under the head). It is optional to grind a chamfer on the end of the bolt (threaded part 45 degrees x ½”) as this makes it easier to slide and locate the top bolt. Ensure there is plenty of copper slip used on the bolt. You will also need to space the upper bolt between the carrier and the metalastic with shim washers. Use a ½” nyloc nut and schnorr washer to fasten the bolt."

 

You might have it centralized, but it would be good to check.  The written manual is in the Library:

 

 

 

[Legs]

Thank you @JohnCh, from the eyeball it does seem like it's not centered on the bottom bolts, but because it's implied and I split the washers I thought, it must just be shadows or bigger welding on one side skewing the appearance. But this makes me think it really might not be centered. I was trying to measure between the case and the inside, not easy. Measuring to the outside of the frame should be much better and accurate 👌

[Legs]

Diff Day Two

Diff's up 2-0. I reshimmed the bottom bolts to get the diff frame to rear ARB frame tube as close to even on both sides as possible. Can't say it's down to the mil, but it is definitely closer than it was. Getting the second set of washers in took way longer this time around 🥵 I also removed the makeshift cradle so the jack can push on the diff from further back to better utilize the front bolt pivot point. I was hopeful the top holes would be better aligned now, but it seems to not have made any bit of difference. The holes are pretty close to aligned vertically, but the diff's are still 1/8" too far to the rear. I don't understand how any bit of pushing and shoving can make up that amount, on both sides. A bit discouraged for the moment, but tomorrow is another day.

Edited Thursday at 11:35 PM by Legs

[KnifeySpoony]

You have to deflect the bush enough to get the bolts in. Massive PITA and takes a lot of muscle/prying/hammering/swearing.

[Legs]

Diff Day 3: It's done.

 

I honestly still didn't think it was going to happen today - spent another 2 hours moving, jiggling, hammering, with no change. Another hour passed with my wife maneuvering the crobar been the diff and the jack. At some point, she got it just right and a few knocks with the 5lb hammer, the bolt started to go in and it just kept going. Lathered it up with more copper grease and sent it home. We promptly went out for a deserved beer 😆 I'm glad that's done with. Thanks for the words of encouragement!

 

PS. If anyone sees this who hasn't installed their diff, remove the plywood boot floor and it makes getting access to the top washers very easy. You can get a full view of them and easily use a flat head to push on them 👍

Edited yesterday at 01:22 AM by Legs
Adding a PS