[Hairy Spider]

Hello All,

Well I couldn't let it lie so here we go with a bulkhead mod...

The Holy Grail here was to take a stock unmodified 501 arm and fit it to the car. I'll tell you now that I didn't do it. Physically it can be done (bar the drilling of the outer hinge pin holes) but I chose not to and I'll come to that in a bit. The next best thing obviously is to minimise the time and effort required to take a pack of 501 arms and fit them on the car and that's what I've ended up with. I can now take a 501 arm and have it ready to fit on the BJ4 in about 2 to 3 minutes.

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Let's start with comparing a fully modified arm against a partially modified arm and bulkhead



So on the left we have the arm as modified per the original post. The bulkhead on the left is unmodified. On the right we have the modified bulkhead and a significantly less modified 501 arm compared to the one fitted on the left. The important thing here is that the 'precision' modification is done on the bulkhead and not the arm.

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The Bulkhead Mod :

Inserts...



Bulkhead...



Note: This photo was taken before I'd finished and there is a small ridge running top to bottom where the bulkhead has been filed away. You need to file this flush with the edge of the bulkhead otherwise the arm will bind on it. Note also that the edge of the filed area has been rounded off so it doesn’t bind on the wishbone.

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The final part of the mod will require you to either modify the arm or the bulkhead. Here's why...



The issue is the gap between the pin and the arm. JConcepts... big, Tamiya... small. I looked at grinding down the bulkhead but I felt that the amount you would have to remove would potentially weaken it. You may disagree and if anyone out there has done it then why not share with the group ? I'm content to leave it at that as the arm mod can now be done so quickly with the bulkhead modified in the way I've done it.

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So, the arm mod is now reduced to drilling the caster block hinge pin hole with an imperial 7/64 drill and ripping 1-2 mm from the arm to increase the gap between the arm and the bulkhead. This does not need to be a precision cut which is why it takes no time to do (with the right tools of course. God Bless Dremel ). There is no filing/fitting/filing/fitting/etc... as with the full arm mod above.

A couple of hints on drilling out the hinge pin hole.

• Put some tape on your drill bit so you know how far to drill. Use the pin for guidance.
• Be careful when you’ve been through the first hole and you going into the second. I found that the drill bit could bite in and you could be through the end stop before you know it. Then you’ll have to mimic the screw stop on the other side to stop the pin falling out.

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One final shot of the bulkhead back on the chassis and that about wraps it up. I guess only time will tell if this has all been worth it but the 501 arms definitely look and feel like they should be stronger.

Regards,
Jon.

Faversham Off-Road Car Club