By Jan Willem Briër,  The Netherlands  ( to my other bus pages )

How to replace a rotted rocker panel
or "welding for the compleat idiot"


If your rocker panels (outer sills for those in the UK) are of the see-through variety they need to be replaced. The cost of the new panel is negligible. So many bus owners (like myself) have ordered these panels some time ago and all that remains to be done is to weld them in place ..... That's where the trouble starts.  I had never undertaken such a job. I had no welding experience whatsoever. Pressed by time (annual inspection coming up very soon) and an urge to do this myself (disappointed by work done by others) I bit the bullet and went ahead. The result was so encouraging that I wanted to share my experiences so others can perform the same procedure. As I said I had no welding experience and I still had to acquire many of the necessary tools. All in all it took me about 10 hours to do the entire job. That seems a lot. However most of the time was needed to do the prep work. The welding itself took only about an hour. Since this was my first attempt I took my time realising that I wanted to do it right rather than having to do it over. The end result was well worth the effort. The car passed its official inspection without any problem. I was even commended for a very professional welding job!


Cut out the old rocker panel. That's easier said than done. The end result of your work will depend largely on how well you did this part of the job. To make life easy for you I will explain this procedure in great detail. I have even gone so far as to prepare a couple of drawings so you will understand how these parts fit together. Note that I did this work on a '77 bay window bus.

Fig 1

NOTE: The drawings are not to scale!

Start by cutting away the sloped part of the original rocker. The best tool for this purpose is a grinder with a cutting disc. Such a tool will set you back about $50. Note that the rocker is spot welded to the rest of the car at locations A  and B. After cutting away the sloped part you will have the upper and lower parts of the rocker  with the spot welds still attached to the rest of the car.

In order to provide a solid base for the new welds you need to grind away all of the remaining rocker at location A. Be careful not to cut into the outrigger. We need it to remain in place but with a good shiny surface. The success of your welding depends on how clean the surfaces are.

Note: Later I found out that cutting out spot-welds is more easily done using a special spot-weld drill bit. Ask your FLAPS for this tool.

The upper part of the old rocker needs to be cut away too but not entirely. It depends on your new rocker. If the new rocker has a U shaped rubber seal channel that clicks into the old one you can leave that part of the old rocker in place. If it does not fit (like mine) you will have to remove the channel for the seal as well. I left the uppermost horizontal strip in place (the black part in fig 3). The old seal channel has a small ridge that keeps the seal in place. I left that part of the old rocker as I wanted to keep this ridge which was not present in the new one.


After all the cutting and grinding is done you have to examine the state of the outrigger (or inner sill). In my case it was in reasonable condition. However if you can poke a screwdriver through the outrigger at any spot you choose you need to replace this part as well. I presume that's a more complicated procedure. I have not yet done that so I have no clear-cut recipe for you. What I did do is to remove all of the rust that I could get at. Next I sprayed chemical rust converter into the outrigger. Let it work into the rust for several hours then clean it using water and soap.  Next I sprayed rust inhibiting paint through all of the holes that lead into the insides of the outrigger. I guess that will preserve it for a number of years. It's the best I could do. Cars are built to be biodegradable anyway but in our climate it does not take very long . You can not stop this process, only slow it down.

Does it fit ?

Try the new rocker on for size. Now is the time to see if you did your cutting right. The new rocker should fit without leaving gaping holes. I was careful not to cut away too much material so in this stage I had to grind a little more on the left and right sides to make sure the new rocker fitted snugly in to place. 

Prepare the new rocker

Depending on the source of the new rocker you may have to perform minor surgery on the metal. In my case I had to remove two small pieces of metal from the seal channel. After removing all stickers etc from the rocker we can prepare it for welding as described in fig 2.  Most likely your new rocker will have been primered at the factory. We do not want paint on all of the spots that are going to be welded. So use your wire brush or sandpaper to clean all places where you intend to weld.

Fig 2
You need to drill a series of small (4 mm) holes along the lower part of the new rocker. We will use these holes to simulate spot-welds (they are called 'plug-welds') using our MIG welder. Along the upper lip we need to make small triangular cutouts. Do not drill holes here because you will probably not be able to get at them with your welder. The nozzle is to wide to fit into the seal channel. However you can just get at the these cutouts and weld against the remainder of the old rocker (location B in fig 3).

Do the welding!

Fig 3
The new rocker is welded in place with plug-welds at locations A en B. Note the remainder of the old rocker at location B.

In addition to these "plug-welds" we will have to weld up the vertical seams. Do only a few milimeters at a time to prevent creating big holes rather than closing the gap.

Mvc-006f.jpg (37644 bytes)Here is a detailed description of the welding technique. Note: The photos are made while practising on an actual (discarded) new rocker panel. Clamp the rocker firmly to the metal of the outrigger.
You may have to use additional clamps to get it accurately into place. Do not start welding until you are absolutely satisfied that the rocker is in the correct position. After you make the first weld you cannot change it anymore! 
Mvc-008f.jpg (41070 bytes)Position the nozzle of the welder exactly over the middle of the hole. Press the feed button for a few seconds.   The exact time depends on your welder and welding skills.
That's why you need to practice before you start on your actual car. While welding you want to hold the nozzle at a right angle to the metal. The idea is to fill the hole entirely. If you have not filled it completely at the first attempt you can make a second weld at the same spot.
Mvc-015f.jpg (32068 bytes)This is how the welds should look like. Note the one on the right which looks very good. The metal has flowed very well and filled up the entire hole. The one on the left is not done quite so well.
Start with the lowest voltage or current setting of your welder. A high setting will most likely burn big holes in the rocker and outrigger. That's not what we want.

Finishing touch

Mvc-017f.jpg (64201 bytes)After you have finished welding it's time to clean things up. Grind away any excess metal, however be careful and do not cut into your new rocker panel!

Note: this photograph was taken during a practise run.


Mvc-019f.jpg (47426 bytes)The picture below shows the result of a few seconds grinding. This particular weld looks quite good. When it is finished this weld will be completely invisible.

Bare metal should be wirebrushed. You may need to use some bondo to fill in pits in the welds. Remember that these welds are vulnerable to new rusting. I put a layer of rust inhibiting primer over the whole rocker and finished it with the famous Taiga Grün.  I did not even spray the paint on. Just used a good quality brush. That's good enough for me at this time. The last thing I did was to spray "ML" protection into the insides of the rocker. This stuff comes in a spray can with a special thin hose and nozzle. Use the holes in the outrigger to insert the nozzle and give it a good spray. This will prevent additional rust building inside the new rocker and help seal the new seam.

The end result

Mvc-022f.jpg (57096 bytes)This is how the end results looks, a rock solid rocker panel. No longer that browny bubbly half rotted look but firm, shiny and freshly painted. This will last you for a good number of years. And it will make you an even more proud owner of your bus. Note: I still need to replace the sliding door seal.

Tools and materials required for this job

In order to carry out the work described here you need the following tools in addition to the standard set of screwdrivers, pliers, hammers etc.

panel.jpg (4700 bytes) A new rocker panel
I bought mine at the local FLAPS for only $7 (tax included).
Mvc-003f.jpg (61133 bytes) A grinder with a cutting disc
I had never used a grinder before. Be sure to wear safety goggles and gloves. From experience I know that's important!
Mvc-001f.jpg (49523 bytes) A MIG welder
I had never used a welder before. I did not even know what type of welding was required. After some research I found that a MIG welder is needed. I used one of the cheapest models available. It's an "Easy MIG 120" gasless unit. It uses 0.9 mm flux core wire. I found it to perform very adequately for this job. It's price? Around $200
Mvc-002f.jpg (37545 bytes) A spraygun
Having a spraygun helps but you can do without. I used it to spray rust converter and primer into the hollow outrigger.
ml-spray.jpg (58513 bytes) ML rust preventative
Using the hose and nozzle I sprayed this stuff into the rocker and outrigger after all the work was done.

Comments or questions: Please e-mail me !

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