Article: Pocher K74 Mercedes Benz Spezial Cabrio A rebuild

[CTDavies]

To avoid white plastic showing through any gaps that might still occure later, I painted the inside of the plastic ring widener as well as the back side of the hub core brown.



It would have been easier to prebuild the wheels and then airbrush the whole thing but on the Mercedes the balance weight containers were chromed so everything has to be prepainted, even the spokes. For painting the spokes I made several strips of thick balsa planks which were given a few coats of grain filler ín an attempt to prevent dust. On a grid I predrilled where I mounted the spokes as I was afraid that just pushing the spokes into the balsa would just end up crushing it instead getting a firm hold for the spokes.



My favourite paint store made me a can of enamel paint of the brown colour we decided to use. This way I could airbrush the spokes instead of using the rattle can, where it's more difficult to control the build up of paint.



When the paint had thoroughly dried I just turned the spokes around, ie. poked the painted ends into the balsa to expose the unpainted ones, which were then also airbushed



To paint the spoke nipples I threaded them all onto thick nylon thread. The thread had just the right thickness to prevent them from getting blown about when being airbrushed. They needed to be painted on all sides which is why a small gap was left between them. I also used my airbrush here.



This is how I ended up with around 800 prepainted spoke parts

[Ton]

Wonderful job and report Chris!

[CTDavies]

To get the hub back plate to fit right the hole in the plastic core had to be widened quite a bit first.



So now it was time to actually build the first wheel. Well now, at the time of writing, I have already built three so most of the bugs have now been sorted out and what I am showing you here is the best of the three wheels I've built so far.

I started on the rear side spokes, just as when test fitting earlier, so the plastc rim and hub core was mounted to my CAD designed jig.



The first thing I found out was that using the soldering iron to fix the spoke nipples was a bad idea, because it caused more damage than it did good. So I simply did it the way Pocher intended, with mixed success. Some nipples went into their notches very well, some didn't, but here I just used a drop of CA to persuade those bad ones to stay in place. On the first spoke 'vee' the left nipple wasn't pressed into its notch yet, because the last one needs to pass under it.



I worked around anti clockwise and the right spoke of the last 'vee' was neatly tucked under the left one of the first 'vee'.



When trying to mount the inside metal ring (the one with the plastic widener) it turned out that too much spoke ends were in the way. To improve fit the plastic extension was tapered to a sharp edge to keep clear of all nipples buldges and spoke ends.



The metal hub back plate was added as well as the brass part before I could add the jig for the other side.



To make sure that everything settles down where it needs to be I attached large clamps at the tips of the jigs, that line up for this purpose. It didn't really matter if the hub core was accidently removed as it still needs to be set at the correct relative position to the rim spoke notches.



Before I could add the long outside spokes the balance weight containers needed to be put in place. I was warned by Paul Koo's excellent Supplemental Instructions DVD-Rom that the core of the balance weight is too thick and stands proud of the plastic rim and need to be narrowed down here otherwise the next metal ring won't fit properly.



The air filler valve also needs to be put in place before the long spokes can be tackled. You can see that I didn't stay with the Pocher instructions here, or it would have been added long ago. I simply opened up the hole for it with a small drill bit and took away most of the threaded end of the valve and stuck it in place with quick setting epoxy .



You might have noticed that large gap between the hub core and its back plate. I didn't worry about this now because later when the brass hub parts are added it will all be pulled together.

So it was time to move on to the longer outside spokes. For some bizzare reason I forgot that Dr. Koo also recommends bending these and thought they would fit as they are. Well that was wrong, because after adding several 'vees' it became apparent that their apexes moved further and further away from the hub.



After a quick glance at the Supplemental Instructions I saw that Dr. Koo also bent these long spokes so I did accordingly.



Here I also moved around anti clockwise tucking that last spoke of the last 'vee' under the first one.

[CTDavies]

This weekend was more like that Christmas holiday buildathon I was hoping for although I didn't really spend that many hours in my 'Bastelkeller'. Most of the prep work was done during the week. Here are some obligatory End Of The Day glam shots.



Thanks for stopping by

[CTDavies]

So I had built three wheels to determine where all the bugs are, the next three should be a piece of cake, I thought - haha!
I found out that the way I widened the outer ring wasn't quite enough, so I reverted back to Marvin Meit's hole saw method. The outer rings were already painted of course, so after widening them all a bit more they all needed to be repainted. The following set of images shows you exactly how I implemented Marvin's Way. A hole of the correct size was cut into a thick piece of laminated wood and the ring placed around it. The 54mm hole saw was placed on top of the ring with the open end up and a mid sized hammer put in the hole saw. Then with the biggest hammer I could find in my tool box I literally smashed down on the mid sized hammer, driving the hole saw half way down into the ring.



The hole saw with ring were removed and placed back in the hole, only this time the other way round and with a few sturdy taps the hole saw was driven out of the ring again.



The rings were, as previously mentioned, badly scratched by all this abuse and needed a respray. Widening the inner diameter also brought the inner bulge further down making a bad fit onto the plastic ring, so I removed a bit of the bulge with my drum sander.



Next came the time for the Mercedes 500K wheel assembly line I was waiting for. I still wanted to build an extra wheel incase something bad happened and one had to be discarded. I started off as previously with the shorter inner side spokes and the rims mounted to my wheel building jig.



When these were all done I turned the wheels around and added the other side jig. To help things settle down in place the whole assemblies were tied together for a while with some large c-clamps.



The first jigs were all removed exposing the outer side of the wheels with the hub. Now the balance weight containers were added as well as the air filler valves and finally the long spoke 'vees'.



When building the first three wheels it became evident that the four screws Pocher provides for pulling the whole wheel assemblies together are just not up to the job. I removed the paint from the plastic rim and added a good coat of slow setting heavy duty monster epoxy .



I still used the screws to mount the rings in place and they were driven down as far as they would go without ripping up the threads in the plastic rims. I added the hub rings and the second jig was removed to make space for the next step.



For this I made some 6mm birch ply rings that fit precisely around the bulges of the metal rings. The wheels were sandwiched between two of these and the whole thing trapped between six large c-clamps. To remove gaps between the various rim parts some brute force was required - and was provided.



Unfortunately I only had enough c-clamps for two wheels a time. I let the epoxy set for 24 hours before the wooden rings were removed, everything inspected and the tires added.



I had only ordered five tires from Model Motorcars because I had noticed that the spare wheels build up way too high in the wheel well so I had thought of using a spacer dummy under only one spare wheel to bring it further down more inline with the rear of the body. Here I've installed two Pocher wheels to show you how far they protrude out of the wheel well.



The Pocher tired are much larger than the Model Motorcars replacements and are closer to what an AFV needs than a 1930's sports car. Here are some comparison shots to show you the difference.



Now I'm going to have to order one more of the Model Motorcars ' tires. With them being so much thinner than the Pocher tires I can do without that spacer I was going to use in the wheel well and actually put two full wheels in the well as on the full size. But for now it's back to the body.

[CTDavies]

Here's an image of the prototype I recently found in a german book. You can see how deep the spare wheels sink into their wheel well.

[CTDavies]

I was getting a bit worried that the whole thread was getting a bit derailed when I abandoned the body and moved straight on to the wheels, but in hindsight that was just the right thing to do, because with the Model Motor Car wheels being so much smaller, I needed the right size for the next step:

The rear fenders on the Pocher kit are a bit too large, probably due to their own large wheels. It's impossible to change the size (of the fenders) without scratch building a whole new body but with the new wheel in place is becomes very apparent that the wheel bay in the fender is also way, way too large. The following picture shows the first paper template to determine the correct bay size, but it shows very nicely how oversized the bay actually is on the kit.



So I made several templates, starting with one on thin plasticard and several others on paper before I found a size I felt was quite right.



The final template was transfered onto 1.5mm plasticard and cut out. This new skirt was then clamped to the fender and the outlines engraved with a needle before the cuts were made to match the plasticard skirt.



I added several tabs to the skirt to get the best joint here.



The fender on the body was cut out to match its outlines...



...before it was then glued in place



So the wheel bay was now the right size, but the raised mould line now had to be move down quite considerably. To achieve this I added a second piece of 1.5mm plasticard on top of the skirt with an outline that was determined using, again, several paper templates. This second piece was only tack glued for now to add the final touches.



The joint line of the plasticard skirt was drenched with a resin mix to add strength and was left to set overnight. This was cleaned up the next morning and Green Stuff applied to take care of any remaining imperfections.



The second plasticard piece, the 'trim extendor' if you will, was permanently glued in place and the joint line filled in with Green Stuff...



...which was cleaned up again, after which the whole thing looked like this:



All I had to do now was to repeat the whole Shebang on the other side



This is where I am now. I was hoping to have the fenders primed tonight but, allas, it was not to be. Maybe some time during te week.

[CTDavies]

Wow! It's 23:04 Central European Time and I have just crossed the 30.000 views mark. Thanks guys for being so interested.
It will be a year on this project this April, so I think I need to hurry up a bit before then to show you that within a years' work on a Pocher a lot ca be achieved.

[kmeaders@q.com]

Amazing work. Thanks for sharing all this. Ken

[Egon]

Hi Chris. Just wondering.
Do you have some pictures of the rear chassis, I find it very strange that the body flows in midt air in the rear with nothing to hold the body in place, is the pocher chassis missing that part or how ?