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Building a Pre-Add BRM

10855 Views 81 Replies 18 Participants Last post by  Rail Racer
The combination of an apparent high level of interest in Mac Pinches Pre-Add bdies as decribed in "News" and the recent arrival of some of Mac's new laser cut chassis has prompted me to start another project along side the W154/Patto chassis that is ongoing.

Thinking that there might be some interest in this project, I am going to document it in photos and (hopefully) brief text as it progress.

These will be a series of "real time" progress reports, not a "how to" since what I describe in one post may well be reversed in the next when I discover that it didn't work! I'll try to keep a rough log of time and cost.

The bits and pieces:

In no particular order: the body molding, driver, vac-formed screen and metal castings for the steering wheel, exhausts and filler cap (all part of the body kit) There are actually two chassis in the picture - on the lower right the laser cut chassis as supplied and spread about the middle, the parts after cutting and removal of the webs. The rear axle carriers/rear motor mount are "stuck" together. The fit of the parts is so good that the assembly is stable without soldering! Also in the picture is a guide and guide shaft bearing. One of the first things that I do with any commercial chassis is to try and figure out what guide shaft fits the hole. This is of particular interest for laser cut steel chassis because my experience is that these holes can oly be enlarged with some difficulty, the steel being very hard. In this case, the TSRF guide made for conversion of plastic chassis is a perfect fit and, on preliminary examination, to be short enough so that it will not extend beyond the front of the car (important for some rules)

Now let's do the numbers: A quick Google search yielded:

LOA: 158"
Width 56"
Height 35"
WB 98"
Wheels and tires: 5.25 X 18 front, 7.00 X 17 rear

If I believe my digital caliper, the wheelbase is spot on and the length is very close (perhaps 0.10" too short, but, the body that Mac has modeled differs from the one pictured on the site so I'm going to call it perfect!

A listing of tire dimensions for Dunlop Vintage Series tires yields:

7.00 X 17 30.2" diameter
5.50 X 18 30.1" and 5.00 X 19 29.6" so I'm calling 5.25 X 18 as 29.7"

This translates into 0.94" rear tires and , rounded to /100s, the same at the front.

Quick dimension check: The distace from the center of the rear axle carrier to the bottom of the chassis is about 0.288" If we subtract that from the radius of the proposed rear tire, 0.47", we are left with 0.18", plenty of room to add a weight pan and still meet a 0.125" ground clearance rule.

Second check - height is listed @ 35" or 1.1" in 1/32 scale. Knowing the axle height we can then check the body to see where the axle would be to give us that height in the finished car - and it turns out to be exacltly where Mac has placed the top of the rear axle slots!

Little worry (postponed until the initial chassis assembly is done and a motor fitted) - the fit between the top of the motor and the dash is the limiting factor for positioning the body on the chassis and, at first glance, it is a problem. The decision will be: can enough be ground off the bottom of the dash to accomodate the motor or will the dimensions dictate a front motor placement (and, in the latter case, isn't it nice that the chassis kit includes twoadditional motor mounts!)

An issue which has arisen long before its time: decoration: I am not really enamored of the peculiar diseased liver green that was chosen for these cars! (I recognize that there may have been budget constraints but did they really have to use paint left over from the redecoration of the railway station loos?) Any suggestions as to alternate correct liveries will be appreciated. I reserve the right to assign the car to Ecurie Martini and since this organization (long predating the red, white and blue "Martini" sponsorships) is a Belgian/American consortium, I'll paint it yellow!

Time so far, hands on and on the net, about 2 hours - parts @ current exchange, about $50

Next steps: chassis assembly, motor, axles & gears

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You've got me hooked Martini! I'll be logging on in expectation on the hour every hour. My BRM's still in the pending file, so I hope you'll make all my mistakes for me!And I think the duck egg blue is great and should be adhered to! Mmm, municipal loos....
I`m hooked too. This is just what I needed to inspire me. Best of luck...we`ll be watching closely
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QUOTE ...did they really have to use paint left over from the redecoration of the railway station loos? Any suggestions as to alternate correct liveries will be appreciated...
An alternative to the er.. pee green could be the dark green as run from late 1952 and into 1953?

Whatever, thanks for the feature EM - a really good read and I look forward to seeing the car as it is built
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Good timing, i've just bought some of these chassis. Up till now I've scratchbuilt chassis for Macs bodies.

I've also used nostalgia bodies from Oz, cheap but less detailed and a long waiting list but they do make some cars Mac doesn't (yet).

Now, if only we could make it sound like a 1:1 V16

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Next steps: Warm up the soldering iron. It's a real treat to work with well made parts. Everything fits together perfectly - no hammering, bending or colorful language! The various pieces have reasonably large fastening surfaces so I decided that a high strength soft solder would be sufficient. I like "Tix" - it has a low melting point but is very strong. Stay-brite is also good. Contrary to some opinions, i think that steel is esier to solder than brass with the right solder and flux (acid). It is a poor conductor of heat so the heat stays were you put it, the joint region heats up fast and neighboring joints are not disturbed. I also believe is big irons. Most people use 60-75 watt pencil irons. Unless the space is too small to accomodate it, I use a 150 watt truncheon with a pyramid tip - when I want hot, Ii get hot! here's the result -still needs a good scrubbing and sanding:

Dead easy - just tin one of the surfaces, apply flux, put the parts togethr and heat. the parts fit so well that you don't need 4 arms to keep everything in alignment.

After attaching the rear axle carrier/motor mount, I soldered in a pair of bronze bushings so that I could get an accurate position for the rear axle to double check the wheelbase. The Pre-Add chassis offers 6 wheelbases by using 3 different postions on front axle carriers that can be installed in 2 ways. The BRM wheelbase is 98" or 3.0625" in 1/32. I found two choices: 2.96" and 3.205" (these are rough measurements made by eyeballing axle centers and lining up the points of a dial caliper) I chose to go 0.010" undersize and fitted a length of 1/8" OD brass tubing to the appropriate holes and soldered in the front axle carriers followed by the guide plate which fits between them and finally, the bushing for the guide.

A little grinding and the chassis dropped into the body:

Then the TSRF guide was "offered up" Ah, well, so much for eyeball estimates - the guide extends beyond the nose by 1/16" or more and that will get worse with braids installed:

Back to the parts bin...after all, it is and ordinary 1/8" post - and here's an MRRC one:

Now, I have not had the best of results with these guides but perhaps it is just a matter of learing - decision pending (do I want to try for the race win or the concours win?)

And, thanking people for their suggestions:

QUOTE And I think the duck egg blue is great

Is it really blue - the pictures I have all look to be very pale green I could live with a light blue.

QUOTE An alternative to the er.. pee green could be the dark green as run from late 1952 and into 1953?

Did the P 15 run under those colors or was it a later version?

chassis soldering - 30 minutes
body grinding and fitting - 45 minutes
pondering the guide problem -I hour!

To be continued......

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Duck egg blue, perversely, is a sort of pale green I believe. But now the real question is can you make it throw pistons out of the side and dump oil on the track just like the real thing?
But thanks for a great project- this is REALLY interesting. JP- have you sent Mr Martini his Model Cars plan? It'll have to be the three-armed pullover otherwise.
Heh heh, EM reckons that with Mac's new chassis you don't need four arms any more, so, a three armed sweater would suit just fine howmet

Regarding the colour, I think that the darker green was not adopted until after the nose blister had been added (to clear the larger radiator fitted because of overheating problems). So, if you go for the concours option EM I think you might be stuck with the pale green
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...then again I think your Martini livery might be The right one. I think that would look good Any time, any place, any where.

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If you do deside to go for the concourse points(and we all know you will),Humbrol #1 is almost a dead match.Maybe with a splash of white to tone it down a bit more,but,it is pretty close right out of the tin.

I should have my two eared knock off inserts ready in about a weeks time also.

"Duck Egg" and "Sky Type S" are actually the same color. Sky is the official designation, Duck Egg the fitter's designation because everyone could see the green tinge.
Ex RAF stocks were cheap and a number of cars used it until about 1960. Actually, I find it rather attractive.
The only BRM Dark green I remember chasing down was called "Brunswick". This particular color has more variants than you can immagine. Some 20 years ago, i got a chip from the manufacture of the paint BRM was using(long story, friends in ECRA....) That particular green was one i matched by taking Floquil's Brunswick and adding a little Dark Blue. Floquil's is a railroad color and a little to gray.

thanks E-M it,s looking good, whem i first started these kits i have the grandiose idea of building each kit, super detailed, all to run perfectly, but with cleaning, doing the washing, cooking, shoping, onlt 2 where built in a very basic form, and NO! im not going to take a wife to help out.they are floating about the uk somewhere? just to back up a couple of point allready made, the mk 2a only ran in the light green, mk 2 &3,s where BRG , the light stuff was ex RAF paint, im wondering if there is something that could be had from the aircraft kit builders paint store?. a thing i have found with the chassis, if you take a little metal from the side uprights that fit into the base of the chassis, this gives for and aft movement of these uprights thus allowing the chassis to be used for other cars macp
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QUOTE and NO! im not going to take a wife to help out

Odd, my feeling is that if I didn't have one, I might make more rapid progress!

QUOTE a thing i have found with the chassis, if you take a little metal from the side uprights that fit into the base of the chassis, this gives for and aft movement of these uprights thus allowing the chassis to be used for other cars macp

Very good point - I simply didn't think of that!

No progress last night - wine tasting dinner - head should be clear by about noon.

Next steps involve another dive into the parts bin: First thing to address is the "BRM sound" - and the fact that I think a fair bit of weight will be needed to keep things upright so my first try will be one of Patto's "Little Rippers", reputed to be good for 37,000 RPM, geared about 4.5:1 to both handle the weight and provide some brakes. Because of the rear wheel dimensions, this will be similar to about a 3.8:1 gearing in a model of a current car.

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QUOTE (mac p @ 3 Mar 2004, 01:20 PM)NO! im not going to take a wife to help out.
Get a mistress instead Mac! The more I see Mac's cars being built, the more I think I need one. Any chance of some more piccies EM?

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Yes, as I indicated, the "Ex-RAF" color is listed as "sky type S" or "Duck Egg" in the catalogs. Everyone makes it. My favorite is Humbrol, they are a little anal about getting the color right. Going into more detail is a kind of a pain...In the US the humbrol military colors are difficult to find. And in Britiain, I assume that things like Floquil are tough to come by.

Anyway, Sky is easy. Besides the BRM, Moss used it on a variety of their cars. Including those wire wheel equipped Lotus 19s!

It is mixing up the "BRG" that causes the problems. The short version is that there IS NO SUCH COLOR! Lots of things got called BRG. In BRM's case, the supplier listed it as "Brunswick" green. And the chips I aquired match no known BRG any hobby company has produced.

difflock, iv got 1, why do you think i look like this, im only 29!!
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QUOTE In BRM's case, the supplier listed it as "Brunswick" green.

Rocky, I have a full CD on a similar discussion.... "Brunswick" green it is!

Kind regards,

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And now the tale of a couple of 180 degree turns (If anyone went out and ordered parts on the basis of my last post - I warned you at the outset)

Time to fit a motor: With the guide problem semi-solved, my next concern was the clearance between the motor and the dash (fascia across the water) In went a standard FK can (TSRF, Little Ripper, Cheetah, Fox etc.) and into the body. As I expected it hit the dash. Burr in the Dremel and grind away - but how much? I made the decision that I would not cut beyond the point of the preformed hole for the steering wheel. Cut and try again- the chassis still would not fit all the way into the body. 3 choices:
1. Cut more and glue the steering wheel to the top of the motor - not acceptable
2. Go to a front-mounted motor - good choice but not for this project - only as a last resort if there is no alternative
3. Different motor - I have an assortment of mini-motors but while poking through the parts boxes, I took out an SCX motor - it is 0.56" high vs the 0.6+ of the FK can - enough to make a difference - take a look:

40/1000" is just enough! Here is the motor mounted:

The installation is not without some problems:The contour of the can is different from the FK (a bit wider at the flats) requiring that the inner upper coners of the chassis rails be filed a bit. The shaft-end stamping of the SCX motor is not exactly a precision part and when mounted with the single available screw hole (note- drill an additional hole in the next chasssis while it is still in the flat), the bottom is "pulled" and the motor slopes down towards the front. This cannot be corrected by installing the front motor mount . the chassis simply flexes. One could solder the motor in but I was unwilling to do that at this stage. - Solution - a high tech shim (folded decal backing stock) at the lower edge of the motor mount:

With this in place, the front motor mount was set and soldered.

So, the idea of a high revving motor with short gearing has gone by the board - and, as it turns out, just as well. When I began to fit the gearset, I immediatley realized that the spacing between the axle carriers was too narrow for any of my 64dp metal gears! They all have an external (opposite the gear teeth) hub in contrast to the typical plastic crown which has an internal hub. I fitted a Slot-It 3:1 gearset. These are nice gears, perhaps the best of the molded plastic but my prejudice is that a well bedded 64dp metal set is smoother and more durable. Does anyone make metal crown gears with an internal hub?

With one exception, the rest of the project should be simple plug and chug. The exception: wheels and tires.

The P 15 mounted 17" wheels at the rear and 18" wheels at the front. Nothing in my parts bin nor on any of the web sites I visited had an acceptable combination of diameter and width. I do have some 60's 1/24 wheels that are close but they are all made for threaded axles and boring and bushing them is a fiddly task that I have never done right. The simple answer is to chuck up the aluminum bar and turn away but I am going to try an alternate approach. A 17" wheel will have an outer rim diameter of 19-20" or about 0.62" in 1/32 scale. The diameter of the ridge of the BWA wheels is 0.62" and, the really hard work, getting a round OD and a concentric, square bore, is already done so I shall machine off the outer rim of a wide BWA wheel, cut a tire depression and drill and tap the inner rim (AKA the brake drum) for a 1-72 set screw so I can glue the tire on and true is prior to mounting - like this:

The broad dashed line defines the area to be removed, the dotted line the tire recess and the little bulls-eye the location of the new fixing screw. I think I can find a suitable Ortmann tire - probably a narrow 1/24 front - to get me to the desired 0.97" tire diameter.

The fronts are still "under review" I am thinking about simply turning the whole business out of delrin -light, easy to turn and perhaps the characteristic clatter of hard wheels on a track will offer a simulation of bits and pieces falling off, rods exiting crankcase etc. I have also picked up some O-rings with a 3/16" section and want to see how they will look mounted with the outer surface gound flat.

The best laid plans...........


About 2 hours of fiddling around
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One suggestion is to (if you have or can access ) take a wheel from an Airfix Auto union D type and use this as a template for the wheels using the inserts and tyres to make moulds and hey presto you have an aluminium hub A silicon tyre and a passable resin wire wheel insert. Time consuming but looks OK.
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