Polyester resin casting new light lens for a bullnose Saab

It is becoming increasingly difficult to find new directional light lenses for the two-stroke bullnose Saabs. Or actually it seems almost impossible. And I need four of them for the Saab Sport – and a few spares wouldn’t hurt.

I have a few lenses that are in more or less decent shape, so I figured I could try and make copies of them. I read about polyester resin casting using a silicone mold, and decided to give it a try. This is a pretty popular way to make hobbyist plastic parts for model railways or scratch built scale models, so i figured it can’t be too difficult.

One new resin cast Saab directional light.
One new resin cast Saab directional light.

I was actually somewhat surprised, but making a polyester resin casting worked out very well as you can see above. Basically what you do, is make a two-part mold (it needs to open up to remove the finished piece) out of silicone mold rubber. The mold rubbers available come in many flavors – soft, hard, heat resistant, not heat resistant, etc. Then you pour in polyester casting resin and wait for it to cure and harden. After it has cured you open up the mold, take out the part and remove any overflow or excess resin. You can buy suitable materials in most hobbyist stores or online.

I used Efco silicone mold rubber and polyester casting resin.
I used Efco silicone mold rubber and polyester casting resin.

As I have not done any of this before I used what the local hobby store had (Harraste, Tampere). Efco Silicone mold rubber and Efco Polyester casting resin. Efco Polyester resin is water clear and should make very nice clear plastic parts. There are a few drawbacks – polyester resin is hazardous to your health when casting and it does shrink a bit when curing ( 6 to 8 %). So you will end up with a slightly smaller part than the original.

UPDATE: I have been recommended UV protected polyurethane instead of polyester. It is more impact resistant and should not yellow over time. I tested the polyester lens and it does break quite easily. I will try out polyurethane and report on the results.

Both – the silicone rubber and the casting resin – are two component chemicals, so they are mixed in a very specific ratios with the accelerator. There is no hurry in the mixing as the working time is usually at least 15 minutes before they start hardening. Read the instructions.

Making a silicone rubber mold

Casting the first mold half.
Casting the first mold half.

First I cast one half of the mold. The inner part of the light lens. You need to make a little tub for the part and design it so that the silicone rubber doesn’t get too much under the part. Otherwise it is hard to remove the original from inside the silicone.

The silicone mold rubber copies all the surface detail on the original piece. Including tiniest scratches.
The silicone mold rubber copies all the surface detail on the original piece. Including tiniest scratches.

As you can see from the photo above the silicone reproduces all the surface detail of the original piece. Including all the scratches and other imperfections.

Even the Hella company logo is reproduced very nicely in the mold.
Even the Hella company logo is reproduced very nicely in the mold.

When the first half was done I applied some mold release (Vaseline grease) on the edges of the first half. I then put the original light lens back in the mold and made a new tub for it, proceeding to cast a new layer of silicone rubber on top.

Both mold halves done. I used regular Vaseline grease as mold release.
Both mold halves done. I used regular Vaseline grease as mold release.

Polyester resin casting

Next I cut a few holes at the highest point of both ends of the ”lid”, so I can pour in the polyester resin. The second hole is for the air to escape as the resin displaces it. You know that the mold is full when the resin comes out of the second hole.

Removing the polyester piece from the silicone mold can be tricky.
Removing the polyester piece from the silicone mold can be tricky.

Above you can see the cast part still attached to the mold half. On the left you can see the small square hole where the resin was poured in. There is a similar hole on the other end. The holes need to be at the highest point so you will not end up with a partially filled mold.

As the silicone is quite stiff and the polyester resin shrinks a little when curing it can be quite tricky to remove it from the mold. Despite being careful I tore the mold a little. Nothing to prevent using it, but I need to be more careful with it.

Silicone molds and the resin cast directional light lens for my Saab Sport.
Silicone molds and the resin cast directional light lens for my Saab Sport.

Above you can see both the mold halves and resin part just removed from the mold. Some cleanup required.

Polyester resin cast light lens on the left. Original Saab part on the right.
Polyester resin cast light lens on the left. Original Saab part on the right.

New polyester resin light lens for the Saab Sport on the left and a Saab original on the right. So far looking great.

There is one more downside to polyester resin. Most of them yellow over time if not UV protected. You can coat the piece with UV protecting agent though. Some of the resins also contain UV protection chemicals.

I don’t know how good the Efco resin is in this respect so I’m going to test the part in my two stroke. I’ll install one polyester lens on the car and store another in dark cool place for the same period and see if there is a difference.

Also I don’t know if the resin can withstand all the weather – rain, sun, stones etc. as well as the original. But I think after the summer I will pretty much know if polyester lenses are a go for the Saab Sport.

Please let me know if you have experience in polyester resin casting parts and know suitable resins with good UV properties.

Saab Sport & two stroke gear box restoration

I’m taking a break from the Saab 99 turbo metal work. Just to do something else for a while I decided to inspect and repair some two stroke gearboxes. Also a friend asked me to fix his shortnose 95 noisy gearbox.

Finding the necessary bearings was not exactly easy. I did have some new bearings and components that I used on the Saab Sport rally car gearbox. Some are simply not availlabe, like the 25x29x28 mm 2nd gear needle bearings. I needed to find a suitable replacement.

I also did a spare box for the Sport. I got offered a V4 Special 1 drive gears. Fitting them in a two stroke gearbox required using some bearings and the side axle from a V4 box.

The 1964 Saab Sport gearbox

Some of the other gearboxes

Saab service books and spare parts catalogues online

saab-katalogs-online

I was googling the other day trying to find a copy of the Saab 99 spare parts catalog with the 1978 Turbo included (it’s not in all the spare parts catalogs). I seem to have misplaced my own copy…

I didn’t find the 99 catalog, but there are a couple of sites that have pretty cool stuff available, including Saab Sport, Monte Carlo, and Sonett Workshop Manual supplements. But also some brochures and other catalogs, accessories etc.

Check these out:

http://www.vintagesaabmanuals.org/

http://www.saabklubdanmark.dk/X-Files/

Saab Sport – needle bearings, regular and Sport heads

Last wednesday I went to pick up a few parts for the Saab Sport. I found a bunch of used and NOS parts, and spent a ton of money… The Sport parts are always more expensive than the regular stuff…

But, as anyone who has owned a Sport knows – it’s a completely different car than the regular Saab 96 bullnose. Most people look at a Sport and since it looks like the regular 96 think there’s not a whole lot of differences. But there is a lot – basically only the body is the same.

A few examples:

– the complete interior including seats, panels, dash, metering etc.
– Hubs and brakes
– Gearbox ratios
– The engine is completely different with oil pump, different crankshaft, block, head, carburetors, aircleaner
– Body trim

And if you go more into detail you find more stuff that’s different. That makes parts hunting bit of a challenge, since you need to be ever vigilant not to miss Sport specific parts unintentionally.

A couple of examples:

At the place I got the parts from there were about a dozen two-stroke heads in a single pile. We checked all of them to see if there were Sport heads in there. There were two. Here’s how to spot them:

Here's Saab Sport head (left) and a regular 96 head (right). From the top there's not a whole lot different other than the Sport head having smaller bolt holes.
Here’s Saab Sport head (left) and a regular 96 head (right). From the top there’s not a whole lot different other than the Sport head having smaller bolt holes.
Underside. Here's the real difference - the Sport head has a wider squish area (around 12mm) than the regular head (around 9 mm). The chamber volyme on the Sport head is also smaller, which increases compression ratio.
Underside. Here’s the real difference – the Sport head has a wider squish area (around 12mm) than the regular head (around 9 mm). The chamber volyme on the Sport head is also smaller, which increases compression ratio.

And here’s also a small but important difference:

The Sport has wider needle bearings on the piston pin than regular 96. So – rebuilding a Sport crankshaft or with a tuned engine you really want to use the wider and stronger needle bearings. But they can be hard to spot if you cannot compare them to the smaller ones.

Saab Sport needle bearings in original package.
Saab Sport needle bearings in original package.
When put next to the regular piston pin needle bearings the Sport ones are visibly larger.
When put next to the regular piston pin needle bearings the Sport ones are visibly larger.
Two packets needle bearings sets in various over and under sizes.
Two packets needle bearings sets in various over and under sizes.

Lockheed brake master cylinder, V4 corrosion repair, two stroke fuel lines

Just a little update.

I promised to do some welding on a V4. The corrosion was worse than it looked (as it always is) but we got it done. I have also been collecting parts to fix the fuel issues with the two-stroke. And I started to fix the Lockheed brake master cylinder of the Sport.

A few pics: