1975 Kawasaki S1 Rebuild: Installment Four

Rebuilding this bike – which had been sitting for probably 20 years before I got it – required more than just a clean-up and refreshing of the mechanical parts.

The frame, for example, needed to be stripped to bare metal to do a proper job of bringing it back. The original factory paint had been chipped or flecked away in several areas and there was a good bit of surface rust that had to be gotten rid of. I decided to media blast the frame, and this in turn led me to rationalize the purchase of a media blaster – my new buddy, Mr. Bone Stripper. I reasoned I had two options: One, pay a body shop to do the stripping (and painting) or invest in a media blaster and do it myself. I chose the latter course because not only is it much less expensive, long haul, but I’d have a new tool as well as a new skill.

The blaster rig, an “outside” unit (as distinct from a cabinet/enclosed unit for smaller jobs) cost me about $350, which included the unit itself plus accessories such as spare ceramic nozzles and a good hood to wear while doing the work. The ceramic tips wear away as the media material shoots through it, auguring out the little hole, which eventually reduces the airflow and the effectiveness of the blast stream – especially if you’re using an air compressor of less-than-ideal capacity, which I did. My 150 gallon unit was just barely adequate to run the blaster, using the smallest diameter ceramic nozzles. Eventually I will invest in a better (larger) compressor, around 300 gallons, that can maintain about 15 CFM of airflow. That will make future work easier. But if you, like me, are on a budget, a smaller compressor will work – it will just take a little longer to do the work.

If you have never blasted before, it will also take a little bit of practice to get the hang of it. The instructions that come with the unit are just a starting point. You will have to learn by doing, in particular, learn to get a feel for just how much to open the valve that controls the flow of your blasting media. Open it too much (or too soon) and the hose or nozzle will clog. Then you have to stop, shut off the airflow, remove the hose from the unit, shake out/clear the stuck blasting media and then try again. I started with small stuff, for example, the gauge cluster housing and then the chain guard.

Once I dialed in the air flow and media flow, the work went fairly smoothly. I used a pair of vise grip pliers to hold little parts like the chain adjuster “blocks” (and their bolts) that you can see in the photo on the left. You will want to wear a pair of heavy gloves because the media material will do a job on your skin if the spray from the nozzle hits you – and it will hit you. Fine particles ejected by a 90 PSI airstream go everywhere.  The blast hood is an absolute must. Do not cheap out. These cost less than $30 – cheaper than the pirate eye patch you’ll be wearing if you don’t wear the hood.

For the rest, just wear old stuff.  Some recommend wearing a full astronaut/bio-warfare “onesie” – but it was just too damned hot to do that and I found that so long as you protect your eyes and hands, you’re ok. You will get dirty, but unless you actually point the business end of the blaster at your flesh, you won’t get any Blaster Burns.

One other thing: Buy a respirator/breather. Media blasting is one of those things – like painting – that can really screw your health if you play stupid. Buy a good one that completely covers your mouth and nose and which has a particulate filter specifically designed to protect you – your lungs – from fine particles.

With all that stuff covered, on to the blasting. I got the chain guard and gauge cluster done  then moved on to the swingarm – a larger piece. By this time I had gotten a feel for the blaster and got it stripped down in about 5 minutes. Important note: When you are working on parts that have delicate interior surfaces (such as machined areas or sleeves for bearings, etc., like the swingarm’s pivot) be sure to thoroughly seal off the parts where you don’t want grit to go.

Here is an “after” shot of the rehabbed swingarm. I managed to lose the “before” pictures I took, when it was uglier than Lurch in the morning. Before blasting it, I had to degrease it, which I did by hand with solvent and brillo. Once it was clean and dry, I proceeded to blast it, followed by a coat of primer and three coats of gloss black. Here is the finished piece:

Next, the Big Job – the frame. Having successfully done the small parts and becoming One with Mr. Bone Stripper, I was ready. I propped it on a large stump I have outside of my workshop – good support and plenty of light (and air, to dissipate the flaying paint and flying blast media). If at all possible, you should do this kind of job outdoors. Inside, it will make a mess like you won’t believe. 

It took me a good two hours of work to completely strip the frame down to bare metal; to get at the old paint in every nook and cranny (there are many of these) as well as to thoroughly strip away all the (mostly) surface rust that was all over this poor old bike’s skeleton. Here is the stripped frame. It looks like it just came off the Kawi assembly line; brand-new and ready to be primed and painted.

Speaking of which: It is important not to wait long after you strip the frame (or any other part) before applying at least one coat of protective primer. Otherwise you risk surface rust – and having to re-blast the entire thing a second time. Bare, unprotected metal will rust very quickly if exposed to moisture and unless you live in Arizona or some such place, even the trace humidity in the air will get rust going faster than you might believe – unless you’ve actually made the mistake of leaving bare, unpainted metal exposed to the elements.

So, to avoid this, I primed it almost as soon as I was finished blasting it. I used a self-etching primer, ideal for work like this. It is not necessary to sand the primer before applying the final coat and the stuff does a good job of prepping an “industrial” (read: a little rough) surface for painting. I jimmied up a rig to get the frame in the air, so that I could get at all the nooks and crannies/weird angles. A pair of bungie cords with one hook through a frame eyehole and the other hanging onto a large screw worked perfectly for me.

I let the primer dry overnight. The next day – a warm, dry, sunny day (avoid painting on wet/humid days) – I sprayed on the first topcoat. I let that dry a little – about 30 minutes – then applied another coat. One more, about thirty minutes later, and I was done.

The frame looks brand-new again.

Here is a wide-view plus a close-up. The trick to painting is to apply just enough to get it “wet” (it will look glossy) but not too much that it will run. I used fast-drying enamel (gloss black) to do the deed and am very happy with the results. Some people prefer powder coating – which is more durable, but also more expensive because it will almost certainly require you to farm the job out (unless you spend a fortune on a powder coating rig and  the oven you will need that’s big enough to swallow an entire motorcycle frame).

The next installment will cover the build-up of the rolling chassis. I am now scrounging NOS/replacement bits and pieces, including a set of “correct” shocks and (ka-ching) a set of NOS rims/spokes, which will be one of the major unavoidable expenses associated with this resto. I’ve already restored the main gauge cluster (see photo below), which involved finding a replacement tachometer (original beyond repair) and cleaning/blasting/painting the housing.

But it’s ready to go – and just waiting for a working bike again.

In the distance, I think I see a pinpoint of light at the end of the tunnel….