1975 Kawasaki S1 Rebuild: Installment Nine

Print Friendly, PDF & Email


The S1C’s bodywork – including the tank – is now finished and installed. Everything has been repainted in the correct Halibut Blue, with correct reproduction decals and pinstriping. The finish – done by Precision Motorcycle Painting  – is modern base/clear. The original factory finish was lacquer/enamel, with no clear coat.

To get an idea of what I started with and what I ended up with, here’s a “before” picture of the bike’s tank. It was a mess, inside and out. The underside had some severe rust along the weld seams – the result of sitting for probably 20 years after having been left with a gallon of gas inside. This alone would have probably necessitated cutting out the bottom and welding in a new section – major work and major bucks.

Then, there was the interior of the tank to deal with. Also rusted badly. Rather than try to rehab the bike’s original tank, I decided to replace it with an identical unit in much better overall condition I picked off the carcass of  an S3 parts bike.  The donor’s tank was physically solid, with no significant rust. It was just faded and needed to be boiled out and sealed – then painted. I think the end result came out well!

Before installing the side covers, I installed the new “250” badges, which are reproductions of the originals and which (I discovered) have slightly different (larger diameter) mounting tabs than the factory badges did. This was easily dealt with by slightly hogging out the mounting holes in the side covers to just slightly less than the diameter of the tabs. Slightly less, to provide a slight friction fit to keep them snug and tight.

I also used some very thin rubber gaskets between the tail piece and the frame – which Kawasaki did not use originally. Reason? Unlike modern bikes which mostly use plastic body parts, these old Kaw triples have metal bodywork, including the tail section. By sandwiching in the rubber gaskets between the frame and the tail section, I avoided scratching the paint (and exposing the rust-susceptible metal) on both the frame and the tail section. Use thin gaskets to avoid messing up the alignment of the panels.

Purists may notice the seat. It is not quite correct for the ’75 S1C. That’s because it came from the ’74 S3 400 parts bike. S3 seats are very similar, but Kawasaki added a stainless steel strip along the lower edge to dress it up some. I like the look and since this is not a 100 percent concours restoration (other deviations include a disc brake front end in place of the factory-correct – but horrendously inadequate – front drum brake) I decided to run with it.

I still need to have the seat recovered – but the donor bike’s original is in good enough shape to install for pictures. I also have a new brake/tail-light lens on order from Kawasaki Triple Parts. The original part if ok but has some scratches as well as yellowed lower section (for license plate illumination).  The new part will look, well, new

The engine itself is now in process. Here is a picture of the top end – cylinder heads, cylinder jugs and (new) pistons. These are refurbished, refinished and ready to install – including new needle bearing “cages” for the connecting rod small ends and fresh copper gaskets for the heads and fresh case gaskets for the lowers. I am hung up – momentarily – on splitting the engine cases and dealing with the bottom end because of a tough and very recalcitrant ignition rotor that just doesn’t want to come off the crank. I have the special Kawasaki tool the shop manual says you need to pull the rotor off the crank on order. Once the tool gets here – and once I get the rotor off the crank – I can split the cases, send the crank on its way to the machine shop for rebuilding (with new crank seals) and check the transmission and other internals to see whether they’ll require any first aid.

I have a next-to-no-miles (2,200) clutch pack which I will use – but even if I didn’t have a good used set service replacement discs are readily available. If the S1’s transmission is damaged, I have the S3’s transmission – same unit (though external sprockets are different, fyi). I am hopeful the S1’s transmission will not need any repairs and that the only major work will be re-doing the crank and crank seals. This job requires special tools and a machine shop, incidentally, because the two-stroke Kawasaki’s crank is a pressed-together unit. The S1, S2 and S3 all use the same crank (and rods). 

Another common part the S series bikes share is the oil pump, which is mounted to the clutch cover case and driven by a plastic gear eccentric that’s fed from the crank pinion. The pump itself consists of a metal housing enclosing a piston, with three clear plastic lines sending the two-stroke oil to each of the triple’s three cylinders. None of these parts are reproduced, so if your originals are damaged you’ll have to scrounge a viable used set. I was lucky here in that my pump and lines were all intact and more than that, in very good shape. A thorough inspection and cleaning was all that was needed.

While waiting for the special Kawasaki tool, I began the (hard, long and requires much patience) job of polishing the various engine cases. I began by cleaning each part with warm water and Brillo – to get rid of oil, especially. Once clean, the sanding could commence. I used the wet sanding method because it makes less mess and (I think) the paper lasts longer. I partially filled a 5 gallon bucket with warm water and just a drop or two of dishwashing soap. I  immersed the part in the water, then began sanding – starting with 400 grit and ending with 2000 grit. You may need to start out with something rougher to deal with deeper scratches. By the time I finished with the 2000 grit, the part had the look of fresh cast aluminum.

Next came the actual polishing. I used a fairly gritty graphite “cutting” compound followed by a less abrasive (red) compound to get the following results.

They are not perfect, but they look pretty good to me. In fact, they have that patina of age I have been striving for, with my goal being a bike that looks more like a very well-preserved, low miles original than a freshly done restoration to factory new.

What do you think?

Next installment – the engine – will be coming soon!



  1. As for polish after the rough work I always found Simichrome to be the fastest by far and gie the best finish also.
    I tried several others in my days of having no money and I always found Simichrome to be the best. I last bought it in bulk from (by memory as it has been a long time) Competition Chemicals someplace in Iowa. I bought several cans and have not had to buy more in the past 30 years. I would not mention it unless I found it to be superior as I think a lot of your efforts on your web site and your views on most everything.
    I am more of a British and Italian biker myself. All of my stuff is rather old as I haven’t done much of anything with it for many years. I did buy a Buell 1125 CR and a Ducati 600 (mostly for strip and re-sell after I find that the rotten Eurozone will not allow Brembo to sell seal kits for brakes) this past summer but it is beyond my capabilities for performance and comfort. 61 years old and the meat is not there any more. I must build up again for that, butt I will never have the sharpness that I once had, so I don’t push it much any more. Trolling for protracted pain is not in my book any more.
    Someday when you run out of anything to say, which isn’t likely, you could mention how the Eurozone has forbidden sales of seal kits for all braking systems on bikes and cars. That just makes affordability of a decent bike more impossible for a younger rider with mechanical knowledge, but low earnings to have a decent used bike or car. “Safety” costs blown to unaffordability is the gombit game. I do hate them for making the used bike purchase for an employee end up getting parted out because of the Euro bureaucrats’ parasitism on the young people.

    • Hi Erie,

      Thanks for the tip – I’d never heard about Simichrome; not sure we even have that over here. I’ve used Wenol for metal polishing with good results; Zymol’s my favorite wax.

      Did I read your post correctly on the legality of replacement seal kits? These are illegal in the Eurozone? Really? You mean, if a person needs a rebuild kit for a brake caliper, they’re not legal to purchase/sell?

      • Yes, that is correct, and furthermore they are not legal in the USA.
        Go try to find caliper or cylinder kits, they do not exist. One has to buy all new; safety ya know.
        I don’t know what it is like for Brembo brake add-ons for cars. Do any of your subscribers know whether rebuild kits are available for BREMBO calipers/cylinders? I’d rather have Wilwood, and thanks.

        • Wow – about Europe.

          But they are legal here. Heck, I recently (with a month) ordered a rebuild kit (with seals) for the S1’s front caliper. Numerous web sites offer them. I’m also pretty sure I can legally get a caliper rebuild kit for my old muscle car. I’m unaware of any change in the law that makes the sale of these parts illegal.


Please enter your comment!
Please enter your name here