The Yoshimura ST-1 lets the oil-cooled 1200 show its true colors
The oil-cooled 1200 engine had its top-end punch dulled by the cam characteristics. To put it another way“the tachometer climb and speed don’t sync up”is how I’d describe it. With the Yoshimura ST-1 installed, the engine speed climb and vehicle speed sync up nicely.
Crack the throttle and it accelerates hard—that’s what a true oil-cooled bike feels like.
We’re going to make the cam sprocket adjustable with elongated holes
You don’t need to elongate the holes that much—just enough to adjust between the lobes is fine. I still remember back in the day when someone told me to elongate the sprocket holes with a file!
This Hayabusa sprocket is easy, but GSX-R sprockets are all hardened, so it’s a pain. I have a distant memory of it taking a whole day just to elongate two sprockets… The Yoshimura ST-1 is so precise that sometimes you get the exact spec without any modification. But the world isn’t that kind, so we elongate the holes on every bike.
Once all the prep work is done, it’s just a matter of swapping it in
The actual work isn’t much, but the prep is tediously time-consuming.
We spend time on the tedious stuff like elongating the cam sprocket holes, deburring the cam holder, polishing the cam, and beveling the cam lobe edges. We adjust the valve timing, do the valve clearance adjustment, readjust the cam chain, and we’re done installing. The cam chain is automatic, but to do it right, you need to feel the current state of the cam chain and adjust accordingly.
Plastic and rubber engine components matter
The slider, bathed in oil over 100 degrees and scraped by the chain, is the unsung hero. Over time it hardens like ceramic.
It has a bone inside so it won’t snap easily, but it’s still an important part. A new one is so flexible you can dig your fingernail into it. The rear side can’t be replaced without splitting the case, so we only do the front.
Quick and easy assembly is complete.
We do a final check of all components, pour plenty of engine oil from the top, and seal it up. It’s also important to do a good dry crank to circulate the oil before starting.
At around 60,000 km of mileage, the cam showed no scuffing and was in excellent condition. I get the impression that scuffing is reduced when you maintain stable oil pressure during use.
We also made sure to sync the carbs properly. Stable idling gives you peace of mind, and smooth low-speed response means better rideability. It’s one of those small improvements that add up to make a real difference.
We also re-wet blasted the breather cover. This year’s number one best buy: the Reborn wet blast. It’s a tool that saves time and dramatically improves the finish, so if you’re thinking about it, definitely check it out.
Potential problem areas going forward: Signal generator
The inside gets soaked in engine oil, so the wiring is in a pretty harsh environment. Most bikes’ wiring is already hardened like plastic, and if you touch it, the insulation cracks.
It doesn’t cost much, so if you’re planning to ride for another 5 years, it’s a good idea to stock one. *Of course, I already have one…
The elongated holes take a bit of work. Starting with craft paper and ending up with a shape like this. Pretty much the same as the original. We drilled the case for the M4 positioning bolts.
Then apply Megmix and lock it down with bolts. It’s fixed so securely you can’t remove it anymore.
We adjusted the headlight beam and we’re done. This will pass inspection as-is, so no worries!
The Daytona D-UNIT (early model?) connectors are shot~ So I rebuilt them while I was at it.
Blast from the past! GSF1200R/R number
Still keeping it in storage…Nostalgic, right? I love this hand-drawn Petty era the best.
It still looks cool! It was pretty ahead of its time…
I ended up riding about 40 km on surface streets during break-in. Given the recent generator connector melt issue, I wanted to check on that too.
Rather than replacing the regulator on this early generator, I think the best approach is to get a later-model generator and swap it in.
It’s all running great now. Carbs really do respond well to vacuum!
ポチップ
