Installing Yoshimura ST-R Camshafts


Most riders with a mechanical background or a bit of natural mechanical ability can fit camshafts by following the correct workshop manual for their motorcycle. However, setting valve timing using adjustable cam wheels is another job altogether and one that requires patience, understanding and confidence. One mistake and your motorcycle engine could be history.

Opening a new box of Yoshimura camshafts is a religious experience. First, there's the Yoshimura logo that we all recognize so much and instantly relate to performance.

The Yoshimura ST-R camshafts we have are perfect for street and ride day performance but not ideal for maximum performance. But it is all about compromise and making the motorcycle a great sportsbike. These Yoshimura camshafts will do it.

Since the early days the Suzuki GSX-R K5 was original meant to be a track-bike, now we are fitting Yoshimura ST-R camshafts to that motorcycle, and hope to make it also a amazing street machine.

The inlet camshaft specifications are 10mm lift LC 105 degree, BTDC 22.5 degree 1mm open, ABDC 53.5 degree 1mm close and 256 degree/1mm duration with a valve clearance of 0.20mm. That's a nice big fat cam that's for sure and a valve lift increase of 0.80mm over Suzuki stock camshaft.

The exhaust cam is milder and there are reasons for it. Although the rule 'what goes in must come out' applies, running a maximum lift and wild exhaust cam is plain too loud for the road as the exhaust valves open so early that the noise wll attract the wrong attention from the boys in brown (police).
The Yoshimura camshaft is good compromise if there is such a thing. Our mechanic preferred exhaust cam specifications of 8.81mm lift with ideal timing of 81 degree/50 degree is too radical – although it would be perfect for getting those combustion gases out quickly. So we settle for the Yoshimura ST-R of 8.6mm but with more reserved timing of 72 degree/50 degree. Yoshimura specifications are 8.6mm lift LC 110 degree, BBDC 56 degree 1mm open, ATDC 16 degree 1mm close and 252 degree/1mm duration with a valve clearance of 0.25mm.

Once the Yoshimura box of goodies is checked, it is time to set the valve clearance for the Yoshimura camshafts. This needs to be done on at least one cylinder in order to set the timing but I always say just do them all...

To avoid the job of installing the new cams simply to measure clearances, than take them out to adjust shims, I measured the clearances earlier with the stock Suzuki camshaft and noted the shim size under each bucket.

The Yoshimura camshafts have a base-circle with a 27mm diameter, while the Suzuki stock camshafts have a 28mm base circle. This is a reduction of 1mm, which is divided by two and equals a clearance difference of 0.50mm. Therefore as a base point – to achieve the same valve clearances as I had measured with the Suzuki stock camshafts, I need to add 0.5mm to each current shim. Most shims in the Suzuki stock head are around the 150 to 155 size so with the swap done, most shims are within the 205 to 207 rance. So, that gives the clearance within the stock range fo adjustment. We want 0.20mm IN and 0.25mm EX. To achieve this I simply adjust the shim size as required and most end up around the 207 size IN and 200 to 205 EX.

The next job is to double check the collets and retainers on the valves and apply some engine oil with an oil can. Fit the shims and buckets and then apply some more engine oil on the cam tunnels and on the top of the buckiets.

Give the camshafts a good wipe over. The Yoshimura ones appear to be coated in DLC (Diamond Like Coating), which is great. Align the sprockets as per the instructions that come with the camshafts and tighten the retaining bolts lightly. These will be Loctited later once timing is achieved.

Ensure the camshaft chain guides are in place and the chain is free. Then using a TDC stop, set the engine to TDC on cylinder number one. Slip the exhaust cam in first and fit the cam cap ensuring all dowels are in place and surfaces; oil channels and threads are clean. Tighten the cap in sequence as specified in the manual. Repeat the process with the inlet cam, ensuring the timing marks are as close as possible to ideal with consideration for the amount of slot in the cam sprocket available. You want to give yourself maximum opportunity for adjustment.

With the camshafts in and the camchain tensioner in, measure the valve clearances on cylinder number one to ensure your calculations are correct before preceding any further.

The first step is to fit a degree wheel. I have an old one I have for ages that goes on the alternator end of the crankshaft, so removal of the left hand engine cover is necessary.

Then make a pointer for the degree wheel out of a piece of welding wire and bolt it to the engine above the degree wheel.

With the TDC stop in place or a dial gauge determine TDC on cylinder number one (BDC cylinder number two) and set the degree wheel to TDC. Now it is critical moving forward that you don't bend or move the pointer!

To mount the dial gauge with a magnetic base, we use a small 20x30mm mild steel plate with an 8mm hole drilled in it. This gets fastened to the cylinder-head and the dial gauge goes on it via the magnetic holder. Use a long pointer with a flat curved tip it possible.

Align the dial gauge on the top of the exhaust bucket of the number one valve.

The four-stroke cycle is induction – compression – ignition – exhaust – and takes two rotations of the crankshaft. We start the cam timing at TDC on the non firing cycle – so just after all of the exhaust gases have been vented. The exhaust valve is just closed and the inlet valve about to open...

If the exhaust lobe is coming off the bucket and the inlet taking up, we're at the right point.

Set the dial gauge on the inlet valve bucket and zero it, then rotate the engine back until the dial stops moving. This gives you live inlet valve lift at TDC. The valve was slightly open at TDC and is now closed – the difference equals current lift at TDC. Do it a few times to ensure dial gauge pointer flex is not interfering. You can ten determine how close you are to desired specifications. If you have too much lift, loosen the sprocket bolts and rotate the cam anti-clockwise. If you have too little lift, go the opposite way. It takes time to get the numbers right and lots of patience. And many coffee breaks...

Once right, Loctite and torque the cam sprocket bolts to specification found in the workshop manual.

The exhaust can is next remembering that adjustments are opposite in rotation to the inlet cam.

Yoshimura specifications are at 1mm lift, inlet cam opens at 22.5 degree before top dead center, and closes at 53.5 degree after bottom dead center. The exhaust cam opens at 56 degree before bottom dead center, and closes 16 degree after top dead center. We set the cams to IN 52 degree/87 degree MLP 100 degree and .404 with .144 LATDC and EX 72 degree/40 degree MLP 110 degree and .328 with .100 LTDC.
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