I’ve treated myself to a shiny toy not too long after I started working in IT: a 2004 Honda VTR 1000 SP-2 (branded the RC51 in the US). It’s immense fun to ride and makes all the right noises when you twist your wrist. I’ve spent two summer holidays in the Alps on this bike and another three days on a race track in the south of France. With riding comes maintenance, something I enjoy doing myself. I’ve always had a fascination and curiosity with technology: if it makes a lot of noise, looks pretty and goes fast that’s even better. It’s a chance to get my fingers dirty, learn something new, assure myself it’s done correctly and save some money while I’m at it. A while ago I had to perform a valve clearance adjustment due to hitting the 30k km mark. A job that scares most people right from the start, but actually isn’t that hard if you pay attention. Read on to find out how to do it on a VTR SP-2 / RC51!
A combustion engine is pretty easy. Take a crankshaft and attach two pistons. A crankshaft turns linear motion (pistons moving up and down) into rotational motion. Moving the pistons up and down is done by igniting a mixture of fuel and air in a cylinder. Getting this mixture into the engine requires valves. That’s pretty much it.
Suck in the mixture through the intake valves on the downward motion. Close the valves and compress the mixture on the upward motion. Ignite the mixture and it will rapidly expand, forcing the piston down. Momentum will take the pistons upwards again, at which point the exhaust valves open. Exhaust gasses are forced out, exhaust valves close and the cycle begins anew with taking in new mixture. Bolt a flywheel, clutch, gearbox, chain and rear wheel to the engine and you can ride (that’s assuming you can wheelie indefinitely, otherwise you’ll need some extra parts to keep it comfortable).
Zooming in on the valves, they are actuated by camshafts. A camshaft is a shaft with lobes on it. The SP-2 has four of them: being a V twin there are two cylinders which are not in line, thus requiring separate camshafts (contrary to a car engine that usually has some cylinders in line). Each cylinder has dual camshafts: one for the intake, one for the exhaust. Each camshaft actuates two valves each, bringing the total number of valves to eight.
This is the rear cylinder opened up. The left camshaft is the intake side, the right one actuates the exhaust valves. When turning, the lobes push on the valve buckets underneath, which will move down and push the valve down into the cylinder. Rotate the camshaft some more, the lobes move out of the way and the valves close again.
There’s a little bit of room between the valve bucket and the camshaft when in the resting position as displayed above: this is the valve clearance. Contrary to popular belief, this clearance usually doesn’t get bigger with wear but tighter! This is due to the valve seats and the valves themselves wearing, allowing the valves to “stick out further”, using up the valve clearance. If you don’t adjust, at some point all the clearance will be used up and the valve will always be in an “slightly open” position. This reduces compression of your cylinder (= less power) and more importantly, will not allow the valves to cool down. This is a bad thing and will burn your valves costing a bucket of money to fix.
Before you can look at your own camshafts you will need to remove quite a lot of parts. The rear cylinder is underneath the fuel tank: the front one is near your forks. To be honest, the front cylinder is a pain in the behind to service since too many components you don’t want to remove are in the way, limiting room to work.
Some rules and advice:
- Wait till your engine is cold (<35°C) before you start adjusting, otherwise you’ll get faulty measurements.
- Ensure you have quality tools (torque wrench, proper fitting sockets) and a clean workspace. You’re opening your engine and don’t want to end up with buckets of sand in there. You’re also working with steel bolts in aluminium/magnesium parts: you can easily wreck the threads and ruin you engine, so pay attention.
- A service manual is highly recommended. This is already a long post: if I’d describe every single bolt and washer it would be even longer.
- Perform the valve clearance adjustment at your own risk. It’s a pretty straightforward job, but if you drop a valve shim, spanner or sand in your engine, you wreck a bolt or if your engine blows up after adjusting: find someone else to comfort you while you cry your eyes out.
Let’s start! You’ll need to remove:
- Lower inner fairing.
- Lower fairings.
- Air guide plate (or loosen the oil cooler depending on model).
- Couple of tubes that are in the way (PAIR system, crankcase breather hose, etc).
- Fuel tank (make sure it’s near empty before you start or you’ll run out of containers to drain it in!).
Remove the spark plug caps and the cylinder head cover bolts and you should have four shiny camshafts looking at you.
Measuring the valve clearance
Now remove the timing hole cap and crankshaft hole cap. Lets start with the rear cylinder, since it’s easiest to reach and work with. Rotate the crankshaft counterclockwise and align the RT mark with the index mark in the timing hole.There are also index marks on your camshafts (near the gear-end), which should be flush with the cylinder head and facing outwards.
If they are not facing outwards, rotate the crankshaft one full turn and check again: they should now line up and point the right way. Use a feeler gauge to measure the clearance: use the thickest (combination of) feeler(s) that moves in with ease. If you need to force it in you’re using too thick a feeler; if it wiggles around it’s too thin. Measure all four valves and make a note of the measurements.
Rotate the crankshaft counterclockwise one full turn, then keep on turning till the FT mark lines up (450° in total). Now measure the front cylinder valve clearances and write them down. You should end up with something like this:
Adjusting the valve clearance
The official clearances are:
- Intake: 0,16 +- 0,03 mm / 0,006 +- 0.001 in. So anything between 0,13 – 0,19mm is OK.
- Exhaust: 0,31 +- 0,03mm / 0,012 +- 0,001 in. So anything between 0,28 – 0,34mm is OK.
All my exhaust measurements were too tight so needed some adjustment. Three of the intake valves were OK according to the range of allowed clearances. Adjustment shims can be purchased in intervals of 0,025mm ranging from 1,2mm to 2,45mm. You will not always be able to end up smack in the middle of the range of valve clearance. In this case, I opted to aim for the looser side of the range: they will tighten over time anyway so this will give me some extra slack. This also means I still adjusted the intake valves: from 0,15mm to 0,175mm, which is a bit closer to the 0,19mm upper limit.
Calculate your new shim thickness. For example, if your exhaust valve measures 0,22mm you may want to add 0,10mm of clearance so you’ll end up with a clearance of 0,32mm. Calculate this for all the valves, then disassemble some more: remove the camshaft holders and camshafts. Keep them clean and lay them out so that you can place them back correctly once you’re done.
Next, remove the valve buckets. Be warned: the adjustment shim is inside the bucket! Sometimes it sticks to the bucket and comes out along. Sometimes it stays in place on the valve and you can remove it afterwards. In other times it will stick and drop out of the bucket as soon as you clear the valve, aiming for the gap between the valves like it does it on purpose. Expect the unexpected and DO. NOT. DROP. IT. INTO. THE. ENGINE.
In the picture above you can see the bottom left valve with the valve bucket and shim inside. The top left has the bucket removed and the shim in place. The valves on the right neither have a shim nor a bucket. When removing them, make a note which shim and bucket belong to which valve!
Now measure your old shims. Not all shims are the same thickness, not even in a stock engine. Use your current shim thickness (which is why you needed to needed to keep them apart) and the adjustment to calculate your new shim thickness. Write it down. At this point you can re-use your old shims and/or buy the missing shims that you don’t have. For example I re-used the IN FI shim in the IN RE position on the rear cylinder.
Install your new shims and the valve buckets. Mix up a solution of molybdenum grease and engine oil (1:1 ratio) and cover your valve buckets. Install the camshafts (make sure the index lines are flush and pointing outwards) and cover the lobes & camshaft journals with the solution as well. Install your camshaft holders (IN arrow pointing to the intake side) and tighten in a criss-cross pattern to 23Nm (17 lbf-ft). Rotate the crankshaft a couple of turns, line up the marks again and check the clearances. If you did everything right: congrats, they should now be in the allowed range and your valves aren’t hitting your pistons. If they’re not you probably did something wrong: retrace your steps!
Apply some sealant to a new gasket and stick it on the cylinder head head cover. Check the O-ring is in place (officially you’ll need a new one but use your own judgement) on the dowel pin sticking out near the spark plug. Apply some additional sealant on the semi-circular part of the gasket and stick that on the cylinder head. Install the head cover bolts and tighten to 10Nm (7 lbf-ft).
Congrats! One easy cylinder done, now repeat these steps on the front cylinder.
- Rotate the crankshaft and line up all the index marks (1x crankshaft, 2x camshafts).
- Remove the camshafts, valve buckets and shims.
- Measure the shims & acquire new shims.
- Install all parts and rotate the crankshaft counterclockwise a couple of times.
- Check the clearance once more.
- Once you’re confident everything is right: close her up. Keep small kids away while you do this: more than a bit of cursing was involved in closing up this cylinder as the gasket either fell out of the head cover due to gravity or due to me bumping into the cylinder head/oil cooler/fork/radiator fan/higgs bosons.
- Reassemble your bike.
You CAN do both cylinders at the same time and save yourself a trip to the store, but to me it wasn’t worth the risk of messing up the timing in favor of half an hour to and from the store and 1 or 2 extra shims. This way I could line up all the index marks and then not touch the crankshaft until I was done with one cylinder, avoiding the risk of messing up the timing and serious engine damage.
Start her up and take her for a gentle spin around the block. Check for leaks: I initially used a wrong gasket sealant which wasn’t suitable for flexible/rubber gaskets and would thus start to leak oil all over my exhaust. Which is fun if you want to signal for help with big plumes of blue smoke, but not so funny if your rear wheel is right behind that exhaust pipe…
That’s it! You’ve adjusted your valve clearance on a VTR 1000 SP-1 or SP-2 (or RC51 if you live in the States). Take it gently for a couple of miles, then take her on a race track and rev her for all she’s got: the sooner you can do these adjustments all over again!