Once the new main bearings were in I thought that the rest of the bottom end assembly would be easy! Oh no… I actually ended up taking things apart numerous times trying to get the thrust washers right, and also found getting the crank sprocket on very difficult…
First I applied a light even smear of moly grease onto the new bearing shells. Then I installed a new blue (code) thrust washer onto the inside pins at the rear of the crankcase. Retrospectively this probably should have been a green or yellow but more on that later.
I then carefully lowered the polished crankshaft into the case with the case positioned vertically initially. You have to angle and tilt the crank to get the couterweights safely into the case. Next the front bearing carrier was installed with its new bearing. To do this I gently heated the crank case with a propane torch and put the carrier in the freezer for a few minutes. It nearly dropped in but took a few taps with a plastic mallet to help it the rest of the way. I temporarily installed two nuts on diagonally opposite studs of the carrier.
From this point it is important to BLOCK THE CRANKSHAFT. You may have heard this term before- to clarify, with the crankshaft in the case and only the front and rear bearings supporting it, it can move forwards and backwards a considerable distance. It can move far enough forward that the inner thrust washer can fall off its pins and dangle on the shaft.
If this happens at this stage when you just have the front bearing carrier installed, and you notice that it has happened, it’s not a disaster- you can remove the bearing carrier and lift the crank and correct it (or if you are VERY lucky you might be able to flick the washer back onto its pins through the cylinder opening without lifting the crank out.
BUT if you don’t notice that this has happened and you install other components such as crankshaft sprocket, bearing and, heaven forbid, flywheel, you are in a world of trouble. If you tighten the flywheel with the inner thrust washer not on its pins, it will damage and bend the washer.
BLOCK YOUR CRANKSHAFT EVERYTIME THE FLYWHEEL IS OFF. When the flywheel is on, the forwards and backwards movement of the crank is much less (this is called the endfloat and it’s what we’re about to measure) and the inner thrust washer will be safe on its pins.
To block the crankshaft I used the Cycleworks bearing carrier removal tool as shown. With the bearing carrier nuts in place this effectively pushes the crank backwards.
Measuring the Crankshaft Endfloat
The endfloat of the crankshaft is set by the combined thickness of the inner and outer thrust washers. When the flywheel is installed it prevents forward movement of the crank when it hits the outer (rear) washer.
The specified float is 0.08-0.15 mm when dry, and most experts seem to suggest aiming for around 0.1mm.
To measure, first install a thrust washer in the outer or rear position and enlocate it on its pins. I used a blue as I had two new blue ones. Two blues will get you in the ball park and most people don’t have heaps of these washers lying around (they’re quite expensive). Carefully install the flywheel ensuring the thrust washer stays on its pins. This is a temporary installation so don’t worry about lining up TDC and also use your old flywheel bolts. These bolts are stretch fit and only meant to be used once. Keep your new bolts for final assembly. The bolts don’t have to be torqued to spec- just tight enough that the flywheel is properly seated on the crankshaft (around 20Nm will be enough). When the flywheel is in place you can remove your blocking apparatus.
Now set up a dial indicator as shown in the picture and push the crankshaft as far back and forward as it will go. Take a measurement. This is your endfloat. If you are too high (>0.15mm) you will need a thicker washer and it’s obviously easier to replace the outer one than the inner one!
In theory you are meant to measure the thickness of your outer washer, and add the difference between your measured float and your goal float giving you the approximate thickness you need. You then find the washer that is closest. In practice though there are only 4 thickness and there is about 0.48 between them (although there is a bit of variation).
My endfloat with the two blue washers was 0.12. I considered trying to get this closer to 0.09/0.1 by swapping out the blue thrust washer for a yellow, but in the end I thought 0.12 was probably acceptable and left it.
Camshaft and Timing Gear
While the flywheel was still in place I went ahead and installed the crankshaft sprocket (don’t forget the woodruff key) and crankshaft nose bearing. To do this I heated the sprocket very hot in the oven (200c) and used the Cycleworks tool. I have read that some peoples sprocket just pushed on easily- mine (from Motobins UK) did not and took considerable pressure.
To install the sprocket onto my “new” cam, you first have to install the flanged bearing carrier and then put the camshaft in the freezer and the sprocket in the oven. The sprocket can then be installed by tapping it into place with an oversized pipe. It when on easily. It is important to maintain the small gap between the camshaft lip and the bearing flange by inserting a 0.1mm feeler gauge as you install the sprocket. Test this gap again after installation.
Next, I applied some Moly assembly lube to the bearing journals and lobes of the camshaft and installed the camshaft. The holes in the flanged bearing carrier can be lined up and an allen key used to tighten the bolts. I used new bolts and a light coating of loctite.
Before installing the new chain and tensioner, ensure the crank and the cam are at TDC by aligning the timing marks on the sprockets. It’s hard to see the timing mark on the crankshaft sprocket after you have installed the nose bearing so I used a sharpie to ink the sprocket tooth. The tooth on the crank sprocket should align with a valley on the camshaft sprocket at TDC. On my cam sprocket there is a green dot. When the two shafts are in the right position a new chain can be installed with a new master link. My chain had two small circlips on the masterlink (some have a single long clip) and they were tricky to install! Then the new tensioner can be installed and the crankshaft bearing carrier can be torqued down finally.
