Camchain R&R


It lives!

I didn't get a huge number of photos, partly cos the camera batteries ran out, but here's a brief summary of the job with some illustrations.

So, to get to the cam chains. Strip the tanks, bodywork, airbox and carbs off the bike. I didn't get pictures of that as I'm sure you're all far too familiar with the procedure already!

Next drain the oil from the sump (no need to drain the tank), and the coolant. Remove the oil tank - if you remove the rubber hose from the ball valve by opening the metal clip, you won't lose any oil. Remove the generator cover, unplug the wires that go to the reg/rect and disconnect the fat breather tube. Careful with the gasket and it can be reused many times - it's made of metal Then remove the front exhaust pipe, just the header section between the cylinder and the junction under the seat. Remove the water pump cover, then remove all the bolts holding the right hand side engine casing on, and remove that. There's no need to remove the small clutch cover.

Here's what you see when that cover is removed. Notice the marks on the balance shaft sprocket and crankshaft sprocket. When those dots coincide the rear cylinder is set to TDC.

Notice a small dot on the gasket face of the crankcase in the bottom right of the picture - When the dot on the crankshaft sprocket lines up with this other dot, the front cylinder is at TDC.

You need to remove the camshafts, so find TDC for the rear cylinder. The lobes of the cams on the rear cylinder point inwards at TDC. Remove the rear cams. Then rotate the engine (using a large Allen key on the generator rotor) anticlockwise one full rotation plus another 75 degrees. That should be TDC on the front cylinder. The front cam lobes will point inwards. Remove the front camshafts.

Also when you remove the camshafts, remove the top camchain sprocket by undoing the large allen bolt in the side of the cylinder heads. There's a needle roller on this bolt that the sprockets run on. Use a bit of wire or something to stop the camchain falling down into the engine - if it does it's not the end of the world though.

You need to lock the engine for this next step, the best way is to use the KTM locking bolt (or make one) that screws into the right hand side of the crankcase and engages in a recess in the crankshaft. If you peer into the bolt hole with a torch you can see the recess on the crank, thus confirming that the engine is at TDC. Leave the engine locked in TDC for the rear cylinder for all the following steps.

Remove the sprocket from the end of the balance shaft, followed by the balance weight. You can now see the camchain sprocket.

Pry the two Woodruff keys out of the balance shaft, and remove the small sprocket, and remove the camchain. You should now have a bare balance shaft, you don't need to remove anything else form this side of the engine. At the bottom of this photo you can see my home made engine locking bolt.

Next the generator rotor must come off. Here's my home made puller. The small grub screw is 16mm diameter with a 2mm thread pitch. The large bolt is 20mm diameter with a 1.5mm thread pitch.

Remove the large allen bolt from the centre of the rotor. The torque on this is 150Nm so you'll need a large wrench. Screw the grub screw into the end of the crankshaft so it sits just proud of the end of the shaft. Then use the large bolt, which screws in to the rotor, to push the rotor off the crankshaft. Then remove the grub screw again.

Here's the left side of the engine with rotor and freewheel removed, also the idler gear has been removed from the end of the balance shaft. To remove the freewheel (the large sprocket behind the rotor) you just need to remove the small plastic retainer then it pulls off.

Then tap the balance shaft from the right hand side. The manual says use a rubber mallet but I had to use a metal hammer to get it to move. I suppose the danger is that you might damage the bearings. A heat gun on the bearings might be a good idea, but I don't have one.

Here's the balance shaft partly removed. Pull it all the way out (note there's a loose washer on the right hand end so put that somewhere safe first) and remove the cam chain. Install the new cam chain and reinstall the balance shaft. You'll need to tap it back into place with a hammer - the manual says to heat the bearings but I got it back into place with just gentle taps.

Then you can reinstall the freewheel and the gear that sits on the end of the balance shaft. This photo shows the wear on the freewheel where it engages with the device on the back of the rotor. Judging by the photos in one of the TSBs concerning the freewheel, this amount of wear is normal.

At this point, if you need to, you can install the new camchain sliders. Simply undo the single bolt that retains the slider, and remove the slider through the top of the camchain tunnel. Fit the new slider, using a bit of thread lock on the bolt. DO NOT GET THREADLOCK ON THE SLIDER! I say that in capitals because I made that mistake. If you get threadlock, even a tiny amount, between the smooth path of the bolt and the slider, the slider will jam in position. it then becomes very hard to remove the damn thing to clean it up and try again. So be warned, I make these stupid mistakes so you don't have to!

You can now reinstall the generator rotor, torque to 150Nm with a dab of threadlock on the bolt.

Around the other side of the engine, replace the Woodruff keys in the balance shaft. Replace the camchain sprocket (the small one). I had to also put the weight and large sprocket back on the shaft and use the nut to push the small sprocket over the key. It's a very tight fit.

Then fit the new camchain over the balance shaft, and reinstall the top sprocket in the cylinder head. Reinstall the weight onto the balance shaft and the sprocket. As you install the sprocket, rotate the balance shaft so that the dot on the sprocket aligns with the dot on the crankshaft sprocket.

Remember the engine is still locked in TDC for the rear cylinder. So this ensures that the balance weights are in the correct position. The nut on the end of the balance shaft is torqued to 150Nm, with threadlock.

Now is probably a good point to fit the new camchain tensioners too. I poured a fair amount of fresh engine oil over the camchains, sliders, etc once they were installed, so they weren't running dry when the engine starts.

At this point the camera batteries went flat, so no more photos, sorry. But it's all reassembly from here!

The best thing to do next is reinstall the camshafts, before replacing the right hand side engine casing, because you can use the dot on the crankshaft sprocket to find TDC for each cylinder. Rear TDC is when the dot aligns with the dot on the balance shaft sprocket. Front TDC is when the dot aligns with the dot on the gasket face of the crankcase.

The engine should still be locked in the rear TDC position, so install the rear camshafts. The manual has pictures of the marks on the cams that show you what position to install them in. Basically the cross markings on the camshaft sprockets should be aligned with the gasket face of the cylinder head.

Then set front TDC by rotating the engine 360 + 75 degrees anticlockwise. Install the front cams, using the dots stamped on the sprockets to set the correct position. Again this is explained quite well in the manual.

I took the opportunity at this point to check the valve clearances.

Also this would be a good time to do a water pump rebuild if you need to. Mine is still going fine (sod's law says it'll fail next week!) so I didn't bother.

When replacing the right hand side engine casing, be careful to align the groove on the water pump with the drive on the end of the balance shaft. Also remember to remove the engine locking bolt beforehand! :)

Well, that's all the tricky stuff, I think, from there on it's just a matter of reassembling the usual suspects, exhaust pipe back on, airbox and carbs, etc etc.

Anyway, after all that, I got the engine running yesterday evening, it sounded promising, there was almost no chain clatter on startup and none when it was running. I ran it for a while with the old oil and then drained and filled with new oil.

Today I went for a short ride, all sounds good! The startup clatter lasts for only about half a second, previously it was a couple of seconds. And no camchain noises while riding - the main indicator of the problem had been severe chain clatter on the overrun.

So, it's been a long haul, but I think it's fixed!

There wasn't much difference I could see between the old tensioners and the new ones. The old ones measured 48mm in length, the new ones 48.5mm. I suspect that's just the spring "settling in". I don't think there'll be any internal differences as I don't think the KTM part number has changed since my bike was made. The rumours of better/longer tensioners seem to be just that.

I did try to compare the cam chain lengths, by holding an old one and a new one side by side hanging from a straight metal edge. The old one was approx 2mm longer, but it was hard to get them in a position to do an accurate comparison.

It seems the tensioners have only about 10mm of movement (in the spring loaded plunger). By approximating the geometry of the chain path (as two right angled triangles) you can use Pythagoras to work out how much chain stretch will result in the 10mm of tensioner movement being used up. It works out as 0.5mm stretch over 100mm of chain. In other words not very much.

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