Hello! It's this the correct position for the cam's punched dot? The feeler gauge is just level with the bottom of the dot........ this is the second time I've split the motor to try and figure this out.......... although the slot (by eye) looks a little off centre to me.
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cam timing (AGAIN)
- Thread starter Chris k
- Start date
It's hard to put the chain on when it's new. Is yours new?
Honestly, I don't even use that dot, I use the notch on the other side. I think it's easier to use and see. It should point straight up at TDC .....
Honestly, I don't even use that dot, I use the notch on the other side. I think it's easier to use and see. It should point straight up at TDC .....
I don't know what to tell you about the chain being loose. They are usually tight when fresh out of the package but supposedly loosen up quickly once run a short time. Have you run this motor with that chain at all?
Well, what ever way you had it before that was causing all that backfiring, I'd try it the other way. Normally, as the chain loosens and the tensioner takes that slack up, the notch will slowly move to the right, towards the back of the motor. Seems to work OK like that, or at least it has on nearly a half million of these bikes over the last 40 some years.
I just did mine this past winter with the help from the guys here. Was really tight to put on and had to use a few sockets on the head to compress the new gaskets in order to put the link in. Weird that its loose from the get go.
Chris, the fact that your new chain was loose at installation makes me suspect that deck height may have been altered quite a lot. That would cause valve timing error; the adjuster would pull the camshaft CW to take up extra slack. You may want to check valve-to-piston and valve-to-squish band cleanances.
Quick look at it and the cam is about 5 degrees out from being in the right place. The chain is 106 link, 7.74mm pitch for the US spec 447 motor.
That's like half a tooth on the sprocket!?!?? How can this be?? This is proper dopng my head in.
That's like half a tooth on the sprocket!?!?? How can this be?? This is proper dopng my head in.
How do I check this? And where can I find original dimensions?
Couple of things, Chris. First off, degrees of rotation are measured at the crank, and since a 4-stroke cam has to turn at 1/2 crank speed, 5* at the camshaft=10* of crank rotation. 1 tooth on the camshaft sprocket=20* of crank rotation.
Deck height would have to change quite a lot to cause 10* of error. A few things to check: Is a gasket in place at the cylinder base? Do the cylinder top and/or head show signs of having been milled? Is the head gasket thickness .043" or greater?
An inspection of static compression ratio will tell you if the PO monkeyed with deck height. You'll need a degree wheel, a very small funnel, a graduated cylinder, and a dosage measuring vial from the drug store. Pull the engine and block it up on the bench so that a spark plug hole is perpendicular to the ground (straight up and down). That's important--air must be able to escape, and oil must be able to fill the head completely. Lock the crank with the pistons at TDC and valves closed on the cylinder you're inspecting. Loosen the valve adjusters all the way. Add motor oil until it fills the head right up to the bottom of the spark plug threads and no higher, recording the volume of oil you've poured in. Call that number "H."
Rotate the crank 180* CCW through the power stroke to BDC (bottom dead center). As before, add oil until the level reaches the bottom of the plug threads, recording the amount of added oil. Call this number "C."
Use this formula to determine static CR: CR=(H+C)/H; in other words, the total volume of head plus cylinder divided by the volume of the head. An unmodified XS650 motor should show a static CR between 8.4 and 8.6.
Deck height would have to change quite a lot to cause 10* of error. A few things to check: Is a gasket in place at the cylinder base? Do the cylinder top and/or head show signs of having been milled? Is the head gasket thickness .043" or greater?
An inspection of static compression ratio will tell you if the PO monkeyed with deck height. You'll need a degree wheel, a very small funnel, a graduated cylinder, and a dosage measuring vial from the drug store. Pull the engine and block it up on the bench so that a spark plug hole is perpendicular to the ground (straight up and down). That's important--air must be able to escape, and oil must be able to fill the head completely. Lock the crank with the pistons at TDC and valves closed on the cylinder you're inspecting. Loosen the valve adjusters all the way. Add motor oil until it fills the head right up to the bottom of the spark plug threads and no higher, recording the volume of oil you've poured in. Call that number "H."
Rotate the crank 180* CCW through the power stroke to BDC (bottom dead center). As before, add oil until the level reaches the bottom of the plug threads, recording the amount of added oil. Call this number "C."
Use this formula to determine static CR: CR=(H+C)/H; in other words, the total volume of head plus cylinder divided by the volume of the head. An unmodified XS650 motor should show a static CR between 8.4 and 8.6.
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Going thru Chris's previous threads, he's had both the cylinders and the head milled. (Unknown amount). Double ditto on the thicker headgasket (Athena?)
This is all I have on cylinder height:
And, his TDC mark may not be precise:
http://www.xs650.com/threads/tdc-for-cam-timing.51649/
Might consider doubling the base gasket???
Is it possible that Chris has an early model crank and cam with fewer drive teeth and the new chain is for the later set up or some other combination.
How many teeth does your cam sprocket have ?
How many teeth does your cam sprocket have ?
Think I've found my problem.......... if I double up on head gaskets totalling 0.114 (way to much) I can't get the cam chain on the cam and the notch is over the centre in the opposite direction to before. So I'm heading in the right direction with the deck height being too short. Over the years I think this motor has had at least 3 rebuilds Inc this one. So chances are the heads been skimmed at every build resulting in the loss of height........ So I think I'll be looking at a copper head gasket of around 0.0748" or there abouts to bring it back
The cam and crank are both 447. I've measured chain up and it's correct for the motor.
Locating copper stock in that thickness would be a challenge, Chris. Consider 2M's suggestion. At .060", Athena head gaskets are a bit more than .015" thicker than OE, and a second base gasket will add another .020". That will put your deck height very close to where you want to be.
I already have a 0.060" head gasket. I may try another base gasket see where that lands me.
