timing

So I'm about to do my first real top end rebuild on an xs, and I was just wondering if there were any tips or tricks to making sure I have the timing right. For example, how do I know if the pistons are tdc on the compression stroke etc, etc. . I just want to make sure I have as much figured out as possible before I actually tear into it so I don't end up breaking something.

- when the engine is complete, both rockers will rock on the compression stroke
- when assembling you need TDC on the left cylinder, timing is sorted with the cam...with TCI ign wasted spark means you dont have to complete the process with points timing too

So how do I know if it's at TDC on the left side and not the right while I'm putting it all together? I have an old Clymer manual, and it doesn't really give much detail to that.

http://www.650motorcycles.com/CamTiming.html

Have a look at this link. It explains the engine timing quite well. When you take the rocker cover off, rotate the engine until the alternator rotor timing mark is at TDC. Are the left cylinder cam lobes pointing up................if not rotate the engine one more revolution until the left cylinder cam lobes are pointing upward.

This is your reference timing point. Engine at TDC...........left cam lobes pointing up, right cam lobes pointing down............. index mark looking at the left side of the camshaft is at the 12:00 position.............punched index mark on right side of camshaft gear is at the 9:00 position and is exactly even with the top surface of the head. The large pin on right end of the camshaft is at 12:00 also.

Take a few pictures of your engine at that position, and re-assemble the same way. Very simple................you can't go wrong.

Very simple................you can't go wrong.

Click to expand...

- remember those words rg

inxs................I like your humour ...................I'm tying to build up confidence in those less experienced................if we start being honest about all the pitfalls then no one will tear into these engines

Claybear, what the guys are trying to tell you is that the pistons travel together--TDC is TDC. The camshaft controls valve opening and closing, and that's what determines which cylinder is on the compression stroke while the other is on the exhaust stroke. Set your alternator marks on TDC and install the camshaft so that the notch in the boss is at the top. With the cam chain tensioner installed and the pistons at TDC, the notch should be exactly in line with a line struck through the crankshaft and camshaft centers. If in doubt, jam fit a piece of string or fishing line in the hole in the end of the crankshaft, pull it up across the center of the camshaft, and sight on it.

Thanks for clarifying that for me, I was having a helluva time really grasping that. I figured the crank sproket would be off if the wrong cylinder was on the compression stroke. So that's really all I have to do huh? I hear some people talking about degree wheels and all of that, I didn't know what I was really getting in to. Well with everyone's advice I hope to have it together and on the road by this weekend! Then once all of the mechanical bugs are worked out I'll do what I actually understand how to do and get out the cutting wheels.

When you're doing a performance engine with an aftermarket camshaft or just want to get all you can out of a stocker, it's best to degree in the cam. Replacement head gaskets can vary in thickness by almost .020", and deck height affects cam timing.

If you want to be fairly precise, you can do this. First, since you're going to have the head off anyway, get a cheap dial indicator and set it up on top of a piston to find TDC accurately, then correct your alternator timing marks if necessary. If you can find a small clear plastic protractor about the same diameter as your alternator rotor with enough material for you to drill a hole the diameter of the crankshaft, modify it, remove the rotor nut, and snug it down against the rotor; with the alternator marks at TDC, line up the 0 mark with them. If you can't find a protractor that will work, copy the degree wheel from 650 Central, size it to the diameter of your alternator rotor, copy it to transparent film at a copy shop, cut a piece of plexiglass to the same diameter, and stick the film down on it. Remove the right engine cover so that you can turn the crank from that side and avoid disturbing the degree wheel.

I don't know what year you have, but for specs on 256 engines see the Clymer manual, for 447's see the factory manual at www.biker.net . Set your valves to the specified inspection clearance (not the same as running clearance). All OEM XS650 camshafts specify valve opening and closing events at 0 lift; that is, the degree numbers refer to the point at which the valves just begin to open and close. If you don't want to fabricate a holder to set up the dial indicator on the valve collars, insert a piece of cellophane between the tappet and the valve stem, rotate the engine, find the point at which the tappet and valve just release the cellophane (valve closure) or grab it (valve opening), and read the degrees between your stator mark and the degree wheel 0 mark. Do this several times to make sure your results repeat.

griz,
In your earlier post you mentioned getting it lined up straight with the tensioner in place, what's the best way to do that? Should I just put the master link in and not peen it and then move it accordingly?

If you have the cam chain split, sure, that's the easiest way to go about it. If the chain is joined, slide the bearings off to move the camshaft.

Yeah, I actually ordered a new one, going by the book it says that I have to cut the chain, and mike's master links say they might not fit the older chains, so I spent the extra 50 just to get a new one. Figured that would be better anyways to compensate for the years of slack the old one might have.

You did well to get a new chain. "The book" was written originally with reference to the XS1. The XS1 and XS1B had a cross piece cast across the cam chain tunnel, so while the camshaft and head could be removed without breaking the chain, the cylinders could not. The cross piece was eliminated in later cylinders; from 72 on you can do a complete tear down without breaking the cam chain.

While we're on the subject, be sure to center the camshaft accurately when you reassemble; with the bearings on all the way to the stops, measure the distance from the outer edge of each outer bearing to the outer edge of its journal with the depth probe end of a caliper, and make sure the inset is equal on both sides.

Huh, did not know that about the cross peice in the cylinders. Thanks for the advice on the reassembly, I'm sure by time it's all said and done I'll probably have read and re-read all of this info several times.