Cam/Crank chain timing riddle

[Fernando]

I have been at this for some time now, motor back and forth in the frame FOUR times! I am at my wits end.

Replaced front cam chain guide successfully.

When I time the cam shaft (machined slot in 12 oclock position) with the crank (mark on alternator rotor in line with T mark on stator cover) and cam chain tensioner in, I spin the motor counter clockwise via the 17mm bolt on the crank, and everything lines up. I put on the valve head and spin the motor some more some how IT GETS OUT OF TIME, the small hole for the advancer unit (which is in the same position as the machined slot) is no longer in the 12 oclock position but around 10 oclock.

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

Moments before it was at 12, with the cam chain tensioner installed. Is it possible that the gear on the crankshaft has slipped, but only some???? What am I missing here?

 

[Fernando]

Here are some pictures I took after I put the motor in the frame and kicked it over, this is where the timing lands at. This is NOT what I timed it to, this time I put the cam in the 12 o clock position. I also rotated it with a breaker bar with the head attached and sparkplugs in and it never went out of time.

I have even tried timing it back some so maybe it would "slip" into the correct position. I timed it to 1:00 or 1:30 and it jumped passed 12 and went to the position on the picture, what the heck is going on here?????

 

[Paulrxs650]

Hi,

The cam shaft revolves faster that the crank. When you set the timing, are you then going through the four stroke cycle to wind back up at TDC on the piston you originally timed from?

If you turn it one revolution - your timing will appear to be "out"

 

[Fernando]

Hey Paul, Thanks for the reply,

yes I am going through the four stroke cycle. If I am not mistaken if you time it correctly (12 oclock)and rotate the crank over once the cam mark should be in the 6 oclock position. Which it does when I crank it over with a breaker bar, then turn the crank once again and its back at 12 o clock, but when I kick it once back in the frame it moves foward to the pictured position of about 11 oclock (having to look at the picture backwards since that mark is on the ATU).

Does the gear on the crank shaft have a key in it? can that have snapped or broken and it slips only when a lot of force exerted like when I try to kick it over?

I even tried timing it backwards to a 1 o clock position to it would slip foward to 12 but it went past 12 and landed at 11 again, as pictured.

 

[Paulrxs650]

It sounds like you could be a tooth out. Check out this link http://www.650motorcycles.com/CamTiming.html which has a good picture of the timing mark, next to the sprocket which should be vertical when you install the cam. Also just check that your TDC is true TDC - With the plugs out pop a plastic stirrer or similar long thin implement down the bore and turn the engine over by hand til you find TDC - then compare that to you marks on the alternator.
If the cam is out, you can move the chain over a tooth or so by taking the cam bearings off - saves splitting the chain again

 

[Fernando]

Thanks again, but I have read and re-read that post, everything I have done is by the manual and that post. I line up the T mark and have the cam to 12, by removing the bearings and then putting them back in with the tensioner in place. Everything lines up and when I spin it it stays lined up, the issue is it moves when I kick it over, I have no idea how it moves but it does. I have done it three times and everytime it moves forward once I kick it. The last time I even timed it backwards and it still slipped past 12 to the pictured location. Something is letting it slip but I am not sure what?? Trust me I have had other people check me in my timing and it lines up correctly and stays correct when hand cranking the motor. Its the kickstarting force that is making it move out of time. But How?

I have checked that TDC and the T mark on the rotor does line up correctly with the actual TDC of the motor

 

[vr3506]

Looks like you have put in another cam (?)
An XS 1 cam had 2 teeth less

 

[Fernando]

It is the cam that came in the motor, I am not sure if the PO put one in, or the possibility if it is a rephased motor? Is there a way to check if its a different cam or rephased motor? Its a 79 xs special

 

[Paulrxs650]

Hi, OK so just to be clear, did this bike run prior to you changing the guides?

 

[Fernando]

Yes it did, and it ran fine. I started hearing a metal on metal sound, and found plastic and aluminum in the oil filter, once I cracked it open I saw the plastic separated from the guide and replaced it. Thats the only work I did. I did remove the bearings and cam to get the guide out. I didnt put any "other" parts in, different cam or gears or such. Everything came from a completely working bike. Turned on with one or two kicks.

Side note, I did find a 5/16th ball bearing stuck to the magnet on the oil drain plug, but figured this was to the clutch push rod assembly. Could that ball go to something with the timing?

 

[Fernando]

so I pulled the motor again, drained the oil, pulled the sump filter pan out, looked at the crank gear for missing or chipped teeth, I couldnt find anything that seemed out of the ordinary. I could even see the c-clip that retains it.

I retimed the motor for the fifth time, T mark aligned and the cam in the 12 position. As seen in the below photos, then I hand spun it, and checked, everything okay. Then put the head on, hand spun it and it was okay again, put the plugs in and hand spun it, once again everything was fine.

Then held the motor and kick started it, and thats where it came out of time. As you can see in the other pictures, the one with the cam forward in the 11 oclock position. What the heck is going on??????

I tried to upload all photos in the order I took them, so it should be cam in the 12 position, T mark aligned.

Then cam in the 11 postion, and t aligned

 

[5twins]

You replaced the front guide but made no mention of replacing the cam chain. Maybe it's badly stretched and jumping teeth on the sprockets. Or, it could jump teeth if the cam chain tensioner isn't adjusted tight enough (and the chain is stretched). The usual routine when replacing the front guide is to replace the chain as well. If the bike has anywhere near 20K on it, it needs a new chain. They can and do last much longer if properly cared for (adjusted frequently enough), but there's the rub - most of these bikes never got that kind of care.

I should also mention the type D tensioner assembly with no lock nut your '79 may have. It's a major chain stretcher. Every time you install and tighten the acorn cover nut, it can inadvertently tighten the adjuster more. Running the chain too tight leads to premature stretching.

 

[Fernando]

Thanks 5twins, another update is that i timed it and for the heck of it threw it in the frame, and this time it fired up, but only for a short bit, then it went to its old ways. The timing got out and was at the 11 oclock position.

The bike has 14k on it, I doubt the chain has been replaced. The tensioner I believe is a type E because it has the rounded acorn nut and the lock nut with the copper washer.

If this helps the cam shaft looks like its has a 4 on it.

Tomorrow I will try and retime it and make sure the tensioner is perfect, do you suggest it coming flush like the manual says or 1mm out like some people on here have said?

 

[5twins]

I set mine while the engine idles but obviously, you can't do it that way. I shoot more for 1 to 2mm of in-out movement of the rod than for making it flush with the end of the adjuster nut. The actual position of the rod can vary depending on the type of damper washer used or wear on the components. Some in-out movement is more important. No movement means it's set too tight. Excessive bouncing in and out is an indication it's too loose. I recommend you tighten it down until the movement practically stops, then loosen it up a turn or two to put some movement back into it. Once properly tensioned, if that pulls the timing mark on the cam off a bit, that's another sign the chain is all stretched out.

 

[hein weijers]

Camchain stretched or not, or the tensioner adjustment a little off, that cannot cause the chain to jump over the teeth. Even without tensioner you cannot turn the sprocket just like that.
Are you sure the rotor is fitted tight with the key in place?

When you go on kickstarting the engine, does the camshaft timing shift more and more?

Hein

 

[Fernando]

Thanks Hein!
I will double check that the rotor is nice and tight, but it was my thinking since it is keyed in place that it would constantly slip if the key fell out, and rattle between the shaft and the stator cover plate, where I would be able to noticeably tell there was an issue?


No the timing does not continue to slip or move, it goes to the 11 position and just stays there, no matter how many more times I kick it over.

 

[Paulrxs650]

An easy way to check its not the rotor slipping around is to use the method I described above to ensure the pistons are at TDC and then check where the timing mark sits.

Re that ball bearing - no idea how that got in there - Perhaps a PO made a mistake reassembling the engine and clutch and it found its way into the oil galley from the right hand side?? At least it stuck to the magnet

 

[Fernando]

Thanks Paul, and yes I checked it with a stick and also visually moving it before and after the mark to make sure it was at its most upper travel movement. I will tighten the nut some more just to take it out of the equation.

The ball bearing is a serious mystery but the clutch was working before fine. I will measure the push rod sticking out and see if the worm gear is taking up the extra slack, causing the clutch to work but not in the proper manner, and the clutch rod assembly is missing the bearing.

 

[hein weijers]

No the timing does not continue to slip or move, it goes to the 11 position and just stays there, no matter how many more times I kick it over.

And when you turn the crank in the opposite direction, does it stay in the 11 position?

 

[Fernando]

Last night I checked the rotor, it was tight, I timed it up again and this time I tightened the chain tensioner until it didnt have any play, then backed it of a little. Put it in the frame and it fired up, AND STAYED ON! I loosened the tensioner until I couldnt feel the plunger hitting. It was late so I couldnt really tune it but it seems to be much louder than before. I will check the tensioner, valves gap and point timing later on this week, to see if this seems to be the reason why its making so much noise.

Thanks a million 5twins, Paul and Hein, you guys saved me a lot of cash and headache by all the helpful advice. I knew it was something simple that I would be kicking myself in the butt for once I found out what it was, rookie mistake.