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Discussion Starter #1 (Edited)
Howdy gents, I'll try to keep this a short as possible: anybody who's checked and set their own valve adjustment, I need your help.

I followed the Yammy repair manual's valve adjustment guide from 650ccnd to the letter. First problem: the repair manual says to find TDC by aligning both the camshaft sprocket with it's mark on the cylinder head (the dot and pointer) AND the T/I on the rotor with the the AC magneto cover (the T/I mark and the notch), but I cannot do both; when one is aligned, the other is approximately 10-25° off! When the head is aligned, the rotor is 25° off to clockwise; if I align the TI/I and the notch on the rotor, the head is off by around 10° to counterclockwise!

Assuming the camshaft sprocket on the head was more important, I went with that. With hesitation, I continued.

After taking my first measurements, I found that both the intake and exhaust valves were within spec (intake was right on the minimum at .07 mm, exhaust was .14 mm, both within tolerances). I then rotated the crankshaft through 3 full rotations in order to recheck my measurements, expecting no difference, since I hadn't made any adjustments; THIS time the intake was at .05 mm (.02mm out of true) and the exhaust was at .15mm! :(:mad:

My measurements are good, I checked several times, both times, using the "go/no go" method. My feeler gauges are good; I borrowed a second set just to be sure. Both times I (rather comically) stuck my eyeball three inches from the sprocket and lined up the pointer with the center of the dot to the absolute stupid best of my ability, probably accurate to a half-mm or better.

What could be causing these two phenomenon? Are they related? Am I incompetent? Is this a manufacturer's defect, or a parts failure? Do I need to do something different? As is, I'm inclined to simply put the head covers back on and forget I ever mucked with it. While I'm just an amateur, I just removed, rebuilt and reinstalled both carbs and greased the rear drive splines without a single peep of trouble, and after those confidence builders, I'm kinda shocked that things have gone sour so quickly. The manual is not helping me here. Any suggestions?
 

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I hope I can help without sounding as if I am trying to insult your intelligence. Remember that the crankshaft makes two full revolutions for a single revolution of the camshaft. Any angular error on the crank (rotor, flywheel) will be twice the angular error on the camshaft. At least on the bikes I have worked with, the rotor usually has at least two marks. One is TDC; the other is the timing mark for the ignition. The timing mark is usually somewhat advanced from the TDC mark so the spark plug fires before TDC (ignition advance). On V-twins there may be a timing mark and a TDC mark for each cylinder.

The surest way to find TDC is to remove a spark plug and stick a plastic soda straw down through the hole so it rests on the piston. Turn the engine slowly in its normal direction of rotation (this makes sure the timing chain stays tight) and observe the straw. When the straw stops rising, the piston is at TDC. You can usually get "close enough" by using a flashlight to look through the hole so as to actually see the piston. Remember too that the intake valve will have closed probably 150 degrees before TDC and the exhaust valve will not open for probably 150 degrees after TDC, so a few degrees isn't likely to matter.

For every operating cycle of the engine, the crank makes two revolutions and there are two TDC events. At one TDC, both valves are closed and there will be "play" between the lifter and the valves; at the other it is likely both valves will be slightly open and you won't be able to get a feeler into the gap. When you check or adjust the valves, make sure to rotate the crank some multiple of two revolutions before you recheck.

Completely unrelated: How do you get the little "degree" mark into a post?
 

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i just rotate the engine until one of the valves just begins to open, then adjust the opposite valve on that cylinder. when an intake valve is starting to open the exhaust will be on the heel of the cam (no lift) and vice versa. a valve can be adjusted any where along the heel of a cam, and the heel of a cam is 180 degrees of the cam circle. auto engines are adjusted by watching the action of valve rockers so i use the same method on motorcycles. it also says in the manual , adjust to the tighter end of the specs for the best performance. also the flywheel marks should line up at very right edge of the hole not the middle. and the front cam will appear to be off by a half tooth with the flywheel line up correctly, this is normal. i set mine at 3 thousandths intake and 4.5 thousandths exhaust. i know the exhaust is a bit tighter than allowed but it's the only way to eliminate the ticking. i'v rode many thousands of miles with that setting with no problems. i check my clearances every winter and after the 15000 mile mark they never seem to change more than 1/2 thousandth . (.0005) inch
 

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Discussion Starter #4
Thank you both, gentlemen! You've given me some excellent information to chew on as I head back into the garage. I'll post my results when I'm finished! *crosses fingers*
 

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Discussion Starter #5
I hope I can help without sounding as if I am trying to insult your intelligence.
No insult taken at all, sir. I'm happy for every little tip when I'm elbows deep in an engine for the first time. You were wise to dumb it down for me. :D

Completely unrelated: How do you get the little "degree" mark into a post?
Simple, I copied it from the Wikipedia article. Nerd alert. :p
 

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I hope I can help without sounding as if I am trying to insult your intelligence. Remember that the crankshaft makes two full revolutions for a single revolution of the camshaft. Any angular error on the crank (rotor, flywheel) will be twice the angular error on the camshaft. At least on the bikes I have worked with, the rotor usually has at least two marks. One is TDC; the other is the timing mark for the ignition. The timing mark is usually somewhat advanced from the TDC mark so the spark plug fires before TDC (ignition advance). On V-twins there may be a timing mark and a TDC mark for each cylinder.

The surest way to find TDC is to remove a spark plug and stick a plastic soda straw down through the hole so it rests on the piston. Turn the engine slowly in its normal direction of rotation (this makes sure the timing chain stays tight) and observe the straw. When the straw stops rising, the piston is at TDC. You can usually get "close enough" by using a flashlight to look through the hole so as to actually see the piston. Remember too that the intake valve will have closed probably 150 degrees before TDC and the exhaust valve will not open for probably 150 degrees after TDC, so a few degrees isn't likely to matter.

For every operating cycle of the engine, the crank makes two revolutions and there are two TDC events. At one TDC, both valves are closed and there will be "play" between the lifter and the valves; at the other it is likely both valves will be slightly open and you won't be able to get a feeler into the gap. When you check or adjust the valves, make sure to rotate the crank some multiple of two revolutions before you recheck.

Completely unrelated: How do you get the little "degree" mark into a post?
wipe the oil off the dimple and paint it with white out, it will then be highly visible in pics
 

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Pauli466 are your measurements in mm or thousandths? because 3 ans 4.5 thousandths lash seems a bit tight to me but i work on large diesels.
those numbers are in thousandths of an inch. overhead cams allow for very close tolerances. the manual shows ( .0028-.0047 inch ) for intakes and (.0047-.0067 inch) for exhaust on a 650 engine. the only way you can hear the tick on mine is with a stethoscope.some tick is absolutely necessary or the valves will burn but i don't like hearing it over the exhaust. did you ever have to shim the side covers on a cummins to set the clearance for injectors? also the using a straw to find TDC is better than trying to line up flywheel marks. at least with a straw there is no guessing.
 

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those numbers are in thousandths of an inch. overhead cams allow for very close tolerances. the manual shows ( .0028-.0047 inch ) for intakes and (.0047-.0067 inch) for exhaust on a 650 engine. the only way you can hear the tick on mine is with a stethoscope.some tick is absolutely necessary or the valves will burn but i don't like hearing it over the exhaust. did you ever have to shim the side covers on a cummins to set the clearance for injectors? also the using a straw to find TDC is better than trying to line up flywheel marks. at least with a straw there is no guessing.
Yes; I have timed the cam followers on the Cummins engines a time or three. A lot of barring the engine back and forth.... so much fun

I am getting my list together and going to add valve adjustment to my preseason maintenance this year.
 

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"The surest way to find TDC is to remove a spark plug and stick a plastic soda straw down through the hole so it rests on the piston. Turn the engine slowly in its normal direction of rotation (this makes sure the timing chain stays tight) and observe the straw. When the straw stops rising, the piston is at TDC."

This is probably a stupid question, but, why not just watch the rockers for max slack and then adjust per specs. I have done it this way for years. Am I doing it wrong all this time? Cheers, Wavelength.
 

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"The surest way to find TDC is to remove a spark plug and stick a plastic soda straw down through the hole so it rests on the piston. Turn the engine slowly in its normal direction of rotation (this makes sure the timing chain stays tight) and observe the straw. When the straw stops rising, the piston is at TDC."

This is probably a stupid question, but, why not just watch the rockers for max slack and then adjust per specs. I have done it this way for years. Am I doing it wrong all this time? Cheers, Wavelength.
Nothing at all wrong with that tactic. However, I was writing for a person who wanted to find TDC.
 

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Nothing at all wrong with that tactic. However, I was writing for a person who wanted to find TDC.
the thing is he was looking for TDC for valve adjusting purposes, which is totally unnecessary. the only reason the manual uses that method is so both valves can be adjusted at the same time. it's ridiculous to pull covers and disturb seals when you don't need to. TDC really is only needed for cam timing purposes.
 

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Discussion Starter #14
Update: Thanks everybody, I finished the project successfully and she runs fine. No valve noise at all, that is. I'm still dealing with one carb running rich and drawing a lot of vacuum and the other running normal/lean and running considerably less vacuum, but that's for another thread.
 

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Update: Thanks everybody, I finished the project successfully and she runs fine. No valve noise at all, that is. I'm still dealing with one carb running rich and drawing a lot of vacuum and the other running normal/lean and running considerably less vacuum, but that's for another thread.
In your first post you mentioned having done some carb work. Now, you say one cylinder is pulling more vacuum than the other. Check your manual for the procedure to synchronize your carbs. Without going into great technical detail, the cylinder pulling more vacuum has its throttle butterfly less open than the one pulling less. There is usually an adjustment on the linkage between the two carburetors to correct this.
 

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Discussion Starter #16
In your first post you mentioned having done some carb work. Now, you say one cylinder is pulling more vacuum than the other. Check your manual for the procedure to synchronize your carbs. Without going into great technical detail, the cylinder pulling more vacuum has its throttle butterfly less open than the one pulling less. There is usually an adjustment on the linkage between the two carburetors to correct this.
It's actually worse than that, I'm afraid. I'm actually about to post a thread on it.
 

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Discussion Starter #18
omg don't say it, you overtightened and bent a valve.
Good Lord I hope not! :eek::eek: I set them all right to minimum on the first go; after a conspicuous silence of valve noise (which I'm told is a bad thing) and my later issues with compression/vacuum I (out of an abundance of caution) went back in and set them at about 1/3rd of the minimum specifications instead of right on the line. Now I'm getting a fair bit of valve clicking (which displeases me), and more importantly, no improvement in my low 5-pound vacuum on the rear carb. Thus, it was never the valves. Better to be safe than sorry, but still...

Thus, it seems I'll have to go back in again at some point (after I've resolved the low vacuum issue) and put them back close to the minimum. That presumes I'll ever get this damn carb situation sorted out...
 

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Until you get the compression issue sorted out, you are wasting your time worrying about vacuum or carburetors. Unless the engine itself is in good condition, with good and fairly equal compression on both cylinders, the vacuum will never come out right. Loosen all the valve adjusters and make sure you can actually feel play between the lifters and the valves when the engine is more or less at TDC. At this time you are not worrying about clearance - even if you can stick a dime in there it will work. Turn the engine over and observe that the valves are actually moving at the proper times, then try the compression test again.
 
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