Author Topic: Shimming Woes  (Read 12538 times)

Prophet Of Doom

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Re: Shimming Woes
« Reply #20 on: December 09, 2013, 01:16:52 AM »
On hold while I get some transport together.  ETA about a week ago.
Last I touched it I'd moved something and now hitting the piston on a valve I think.

pinholenz

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Re: Shimming Woes
« Reply #21 on: December 09, 2013, 04:30:16 AM »
So that was one of your old xz400's that you bought back?
Only one '82.5  eXtreme Zen 550

Prophet Of Doom

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Re: Shimming Woes
« Reply #22 on: December 09, 2013, 08:02:45 AM »
Yes,
More through coincidence than anything - Since I sold it it's turned into a bit of a lemon

Rikugun

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Re: Shimming Woes
« Reply #23 on: December 09, 2013, 09:42:40 PM »
On hold while I get some transport together.  ETA about a week ago.
Last I touched it I'd moved something and now hitting the piston on a valve I think.
  I've warned you about "touching it" yourself.  This is what happens...   :laugh:  :laugh:

Seriously though, what did you do??
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Prophet Of Doom

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Re: Shimming Woes
« Reply #24 on: December 10, 2013, 01:43:32 AM »
Seriously though, what did you do??
Don't know what I did to cause it, but I've stopped looking at it till I get the other bastard bike going.

Fuzzlewump

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Re: Shimming Woes
« Reply #25 on: December 10, 2013, 01:57:55 AM »
I know I'm a bit late to the show here, but I think maybe I can offer some help, POD.

I recently did a cylinder disassembly/rebuild a total of five times, and I found the same thing that your photos show. As ridiculous as it sounds, it appears that for my bike it is possible for the alignment of the camshafts to be off half a tooth or so without disrupting the free turning of the engine. However, if the camshafts are aligned properly then the engine will turn over much more smoothly and quickly. In getting them aligned properly, this is what worked for me. YMMV, I suppose.

With sprocket and cam setting, we have three marks to align- the dot on the sprocket, the line on the bracket holding the cam down (it's the wedge-shaped line on the side of the bracket), and there's a hole in the end of the camshaft that is drilled into the round part of the shaft that can be seen between the sprocket and bracket when looking down onto the head from above. (See photo here)



Obviously, the idea is that this "camshaft hole" is going to be lined up perfectly with the mark on the sprocket whenever the sprocket is locked properly onto the little dowel pin on the end of the camshaft (and then afterward the sprocket and camshaft can be turned together to line up with the line on the bracket). In actuality, the camshaft hole can be moved slightly to the right or left of the line on the bracket while the sprocket remains in the same position relative to the chain. In other words, the tooth of the sprocket wiggles inside the chain link for a measure of about "half a tooth". If both sprockets are wiggled in the same direction, you can set one of them off a total of one tooth, and your timing marks will look correctly aligned.

Ignore the mark on the sprocket. You want to base your timing here off the alignment of the camshaft hole and the line on the bracket. If those two are in line with each other, then place your sprocket onto the camshaft with the dowel pin in the correct slot (Haynes will explain this). Do this with the sprocket furthest from the chain tensioner first. Have the chain placed onto the sprocket before placing the sprocket onto the cam, and see that the chain from sprocket down into crankcase is as taut as possible while still allowing the sprocket to fit onto the cam with ease. This part is very important- you are setting one sprocket as close as possible to the proper alignment, while leaving yourself plenty of room to play around with the other sprocket until you find the sweet spot of smooth revolution.

Once the sprocket furthest from the chain tensioner has been placed with the chain onto the camshaft, put the sprocket bolt on hand-tight. This next part is tricky and if you accidentally knock the sprocket off the camshaft you could lose that little dowel pin down in the crankcase (I did this, it was a blast. Called over friends and had a party.)

What I discovered here is this: You can rotate a camshaft the distance of "half a tooth" to the left or right and not see a noticeable difference in the alignment of camshaft hole and line on bracket. Do this with both sprockets and you have a total of one tooth off. At this point the engine will turn without locking, but it will be stiff and slow. This is how I found my settings when I first got into my cylinders.

Now that the first sprocket is placed onto the cam with the chain in proper place around it, rotate your other cam so the camshaft hole is lined up with the line on the bracket. Take the sprocket for that cam and place the chain over it so that the tension of the chain between the two sprockets is so tight that you can just barely work the sprocket onto the cam. The sprocket should be a tight squeeze going onto the cam, but then chain tension between the sprockets should loosen a little once the second sprocket slides on. If tension doesn't loosen up when second sprocket is placed on, the the second sprocket needs to be moved down the chain by one tooth.

Put on the bolt on the second sprocket, hand tight, then stick your fingers through the chain tensioner hole and push out the slack in the chain, and turn the engine over counter-clockwise. It should turn very smoothly and with hardly any real effort. If it turns slowly or with a lot of drag, then either your sprocket closest to the tensioner needs to be turned counter-clockwise by one more tooth, or your tension between the other sprocket and the lower crankcase is one tooth too tight.

I hope this all makes some kind of sense. I encountered settings that looked identical to what your photos show, and it took a great deal of experimentation to find out that it's possible for your camshaft timing to be slightly off and still allow for full continuous revolution of crankcase. When you get them lined up perfectly, the difference in ease of rotation is immediately evident even though it only looks like a slight difference with the timing marks.
« Last Edit: December 10, 2013, 02:09:48 AM by Fuzzlewump »
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Fuzzlewump

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Re: Shimming Woes
« Reply #26 on: December 10, 2013, 02:34:50 AM »
Ok, that sounds way too confusing.  :-[

What I'm trying to say is that when it comes to lining up your marks,

 1. Go by the camshaft holes, NOT the marks on the sprockets

                                        and
 
 2. Both cams have a little bit of wiggle room while still allowing the engine to turn. There is not just one setting that will allow free revolution of the engine, but actually two.

       So...

 Set the sprocket furthest from the chain tensioner so that the chain between it and the lower crankcase is as tight as possible, then set the sprocket closest to the tensioner so that the chain between the sprockets is as tight as possible. Test your revolutions by putting your fingers into the tensioner hole and pushing on the chain, and make all your adjustments on the sprocket closest to tensioner.

 I wouldn't allow the chain to move around down inside the crankcase...that stuff is already set and you can make all your necessary adjustments from up top.
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Prophet Of Doom

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Re: Shimming Woes
« Reply #27 on: December 10, 2013, 03:26:00 AM »
Awesome, thanks for the long description Fuzzle.  So far I've been leaving the sprockets bolted on the cam.  Didn't even know about the hole.

Yes I'll take care of the pin.  When I did a practice on my spare engine I dropped one of those plastic oil caps down the chain tunnel - being plastic there's no fishing them out without surgical endoscope equipment

QBS

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Re: Shimming Woes
« Reply #28 on: December 10, 2013, 10:34:16 AM »
Fuzz, thank you for all the effort you put into the above epistle.  Truly a labor of brotherly love.  Well done.

Fuzzlewump

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Re: Shimming Woes
« Reply #29 on: December 10, 2013, 05:51:33 PM »
ROV has helped me immensely and if there is anything I can do to return the favor then I'm more than happy to.  :)

I think it is possible to move the chain around without removing the sprockets, but for me it was easier to get a feel for proper chain tension by pulling the sprockets off and testing one position, pull off and try another, etc.

Once you land on the perfect alignment you'll know immediately. The engine can be turned in both directions with great ease.

I would also suggest turning the engine over for several revolutions before closing everything back up. If alignment is off and the engine is going to lock, it may take more than three or four revolutions to do so (I can't remember the exact number).

Just as a guess, I would say from the looks of your photos that the sprocket on the rear intake needs to be turned one tooth clockwise, while the exhaust remains as is.
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pinholenz

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Re: Shimming Woes
« Reply #30 on: December 10, 2013, 07:16:26 PM »
Hi Fuzzlwump,

For those of us anticipating doing our shims, while we have got the covers off, is easy turning of the engine in both directions a sure test that the chain and cams are properly lined up?. In other words, if the engine turns over sweet and smoothly in both directions using the flywheel nut, its all OK. It aint broke, don't touch the cam sprockets or chains!!?
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Rikugun

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Re: Shimming Woes
« Reply #31 on: December 11, 2013, 07:26:22 AM »
I'm a little puzzled why cam timing being slightly off (without causing piston interference) would have such a dramatic affect on ease of engine rotation. Any theories?
It is far better to grasp the universe as it really is then to persist in delusion, however satisfying or reassuring.  Carl Sagan

Fuzzlewump

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Re: Shimming Woes
« Reply #32 on: December 12, 2013, 11:07:30 PM »
For those of us anticipating doing our shims, while we have got the covers off, is easy turning of the engine in both directions a sure test that the chain and cams are properly lined up?. In other words, if the engine turns over sweet and smoothly in both directions using the flywheel nut, its all OK. It aint broke, don't touch the cam sprockets or chains!!?

 If my understanding is correct, and if my experience is not unique, then yes, everything should be OK as long as you get free turning of the engine. But I wanna be honest and say that I'm still new to this stuff and there is a lot I haven't learned yet. So this is just my experience...I can't suggest that it be taken as gospel.

 Haynes manual says that when installing the cams and sprockets, you should check your work by turning the engine counter-clockwise to make sure that the engine doesn't lock up. It does not explain why you should go counter-clockwise, so I tried turning in both directions and found the turning to be smooth in both directions once  I had the timing set correctly. I didn't have the engine mounted into the driveshaft, and I don't know if that would somehow make a difference.

Haynes mentions turning the flywheel nut for two or three revolutions, but I discovered this is not an adequate number of turns to determine for sure that you won't get lock up. I turned it over two or three times, put the engine back on the bike and had it all back together, pushed the starter....locked up. Had to take everything back apart. When I had everything done over, I turned for a count of about thirty seconds...totally unnecessary, but I had some paranoia to get rid of! lol

I didn't do the shims with the cams still in place because I had everything apart already. I don't know about the difficulty of doing it that way, but I can vouch that Rikugun is correct when he mentioned that you have to be careful how you position your wrench when holding the cams with it. The way the heads are cast, it is very easy to accidentally hit and mar the mating surface for the head cover gaskets if you don't hold your wrench just so.

I'm a little puzzled why cam timing being slightly off (without causing piston interference) would have such a dramatic affect on ease of engine rotation. Any theories?

Man, this is a very good question. When I was doing this work I couldn't make any sense of it...it simply doesn't add up when you consider the basics of how the engine works, so I'm still wracking my brain over it...
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Rikugun

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Re: Shimming Woes
« Reply #33 on: December 13, 2013, 09:39:54 AM »
Quote
Haynes manual says that when installing the cams and sprockets, you should check your work by turning the engine counter-clockwise to make sure that the engine doesn't lock up. It does not explain why you should go counter-clockwise
When possible you should turn the engine CCW because that is it's normal direction. To do the valve lash you must turn opposite at times to accommodate the bucket tool but otherwise you turn an engine (especially OHC) over in the direction it runs. It's less stressful on the auto chain tensioners for one reason. 

I would think 2-3 full crank revolutions would do it. From wherever you start it takes 2 full crank revs to rotate the cams once since they spin at half crank speed. When you took it apart again what did you find was the reason it locked up?  Were the tensioners in place when you test spun the motor? Did you spin it fully twice CCW?

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Fuzzlewump

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Re: Shimming Woes
« Reply #34 on: December 15, 2013, 06:58:45 PM »
The first go around, my timing was off and piston met valves, locking everything up. It appeared that when testing the timing by cranking over the engine, I had turned the crank all the way up to locking point and then stopped just before the engine locked. Once everything was put back together, I pushed the start button and there was no cranking before lockup, just immediate lockup.

Tearing it all apart, I reset cam timing and this time turned the crank several times until I was satisfied there was no lockup. This was done with the chain tensioner in place, as well as the chain guard on the other side. It turned without locking, but was stiff and not smooth. It felt as though compression would build up to so great a degree that I could only barely crank it by hand,  then the exhaust valves would open and rotation was easy again.

I changed the timing by one tooth, did the above test again and this time had a crank that felt strong but smooth, more evenly balanced between compression buildup and release. It puzzled me that there could be two timing settings that would allow free revolution of the engine, this just didn't make sense. My understanding was that there was simply only one proper setting for the timing. So I changed the timing back to the way it was, and then back again. After playing around with it for a while I verified for myself that there are in fact two settings. Because one feels "unbalanced" and the other feels smooth and sweet, I chalked it up to another Vision flaw.

Thinking about it some more, I have only one theory on how this is possible. If the timing is off by one tooth, then the engine should not be able to spin freely- there will be piston/valve contact. I think that on this engine this is not the case...if you are off by only one tooth, the timing of compression buildup and release is maladjusted just enough to create an early buildup and late release, but not enough to cause piston/valve contact. When I felt resistance in cranking, it felt like too much compression followed by violent release. My understanding of 4-stroke intake/exhaust timing is still very limited,  so I'm going with a guess here. All I can say really is what I experienced, and unfortunately not how it could plausibly be.


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Prophet Of Doom

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Re: Shimming Woes
« Reply #35 on: December 15, 2013, 09:12:08 PM »
Thanks for your notes Fuzzlewump, since I have this to do on 2 bikes now it will help a lot

QBS

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Re: Shimming Woes
« Reply #36 on: December 15, 2013, 10:28:03 PM »
So Fuzz, you did all your crank turning experimentation with the spark plugs installed?

Fuzzlewump

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Re: Shimming Woes
« Reply #37 on: December 15, 2013, 11:58:18 PM »
So Fuzz, you did all your crank turning experimentation with the spark plugs installed?

Oh no, I wasn't able to turn the engine over with the plugs installed, too much compression to do by hand.

What I mean is that the resistance/release that I found in turning the crank felt like compression buildup. It didn't feel related to chain tension or locked gears....it was "soft", for lack of a better word.

I took this to mean that even with the spark plugs removed there is a certain small amount of compression that will be built up until the piston has pushed all the air out. Like an inflated tire with a hole punched into it...pressure is built up in the tire but that amount of pressure is steadily decreasing as the total volume of air reduces by leaking out of the puncture.

My understanding is that even when you crank the engine by hand, the piston moves quickly enough to compress some air before it all leaks out the spark plug hole....is this incorrect? Now I'm confusing myself, lmao!
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Rikugun

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Re: Shimming Woes
« Reply #38 on: December 16, 2013, 12:00:04 PM »
I would caution against the notion of gaging correct cam timing by ease of crank rotation. This is going to be highly subjective and non-scientific.  :) There are probably several timing changes that don't result in piston interference but do result in more or less crank rotation resistance. Only one however is the correct factory setting!  :) That's not to say you can't experiment with different settings to (for instance) move the torque curve up and down the rev scale but I'd suggest using a degree wheel for that. More than a basic understanding of 4 stroke theory would help here too.  :)

About the crank rotation resistance - besides "phantom" compression effects another ex[lanation may be relative position of the cam lobes from both cylinders. Depending on their sequencing and how many are approaching, climbing, or fully on the lobe, resistance will change. It's not compression necessarily but the effort to move say two valve springs vs. one at a time and where they are on the ramp.

If the engine has not been apart before it's a good practice to carefully note position of timing marks prior to disassembly. Even then you want to carefully follow manual instructions during assembly. If confidence in the current cam timing is low (i.e. PO's failed attempt) follow the instructions carefully noting crank position, which side of the chain needs to be taught, sprocket index marks etc. and you'll be rewarded with success.  Just my 2 cents. :D

EDIT: re manual instructions... I think Fuzzle referenced the Haynes manual but wasn't there a discussion not long ago where some discrepancies were found in the Yamaha manual in the cam timing section?
« Last Edit: December 16, 2013, 12:11:57 PM by Rikugun »
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QBS

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Re: Shimming Woes
« Reply #39 on: December 16, 2013, 12:07:40 PM »
The spark plug hole is pretty big.  It's not going to provide much compression resistance to hand cranking rpm.  I think that gathering data and drawing conclusions  from it, by turning the crank opposite of the engines' designed rotational direction is a bad plan that may lead you down erroneous rabbit holes.  Get the crank to turn freely and easily when rotated in the correct direction and go forward from there.  Also, don't discount the crankshaft rotational resistance induced by the operation of the valve train.