Bent valves when following OEM manual rebuild exactly

[vcgodinich]

Sorry if this isn't the correct place for this, I have been through the tech forums and didn't see anything, and I can't seem to find anything via search.

I am reassembling my 79 top end after replacing the master cylinder gasket, and managed to bent 3 valves. I followed the OEM manual to the letter. So, when the replacements come in, I don't want to screw them up as well.

Can anyone point to a detailed guide for the camshaft installation?

I will try to spell out what I did below, and perhaps someone can tell me where I went wrong.

I got cylinders 1&4 to their top, checked that the vacuum advance thing was on "T" (it was), then put the head on and bolted it down.

The manual said to just install the cam shafts and didn't say what rotation to put them on to start, So I first tried bolting them down in a position that didn't depress cylinders 1 or 4, since they were up. Then I read about the arrows and the dots on the shafts, so I removed them and installed them aligned with the dots. Neither 1 or 4 was pressing down more than a tiny bit (the intake was a bit open on the cylinder that had just pushed up it's exhaust stroke, but only maybe 1 cm, if that). I put the gears that held the timing chain back on according to the manual, never rotating the engine, and it worked out well. I could spin the engine around manually, and all the dots stayed correct.

So I put everything else back together and tried to crank... and no compression on 2 of the cylinders. Did the pressure test, heard a leak back through the intake AND out the exhaust on cylinders 1 and 2. Disassembled and found bent valve stems.

So... does anyone happen to see anything that might have been done incorrect? Thanks for your time.

[mack]

cams

When you first lay in the cams and start to tighten them down, they are usually off just a bit and have to be rotated with a wrench(that has been ground down to fit) to line the dots up before you slide the sprockets and chain on. That is about the only deviation from what I've learned through practice and the book. Only put one sprocket bolt on finger tight, insert the CCT only then should you rotate the motor clockwise to two full revolutions to bring 1 & 4 back up to check your dot alignment. If it looks good, then rotate to expose the other sprocket holes and put those in, tighten them down and rotate once more to do the final tightening of the first bolt you put in. Always rotate the motor clock wise.
One final word of caution, be very very careful not to jamb the wrench against the side of the casing, it will BREAK THE CASTING FAIRLY EASILY. So grind the big shoulders off a wrench and turn in small increments.

[crazy steve]

...So I first tried bolting them down in a position that didn't depress cylinders 1 or 4, since they were up. Then I read about the arrows and the dots on the shafts, so I removed them and installed them aligned with the dots....

So... does anyone happen to see anything that might have been done incorrect? Thanks for your time.

The manual is murky on this; if you're unfamiliar with a specific procedure or the bike as a whole or just general mechanical work, it really pays to read through the whole manual to look for things like this. But one thing that's forgotten many times is that the service manual assumes a certain level of mechanical knowledge which unless you're a trained tech may or may not be present. And sad to say, many Japanese manuals aren't always clear on some items....

Where did you go wrong? Not checking the cam timing the first time you installed the cams; this almost guaranteed bent valves. When you reinstall the cams after repairs, make sure the dots line up or are pretty close. Even installing the cams on the bench can be touchy; if both cams are installed and you only turn one, valves will contact each other and you'll get bent valves.

[natemoen]

There are also markers on the cam sprockets that need to be on the top side when the cam dots are up.

On the bolt hole landings has a sort of arrow (it isn't really an arrow though) that sucks out.

Sorry its early and I haven't had coffee yet....

[DGXSER]

I would agree with Steve, I would suspect that when you installed both cams without aligning the timing marks, you got valve interference and bent them.

The timing is not only important for piston to valve position but also for intake to exhaust valve position, get them out of time and they can hit against each other and bend the valves. As Steve eluded to, the valves also extend below the mounting surface of the head when they are fully open. Sitting the head flat on a bench and installing the cams can also bend a valve as it is forced into the bench top.

[XS1100 Newbie]

There is a sticky by Steve in the repair section on valve shim replacement. It would probably help on the reassembly of the cams.

[vcgodinich]

Thanks for the replies, I guess I just need to be really careful. Maybe it was the sprockets... I put them back the same way (forward backward) that they came off (I could see the outline / shadow where they were attached), but i didn't see the little "up" arrow. Maybe that was it?

Just a few more questions if you would. If after I tighten them, and rotate the engine 2x to see if they still align... what happens if they are off by one sprocket? Obviously I would fix it, but is there a danger of damage if it's only a bit off during those rotations?

Also, there is no way that the slight depression that occurs on cly 1 during the initial cam installation is causing it, correct? How much clearance is there with the cylinder TDC? Maybe it just rotated a little during install and that caused it...


Anyway, again, thanks for the help.

[LoHo]

The cam sprocket bolt holes with the tabs should be up, although the bike will run okay with them otherwise and not bang valves. It is amazing the pounding those valves take when the bike is running, yet how fragile they are when it comes to being bent. Just a bit of angular contact and you create an expensive wind chime.

[crazy steve]

Being off by one tooth on the cam sprocket either way won't bend valves, possibly even two (no guarantee at two); more than that and bent valves will probably result. This is why it's critical that the cam chain be properly engaged with the crankshaft sprocket when doing this.

Also, there is no way that the slight depression that occurs on cly 1 during the initial cam installation is causing it, correct? How much clearance is there with the cylinder TDC? Maybe it just rotated a little during install and that caused it...

Nope, that's not the problem. It was the first cam install that bent the valves...

There are errors/omissions in the FSM (many documented here), the Clymer reproduces those and adds a few of it's own. You would have thought that Yamaha would fix these in later editions of the manual, but they didn't.....

[crazy steve]

Here's the valve adjustment tip that details reinstalling the cams better than the manual....

http://www.xs11.com/forum/showthread.php?t=35434

[GLoweVA]

Steve's awesome pictorial shows the spark plugs still installed.
I'd pull the plugs out to make the spinning of the engine by hand a little easier when it's time to check those dot alignments and getting to the 'c' position for the CCT adjustment step.

[LoHo]

Or you could just set the plugs in loosely to keep crap out of the cylinders but still allow easy turning. I used corks to keep the holes protected and popped a cork out about ten feet when I was spinning her.

[old_skool]

The timing is not only important for piston to valve position but also for intake to exhaust valve position, get them out of time and they can hit against each other and bend the valves.

Are the intake and exhaust valves that close when they open, if opened together they will contact each other?? The only reason I ask is, that on the 1100 Suzuki's we like to sometimes adjust our valves with what we call a zip tie method, remove spark plugs and crank till you see a valve drop/open, slip a bent in half zip tie through the spark plug hole under the valve, crank it a little further by hand and it holds the valve open to make shim removal easy, if what your saying is true, then rotating the cams in this configuration would cause the valves to collide....?

How can you have the cams timed to the crank position and not to each other simultaneously??

[DGXSER]

I have not run this test personally, but know others who have dealt with the aftermath. So I do not know for sure how far open the valve needs to be to cause this interference. It may well be that the method your suggesting will work just fine as it may not hold the valve open enough to cause the interference.

As to how to have the cams out of time, I meant that turning one cam and not the other with both cams installed in the head, with the head off the engine, is also a bad thing. If your going to work on the head and shimming off the engine, only install one cam at a time. Finish all the shim adjustments. Then move to the other cam after removing the first one. Again, that is with the head elevated off the work surface so the valves do not hit it.

[jwhughes3]

on the 1100 Suzuki's we like to sometimes adjust our valves with what we call a zip tie method, remove spark plugs and crank till you see a valve drop/open, slip a bent in half zip tie through the spark plug hole under the valve, crank it a little further by hand and it holds the valve open to make shim removal easy

Personally I think our valve stems are delicate enough I would never try to block it open like that against the spring, interference or not.

John