WR426f Timing nightmare continues... Finally FIXED!!!

[Wiz636]

Interested in hearing if this was ever resolved...

[William1]

Did you make sure the woodruff key in the flywheel is intact?

[dirtysouth]

Your hypothesis would work except that I had the stock manual decomp cam on when the engine seized. The hotcams was put on in the process of the top end rebuild. Here are my questions: Why does the piston have indentations for each valve? On TDC, how close are the valves to the piston?

One more thing I discovered that explains where on the piston the vavles hit: The piston in the cylinder can be rotated a tiny bit. ?? Probably enough that a valve out of sync would hit it on the side of the valve indentation on the piston. No way in hell I am tearing into a bottom end to replace a crank. I don't have the patience or the skill. My last question before deciding to dump the bike for pennies or fix it: If I leave the crank as is, replace the topend valves and have the timing right, is there any reason why the valves would ever come close enough to the piston to kiss it whether it be on the shoulder of the valve indentations or in the center of them?

Above from your last thread...No Way this is a good thing! Did you work this out yet? I am not sure on tolerances for something like this but I know tight...and that don't seem tight...especially at 10,000 revs:excuseme: This along with a decked head.....I say no sir. See what others have to say about this. Forgive me if I missed the bottom end rebuild in the previous thread.

[Reedus]

Sorry to disappoint guys. I know a bunch of you guys were tuned in to see what the problem turned out to be. I have thrown in the towel on this thing for the time being. I just cant keep throwing money at it in hopes i solve the problem. Woodruff key was intact, so that seemed to rule out bottom end problems. I can't justify throwing another 300 bucks at it in new cams when I have already spent 1600. It is for sale for 2k on KSL.com (local listings) if I can't sell it for that, then maybe I will tear it back down and beat my head against it some more. ?

[Reedus]

From the first post, the problem with the valves hitting the piston on that episode was a forgotten circlip. The pin came out and scored the cylinder wall as well as destroying all the valves when the piston came up and hit them.

[Reedus]

Just a thought that occured to me: Are the cam buckets for the exhaust and the intake the same. I never separated them and most likely ended up with an exhaust bucket on the intake side. I have no idea how to tell the difference between them and don't know if it would make a difference on whether the valve hits the piston on the down stroke of the intake stroke. Anybody with knowledge care to elaborate?

[MotoGoalie]

Just a thought that occured to me: Are the cam buckets for the exhaust and the intake the same. I never separated them and most likely ended up with an exhaust bucket on the intake side. I have no idea how to tell the difference between them and don't know if it would make a difference on whether the valve hits the piston on the down stroke of the intake stroke. Anybody with knowledge care to elaborate?

and what of the shims?

you have your explanation right there, possibly.

So you are also saying you are SURE your cam gear did not spin on the camshaft?

[matt4x4]

reedus - buckets are identical, you wouldn't have been able to shim properly otherwise, but if your piston can rotate some, I'm guessing the big end has something wrong.....likely from the wristpin sliding out sideways.

Even if you'd mixed up buckets and managed to somehow shim it right, you'd still only open valves by the lobes pushing on the bucket - that is all constant - lobes don't start the movement of a valve early unless the cam isn't set right.

Also, look at it this way:

If your piston hit the valves while the engine was running this is the scenario: piston moves up at great force, hits valve which in turn transfers an upward blow though the valve stem, shim, bucket right to the lobe which is trying to turn one way but is now possibly being forced to turn in the opposite direction - so your cam gear could easily have slipped.

I know your using a different exhaust cam, but your intake valves also took a hit and it could well be the intake cam gear that's slipped (or both?)

Also, can you post a nice clear pic or two of:

1. top of cylinder without head attached showing piston at highest part of stroke

(also, note that this would be TDC on your flywheel, so reference that while you're taking pics)

I'd like to see where in relation to the top of cylinder the piston is sitting at TDC.

[Reedus]

Matt, the piston that rotated isn't in the bike any more due to the forgotten circlip and subsequent destruction of the top end.. I put a brand new one in and it doesn't rotate. I'll take some more pics as soon as I tear it back apart. Your theory of a spun cam sprocket makes sense, except that the cam lobes SEEM to be exactly at the 10 and 2 o'clock positions. Even so, I would think that by advancing or retarding the intake by one tooth either way would not be enough to hit a valve. Somebody correct me if I have the wrong assumption.

http://www.southbayriders.com/forums/showthread.php?t=21788

Also, by the way the guy in this link timed his WR426, it looks off one tooth to me on both cams. I looks to me like the intake needs to be turned counter clockwise and the exhaust needs to go one tooth clockwise. Whaddya think? Do BOTH of the horizontal marks on the cam need to be level with the head or just the outer one? That pic confused me, but maybe that is where I am missing the boat???

[Frostbite]

Matt, the piston that rotated isn't in the bike any more due to the forgotten circlip and subsequent destruction of the top end.. I put a brand new one in and it doesn't rotate. I'll take some more pics as soon as I tear it back apart. Your theory of a spun cam sprocket makes sense, except that the cam lobes SEEM to be exactly at the 10 and 2 o'clock positions. Even so, I would think that by advancing or retarding the intake by one tooth either way would not be enough to hit a valve. Somebody correct me if I have the wrong assumption.

http://www.southbayriders.com/forums/showthread.php?t=21788

Also, by the way the guy in this link timed his WR426, it looks off one tooth to me on both cams. I looks to me like the intake needs to be turned counter clockwise and the exhaust needs to go one tooth clockwise. Whaddya think? Do BOTH of the horizontal marks on the cam need to be level with the head or just the outer one? That pic confused me, but maybe that is where I am missing the boat???

The tops of the buckets can be different thickness due to manufacturing tolerances, and are color coded. My 400 had 2 different thickness buckets and had a color dot on the underside of each bucket, some green, some purple. I mic'd them and confirmed that the greens were the same, and the purples were the same, but there was a difference between the thickness of the 2. Manufacturers use color coding on connecting rods in multi cylinder engines based on weights. If you have a bad rod with a green dot, you have to replace it with a green dot rod, or it'll throw off the balance.

I believe the bucket diameters are the same, but Yamaha recommends that you put them back in the same holes as they "break in". I tried switching mine and some are sticky in other holes, which could cause a valve to stick.

If you adjusted your shims to compensate for the extra clearance of a sticky valve, the can would push the valve farther into the cylinder, reducing piston to valve clearance.

One thing I didn't think of 'till just now, it's possible that one or more shims popped out of place under the buckets. If so, that would push the valve down farther, and you wouldn't notice unless you re-checked you valve clearances.

A note on checking clearances - it is very easy to get false readings. The valve springs are very light and a too thick feeler strip can feel "good" even if the clearance is too tight. Also, a stiff feeler strip can give a good feel when the clearance is too loose, but the drag is caused by the stiff strip interfering in the tight space. I had to prebend my feeler strips ot get a proper feel from them.

[02WR426Cali]

Isn't there only supposed to be 13 pins inbetween the timing marks? I thought WR was 13 and YZ is 12. Mine was 13 stock and I switched it to 12 and it runs great! You have 14, but the lobes look ok, so I think the earlier mention of the sprocket spining is correct, so the lobes must be just a tiny bit off. Check ebay, I see stock cams on there all the time, I'm sure they are in better condition than yours.

[Reedus]

If I was dead positive that the cam had spun, I would have no qualms about throwing down on a couple of cams, I just am not quite convinced that therein lies the problem. Tearing down tomorrow again...

[maxtherat]

Again, verify that you are at TDC by checking the position of your piston. Your marks can show TDC but you can be360 deg. from the true TDC. Good luck!!!

[matt4x4]

Anybody checking their valve clearance soon? If so, post up a pic for Reedus - there seems to be a state of confusion with regards to how many pins between timing marks, 14, 13 or 12? Does the manual show anything - I know their pic seems to depict lobes at 9 and 3 o clock exactly which just doesn't seem to be the case in the real world - I noticed that on mine earlier this year too, they're both up a bit from horizontal at TDC.

Here's what's in hte manual, the cam marks are WAY different...but in the one pic you can see the lobes pointing up some - I saw another dwg in my manual that didn't show them that way, but rather 9 and 3:

WRT the buckets, according to the parts Diagram, it's just one part number for all 5, I would presume any differences in buckets is compensated for through the proper shim - and I believe reedus shimmed it all correctly since he's done top ends before and mentioned something regarding valve cxlearances being in check.

Sorry Reedus - WRT the piston - I thought you had stated that your new piston turned a bit side to side, my misunderstanding.

[Matt James]

From reading all of this thread there was only one guy that made sense. You need to put a degree wheel on it with a dial indicator on the bucket and set your valve timing. It's obvious that the cam sprokets have slipped. If you have never done it it is complicated, so find someone who has done it to walk you through. All you need to know is the cam specs, ie; intake opens at ? degrees BTDC and exhaust opens ? degrees BBDC. Good luck

[atitagain]

I agree with Matt and Frostbite... check the cams with a degree wheel. It is the ONLY way to verify if the sprockets are correct.

[YELL-OSNAKE]

Would a 2001 yz426 intake cam work? I have a "spare" good one, that I would give ya for just the cost of getting it to you if this helps....prob not more than $10.00. you said the exhaust cam had been changed, you could use mine to "test" even....just my .02

[Reedus]

Definitely interested in the intake cam. PM sent. As for the spun cam, I don't have a degree wheel and really don't want to throw that much money at bike in order to get it running. If anyone would be gracious enough to let me "rent" their wheel, I would be willing to pay a good price. I took the bike into a small engine shop, and the guy told me that you can't reindex cams that have spun. Just have to bite the bullet and buy new ones. Same story when I called the dealer service department. I guess I will try a new intake and see if the old intake really did spin. Keep posted, and thanks a ton for all the help and info.

Reed

[dirtysouth]

Definitely interested in the intake cam. PM sent. As for the spun cam, I don't have a degree wheel and really don't want to throw that much money at bike in order to get it running. If anyone would be gracious enough to let me "rent" their wheel, I would be willing to pay a good price. I took the bike into a small engine shop, and the guy told me that you can't reindex cams that have spun. Just have to bite the bullet and buy new ones. Same story when I called the dealer service department. I guess I will try a new intake and see if the old intake really did spin. Keep posted, and thanks a ton for all the help and info.

Reed

May wanna check on the exhaust cam too as it was initially bumping the piston if I remember. Seems logical that if the intake spun then so too may have the exhaust. Could take the time if you have the Geometry knowledge to make a wheel from cardstock/posterboard/plasticstock. Just use a pin and a piece of thread and a pencil to trace a circle out (notice the size of the wheel...this makes reading the individual degree marks easier as they would be really close together if the wheel was smaller) then use a straight edge to draw a straight line through the pin hole from one side to the other. Then get a protractor and lay it on that line making all of the appropriate tick marks for your degree increments. Lay a straght edge through the center point and respective marks to trace a line to the edge of the wheel (this will be the most meticulous portion of the project). Label the degrees then glue the wheel to the back of your socket (use a compass to trace a position circle for the socket) with weak 5 min epoxy so that there is no chance of it moving as you turn the crank. Then cut a square (or whatever) hole big enough for the 3/8" drive to fit through and that should fly. Now you have a temp degree wheel. Find TDC using the piston as your guage. The piston will rise to TDC then dwell for a second then begin to fall. Find the spot where it just makes it up before dwell. Then you tie a piece of coathanger or wire to the frame or whatever giving you the ability to move it over 0 and mark TDC when you find TDC. Then you can check your degrees BTDC and etc. having the coathanger/wire as a reference. I know that this sounds crude but it is a cheap way to roughly check your situation. An alternative might be see if a local engine machine shop might be willing to let you leave a deposit and borrow theirs (I would try this first personally if I didn't wanna buy one). Good luck gettin it running and thanks for entertaining my long redneck post:thumbsup:

[MotoGoalie]

ONE MORE THING before we go into the spun cam gear theory.....

https://www.thumpertalk.com/forum/showthread.php?t=614890

have you retensioned the tensioner properly before assembly?