Camshaft trouble!


38 replies to this topic
  • fredszky

Posted March 02, 2004 - 06:57 AM

#21

jchantzWR400F, ive done this. many times.
all i get is no clearance on the intake valves (at TDC)cause the lobes are already pressing them down. it cant be right this way, not with my intake camshaft. i cannot trust the E I marks with a twisted camshaft.

  • Frostbite

Posted March 02, 2004 - 06:59 AM

#22

You can adjust the valve clearance with the head off of the bike miles away from the crank so forget about the TDC mark. Line up the sprocket marks and make sure the lobes are pointing away from the buckets and that should be the loosest spot and that is where you want to set the clearance to specs. The cam timing is a separate issue.

As far as the cam sprockets not lining up, I don’t know much about the pressed on units slipping but it is probably simpler than that. Your bike is a 98. Have you ever replaced the camchain? If not it is probably stretched quite a bit and that will throw off the synchronization between the cams and the crank because the adjuster takes up the slack on one side of the cam chain only. If there were an adjuster on each side of the chain that took up equal slack, the cam timing would remain constant. On the WR and most bikes, the distance between the pins on the adjuster side of the chain gets longer as it stretches and this lets the cams turn backward towards the adjuster side and they move a bit out of synch. The adjuster takes up the slack on the other side and locks the cams in the out of synch position.
For a simple example, think of drive chain. If you lock the front sprocket so it cannot move and pull the rear wheel back so the chain is tight they are locked in synchronization. Lets say there is a horizontal mark on the sprocket and wheel. The top and bottom run of chain is tight so when you move the wheel a bit and then return to the original position the marks will still be horizontal. Now move the rear wheel forward in the swingarm – so the chain gets loose. Pull all the slack out of the top run and check the marks. Now the sprocket mark is horizontal but the rear wheel mark is angled. They are out of original synch. The same thing happens to the cam timing when the chain gets loose.
All engines with cam chains do this and that is why degreeing in your cams is important, especially when your chain is loose to keep the cam timing correct. That is one of the reasons that car racers replace timing chains with gears.

  • fredszky

Posted March 02, 2004 - 07:08 AM

#23

Frostbite >

so what are you saying i should do, when i install the camshafts?

make sure the chain is tight from the crank to the camshafts when i put them on?

  • fredszky

Posted March 02, 2004 - 07:19 AM

#24

Ill try the previous jchantzWR400F post, step by step. just to make sure.

  • fredszky

Posted March 02, 2004 - 07:39 AM

#25

Posted Image

this is my intake cam. i thought i'd show you, maybe you can see if its legit?

  • Frostbite

Posted March 02, 2004 - 08:07 AM

#26

You can set the intake and exhaust valves seperately. You can take the chain off or leave it on and do 1 cam at a time if you have to. Turn the engine so the lobes one cam are opposite the buckets and check the clearance, and then do the same for the other cam. You can even stick in a feeler guage and turn the cam a bit to find the loosest spot. Sounds to me like you need a new chain though.

  • einar

Posted March 02, 2004 - 09:02 AM

#27

That last picture looks wrong Fredszky, the cam lobes should be on the other side of the "I" mark. the lobes should point like " / " when you lay the cam with the E and I the way they should be.

Einar

  • fredszky

Posted March 02, 2004 - 09:13 AM

#28

That last picture looks wrong Fredszky, the cam lobes should be on the other side of the "I" mark. the lobes should point like " / " when you lay the cam with the E and I the way they should be.

Einar


yes, this i've heard from another guy in another forum aswell. this must be the problem.

does anyone have a good picture of a correct intake camshaft?

  • SXP

Posted March 02, 2004 - 09:50 AM

#29

Absolutely right.

A picture is worth a thousand words!

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  • einar

Posted March 02, 2004 - 10:03 AM

#30

I have this link to a picture of how it should look when it is installed correctly, this is with the timing marks matched up on the gear side :

http://mysite.verizo..._rear_view1.JPG

  • einar

Posted March 02, 2004 - 10:14 AM

#31

Gearside picture :

http://mysite.verizo...ks_lined_up.JPG

Pictures are from a 250 WR with autodecomp, but timingmarks and lobes should look the same on yours.

Einar

  • fredszky

Posted March 02, 2004 - 10:37 AM

#32

thanks.

  • jchantzWR400F

Posted March 02, 2004 - 10:55 AM

#33

I also agree that the lobes should be on the other side of the "I" mark. Looks like it's spun....

  • R_Little

Posted March 02, 2004 - 11:31 AM

#34

Too bad its the intake cam. The ex cam would at least give you a reason to get a auto-decompressor cam.

There are a couple of cams for sale on ebay. Maybe you could pick one up cheap.

  • R_Little

Posted March 02, 2004 - 11:34 AM

#35

Also , I would check your intake cam journals too. Put the spun cam back in for a minute and make sure it is not binding in the journals. These bike are built with too tight intale cam journals that can sieze and that will make the sprocket spin for sure.

You don't want it to happen again with a new cam.

Don't ask me how I know, but my head is now on the way back from Mike Crowthers for this very problem.

  • Frostbite

Posted March 02, 2004 - 11:43 AM

#36

The cams can warp if you try to remove them without setting TDC. The valve springs are strong enough to distort the hollow cams if they are putting pressure on the lobes and you take the caps off. If the cam warps a bit it will feel tight in the journals. A straight cam will spin freely by hand with the chain off.

  • hondahater1

Posted March 02, 2004 - 03:20 PM

#37

if the crank is at TDC of the exhaust stroke, the exhaust and intake valves are in valve overlap which means that the two valves will both be open very slightly, and the least bit of crank rotation will relieve either the intake or exhaust valve depending on which way you rotate the crank shaft. Also, Yes the plug does fire on each rotation because the pickup coil is on the crankshaft rather than on the camshaft like you would see on pickup truck or an early model XR motorcycle

  • fredszky

Posted March 05, 2004 - 10:16 AM

#38

Ok, i write this incase someone think they have the same problem as me:

The EI marks on the camshafts is very very wrong. This is not because they are twisted, its because yamaha manufactured them wrong. My mechanics contacted the Yamaha dealer in sweden, and they (Yamaha) faxed over the explanation and illustraded what i just said. This error has offcourse been fixed and later models have correct camshaft marks.

However, the fax yamaha sent was a illustration of correction that seemed wrong (to confuse even more). In their illustration they explained that the camshaft should be twisted from "aligned E-I with horizontal top"(as the book wats it) to +45 degrees clockwise from that. For me however, it would make the intake cams press the valves wide open at TDC. When i tried this i figured that they must really mean counterclockwise instead. I tried counterclockwise 45 degrees and the camshaftlobes was now pointing more or less horizontal to the top (as they should be). I did almost the same with the exhaust camshaft (but maybe 20 degrees counterclockwise instead of 45), unitll it alligned as it should be. I counted 13 pins between.(meaning WR-timing).

i kicked, compression was there :)
i kicked once more (ok maybe 20 times) and it started up, the sound was good. :D

So, don't trust the E I marks too much on the early models!

  • HotCams

Posted March 05, 2004 - 01:25 PM

#39

Get a qualified mechanic that KNOWS how to find lobe centers and set the lobe centers to 105 for each camshaft.

The picture of your camshaft shows that the lobes are in a retarded position from what they should be. The 98 and 99 YZ400F was infamous for this problem. My 98 did it inside of 5 hours of useage. You will either need to replace the camshaft or once you have them set at 105 L.C., mark and weld them in place or replace the cams with new ones, preferably Hot Cams. :)

Tony




 
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