Camshaft trouble!


38 replies to this topic
  • fredszky

Posted March 01, 2004 - 09:58 AM

#1

hi!

im trying to set my clearance on my valves.
the bike is a WR400 '98
the image below is when it's set exactly to T.D.C
Posted Image
when i set the camshaft like this, i get correct clearance on the exhaust valves, but 0 clearance on the intake valves. however, if i turn the flywheel just a bit counterclockwise(so the intake camshaft releases from the valves) i get correct clearance.

the only sollution i see is to turn the intake camshaft one step counterclockwise. (and the exhaust just so they get equal?).. however the problem is, then the camshaft would be even more out of the "E ---- I" horizontal line that the book describes. (is this really awfully bad??)

but thats the only way to release pressure from the valves, right???

im swedish so excuse the spelling

  • Indy_WR450

Posted March 01, 2004 - 10:04 AM

#2

I think I have seen posts like this on earlier model yz400's and it may be that the sprocket has spun slighlty on the cam shaft so they are out of sync with factory position. I am not sure how it is mounted but I recall somone saying that they are pressed on sprockets that can spin under heavy torque. :) It might be time for a new cam or repair the press fit with super premanent loctite.

  • fredszky

Posted March 01, 2004 - 10:27 AM

#3

if the sprocket have turned slightly from the original position, i could just ignore the E I marks and setup after the lobes instead? or is the risk that it will turn even more (because its loose somehow) and really cause some damage later on?

  • Indy_WR450

Posted March 01, 2004 - 10:30 AM

#4

Have a machine shop pull it and realign and loctite it. The manual has spec on the lobe alignment with the sprocket. You may be lucky enough with adjusting one tooth but if it slips or it is not just right you can damage the valves with the piston. :)

  • SFO

Posted March 01, 2004 - 10:38 AM

#5

Both Powroll and Edco will realign and weld the sprockets in place.
Self indexing cam sprockets has been a issue for some folks.
I would consider R&R'ing the cam chain and perhaps the cam chain buffers as well.

  • NuclearX

Posted March 01, 2004 - 12:21 PM

#6

Both Powroll and Edco will realign and weld the sprockets in place.
Self indexing cam sprockets has been a issue for some folks.
I would consider R&R'ing the cam chain and perhaps the cam chain buffers as well.



Can you explain what you mean with "R&R'ing the cam chain" please?

  • Eddie Sisneros

Posted March 01, 2004 - 12:36 PM

#7

Remove and Replace.

  • Frostbite

Posted March 01, 2004 - 04:15 PM

#8

You can set the clearance correctly even if your cam timing is off. Set up so the intake lobes are pointing away from the buckets and check and then turn a bit to check the exhaust the same way. Basically you want to find the loosest spot and this is the clearance you use to figure out what size shims you need.

  • SFO

Posted March 01, 2004 - 04:33 PM

#9

Are you at TDC rolling the crank in a forward direction?
Almost appears that both cams are off a tooth, as far as your picture illustrates.
At the position you note you should be close enough for hand grenades and valve clearance checking.

  • Hick

Posted March 01, 2004 - 07:24 PM

#10

Almost appears that both cams are off a tooth, as far as your picture illustrates.



That was also my first impression, the picture does not look like TDC, it looks like TDC plus one tooth.


At the position you note you should be close enough for hand grenades and valve clearance checking.


Ditto.

If it were me, I'd (temporarily) ignore the crank position, and find the max clearance at any cam position (w/in reason, i.e. w/ lobes oriented "normally"). If this then is way beyond TDC then something is amiss...



Hope this helps.

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  • dominator426

Posted March 01, 2004 - 11:37 PM

#11

That's right...Valve clearance should be checked with sprocket dots aligned. If your sprockets had spun forward, you would actually get normal valve clearance with cam gear advanced a bit, as in the pic.

  • Hamish

Posted March 02, 2004 - 01:20 AM

#12

I find it strange (read impossible coincidence)that both cam sprockets have slipped exactly the same amount. Is the lower sprocket pressed on the early 400's or is it part of the crank like the later models? If it is pressed on I would say that it may have moved. The other thing to do is to check the accuracy of the TDC mark using a degree wheel and a piston stop. I can give details of this procedure if required.As for valve clearance, always check on the centre of the base circle if there is any doubt.

Hamish

  • hondahater1

Posted March 02, 2004 - 03:36 AM

#13

I realy think you have your crankshaft is at tdc of the exhaust stroke, which means that the exhaust valve has just closed and the intake is just opening to start the intake stroke. Both camshafts lobes should be pointing upwards and not even close to the vlaves yet. I sugest rotating your crankshaft one full turn which will turn your cams 180 degrees. Remember the lobes should be poining somewhat up.

  • jchantzWR400F

Posted March 02, 2004 - 04:56 AM

#14

OK, from my most recent experience with changing my wr to yz timing, I too was concerned with the alignment of the timing marks. I did notice that you have 12 pins between 12:00 timing marks. Did you switch your wr to yz timing just before checking valves? If you did, I would bet that your cam chain sliped a tooth on the crank, and that's why both intake and exhaust cams seem to be off a little.

When I did this I chose to start from scratch. Take the cam chain off of both intake and exhaust cam sprockets. zip tie it to the frame. Set your engine to TDC via the viewing hole. Use the "I" in "HI". Make sure that your cam lobes are facing away from one another. Then set the intake cam as it looks in your manual. Put the cam chain on. Now set your exhaust cam 12 pins off of the intake cam. Now check valve clearance. This is the only way to ensure that your cams are in the correct location. I doubt that they have slipped.

  • SXP

Posted March 02, 2004 - 05:22 AM

#15

That was my first thought. The piston comes to TDC once every revolution; however, the cams are (should be) alinged for clearance measurement only every other revolution. I'm assuming he is measuring it at the "correct" TDC.

BTW, that brings up a question I've had for a while - does the spark plug spark every revolution i.e. one wasted spark every two revolutions?

  • sabin

Posted March 02, 2004 - 05:53 AM

#16

That was my first thought. The piston comes to TDC once every revolution; however, the cams are (should be) alinged for clearance measurement only every other revolution. I'm assuming he is measuring it at the "correct" TDC.

BTW, that brings up a question I've had for a while - does the spark plug spark every revolution i.e. one wasted spark every two revolutions?


yes.

BTW the cam lobes must point something like 10 minutes to 2 (13:50)

  • MN_Kevin

Posted March 02, 2004 - 05:53 AM

#17

I agree w/ jchantzWR400F. Yank the cams off and start from scratch.

If I recall, the outboard marks on the two cams (9 o'clock for exhaust and 3 o'clock for intake) are the ONLY marks to worry about.

The others WILL NOT line up, i.e. 12 o'clock.

  • fredszky

Posted March 02, 2004 - 06:23 AM

#18

Look:

When the intake camshaft is alligned exactly horizontal with the top (as the book says it should be) 9, 12, 3, (E at 9, I at 3) the lobes are pressing the valves, hence no clearance. even if i turn the camshaft counterclockwise one step (as my picture shows) i get 0 clearance. if i, from this point, turn the camshaft addtionally 1 step counterclockwise, i get normal clearance. but then the marks E I would be very wrong.

so, the conclusion i think is that the camshaft has been twisted in relation to the sprocket, and therfore the marks E I is not correct.

the question is, shall i install the twisted camshaft (without the help of marks), should i leave the camshaft to some mechanics to fix it right (i dont know how difficult that is, and what the price is), or shall i just buy a new camshaft (~$200-250)

  • fredszky

Posted March 02, 2004 - 06:37 AM

#19

I find it strange (read impossible coincidence)that both cam sprockets have slipped exactly the same amount.


i think its only the intake camshaft thats twisted. if i remember correctly the exhaust camshaft shows clearance when the E I is aligned as it should be.

  • jchantzWR400F

Posted March 02, 2004 - 06:42 AM

#20

Look:

All I'm saying is, before you go off of the deep end. Make absolutely sure that the "I" mark is centered. Make absolutely sure that the cam lobes are facing away from on another. Remove the cam chain from the exhaust cam (loosen the cam chain tensioner first) Remove the cam chain from the intake cam. Set the intake cam like it looks in the manual. Reset the cam chain on the intake cam. Now set the exhaust cam 12 pins (yz timing) or 13 pins (wr timing) off of the intake cam and you will be golden. Now check valve clearances.

A tip to make sure the engine stays at TCD. Put the bike in 5 gear when turning the flywheel. It is very easy to move it past TDC.




 
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