need help! yz 450 cam timing



18 replies to this topic
  • corndogg

Posted May 22, 2013 - 07:00 AM

#1

hello, im sure this has been posted before but i cant find a straight answer, theres two many different answers and pictures to be sure. My problem is i am rebuilding a 2004 yz 450 and im putting the cams back in but they were never marked for timing. my manual shows the two timing marks while engine is at tdc but i cannot get the timing marks on the cam to line up perfectly with the head. the timing marks are a little high on the intake cam and if i turn it back its just below the top of the head. my question is do i want to go a little high of a little low with that timing mark.

also i read about a pin count but theres 3 different pin count numbers floating around what is the correct pin count on the chain for a 04 yz 450.
any info would be greatly appreciated.

cheers!

  • grayracer513

Posted May 22, 2013 - 09:06 AM

#2

To start with, the marks will probably not ever line up perfectly. The question you have to ask is, "will it be better or worse if I move it either way?" Imagine the dot being one tooth away from where it is. Better? Move it. Worse? Leave it. The picture shows a correctly timed YZ450 exhaust cam. See the alternate marks in red.

Posted Image

Starting with the marks on the flywheel, there are 3 radial line marked at or near TDC. Viewing it as a clock face, the first two are at 11:58 and 11:59, and are linked by a horizontal line (sometimes not very visible). Ignore these, they're for using a strobe to check ignition timing. The third mark, then is at 12:00, and that one is TDC.

Start by setting the exhaust cam in place. On the '03 and later models, the exhaust cam will have two timing marks. Place one at 9:00 o'clock, aligned with the gasket surface on top of the head, and the other at 12:00. Be sure that the slack is gone from the cam chain running down from the front of the cam to the crank when you check, and that the crank hasn't moved.

Now, the intake cam. The cam on an '04 might still have 3 marks on the sprocket, or it may be one of the newer ones that only has two. The 3 dot sprockets are from the days before auto decompression, and the same sprocket was used on both cams. They are marked "E" and "I", with the center mark not labeled. These should be placed so that the "I" aligns with the head at 3:00, and the center mark is at 12:00. With newer cams having only two marks, place the marks at 12:00 and 3:00, and align the mark at 3:00 with the head.

This is where the pin count thing is useful: Anyone who has messed with this before (or currently) already knows there's no way to roll the cam chain over the second cam with both of them in their saddles, the intake cam has to be positioned over the center of the head, engaged with the chain, then "rolled" into place in its saddle. Relocating the chain after placing the cam is possible, but not easy. So, if you count 13 (thirteen) pins from the 12:00 mark on the correctly positioned exhaust cam to the 12:00 mark on the intake and set the chain there, it should drop into place and be properly timed.

Just remember that you cannot use the pin count to time the cams. Only the actual timing marks should be used. The pin count for all YZ450's using OEM cams is 13, as it is for MOST 426's. 400's I'm not sure about, and 250F's are 12. If you have a 426 with an OEM YZ450 cam in it, you have to time the intake first and use 14 pins to time the exhaust. See why you find so many "answers" to that question? Use the timing marks only.

To double check , carefully roll the crank backward about 5 degrees, then roll the exhaust cam back as far as it will go without moving the crank, then the same for the intake. Push in through the tensioner hole with a finger and slowly turn the crank back to TDC. Check the marks, make any corrections needed, and button it up. DO NOT turn the engine more than 30 degrees in either direction from TDC without the tensioner in place and active.

  • corndogg

Posted May 22, 2013 - 10:13 AM

#3

thanks, when you say DO NOT rotate the crank more than 30 degrees when the cams are out why is that? as i did not take the motor apart and im not sure if the guy turned it or not. Also my cam marks are out a bit more than the picture shown. im gunna either be high or low either way. ill give it a try high and see what happens. my exhaust valve i can line up perfect just not my intake.

  • grayracer513

Posted May 22, 2013 - 10:42 AM

#4

Look again. The cam in the picture is aligned "perfectly".

The reason to avoid rotating the engine without the chain tensioned is that with the cam chain over the cams and the tensioner out or locked back so as to be ineffective, the load placed on the cams by trying to open the valves has a 95% chance of causing the chain to slip on the sprockets, throwing the engine out of time. Then, if the engine is turned more, the chance of bending a valve arises.

This is only important when the chain is in place and the engine is assembled. Once the chain is off the cams, there's no problem outside of the annoyance of wadding the chain up on the crank.

  • corndogg

Posted May 22, 2013 - 10:58 AM

#5

phew scared me haha, yeah deffinitly hasnt been done other than with the cams out. do you think i should run with the intake cam a touch high with the mark or a touch low.

Edited by corndogg, May 22, 2013 - 10:59 AM.


  • corndogg

Posted May 22, 2013 - 11:21 AM

#6

i guess the best thing would be to see what position the cam lobes should be in. as it sits with the dots a little off the exhaust cam lobe (looking from opposite side of the cam gears) is around 9-10 oclock an the intake is more vertical around 2 oclock. the exhaust cam lob is more horizontal than the intake lobe if this makes any sense.

  • grayracer513

Posted May 22, 2013 - 11:36 AM

#7

If it really does line up in such a way that it seems half a tooth off either way, you probably need a timing chain. Is it new, or are you reusing the old one?

  • corndogg

Posted May 22, 2013 - 12:08 PM

#8

reusing the old chain. i was thinking that but hoping that wasnt the case. when that mark is lined up with the top of the head should you be able to see the entire knotch or just half of the knotch, sorry for all the questions im just losing my mind trying to get this thing to run. i appreciate it.

  • corndogg

Posted May 23, 2013 - 05:26 AM

#9

i think i got it now just waiting for some new shims to come in and ill give it a try. thanks again

Edited by corndogg, May 23, 2013 - 05:29 AM.


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  • grayracer513

Posted May 23, 2013 - 06:39 AM

#10

when that mark is lined up with the top of the head should you be able to see the entire knotch or just half of the knotch,


The marks are at the bottom of the V between teeth. If everything was exactly perfect, the line of the gasket surface would intersect the bottom center of the V: ---> <--- like that.

Do yourself a huge favor and spend $35 on a new chain so you don't blow up your new toy.

  • NitrousR1

Posted May 23, 2013 - 03:19 PM

#11

I'd highly advise you replace your cam chain. THey stretch over time and you would be amazed at the difference in length between your old one and a new one. It's really shocking. U can find them for $15 online. Your worn chain is the reason your dots arnt lining up with the head. It's a lot harder to time with an old stretched chain. That chain will save u big $$$ down the road

  • corndogg

Posted June 05, 2013 - 05:14 AM

#12

cam chain has been replaced an valves have been set to proper tolerances but i still cannot get the bike to fire. checked for spark last night all was good, re did the carb and also good. right now between the intake cam top mark and exhaust cam top mark have 14 pins in between them. both cam lobes are almost horizontal with the casing. and the timing marks are a hair below the casing on both. the bike will back fire every few times i kick it.

i have had the cams out over 15 times in the last two weeks and im losing my mind over this thing. every picture i google is about the wr 450. where should i start next?

  • corndogg

Posted June 05, 2013 - 05:19 AM

#13

and i tried last night with 13 pins in between the two and that didnt work either.

  • wweagleflyer

Posted June 05, 2013 - 10:59 AM

#14

It seems to me that you are on the wrong track if you are trying to change the pin count between cams. Once the cams are installed with the cam caps properly torqued down, etc. and the chain is taut between the two cams, the number of pins will fall out. The only way to change pin count between the cams is to put slack into the chain between them, and as soon as that slack is taken up, your timing will change and the pin count will return to its proper value. The key steps are to:

1. make sure that your crank is at TDC per the timing mark (the "I" mark, not the "H" mark) on the flywheel and the view port on the left hand case.
2. Install the cams to what you think is the correct position by getting the timing marks lined up with top of the head (Exhuaust marks at 9:00 and 12:00 positions and Intake marks at 3:00 and 12:00 positions). The 9:00 and 3:00 positions should line up close to the top surface of the cylinder head.
3. make sure that there is no chain slack from the crankshaft to the exhaust cam to the intake cam (any slack should be between the intake cam and the crank shaft).
4. Reconfirm that your crank timing has not moved from TDC and check the location of the timing marks on the cams.
5. If moving either cam by one tooth (or more) would improve the alignment into the 9:00, 12:00 & 3:00 positions, then make the change and check again.
6. Once you have check everything again, and any tooth adjustment would make things worse, you should be done with the timing assuming you are using a good (unstreatched) cam chain.

If you have done all of the above, and the bike still won't start, you probably need to consider other things like ignition, fuel delivery, valve clearances, a valve leak down check, a compression check, worn camshaft bearings, etc.

Edited by wweagleflyer, June 05, 2013 - 11:02 AM.


  • corndogg

Posted June 05, 2013 - 11:11 AM

#15

It seems to me that you are on the wrong track if you are trying to change the pin count between cams. Once the cams are installed with the cam caps properly torqued down, etc. and the chain is taut between the two cams, the number of pins will fall out. The only way to change pin count between the cams is to put slack into the chain between them, and as soon as that slack is taken up, your timing will change and the pin count will return to its proper value. The key steps are to:

1. make sure that your crank is at TDC per the timing mark (the "I" mark, not the "H" mark) on the flywheel and the view port on the left hand case.
2. Install the cams to what you think is the correct position by getting the timing marks lined up with top of the head (Exhuaust marks at 9:00 and 12:00 positions and Intake marks at 3:00 and 12:00 positions). The 9:00 and 3:00 positions should line up close to the top surface of the cylinder head.
3. make sure that there is no chain slack from the crankshaft to the exhaust cam to the intake cam (any slack should be between the intake cam and the crank shaft).
4. Reconfirm that your crank timing has not moved from TDC and check the location of the timing marks on the cams.
5. If moving either cam by one tooth (or more) would improve the alignment into the 9:00, 12:00 & 3:00 positions, then make the change and check again.
6. Once you have check everything again, and any tooth adjustment would make things worse, you should be done with the timing assuming you are using a good (unstreatched) cam chain.

If you have done all of the above, and the bike still won't start, you probably need to consider other things like ignition, fuel delivery, valve clearances, a valve leak down check, a compression check, worn camshaft bearings, etc.


thanks for the response, i am on the last mark for tdc ( not the H) my spark is good, and the plug has fuel on it when i pulled it after trying to start it. and for the timing, i am getting the marks as close as i can tightening everything down than checking my pin count and if either is off i take it apart and try again haha. ive had the cams out about 15 times in the past few days. i think seeing a picture of what the lobes on the cam should correctly look like when all said and done would really help as that would give me a good idea if im close.


with my timing marks on the intake cam i can get them above the casing but it seems a little high so if i go one tooth lower it is just below the case should i go high or low on this?

thanks

  • wweagleflyer

Posted June 06, 2013 - 05:47 AM

#16

Attached is the picture you requested showing the cam lobe positions when everything is lined up.

Attached Thumbnails

  • LobePosition.png


  • thefickler

Posted June 06, 2013 - 06:36 AM

#17

Are you sure that your timing marks are aligned up as per the manual? I just replaced my cam chain last night, and everything lined up perfectly. I didn't bother to count the links, since I knew where the crankshaft was, and once I got the cams into place, the timing marks lined up.

Didn't you say this was a new chain? Did you go OEM or use another source? Are you sure that this could be the correct chain as well?

  • corndogg

Posted June 06, 2013 - 07:41 AM

#18

This puzzle just got a whole lot more confusing. yea the timing chain is a new oem chain. couple buddys came over last night that are also red seal mechanics and were all confused. all three of us agreed that the timing is lined up correctly, so we checked the compression and we had a reading of 15 psi. so we pulled the head and cylinder again last night looking for a broken ring but all was good. ( brand new rings ) and also did a leak test on all the valves and all were good. this has me stumped.

  • usp4u

Posted June 06, 2013 - 12:49 PM

#19

You said it passed a leak down. In that case, all you need is FAST...
Fuel
Air
Spark
Timing
If you have these, it has to run. It has no choice. Go back over everything.





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