YZ timing mod gone wrong

[_Hitman47]

Hey again, I've been trying to make YZ timing mod to my wr426 and as you could find it out from my other thread, it started badly. When I opened the cover for the first time, I didn't look at my timing marks cuz I thought that setting them would not be a problem. So when I rotated my exhaust cam, intake cam also skipped and I had to match the timing from zero. Thats where the problems started. three dots on camshafts were not level when the piston was at tdc, they were either bit earlier before the tdc, or a bit more after it. So I selected closer one - the position bit before tdc, somewhere in the middle of ignition mark - was the correct one. I was WRONG!

I put the exhaust cam in place and rotated flywheel 2 times to ensure smooth operation. it rotated freely so I assembled motor. When I fired it up, I heard terrible clanking sound from motor. I immediately shut it down and tore down the bike again. I was crazy abut it. I thought that I didn't tourqued down the camshaft enough and increased valve lash caused that noise. I retried it I think about 10 times, now without firing up the bike, just kicking it through - the clanking sound was there no mater what i did. After full day spent on this, I was going to give up but then I decided to turn the intake camshaft one tooth backward an viola - the clanking dissappeared, seems like intake valves and piston were having some good time together ?? hopefully contact was tiny cuz I was able to rotate crank almost freely, and the bike still hold the compression as it did before, I can stand on my kickstand for about a minute.

I then turned the exhaust cam one tooth back leaving 12 tooth between top punch marks - YZ timing. The bike got difficult to start and it wount idle down low, It would backfire into intake as rpm-s dropped and die. So I returned old exhaust timing and everything returned to normal operation. seems like already shifted cam timing + 1 tooth more was way too advanced valve timing.

Here goes my question wr gurus : what can be wrong with my motor? I don't think that cam chain has stretched by so much(about2/3 size of a link), is there any other thing that could go wrong with bike? like cam chain guide or I dont know anything else? Or if anybody insists that its' cam chain stretch fault, can you provide some info on how much motor hours does the cam chain stretch etc? sorry for my english im not native speaker?

[_Hitman47]

Anyone here? will post some pictures of my cam timing this weekend.

[simon@vic]

i would start off by buying a 2003 yz450 exhaust cam and a new 426 cam chain. set your stock 426 intake cam where the manual says to put it (make sure your at TDC). then install the 2003 yz ex cam in its normal orientation (using its dot).

2003 and newer ex cams have auto decompression for starting. well worth the $175-$200

[_Hitman47]

Well actually cam isn't a problem in this case, the main problem is cam chain I think, just wanted someone with experience of dealing with worn chain to confirm it. And even if I went buying any cam out there, it would be a hotcam, they're sold for 130$ and come with auto decompression too - quite a good deal I think.

p.s. photos coming tomorrow.

[2in2out]

Jetting. I did the same with my 426, and it would not start. I went through everything, but what I found was I needed to adjust my PJ and MJ, and needle position.

If I remember correctly I had to go up two sizes on my PJ, one size on my MJ, and drop the clip on the needle.

I know it sounds weird, but I was running on the verge of lean before the cam mod, and way lean after. After I rejetted, the bike ran like a raped ape.

[_Hitman47]

Nope it wasn't jetting, I unscrewed my fuel screw to about 4 turns out then the bike started to sputter of running too rich, so the jetting was not the reason. I took some photos of my timing on mates camera, will post them as soon as I get them.

Actually I got a bit confused, if the cam chain was stretched then intake cam would be rotated even more to the back side of the bike because of stretched 13 links between the cams but it wasn't, it was even bit advanced then exhaust cam.

[_Hitman47]

so here is the pic:

if u cant see the pic, here is the bigger version: http://s1134.photobucket.com/albums/m620/_Hitman47/wr426/?action=view&current=SL371379.jpg

crankshaft is at TDC. you can see that the cams are rotated to the right side, punch marks are not aligning. First I thought that the timing was incorrect and rotated both cams 1 tooth ccw, but then intakes started to cllide with piston ?

I almost convinced myself these days that my cam chain is stretched but look at intake cam, if the the cam chain is stretched so much that it gave such a huge offset at the exhaust cam, intake cam must be retarded even more. In the picture it's like it's rotated to the right side i.e. more advanced then exhaust cam

I'm really really confused and in need of a good advice. hellp me please.

[miweber929]

For whatever reason, can you be 90 degrees off? Otherwise all that slop looks to me like it would line up if you get them all in correct. Do you have them swapped? Don't know if it's possible or not.... X

[_Hitman47]

90 degrees off on cams? man you must be kidding. it would be a stroke off on a four stroke, spark firing right thru open exhaust valve ? look at the punch marks, all three of them can be seen on both camshafts. and swapped what? 3 lobe intake and 2 lobe exhaust? ?

any other opinions?

[SXP]

Post a pics of your cam lobes from the other side with the engine at compression TDC. That should help us get a better picture of what's going on. They should look like this if you have everything set correctly:

[_Hitman47]

Ok, here we go:

bigger version: http://s1134.photobucket.com/albums/m620/_Hitman47/wr426/?action=view&current=SL371380.jpg

the cams are retarded a bit as you can see, the same situation that's seen from front.

[miweber929]

90 degrees off on cams? man you must be kidding. it would be a stroke off on a four stroke, spark firing right thru open exhaust valve ? look at the punch marks, all three of them can be seen on both camshafts. and swapped what? 3 lobe intake and 2 lobe exhaust? ?

any other opinions?

Sorry, early in the AM. Meant 180 on one from another. Forgot about the whole 5 valve thing, used to working on 4 so it does become "possible" at the point.

I'd be 100% sure you are timing from the t mark and not the f mark, put the cams correct and lay the chain on from there. Or instead of ****in' around, replace the cam chain and be sure.

[_Hitman47]

Sorry, early in the AM. Meant 180 on one from another. Forgot about the whole 5 valve thing, used to working on 4 so it does become "possible" at the point.

I'd be 100% sure you are timing from the t mark and not the f mark, put the cams correct and lay the chain on from there. Or instead of ****in' around, replace the cam chain and be sure.

Yammies have H mark and I mark, and I'm timing from I-mark, the tdc one. as for putting cams correctly, as I mentioned in my earlier posts, they don't align in either case, they're about 2/3 tooth retarded as in the pics, or 1/3 tooth advanced and intakes hit my piston at the start of intake stroke.

I would order the chain immediately knowing that changing it would help but I'm not sure. Read my previous posts, I've explained my position quite clear I think. Thanks anyway for wanting to help me though ?

EDIT:

just found this thread: https://www.thumpertalk.com/forum/archive/index.php/t-394574.html

I have not seen a post related to high hour engines and cam chain stretch before so I thought I would post my experience. I have an '05 with lots of hours on it. The intake valve clearance went to zero so I had them replaced. No complaints. Like I said, lots of hours.

When I reinstalled the head and timed the cam the marks would not line up perfectly. The line on the cam sprocket was either slightly below the arrow or almost a full tooth above the arrow. I aligned it with the one that was closer, the one that was slightly below. The bike ran fine, just not as good as before the valve replacement. It was a bit sluggish on the low-end and built revs slowly. It also sounded a bit different. I had friends ride the bike to make sure I wasn't crazy and they agreed that something was a bit off.

I checked and rechecked the valve clearance and timing, replaced the silencer packing (because it sounded different) and checked for any exhaust leaks, and changed the spark plug. None of this made any difference to the diminished performance.

It turns out that the cam chain had stretched enough so that the timing marks no longer work for setting the proper timing. The line on the sprocket needs to be almost one tooth above the arrow on the head for everything to be timed properly. Once that change was made the bike ran as strong as before the valve replacement.

So I guess I just wanted to warn anyone with a high hour engine not to trust the alignment marks. I'd make sure to check the alignment before tearing it down and putting it back to that alignment after a valve replacement. The cam chain can stretch that much.

It think it says it all. ordering cam chain right away ?

Edited November 9, 2010 by _Hitman47

[rowellcory]

i thought it was your intake cam you move one tooth for yz timing i could be wrong its been awhile

[rowellcory]

putt yor timing mark on the fly wheel to tdc and forget those dots and place your lobes in there right postion intake just closing and exsaust ready to open and she will purrrrrr......or buy a new chain

[rowellcory]

sorry i did not understand the problem your saying it runs perfect in this position if it does than your chain must be stretchd

[MANIAC998]

This is from 2010!

Maniac

[DrFeelGood]

He's padding his post count. ?