So I've got a problem here and from the research I've done so far I'm trying to determine what would cause this issue and what's the best course of action now. I'll try to keep it short, but I tend to over explain everything to make sure I'm not missing anything.
Anyway, I've got an 01 yz426 that I've had for 5 years or so now that I've pretty much gone top to bottom repairing/replacing things myself over the years while only putting 60 hours on it (mostly all trail riding). I did the 03 auto-decomp cam right when I first got the bike and shimmed the exhaust valves accordingly. Checked the intakes at the time and they were still in spec so I just left them alone. Anyway recently it was having issues idling after it would get hot so I started with rebuilding the carb and new plug. Everything ran awesome and I went riding for a few hours and the problem seemed to go away.
Fast forward to last Friday. Pull bike out to go camping, check everything over, fire her up as I usually do for peace of mind before I take off and shut her off like normal. Now here comes the interesting part, it ran absolutely fine and I shut it off myself with the kill switch. Drive several hours and go to fire it up after setting up camp and it would kick to a certain point and then stop. I immediately assumed the worst and tried turning it over with a socket as to not mess anything up any further and I could only get one revolution back and forth before it would stop and sound like the piston is hitting the valves. OK, &%$#@!?! Load everything back up and try to have a good time knowing what's in store when I get home.
Came back, did some homework on what I've got to look forward to, and start to tear it open. First thing I noticed was the timing was off causing the intake valves to stay open when around the TDC vicinity. Ok, so I assume somehow the timing chain skipped and bent valves. Check the valve clearances though and the exhaust side is still where I set it 5 years ago, but the intake side was super tight on the right 2 valves (clutch side).
E .25mm .25mm
I .12mm .05mm .08mm
Before I measured the clearances though I ended up taking the cams out to verify the motor would turn over more then once (which it did). First thing I partially noticed was the intake cam stayed in the cap when I took it out (not really thinking anything of it at the time), the bolts were on much tighter then the exhaust bolts I properly torqued years ago, and immediately noticed the right 2 cam journals were wallowed down a bit (doesn't look like the buckets will come out without some work). Go to put them back in to measure clearances and notice the exhaust cam spins easily while the intake cam won't turn without using something to turn it back and forth. Take it back off again and that's when I fully noticed the cam cap is warped causing the cam to get jammed in it. Obviously someone did this before I owned the bike and torqued them down way too much.
So how the heck did my bike go from running and idling fine to this after just shutting it off? I understand the over torqued cam cap and low valve clearance being a factor. I can also understand if this happened WOT on the trail, or hell even it if was running at all. What I can't figure out is how after shutting my bike off this one time my cam seizes while it's not running while also simultaneously my timing chain being loose enough that it would be able to skip when trying to kick it over? Or is that just what I've been dealt this time around and should be happy I got 60 hours out of it with over torqued bolts, rebuild it, and move on?
If that's the case I've done plenty of reading recommending Engine Dynamics in Petaluma, but what should I expect to spend for them to fix it? I would assume that depends on how bad the damage is and whether the cam cap is usable as well as the cam itself. And what else should I look at in terms of inspection and/or replacement other then the timing chain/tensioner/guides and the obvious gaskets? Going to pull the head off today to verify 100% there is no damage to the valves. Thanks in advance for any help and I'll try to post of some pictures later today.
Edited by ladmozx, February 24, 2015 - 08:19 AM.