02 WR426 Valves out of spec?
Posted September 26, 2005 - 10:25 AM
A couple of rides ago i noticed my engine seemed to be more noisy (if that's possible) when it had warmed up and if i held it on about 1/2 throttle it became very "tappy/rattly" like a noisy tappet sort of sound? so i thought it was about time the valve clearance was checked. Also, i don't know if it's my being used to the bike, power-wise, acceleration etc? but it somehow doesn't feel like it has the grunt that it did when i first got it? let me explain and hopefully make this a bit clearer? I bought the bike 2nd hand in March 05 and though i didn't know anything about these bikes, it has been a learning curve all the way with regards to frequent oil changes, air filter maintainence and necessary routine checks etc etc. Also the manuals that i received with the bike have been a godsend for advice and procedures and i would certainly have been lost without them. Through my constant reading i have become very familiar with the important practices regarding basic maintainence and have found them to be an invaluable source of info and knowledge gathering for newbies like me. I am not inexperienced around the garage having built several car engines in the past and not afraid of tackling the fiddly stuff like rebuilds etc, but when it comes to these yamaha engines, well, that's where it's become confusing? The point i am trying to get at is, having checked the valve clearances and found them to be out of spec, why would it seem like it is down on power and noisier when the valves are infact tighter than the specs given, when surely loose valves would be the reason for the drop in performance and increase in noise, not the other way round? I am confused, for common sense would state that a valve that was being lifted fractionally higher because of less clearance between cam lobe/valve rocker than std would perhaps give better flow as it would be open slightly more. Am i wrong in thinking this? I am aware that they need to be re-shimmed anyway as they can indeed cause severe damage to the head by being too tight, but thought i'd try to clarify why it seems to have lost power?
Also, why would it be noisier and indicate that there was too much clearance the way slack tappets would on a car engine? This has completely stumped me? When i removed the cam cover and got my feeler gauges out i was ready to slip a feeler the size of a spark plug in there, but to my dismay, i struggled to slip an 0.10 in almost all of them! All 3 of the inlet valves are below 0.10 clearance and both exhausts are 0.15, very tight i know and obviously my valves have stretched and i need to strip the cams out to determine the shim sizes already in to work out suitable sized replacements.
Can someone clarify as to why it would appear to have dropped power and the increase in the rattling noise? Another thing i've noticed was the alignment marks on the cams don't line up with each other on opposite sides of the head, so i was perhaps wondering if it has had the YZF timing mod done, the inlet cam is perhaps one tooth advanced over the exhaust cam? By this i mean, instead of the marks being at 9 oclock and 3 oclock, the inlet is nearer 2 oclock?
I suppose this is the problem with buying a bike that has had 2 or 3 owners prior to me and i don't know what has been modded and what hasn't?
I hope i have explained my predicament clearly and was hoping that some of you experts could advise me on this matter, as i have fallen in love with this bike and although the weather has started to turn and the bike is due for some long months in the garage over the winter months i am going to miss riding it. It gives me a huge grin on my face when i see pedestrians turn around when they hear this thunderous roar coming towards them. I have converted her into a supermoto and have done approx 2,000 miles since march and according to the last owner who said it'd done that aswell, do you think it's time for a major engine overhaul/rebore or just do the valves? I'd like to put a hotcam in too as the big letdown on these bikes is the starting procedure, i'm on it everyday but still struggle to find TDC
then again, i don't know if it's worth spending a lot of money on a rebuild when i'd really like to upgrade to a 03/04 because of the elecky start.
Thanks for any advice guys and hope you can understand my waffling?
Posted September 26, 2005 - 05:40 PM
Posted September 27, 2005 - 03:50 AM
Now, as for "what's it like with the road wheels on?" i gotta say, it's bags of fun. I used to race MX bikes some years ago and loved the sport but sadly my fitness waned and couldn't compete anymore (bloody kids eh! they have stamina a plenty!) but after witnessing Supermoto events, i thought it would be a good idea to try build one myself for the road so that i could have the best of both worlds with what is considered as an off-road bike but fitted with wheels/tyres/gearing/suspension suitable for road use but have the riding style of attack/feel as if i were on a track. I have to say, that it is nothing but fun,fun,fun! It's great to gas it on every corner or when leaving a roundabout and have the front wheel come up under heavy acceleration, the fun element is unbeatable and it handles like it were a lightweight 125cc, very flickable and very well balanced. The downside to having so much fun though is the pain endured in my backside, these seats aren't the most comfortable in the world, after about an hours ride i gotta get off and get some blood flowing again through my rear, adds meaning to the words... Numb Bum but that is a small price to pay for having such fun. Road bikers are always giving me the nod of appreciation when they see the flexibility of these when on the road, i know they'd love a go too..
trails are good fun too, so it's just a matter of throwing your enduro rims back on and and resetting your gearing and your good to go in the dirt too, as i say, best of both worlds, but a helluva lot of fun on the roads, especially with these Maxxis Supermoto tyres on, they stick like sh#t to a blanket!!!!
Posted Today, 02:32 PM
Your valves don't tighten because they stretch. They don't stretch. They tighten because wear occurs at the valve face and on the valve seat, which lets the valve move up into the head farther. That's one thing.
As to the exhaust cam, there are two possibilities, three, actually.
- If it is not an auto decompression camshaft, the previous owner may have retimed the exhaust cam to achieve YZ cam timing: http://motoman393.th...ech/yztime.html
- If it IS an auto decompression cam, the PO may, as already suggested, have installed a YZ450 cam in the engine to acquire the auto decomp feature: http://www.thumperta...#entry2979654 http://www.thumperta...53#entry4458141
In both cases, the intake cam is timed according to the crank and intake cam marks, and the exhaust is timed so that it appears one tooth advanced. See the links. The third possibility is that he simply timed it wrong.
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