Valve adjstmnt.

I checked my valve lash this evening and found that one exhaust and two intake valves were slightly too tight. I have about 25 hours on the engine and was wondering what other 426 owners are finding when they check their valves? Also, while aligning the marks for TDC, it appears that the cams are slightly off since the punch marks on the sprockets don't quite line up flush with the edge of the head. Since the sprockets are pressed onto the camshafts, degreeing the cams is not a simple chore. I remember someone getting adapters from Falicon and wonder how that turned out.

I would guess I put about 50 on my 426 by the time they had tightened up. My exhaust valves went beyond spec first, I adjusted the intakes a bit later. Both sides had all valves out about the same amount (both exhaust valves were tight, all three intakes were also tight. It seems odd to me that you have one valve tightening appreciably more than the other. But I just used a plain old feeler gauge set so we’re not talking about a high level of precision.

I think Taffy was going to degree the cams on his WR but I don’t know how he plans on going about it.

I did not notice any misalignment of the punch marks relative to the TDC mark on the flywheel.

Boit- I noticed the TDC mark off just a bit on mine too, but in the manual it also says that it is on TDC when the cam lobes are facing directly away from each other, so that's how I did it. Also, you guys said that your valves were "tight" after use but wouldn't the clearance be more with wear or am I misunderstanding you? Mine were all right in the center of the tolerances but I used a feeler guage too, and I've only checked them the one time, after about 25 hours. The next check will probably be a winter project for me along with the other normal stuff...


Mike, typically as the engine gets some time on it, the valves will drive deeper into their seats, hence, causing the valve lash to get "tighter". Since you are checking the lash when the cams have reached the part of their cycles where they should NOT be putting any pressure on the tip of the valve stem, it's unlikely that there will be wear on that section of the cam lobe. Of course, it the owner lets his oil get dirty, or the cams don't get proper oiling, you can experience wear. If that happens, the wear will be greatest on the tips of the lobes that push down on the valves the hardest and on the valve stem tips, thereby giving a gap when measuring the lash. If that's happening, the engine performance should drop off gradually since the cams aren't opening the valves completely, and they may lack proper duration.I removed each bucket to make a record of what shim is on each valve. I have 3 valves that have #180 shims, and two that have #179's. Now, I find this rather odd since the manual states that shims are only available in increments of .05mm. I ran down to a local dealer who had none of the shims I need so I've ordered them from HSLM. FYI, if you haven't checked out HSLM, they have a microfiche for every part for the 426 setup on their website....very handy. Anyway, I decided to go ahead and reassemble everything to get practice at reinstalling the cams and getting the timing correct. It's no easy task getting the second cam installed under the chain. It really takes patience and a gentle touch. The manual says to drain the coolant and remove "the" radiator. I was able to do the job without doing that. I simply slid the compression release rod out just enough to remove the bucket. It's a little tricky getting it back in while getting the tension spring in the correct position but I did it without assistance. I'll ride the bike a little while waiting for the shims to arrive. I don't think the valves are tight enough to cause any damage as long as I don't run it really hard.

[This message has been edited by Boit (edited 10-10-2000).]

I checked mine after about 2 hours and found that all of the intakes were a bit tight but the exhausts O.K. Those with a little experience around four strokes (not me) claim that it's no big deal if the intakes are a bit tight, but it could be a problem if the exhausts are. Don't know why exactly - possibly because the exhaust valves run hotter and expand more, increasing the possibility of contact with the piston?

I'm a little bit "fumble fingered" when working with small parts (C-clip and locating pins) that could fly into unknown places, so I don't enjoy making this adjustment.

Just a note: the cam cap should easily "seat" into place with just the force of your fingers, or at most, lightly tapping it into place. If you have to torque the cam cap bolts to get the cap to seat, then the C-clip is not properly positioned. A mistake here could cost $$$$.

Plug all openings where a part could fall into and avoid all distractions. :)

[This message has been edited by holeshot (edited 10-10-2000).]

Originally posted by Boit:

[bI have 3 valves that have #180 shims, and two that have #179's. Now, I find this rather odd since the manual states that shims are only available in increments of .05mm.

[This message has been edited by Boit (edited 10-10-2000).][/b]

Mine also had odd sized shims from the factory. Someone in this forum pointed this out for those wanting to be right in the middle of spec. The idea was they could go swap their shims with a Yamaha mechanic, who presumably would have a collection of odd sizes after performing adjustments for his customers. This would be the only way (short of machining some shims) to get between a .05 mm increment.

In short, finding odd shim sizes on your bike is normal.

Mine had odd size shims also. When I went to the parts counter, they had a collection of odd size shims in a box under the counter, (taken from bikes they had serviced) so I selected from there.

I was also able to swap one shim for another (of those already installed on my bike).

[This message has been edited by holeshot (edited 10-10-2000).]

Thanks for the replies and input. It's been very helpful. I got my bike back together this evening after having it torn down to the frame for a good once-over and also to have the suspension done by MX-Tech. I was having a little problem with the exhaust popping syndrome when chopping the throttle so I removed the carb to check the jets and accelerator pump circuit. The pilot jet was partially clogged along with the accelerator pump circuit. The bottom of the float bowl was quite filthy with rather large particles of who-knows-what.I also installed a Factory R&D P38 accelerator pump bottom plate and went to a #160 main jet with the fuel screw at 1 3/4 turns out as a starting point. Then engine started on the third kick and I can tell already that it is much improved. After it was warmed up, I idled it down to just barely running and then rapped the throttle a few times to see if it would spit and stall. Not once did it stall or hesitate. Throttle response is very crisp. I can't wait to get out to the track to check out the suspension and if my carb tuning is going to pay off...hopefully, I can go Friday afternoon. HOT DOG!


just change one thing at a time, take it nice n'easy.

have a good ride


Taffy, yep, the good thing about aging is the accumulation of wisdom. I've learned the hard way to take things one at a time and be realistic about what to expect. BTW, I'm still waiting on the cylinder and head gaskets from HSML and will give you the thickness.

I reassembled everything very carefully and went riding last Friday expecting to need to do at least a little fiddling with the carb fuel screw. As it turned out, I didn't have to put a wrench or screwdriver anywhere on the bike. Apparently, evetything was spot on! It couldn't possibly carburate any better now. Gone completely is the exhaust popping on decel and not once did the engine, hesitate, hiccup, or stall. Throttle response is excellent.The MX-Tech suspension is fabulous and on top of all this, I had NO arm pump! Being sugar free apparently has cured this nagging problem for me. After riding, my sweetheart took me to dinner. This was the best day/evening I can remember in ages!

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