bike won't start

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#1
Hey guys,

I've got a friend with a 2000 YZ426. He just had the engine (bottom end and top) rebuilt. Today is his first attempt at getting it started and we can't get anything to happen. He says it doesn't feel like it has much compression (may take a little run in time for the rings to seat, right?), we've checked to ensure we're getting spark (we are), now he's going to pull the plug again and dump a tablespoon of fuel down the plug hole to ensure it's getting fuel. We've tried bumpstarting it (and kicked it several times, but not getting much of a response......an occasional backfire). What are we missing? It doesn't have the automatic decompression, but he's able to kick it over without pulling the decompression lever. Any and all ideas welcome!
 

nikki

Moto Junkie
Joined
Apr 21, 2000
Messages
5,802
Likes
1
#2
Check the valve clearances to see if they are in spec.


When we put rings in my 250F, we put it back together and I could push the kickstarter over with my finger. Why.... because an exhaust valve shim wasn't sitting in the groove and it had been lodged making the valve cap sit much higher, therefore the exhaust valve was always open.

May not be your problem but it took us about 4 times of pulling everything apart and putting it back together before we figured it out.

Also make sure that the cams and cam chain are all lined up as it shows in the manual.
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#3
Thanks Nikki, we'll definitely check that, once we weed out a couple of other things real quick.

He pulled the plug and there is definitely fuel in the cylinder, he said almost enough to probably flood the engine...and the plug was wet.

He says it feels like the decompression is stuck open so we're going to research that real quick...we may have to pull the head anyway, then we'll check those valves.

Anyone else have a problem similar to this on their thumper but come up with a different problem?

Thanks!
 

nikki

Moto Junkie
Joined
Apr 21, 2000
Messages
5,802
Likes
1
#4
I'm guessing your friend had someone else do the work so I'm not sure how familiar he is with valve clearances and stuff... so here's a quick "how to" if it's the same problem that I had:

Check valve clearances:

Remove seat/tank/shrouds, spark plug cap, 2 bolts in valve cover, and valve cover. With piston at TDC (use TDC window/nut behind two caps on the case shifter side - its in the manual), measure valve cap to valve puller clearance on the 5 valves with a feeler guage (get an any auto parts store for a few $). The "in spec" clearances for exhaust and intake valves are different and listed in the manual. If he doesn't have a feeler guage and it is a shim out of the groove, push around the kickstarter to where the valve caps are flush and you'll see (or feel with your finger) one sitting higher than the others.

If there is one that looks/measures higher then.... to put the shim back in the groove:

With piston at TDC, use a paint marker or white out or something to mark where the cam chain lines up with the cam sprockets. Remove cam holders (a bunch of 8mm bolts - beware of the C-clip spacer don't drop it), and loosen cam chain tension through tensioner (need small screw driver), tie a wire or something around the cam chain so you don't drop it in the case, then remove cams. Use a magnet to lift the valve cap covers up and hope to find a shim not sitting in the groove. Put it in it's groove, put the cap back on, put the cams back in, line the chain back up, put the cam holders on, tighten the cam chain, put the valve cover back on and you're good to go.
 

holeshot

Crazy Russian
Joined
Jan 25, 2000
Messages
1,823
Likes
0
#5
The '00 426 (manual decompression) should be nearly impossible to kick through without the decompression lever pulled. Standing with all my weight on the kickstarter and handlebars, it took about 15 seconds to drop through the stroke (this was my el-cheapo compression test).

Check to see if decompression lever is adjusted right and that it's not being held open by a poorly routed cable.

(Ooop, the last three replies were posted at neary the same time).
 
Last edited:
Joined
Oct 30, 2003
Messages
55
Likes
0
#6
If you can kickstart a 426 without the decompression, you have a problem. Where is the decomp. handle? Is the actuator opened? That would do what you described.
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#7
Ok, the exhaust caps look to be aligned (one not portruding any more than the other).

The decompression lever cable is loosened as much as it will go, but still may be a little tight. We removed the cable completely from the lever and it still has no compression.

The manual doesn't explain at all how the decompression should be "plugged" into the engine, basically it just shows that you push it into the head without any rhyme or reason, and that's what we have done.

I'll go back outside and take a better look.
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#8
WHile I was in here typing, he removed the cams and then one of the exhaust valve caps and shims. He then put the shim and cap back in. When I went back out, I noticed one cap was a 1/16" or so higher than the other (wouldn't have noticed it with the cam in). Sure enough when he put the shim back in, it didn't sit flush (canted at a slight angle), not allowing the cap to sit low enough. We don't know if it was this way before or not though.

The manual only shows how to measure cam to cap gap using plastigauge, can you use a feeler in the same manner? Also, is there any "special" way we should be plugging that decompression deal back into the head? It appears to us that it doesn't really matter. But, it's kinda fishy having zero slack in the cable (especially for a 4 year old bike).
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#9
OK, it's not the decompresssion lever/system. There's enough play to prevent it from pressing on the exhaust valve cap. It seems the ONLY places we could be losing this compression is: 1. exhaust valves (it's not the cams pressing on the caps...so maybe the valves themselves aren't seating properly?) 2. Rings....it's got new rings though and he installed them correctly (so this shouldn't be the problem) 3. decompression system (we've just ruled this out) 4. leaky gasket (but can't check this until we get the bike started. So, I guess the only thinig stated above is the valve itself not seating properly in the head. Correct?
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#10
Well, we've pulled the head completely off. The valves are seating properly and the rings (new) were aligned correctly (or not aligned which is the way they should be).

He just noticed that two of the three intake valves have been switched (the middle valve with an outside valve). Looks like the dealer may have screwed up. We are on our way up there right now. Will let you know if this may be the problem.
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#11
That was the problem. Seems the intake valve in the center is longer than the two outer valves. The mechanic at the dealer switched the middle valve with an outside valve. With the head off, the valves would seat properly, but once the cams were installed onto the head, there was constant pressure on the outer intake valve (the one that should have been in the center) causing it to remain open ALL the time (hence no compression....it was leaking out through the carb). We quickly ran it back to the shop (we don't have the tool necessary to remove the valves) had the guy switch them (30 minutes) put the engine back together and it started 3rd kick.

Nikki thanks for the original tips. The mechanic at the dealer and another friend also told us to check those shims for the same reason (my buddy even put the caps back on once with a shim crooked...so it's easy to do).

As far as the other recommendations with the decompression system...they were right on.....we knew we had a compression leak somewhere and ruled that out pretty quickly, but it got us to thinking about what else could be leaking the pressure.....we just so happened to notice that two of the intake valves had two small dots on each of them and one intake valve only had one. We celebrated with cold brews once we realized the mistake!
 

jboomer

Subscriber
Joined
Jan 5, 2002
Messages
1,420
Likes
0
#12
Well, we took our bikes out to the track today, so he could break in his new engine. He had a couple small little things he had to correct (an oil line seal had gone bad and he failed to put a washer on the oil drain bolt--both things we fixed right then) but all in all, everything went good, until about 6 laps into his ride. He came around a corner then suddenly the bike started "squealing" like a scalded pig. He hit the kill button as quick as possible and a couple of us went over to see what had happened. We weren't able to turn the engine over at all....so we rolled it back to the truck. When he got home he removed the clutch side cover because he thought it may just be the kickstart gear installed wrong (wouldn't be the first thing the mechanic screwed up). Well, turns out, the gear that mounts to the clutch cover had come out of its little notches, the circlip that holds the gear to the small shaft it mounts to came loose and proceeded (along with the shaft) to run itself through the engine. Now, all he can find is the gear, everything else came out of the oil drain in small pieces. Probably completely toasted the engine. He never removed the clutch cover when he took the cases in to have the original bottom end changed, so it was definitely the mechanic that did it wrong. He's pretty busted up about it, unfortunately the mechanic won't be at work tomorrow or Monday. Figures. It took the mechanic 8 weeks to split the cases and replace the gears (my buddy had already ordered all the parts and were able to take them in with the engine--fortunately he was only charged for 3 hours of labor), it'll probably be spring before he gets the bike out of the shop this time. We think the mechanic should be liable for the damages since it was his bad workmanship that caused this problem, we'll see if he'll take responsibility for it or not.