no compression and will not start

I ORDERED IT FROM A YAMAHA WAREHOUSE DEALER WITH LOW PRICES. IT WAS AN ADD IN THE BACK OF MOTORCROSS ACTION. THE CASTING APPEARED UNDAMAGED AND SHINY NEW.

Originally posted by no thump:

A MOTOCROSS SHOP WITH 20 EXP THEY ADVERTISE CHARGED ME 65 BUCKS OR 1.5 HR'S TO INSTALL THE VALVES.

my problem turned out to be the 20 year veteran mechanic installed my intake valves incorrectly. the middle intake was on the outside while the outside was in the middle. so the middle intake never fully closed!! the mechanic was hickman racing or atomic 22!! 65 bucks to f--- my bike up!!

thanks,

Originally posted by no thump:

DETAILS: 99YZ 400 RACED LAST 2.5 YEARS.

DROPPED A VALVE, VALVE WENT INTO PISTON AND THEN INTO HEAD. SO I REBUILT THE MOTOR, NEW PISTON, HAD CYLNDER RESLEEVED. PURCHASED NEW HEAD AND NEW VALVES TO GO WITH THE HEAD. VALVES LIFTERS GO UP AND DOWN WITH THE CAMS, THEY APPEAR TO OPEN AND CLOSE. TIMING IS MATCHED UP WITH THE I ON THE CRANK AND EIEI ON THE CAMS JUST LIKE THE OLD MANUAL SAYS. PROBLEM: THIS DAM BIKE WILL NOT START, BACK FIRES OH ABOUT EVERY 10 KICKS. AND I DO NOT NEED THE DECOMPRESSION LEVER, MOTOR TURN OVER EASY. WHAT THE HELL IS WRONG? WHERE IS THE COMPRESSION?

PLEASE HELP!!

I don’t get it…

So the middle valve is a bit shorter, thus with the longer outside valve in its place it was hanging open…

But then the middle valve clearance would have been zero at TDC (Compression), how did this go unnoticed???

One more reason (I’m up to # 3,987) I do all my own work (whenever possible).

Anyway, thanks for the update, glad you are back in bidness.

Hick,

He says (up the thread a bit) that with the smallest shim available the valve was hanging open, but if he completely removed the shim that it measured in-spec and ran.

Thanks alot for the update. I must admit that I was not aware that the intake valves were not all identical. I just took a look at the fiche and see that two are alike and one is different. Apparently the center valve has a slightly shorter stem. I won't forget now. BY the way, did you find out what shim he had to use when he put the center valve in one of the outer positions? It must have been a very thick shim? He should have realized somehing was amiss when he had shim ranges that were WAY out there! When I checked my valves the first time, I had three 180's and two 178's.

Originally posted by sirthumpalot:

Hick,

He says (up the thread a bit) that with the smallest shim available the valve was hanging open, but if he completely removed the shim that it measured in-spec and ran.

Thanks, at least one of us is paying attention. I’m not in any way trying to flame no thump for not finding the problem, I only read his update and I guess I (incorrectly) assumed the mech. installed the cams and put the motor back together without noticing his own mistake.

I guess the mechanic just built the head, leaving it for no thump to figure out. It never occurred to me the middle valve would be shorter, but when you picture the concave combustion chamber it is easy to see why it must be.

no thump; yes the intakes are different in length. if you run a valve w/o a shim, i am pretty sure you can expect to break a valve cotter pin. even more scarier, if you mix the intake valves they will bend. these were some other problems i encountered.

my main proble is i'm a working professional with (3) young ones in day care!!!. (probably be able to start race team when little ones get out of daycare)

i may only get to take the bike to the track once or twice a month. i do not have the time to repair or money to pay 40 bucks an hour.

so i took my bike to a motocross shop that has a web page and 20 years of experience. (this is my first ever 4 stroke) i knew little!! wow, i got screwed!!

but, the good news is, i'm a 4 stroke expert with the tools know!!

i'm afraid i still have 1 small problem. or it could be a big problem. my bike is smoking out of the exhaust. i'm burning oil on a new top end. remember the clown (hickman racing, atomic 22) who almost f---ed up 700 bucks of new motor parts. he handled the work on my cylnder!!

i suspect my weisco rings are not off set or oil ring is some how screwed up.

but my bike will not start today. i suspect the plug is fouled i pray!!

wow, have i ever needed a new bike badly!! and the economy is sinking!!

i suspect this bike is forever cursed mechanically. i dread the thought of tearing this machine down again!!

thanks

so,

Originally posted by Hick:

Thanks, at least one of us is paying attention. I’m not in any way trying to flame no thump for not finding the problem, I only read his update and I guess I (incorrectly) assumed the mech. installed the cams and put the motor back together without noticing his own mistake.

I guess the mechanic just built the head, leaving it for no thump to figure out. It never occurred to me the middle valve would be shorter, but when you picture the concave combustion chamber it is easy to see why it must be.

I know that this isn't what you want to hear, but you will almost certainly save yourself much time and money if you go ahead and take it apart and check it out. If you've worked on a 2-stroke then you should be ok with a 4-stroke if you keep the manual handy and take your time. You may have to lock yourself in the garage for a couple of afternoons, but if you keep running it as is then there is no telling what may happen to the internals. Just my $.02, I wish you the best of luck.

i have runj into new problems or still have old problems. it will probably never end. my bike has decided not to run know at all. the problem is the cams become untimed while the bike is running. (they were set on tdc prior to running) i no longer have eiei and the i on the fly wheel. so i suspect my chain adjuster is shot (it does not stick, appears to be ok) my cam gears are worn are my chain is shot. has anyone had this problem?

Originally posted by sirthumpalot:

I know that this isn't what you want to hear, but you will almost certainly save yourself much time and money if you go ahead and take it apart and check it out. If you've worked on a 2-stroke then you should be ok with a 4-stroke if you keep the manual handy and take your time. You may have to lock yourself in the garage for a couple of afternoons, but if you keep running it as is then there is no telling what may happen to the internals. Just my $.02, I wish you the best of luck.

Yes, I've seen this a couple times. Only on bikes that the tensioner was installed without being retracted. This puts a huge amount of tension on the chain and stretches it. I had to replace the chain and 3 intake valves on a '99 400 due to this. You may be able to tell how stretched the chain is by how far the tensioner plunger has to extend to take up the slack in the chain.

------------------

MX Tuner

thanks, i will order a new chain and go from their. seems like i have too much slack.

QUOTE]Originally posted by MX Tuner:

Yes, I've seen this a couple times. Only on bikes that the tensioner was installed without being retracted. This puts a huge amount of tension on the chain and stretches it. I had to replace the chain and 3 intake valves on a '99 400 due to this. You may be able to tell how stretched the chain is by how far the tensioner plunger has to extend to take up the slack in the chain.

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