Never again!

justin_yz426 · Jul 29, 2004

I will never buy another Yamaha again. This is the second time the motor exploded. This time right after only 20 gallons of race gas through the motor. Since the last explosin. Now I need a new valve and all the stuff to go with it. New piston, cylinder and possiably head.

husabutt · Jul 29, 2004

Justin:

Sorry to hear about your YZ. All four stroke high performance bikes seem to be somewhat high maintenance. I wouldn't necessarily condemn Yamaha especially since my wife just got a yfz quad but as its been said before there has never been a better time to buy a new Berg (especially with the BMG discount if that is still going on).

justin_yz426 · Jul 29, 2004

The way I took care of this bike. It should not have a single problem! I'm so pissed right now. I'm not going to be able to fix it for a while.

wildbill · Jul 29, 2004

Sorry about your YZ.When ever you are ready try to find out the cause.I went through something similar a while back.I heard so much gloom and doom until I was about to take my bike to the landfill.Take a break and don`t dwell on it for a while then make up your mind on what to d

ne thing I can tell you is if it wasn`t for the people on this site I would not be ridding today.Take care.

justin_yz426 · Jul 29, 2004

Yeah the people here are awesome! I dont have a Husaberg. But everyone still is nice and welcomes me and is friendly. Thats rare now a days.

BundyBear · Jul 30, 2004

Junkies & pushers are usually friendy when a potential addict walks willingly into the den!

PowerFiend · Jul 30, 2004

What year YZ? If it is a 2000 model this is a common problem with the two piece valves they had that year. Your best solution would probably be to get some KibbleWhite valves for it.

For all the YZ and WR 4XX's their is a potential for the piston pin to seize and or for 3rd-5th to take a crap(rounded gear dogs). The fixes seem to be to get a Falicon rod with better small end bushing, and to swap some shims around in the tranny so that the dogs more fully engage.

The 450 exhaust cam or the Hot Cams with auto-decompression is also very worthwhile and something I personally recommend.

...the above two issues is the main reason that I bought the Berg for Motard racing. The above issues happen sooner when you throw asphalt at the Yamaha's. :wink: So I plan to keep mine mostly on the dirt(Its plated).

justin_yz426 · Jul 30, 2004

Yeah I know about the valves. That was the first explosion. I replaced them with one piece valves. Now I have the piston sounds like it's slapping/rattleing in the cylinder. Maybe this is the wristpin problem. Also when it failed my decompression lever stopped working like the valve dissapered. But i'm not going to tear it down for awhile.

Holeshot550 · Jul 31, 2004

justin_yz426 said:
I will never buy another Yamaha again. This is the second time the motor exploded. This time right after only 20 gallons of race gas through the motor. Since the last explosin. Now I need a new valve and all the stuff to go with it. New piston, cylinder and possiably head.

Race gas? I think thats your problem. Don't use it in your husa either.
grtz Sieb

justin_yz426 · Jul 31, 2004

Well it reqired it. I was running 13.5.1 compression. The berg will just be slightly moded. Like a full exhaust and airfilter. Other then that she will be my go and play bike.

Taffy · Jul 31, 2004

at best mix it 50/50% and next time ask the experts first. newtons third law; for every action there will be an equal and opposite reaction. converted to bikes that means change one thing and if you don't understand everything about what you did you will get a reaction that you don't control.

Taffy

husabutt · Jul 31, 2004

Holeshot550 said:
justin_yz426 said:

I will never buy another Yamaha again. This is the second time the motor exploded. This time right after only 20 gallons of race gas through the motor. Since the last explosin. Now I need a new valve and all the stuff to go with it. New piston, cylinder and possiably head.

Click to expand...

Race gas? I think thats your problem. Don't use it in your husa either.
grtz Sieb

Why would racing fuel cause the engine any harm? It seems to me that the worst case scenario would be too much octane causing too slow of a burn and therefore only reducing horsepower. Justin said he was running 13.5 to 1 compression which would require race fuel. Would it not? I seriously doubt his bike would not have detonation or preignition with pump fuel. Now if he was running Av gas this may be a different story but I still don't see how it could seriously damage the engine.

Taffy · Aug 1, 2004

the first thing you ought to be saying is "ok lads, what is it about race gas/avgas that i don't know?" and not say just like 'YZ' did that "i know, i'll shove race gas in, i know what will happen!'.

that isn't the attitude at all and it's why people write books and make a living out of tuning.

i used to read up on this stuff years ago but i'm rusty now but i think it goes along these lines;

it runs cooler which may not help the metallurgical properties of the valves

the flame is retarded by the fuel; slowed down which may cause an inbalance in the pressure on the top of the piston

the plug won't like it and may be throwing out the wrong kind of spark

it will have the wrong plug heatrange in. these two cause the biggest troubles

you need a quality plug of the correct heat range

a delayed flame will burn all over the bore walls with the piston halfway down the bore as well as all around the exhaust valve. now the temperature of the flame is around 400 degrees as i recall but if the flame is doing a 360 around the exhaust valve, and it's running lean; the temperature will reach 1300 degrees around the exhaust valve.

you can get 13.5 to 1 compression by simply closing up the squish to the correct gap of 1mm or .040" in old money. this way you have a flat piston that takes the pressure down the middle instead of the pressure sliding off a 'crown' - bit like one of tyson's punches! you know-missing!

then you've got the fact that ever since i've been a member here nobody has taken a blind bit of notice when i say to them that to get a correct plug colour you have to SPLIT THE PIPE AND LOOK DOWN THE MIDDLE!

then, if you don't have a proper squish you get pressure down the bore sides which pushes the rings off the bore wall and makes the piston float.

if the piston floats-it slaps! if it slaps the gudgeon pin may take too much pressure. don't forget that yamaha have a history of making the "wrist pin" (USA) too small. i had two SR500's in the seventies and the first WR400's from '98 had them ALL fail!

i haven't even mentioned the jetting yet!

i haven't even mentioned the ignition advance curve yet!

so lads, any more questions?

Taffy

husabutt · Aug 4, 2004

Taffy said:
the first thing you ought to be saying is "ok lads, what is it about race gas/avgas that i don't know?" and not say just like 'YZ' did that "i know, i'll shove race gas in, i know what will happen!'.

that isn't the attitude at all and it's why people write books and make a living out of tuning.

i used to read up on this stuff years ago but i'm rusty now but i think it goes along these lines;

it runs cooler which may not help the metallurgical properties of the valves

the flame is retarded by the fuel; slowed down which may cause an inbalance in the pressure on the top of the piston

the plug won't like it and may be throwing out the wrong kind of spark

it will have the wrong plug heatrange in. these two cause the biggest troubles

you need a quality plug of the correct heat range

a delayed flame will burn all over the bore walls with the piston halfway down the bore as well as all around the exhaust valve. now the temperature of the flame is around 400 degrees as i recall but if the flame is doing a 360 around the exhaust valve, and it's running lean; the temperature will reach 1300 degrees around the exhaust valve.

you can get 13.5 to 1 compression by simply closing up the squish to the correct gap of 1mm or .040" in old money. this way you have a flat piston that takes the pressure down the middle instead of the pressure sliding off a 'crown' - bit like one of tyson's punches! you know-missing!

then you've got the fact that ever since i've been a member here nobody has taken a blind bit of notice when i say to them that to get a correct plug colour you have to SPLIT THE PIPE AND LOOK DOWN THE MIDDLE!

then, if you don't have a proper squish you get pressure down the bore sides which pushes the rings off the bore wall and makes the piston float.

if the piston floats-it slaps! if it slaps the gudgeon pin may take too much pressure. don't forget that yamaha have a history of making the "wrist pin" (USA) too small. i had two SR500's in the seventies and the first WR400's from '98 had them ALL fail!

i haven't even mentioned the jetting yet!

i haven't even mentioned the ignition advance curve yet!

so lads, any more questions?

Taffy

Well..............Ummmmm..........................No that just about covers it.
Thanks

justin_yz426 · Aug 4, 2004

I was told to run race gas. The guy who tuned my bike also builds the USA dirttracks bikes for a couple guys. Now that I think about it. I have run regular pump gas and it dose not like it. It pop's and backfires.

Wait I just thought of something!!!!! :!: :!:

When it blew up the first time. The intake valve broke off (two piece valves). Anyway the motor turned over approx. 800-2000 times. With the head of the valve in the combustin chamber. It punched a hole through the piston and destroyed the head. I think that would put an incredible amount of stress on the wrist pin. Correct me if i'm wrong. Now when I rebuilt the motor and added these upgrades I left the wristpin, complete crankshaft, all bearings, and connecting rod alone. So all that stress from the valve probably cause a weak part and one of those to fail. Yeah it lasted for a bit and it is now starting to show.

I cant belive I did not think to check/replace these components. I feel so f^^king stupid! I'm going to go and pound my head against the wall.

iceman · Aug 5, 2004

I'm going to go and pound my head against the wall.

Do it man!
It feels soo good when you stop!
Cheers Ice.

Never again!

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