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First like to start off saying what a truly great forum you guys have here! I was buying a parts bike from a police officer on craigs list and he recommended this forum to me.

I bought a 01 yz 134cc from a kid in town, seemed to run good until I got it home and found that there was no air filter or basket and the head gasket inner oring was blown. Long story short I ended up doing a complete tear down and restore including powder coated frame, full set of work guards, plastics, graphics, all the Bearings were shot, I did a hundred dollars worth of head work from the detonation pitting that occurred? and a 20 dollar hone on the nikasiled cylinder. new piston/rings.

Im at the point where Im assembling the top end and got a measurement of .25 for the squish band. Im assuming this is good? side note, not sure what type of spark plug to install that would have the correct reach now. So im using a click type torque wrench, bought from harbor frieght, set to 22 lbs. to tighten the base nuts, and snapped the stud bolt clean off before I heard the darn thing click (idicates torque reached), 6 bucks per stud bolt + $19 shipping. Id like to ask any one has any bad experiences with these harbor freight torque wrenches and how important it is to set the correct torque on the base nuts..

Heres some pics I took of the cylinder piston and head just for fun. Any helpful tips would be great!

img3430ax.jpg

The piston was definitely contacting the head.

img3452x.jpg

The top of the piston is warped, concaved in the center. from over heating?

img3777g.jpg

would any one like to see how the head turned out?

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.25 is dangerously small, .45 is usually the smallest you should go for squish. Honestly just by looking at those pics it instantly looks like the squish was so low that it was stamping the piston, as the picture shows.

That piston is in TERRIBLE shape too, look at all the scoring on the side. Someone didn't know what they were doing, that's for sure.

Looks like buddy shaved the head to make his compression ratio higher, or something, point being it looks like he just eyeballed it :thumbsup:

How is the cylinder, is it true on both ends, or warped as well? How do the ports look?

The cylinder is the most expensive part, so if it's ok then you saved yourself some money. If it is not I would recommend getting it bored out again for a 144 kit or something.

If you find a good condition stock cylinder then you can go back to stock.

Either way you're looking at a new head and a new piston for sure judging by the photo's.

It probably was once a nice bike but looks like someone in-experienced starting doing their own mods and ruined it.

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If your going to use a torque wrench buy a small inch pound one, don't trust those big 1/2" drive foot lb ones. squish should be `.040" or 1mm.

the 134 kit may have used a piston with taller or domed crown, and the head didn't get reworked??? or someone shaved it? or the rod bearing(s) had play in it???

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+1 I 100% agree... that piston and head looks terrible. Someone had no clue what they were doing! .25 is extremely low! Looks like they put a few hours on that piston with it hitting the head. Might not be a bad idea to measure the rod, I had a buddy have the same thing happen and it was because he had the wrong rod in his crank causing the piston to hit the head. Although your problem is likely from the squish.

I got my torque wrench from harbor frieght and have had no issues with it. Although I dont typically use it to tighten the base nuts, I just hand tighten them in a criss cross/ star pattern then give them about a 1/8th turn with a cheater bar... I only use the torque wrench for the head nuts.

Id like to see what the head looks like now though!

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Thank you, talk about quick responce! Ill remeasure the squish band correctly. The cylinder is fine now with just a hone. dont know how, but machine shop said its strieght..good to go.

New head price qoute was $300 from Yamaha. isint it posible to raise the squish with gaskets? heres what it looks like now.

img3782h.jpg

Scoring was caused by there being a lack of air filterage, heh.

Those are some deep gouges my friend.

img3788u.jpg

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Beauty and the Beast. Haha

MAX!!!

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I have the smaller harbor freight torque wrench and have it professionally calibrated and certified by a company for my work. It has never needed adjustment other then the first cal. They said it was off by 2 in lbs. Good purchase. -BIG DAN:thumbsup:

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Head looks good now. It must have been pinging like a mother to do all that pitting. I think you will need to run some kind of race fuel, depending on the volume of the new head.

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looks like I have 2 options, shave the squish band on the head down (free) or raise the cylinder up with a base gasket (shouldn't negatively effect port timing). Im looking to run on pump gas, so what clearance measurement am I supposed to aim for + -? your opinions are greatly appreciated :thumbsup:

p.s. thanks for the tip on the torque wrench, glad I got a good one. definitely gonna get put it to use.

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If your going to shave off squish from the head to create more room, you need to compensate for the combustion chamber volume as well as they are linked. Too low of a volume will give you a compression ratio that your pump gas, let alone possibly race gas will not be able to handle, resulting in a blown piston once again.

For good squish with a regularly sized combustion chamber (something you no longer have as the head itself was shaved) is .45

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Ok soory if im slow on this as I am not a tech. From my understanding the cumbustion chamer was done on the head as well a new squish band was cut .25mm deep to compisate for a 56mm bore. So what is your suggestion to fix my problem? thank you.

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The erosion on the cylinder is going to cause you problems down the road. It looks like the head is still at 54mm? Slide it on and look down the cylinder to see if it clears the bore. The head can be machined. The cylinder will be expensive to correct. Machining/welding and or a spacer plate at the bottom, then studs are too long. Maybe a new/used cylinder? If that piston damage is from dirt (looks like rocks), your crank is probably wasted.

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Ok soory if im slow on this as I am not a tech. From my understanding the cumbustion chamer was done on the head as well a new squish band was cut .25mm deep to compisate for a 56mm bore. So what is your suggestion to fix my problem? thank you.

I'm not a tech/expert either, but you bring up a valid point that I missed. This is entirely possible, but looking at your piston in which it was smashing into the head shows that something was not done right, which leads to a possibility that nothing was done right.

If I were you and you want to save that head, you should send it into an expert in which he can determine if that squish is acceptable for that size bore and determine if that combustion chamber is of the right size for a particular octane fuel.

IMO you need to know these things before you start doing any modifications and repairs, cause if you don't you can detonate or pre-ignite causing more problems than you already had.

When you figure these things out then you can start putting things back together.

IF you don't know anyone, I would HIGHLY suggest that you call RB Designs at this link

http://www.rb-designs.com/contact-info.htm

He's the man with the plan, he really knows his stuff and he can point you in the right direction. His prices are reasonable and I'd say 80% of the people on this entire board use him for head work.

Give him a call and discuss your situation, you know what your doing so he should be able to tell you what you need to do no prob.

good luck buddy!

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Thank you for the replies. If you read the entire thread,, you will find that I have already have had head & cylinder work done by a qualified machine shop with dirt bike history. Information was given to them in respect to bore size and previous history/ problems. When I received the head back, the shop told me he would remove more material from the squish band if need be. Ill have to wait for new stud bolts to remeasure the squish band, but from my initial sloppy attempt it looked like it was around .30 maybe .40 . The crank and cylinder are in perfect working order, I would have definitely mention otherwise in my previous posts. Now I'd like to figure out where to go from here; gasket or squish band rework? thanks for your time/interest. I appreciate the link, will bookmark*:thumbsup:

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... Ill have to wait for new stud bolts to remeasure the squish band, but from my initial sloppy attempt it looked like it was around .30 maybe .40 . The crank and cylinder are in perfect working order, I would have definitely mention otherwise in my previous posts. ...

If you mean 0.30" you have way too much clearance. If you have 0.30mm you have way too little. You should have it set to about 0.045-0.050" or about 1.0mm.

I recommend you measure what you have using the information from RBDesigns web site. Then send your head to them with your gauges and have them recut it. They do very good work and many on this site recommend them. There is lots of great information on this under the FAQ sticky at the top of this forum. I had them machine mine. Their work is great and it really does improve performance.

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Ill remeasure and post my findings back. like I said I just spent $100 dollars on the head and they are willing to additional work for free, so Im really inclined not to spend more money on head work, does this make sense? any ways thanks, Ill be back with a accurate measurement. Thanks.

p.s. I did mean 0.30mm btw soory

Edited by outblast

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Even if you send your head out, you need to provide them with an accurate deck height measurement, other wise they are just guessing. I'd also want them to know what the dome angle was when using a non stock piston. Might want to measure the deck height, pull the piston back off and send it with the head. Correction of the squish band may also include changing it's angle. Check my link on measuring deck height http://www.2strokeheads.com/tech1.htm

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Your machine shop may be a reputable shop with motorcycle experience, but your best bet is to send the head to someone with intimate knowledge of the YZ and you'll get much better results. Anyone can cut metal, but I'd feel better knowing its being done by someone who knows exactly what to do with the YZ engine.

Honestly if I had an engine that looked like that with so many unknowns (and especially no air filter), I'd pick up a new head/cylinder/piston already set up for the 144.

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well, Im dropping the engine off to have the deck height measured, and squish band corrected with an angle that corresponds with ta 56mm wiesco piston top. Thanks guys.

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