I know, this is a bomb forum, but I need to know some info, and I'm posting this same thread on the Yamaha side, my bet is the folks over here will come up with more valueable info than the yammy side. I know some of you bomb owners have to have a YFZ in your stable......

I have an 05 YFZ that I installed a GYTR hour meter on when bike was new, I have 150hrs on it now. I had the yz cam mod done at 20hrs, and valve clearence checked at that time. I just had the valves reshimmed at 150hrs, and the mechanic that I took the bike too claims that 150 hrs is a LOT of time. The bike still runs great without any unusual engine noises. My question is how many hours are some of you folks getting out of your YFZ before anything major needs to be done? The mechanic says that rods tend to break, pistons tend to go sideways, and valves break after a lot of hours, I don't quite buy this, but what have you guys/gals experienced? Thanks for any replies to this thread. After a year of trying to keep up with DSNUT, and folks like Scatter...I have to make sure I don't blow my motor up from excess wear....

Cam mod
48 pilot 175 main
full Yosh TRS
Pro-Flow K&N
other than that stock, entirely sand dune riding.

 

ive heard anywhere from 150 hours to 250 hours....at a yamaha shop they recomended 150 hours for a new piston.

 

Reliability is in direct proportion to the rpm range you ride in.
That is , if you exceed 9,000rpm with your motor on a regular basis, its life span is shortened quickly.

Have a compression check and if 15% less than when new, re-ring piston and install new oil seals. If more than 25%, be ready for possibly more parts to be changed.

If piston aand bore have excessive wear, than a rebore and new piston will be required.
Every 2 years the valve springs should be changed on a motor that exceeds 9000rpm on a regular basis also.

To get high horsepower out of a small motor is like having a 2 stroke motor. Maintenance is higher than a lower rpm motor.

 

ive heard anywhere from 150 hours to 250 hours....at a yamaha shop they recomended 150 hours for a new piston.
>>>>>>>>>>

WOW, if a person rode frequently that could be a fairly often repair/maintenance issue. What about the titanium valves? My buddy just bought a new YFZ, personally for the kind of riding we do I thought it was a mistake, we won't be racing or hardly ever see a motocross type track so my suggestion to him was the Raptor 700 but he was dazzled by Yamaha's claim that the YFZ is the fastest production ATV or some crap like that, I just know I kept blowing by him in third gear when we drag raced.

 

Ya that sounds a little steep for someone not racing. Dealer told my buddy that got one to change the oil every 9 hours. Sounds like alot of maintenance and money for a weekend rider.

 

Yes...it sounded WAY to early to me for a new piston...thats just what i heard. I ride with a guy who has a yfz and is as hard as you could possibly be on a engine and he has well over 400 hours on it by now if more and shes still running.

 

Hey guys, thanks for the feedback, sounds like there is quite a range of opinions on how many hours you can put on these little motors. We tried doing a compression check, and it doesn't work, seeing as the exhaust cam has an auto decompression function. I would say that most of my riding is done well under the 9K range. I guess I would ask now, has anyone experienced a catastrophic break down? 400hrs is a heck of a lot of hours, I feel sorry for the butt that has experienced 400hrs on that 2x4 of a seat. I couldn't stand my seat, so had extra foam put in it.

 

I think OMR pretty much summed it up in this thread. Good advice OMR.

But with the hours mentioned, I would atleast replace the rings. Heck, I would just go ahead and replace the piston, check the cylinder for scars while I have it down. Never can be too careful.

 

Well I have a St. A's trip planned for 4th of July, then I'll tear it down. Any advice on type of piston I should replace it with? With these little tinker toys motors, can I go higher than the OEM 11.9:1, and still retain the reliability that I've experienced so far? Does higher compression put more wear on the valve train? and lastly, what should I be doing with the valve train? OMR mentioned new springs, but what about the actual valves, the most recent valve adjustment I had, the intake valves had pocketed up in the head by about .005-.007, so reshimmed them. Exhaust valves were right on .008-.009 tolerence.

 

When you pull it down, I would just go ahead and put some kibblewhite valve springs in, KBR 12.5:1 piston/rings and be finished with this project.

PS: The higher compression will add a little more stress on the valve train, but nothing the new heavy duty valve springs shouldnt take care of.