YZ 85 Break-in

[gremmen]

Just bought a New 08 Yamaha YZ 85 for my Nephew. Having read the Manual it said to run 15:1 oil/fuel for break-in, then take off the Head & Cylinder and check piston for high spots. Then you run 30:1 pre-mix after that. I'll run 32:1 though.

Is it really necessary to go through all that for break-in ? I've seen other new bikes come out and just run the the recommended oil/fuel ratio and do great. I have not worked on 2 strokes and am a little worried about taking off the head & cylinder myself. But will if necessary !

Thanks

 

[plynn41]

Honestly, I don't know anyone who follows that routine. You'll get different advice here, but I think the majority of people will tell you to run the same oil mixture at break-in that you will run afterwards. When I put a new top end in my son's YZ85, I made him ride it around the yard nice and easy for a few minutes, then let the bike cool off, rechecked the torque on the head nuts and made sure the hoses weren't leaking. Then I told him to ride it as hard as he wanted. Have had no problems, and he has raced it 4 times on that piston.

 

[gremmen]

Thanks, Thats kind of what I was figuring, just ride it.

 

[helio lucas]

taking off the cylinder and head is a pretty easy and straight foward job. since you have the service manual the only thing you might need is some gaskets.
just because anyones not do properly the job doesn´t mean you shouldn´t. it´s the best and safest way to insure a good running bike.

for the record, if i have time, i always inspect the top end after a break in. actually, from time to time i inspect it on my bikes, after a break in or not! :cool:

 

[gremmen]

Well since i'm away at work and won't be home til the 28th, the wife took the boys out to the track to ride. Several months ago I bought them new Honda CRF's, an 80 & a 100. Didn't take me long to figure out these are not Motocross bikes, due to lack of any shock adjustments or add-on. I was going to buy them new 2 strokes for next year but found a couple deals I couldn't pass up. One was a 2006 Suzuki RM 125 in mint condition (only raced once) and had some cool add-ons like Fatty pipe, and controls. For the younger boy, the Yamaha Dealer made me a deal on a New 2007 YZ85. This was the bike I was concerned with Break-in.

Since they were going to go riding without me, I made my wife insure that the YZ was rode easy for 10 minutes, then a cool down time, then the same again one more time. She said the boy followed those direction. Then just went out Balls to the wall and had fun. Everything appears to have gone fine. They will ride a couple more times before I get home, then I'll go through the two to check things out. I build & race small and big block chevy motors, so these little motors shoudn't be to hard.... I hope.

Thanks for your comments

 

[_JOE_]

From my understanding the bearings are what require break in. The rings were probably seated by the time the bike made it to the starting gate. 9 times out of 10 you'll have no issues with the factory top end but it never hurts to check (as long as you pay attention and do the job right). Some will say to replace the ring(s) any time the cylinder comes off as well as the gaskets. If you will sleep better go ahead and pull the cylinder off and look at the piston/cylinder and measure for piston to cylinder clearance and ring end gap. Or you could just do like pretty much every other new bike owner and ride it.....after all it's only like a 10 hour piston life bike anyway, right? ;) And if it siezes you can make it a supermini! :)

 

[plynn41]

From my understanding the bearings are what require break in. The rings were probably seated by the time the bike made it to the starting gate.

Agree with the second statement, question the first. Bearings on a car engine need to be broke in, but I can't see where the roller and pin bearings used in a motorcycle's bottom end need to be broke in. The breaking in process involves strategic wear, and I don't think it's a good strategy for roller and pin bearings to have any kind of wear.

And if it siezes you can make it a supermini! :)

X2 :nod:

 

[_JOE_]

Agree with the second statement, question the first. Bearings on a car engine need to be broke in, but I can't see where the roller and pin bearings used in a motorcycle's bottom end need to be broke in. The breaking in process involves strategic wear, and I don't think it's a good strategy for roller and pin bearings to have any kind of wear.

That's just what I've heard. I do know that a new bearing is more difficult to turn than an old one when spun by hand. I've never heard of anyone having bearing issues from lack of easy break in.

 

[plynn41]

I do know that a new bearing is more difficult to turn than an old one when spun by hand.

You're right--that is odd, isn't it? I think that new bearings come coated with a sticky grease that may be the culprit.

 

[gremmen]

The V8 race motors we build are all on the loose side when it comes to bearings and ring gaps, since we're spinning them up to 8 grand. We rely on good oil and pressures. We have used Roller Bearing Cam Bearings with great success, and they are harder to rotate new due to the oil they were shipped packed with. A good cleaning with solvent frees them up.

I think the biggest concern would be piston life with a 2 stroke, due to the rpm's it is turning. I can see changing rings each time as well. Anyone know what the life is of the cylinder sleeve ?

 

[plynn41]

That nikasil plated cylinder will outlast quite a few sets of rings if you keep dirt out and nothing melts down. My son's '03 is on the original bore, and I don't know how many piston and ring sets have been through it. Probably 6 to a dozen--the bike was raced weekly by the previous owner, a pretty serious mx family. We've put one top end in it in the 2 years we've had it.

 

[_JOE_]

Yeah, the cylinder will last a LONG time as long as you keep the piston fresh and keep the incoming air and fuel clean and properly metered. If you let the piston wear it can oval the bore from rocking.

 

[scottiedawg66]

I break in two strokes several times a year with good luck. just mix to 32:1, do a few heat cycles. and rip like a mad man!

 

[gremmen]

Is there a brand of Piston Manufactures that is better then others for longevity. Are there any Coated Pistons out there.

 

[plynn41]

Vertex :cool: