Top end break in?

10 replies to this topic
  • moto_madman

Posted June 09, 2002 - 02:53 PM


What do you guys do to break in top ends on two and four strokes. I was doing some research on the topic and i get a different answer every time.

  • sirthumpalot

Posted June 09, 2002 - 03:07 PM


Follow the directions in the manual. All engines are not the same, the engine manufacturer (or manufacturer of the specific part which you are replacing) will give you the best advice.

  • moto_madman

Posted June 09, 2002 - 03:52 PM


Yup, i use the procedure my local mechanic told me. Its close to the manual and i dont let top ends go for more than half a season. I have always wondered how the pro's mechanics do it. I dont think they ride around the pits for half an hour.

  • Fireballsocal

Posted June 10, 2002 - 03:26 PM


Follow the manual to the T. Alot of people say break it in hard and you can ride it hard. I've never had the guts to do that myself but following the manual got me three years on the YZ400 and going on 5 years on the banshee. I can go easy for a couple tanks of gas if I get that kind of life out of the bikes.

  • yznvegas

Posted June 10, 2002 - 03:42 PM


Following the manual when it comes to 2-smokes is not always the best advice. Reason being, sometimes when you rebuild the top end a Wiseco piston is used and these pistons are much more seizure prone than the oem piston. They require heating and cooling cycles before you can get on it.

1) let bike idle until up to riding temperature, shut the bike down and let it cool completely, repeat this step 2 times.

2) ride the bike for about 10 minutes at no more than 1/4 throttle, let cool completely

3) repeat step 2 but go through the gears and use no more than 1/2 throttle. let cool completely

4) ok, now you can ride the bike but don't rap it out for the first tank of gas.

I also use more oil during break in, like 28:1 rather than 32:1

Good luck and let us know the results. :)

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  • Vanilla_Gorilla

Posted June 10, 2002 - 04:14 PM


best break in for any 2 stroke is a 15 minute idle, 15 minute cool down, 30 minute idle, 30 minute cooldown, and a 30 minute east ride under 6,000rpms with an hour cooldown afterwards, then your all set. the pros simply idle the bike for 30-45 minutes, then they race on it. A four stroke should be broken in by doing 3-5 slow 30 minute rides under 6,000 rpms, then finish the tank without going wide open on the throttle, then your all done!

  • moto_madman

Posted June 10, 2002 - 04:27 PM


I think ill try that. It seems to be what everyone is saying. I broke a Wiseco in in a cr80 i built for a friend. I let it warm up a little, then varied the RPM and load for about 20 minutes with 1 hard run accross the back yard at the end. I let it cool down and went easy on it for the first tank of gas. That damn bike would not die. Beat the hell out of it for two years including winter riding. It lost a little compression but ran like a champ. He sold it a few months back and the new owner hasnt done a top end and it still starts without a problem.

  • moto_madman

Posted June 10, 2002 - 04:28 PM


also, im using a vertex piston in this rebuild.

  • Vanilla_Gorilla

Posted June 11, 2002 - 05:32 PM


bad move with the vertex, ive had bad luck due to the coating that is use din vertex pistons. i recommend a Pro-x piston, or a balanced wiseco piston from MCR.

  • freestyle111

Posted June 11, 2002 - 06:06 PM


motoman,i tried to get vertex piston but i was told by several company including Sudco that Vertex doesnt make piston for yz400 or 426 never made one for yz400,426.where are you getting yours

  • moto_madman

Posted June 12, 2002 - 02:56 PM


I know the owner of the local shop well. He reccomended the Vertex. His race team has been using them with good results. As long as it lasts through this season and into early next season it will be fine. If it blows up im not going to be happy. This f#$%in rebuild and the list of trashed parts burned up my cash so i wasnt able to get the CR 500 i wanted. :) I really could have used a back up bike this past few weeks.

Freestyle, read my signature. I ride a 98 RM 250 not a 426. If i was just out to have fun i would have bought the 4-stroke but im hoping to get an AMA Pro Racing license in a few years (it is NOT easy) so im sticking to whats familiar for now. Vertex only makes 2-stroke pistons.

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