how do pros break in a top end?

[Moto Madman]

I was at southwick today for the national. I was just wondering how the pros break in a new motor. I really dont think the mechanic rides around the pits for a half hour. A few years back i saw Boniface's mechanic reving the s**t out of the motor while the bike was on the stand. Could this be it?

 

[JUSTRIDE415]

Good question. i have no idea

 

[Rich Rohrich]

They don't.

 

[Moto Madman]

So you're saying they just jet it to compensate or do they use some trick to seal the rings?

 

[Rich Rohrich]

Correct matching of ring materials, ring profile (shape) and surface finish on the bore eliminates the need for break-in usually at the expense of component longevity. Jetting has nothing to do with it.

 

[Moto Madman]

Thanks for clearing that up. I was thinking jetting because i know that new motors run rich. I had no clue why they would run with leakin rings. I'm still recovering from 9 hours of race gas fumes so im not thinking very smart right now.

 

[Rich Rohrich]

Originally posted by Moto Madman
Thanks for clearing that up. I was thinking jetting because i know that new motors run rich.

New motors don't run rich. People will on occasion richen the jetting on new two-strokes in an attempt to keep cylinder temperatures low. The value of doing that is certainly open to debate.

 

[Moto Madman]

What i mean is the rings are not completely sealing yet so fuel passes by them creating a rich condition at low to mid rpm. By the way, back to the pro question, is the only secret in the ring and the cylinder coating or is there a trick in the piston also?
Rich, thanks for taking the time to answer my quetions.

 

[Rich Rohrich]

Originally posted by Moto Madman
What i mean is the rings are not completely sealing yet so fuel passes by them creating a rich condition at low to mid rpm.

That's not how it works.

Cylinder finish and the ring package with a properly sized bore is pretty much it.

 

[Moto Madman]

so why does the the plug get oily during break-in? Also, are there any good books on the topic out there?

 

[Rich Rohrich]

Try Eric Gorr's book.

http://www.ericgorr.com/books/books.html

 

[Moto Madman]

Cool! I think i'll be ordering that soon. Thanks for your help.

 

[Chili]

I just got my copy of the book today and after just a quick glance so far I am already thinking it was money very well spent. The only downside is learning what the flaws/weaknesses of my 86 RM125 are now I'm afraid to kick it over :)

 

[jmics19067]

so why does the the plug get oily during break-in? Also, are there any good books on the topic out there?

well I can think of two reasons why MY plug is oily during break in.

1st ,I cover everything in oil when rebuilding so it will take a bit before it all clears out

2nd I am usually very easy on the bike when trying to break in, that , and usually running on the rich side of jetting. Without opening it up and putting a real load on the engine I really dont generate enough heat or airflow to clear things out.

 

[Durt Cycler]

I agree with jmics19067.

 

[Jaybird]

Rich, doesn't piston material (cast/forged) play a role during break-in? And, do you feel that ceramic coated pistons have any advantages/disadvantages?

 

[DEANSFASTWAY]

You always run your mix at 15/1 wow you must go through some oil , HUH? Msot race mechanics just heat cycle the motor once before a race or do nothing at all . Big teams start with new top ends & clutches before every event , trhats what Ive seen .

 

[Rich Rohrich]

Originally posted by Jaybird
Rich, doesn't piston material (cast/forged) play a role during break-in?

It's more of a setup issue with bore sizing than anything else.

Originally posted by Jaybird

And, do you feel that ceramic coated pistons have any advantages/disadvantages?

Yes

 

[CanadianRidr]

Okay whenever I run a new top end I don't touch the jetting or anything of that sort. I just richen (ahem lean or however the correct way to say it) my mixture. Ill go from 36:1 to around 20:1. Is there anything wrong with this Rich?

 

[Rich Rohrich]

Originally posted by CanadianRidr
Ill go from 36:1 to around 20:1. Is there anything wrong with this Rich?

You'll tend to lean the air/fuel ratio by doing this and could possibly end up running the engine a bit hot or run into a knock situation from lugging the engine with the jetting too lean . If things were done correctly during the rebuild you have nothing to gain from switching the oil ratio for break-in.

 

[Jaybird]

Originally posted by Rich Rohrich


Yes

Heat transfer/added weight?

 

[Jeff Gilbert]

While at the Lake Whitney races a couple of weeks ago HOH delivered a new bike to the guy pitted behind me. I was there when they unloaded it and all the mechanic did was put gas in and start the bike up. After about 5 minutes of short revs and an almost idle the mechanic revved to about 1/4 to 1/2 throttle for short durations then shut it off. He said it was ready to race after it cooled down, the only thing left was jetting and that would be done after practice.

 

[DEANSFASTWAY]

Who runs 15/1 Ill bet the bike hardly runs? Ill bet hes gotta repack his silencer after that . Its sometimes good to retorque the cyl & heafd bolts after a heat cycle espescially with fiber gaskets .

 

[Jaybird]

Dean,
If 15/16:1 was the only fuel you had, how would you jet to make it run proper? Also explain to me why there would be so much spooge?

 

[WoodsRider]

Back when I raced the 1/4-mile with a turbo pancake 4 VeeWee, I experimented with various piston to jug clearances, jug surface finishes and piston ring combinations. The car consistently ran in the low 13s (remember we're talking about '67 Volkswagon Beetle here) yet engine life was extremely dependant on the combination of parts. I had engines that lasted through five nights of racing (usually four to five runs a night) to engines that were a one run only "special." The engines never went through any type of "break-in" procedure. They were simply warmed up and then ringed to the moon.

This did require precise blue printing to achieve optimum bearing clearances, and careful installation of the crank and cam. Luckily all that information had been well documented by other VeeWee racers and I never experienced a bearing failure.