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What is the best way to break in the engine for the Honda Grom? Are you a believer in the hard break in or the soft? What does Honda recommend for the MSX125?
 

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I'm a believer of the soft break in myself. I don't want to put too much stress on a new engine. I think most would agree with me. I would also try and stick to highway driving especially in the beginning.
 

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Break in

I have 11 motorcycles to include 3 z50s, 3 ct70s and have been a mechanic for 16 years. Im only speaking from experience when i say a soft break in may not get your rings seated properly. Read the motoman link i posted and decide for yourself. I broke my grom in with that method and 2 other bikes and i have no problems and they don't burn oil at all. Nikasil cylinders are not as critical and metallurgy is much better than they used to be so there is really little risk of you breaking it in the wrong way. I am not sure if the grom has a nikasil coated cylinder though. Either way, a soft break in is not, in my opinion the way to go. With that said don't redline it everywhere either. You need to do cycles of acceleration and engine breaking to put outward pressure on the rings and wear the rings into the cylinder so they can seal properly.
 

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I believe in a soft break in that involves a bit of hard riding just to help expose it to higher demands but at the same time keeping it as a soft break in 80% of the time. Kinda like how people bed-in brakes.
 

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I always stressed hard break-in's and the article posted above puts it well as you guys will see in the quoted text below:


How Do Rings Seal Against Tremendous Combustion Pressure ??
From the actual gas pressure itself !! It passes over the top of the ring, and gets behind it to force it outward against the cylinder wall. The problem is that new rings are far from perfect and they must be worn in quite a bit in order to completely seal all the way around the bore. If the gas pressure is strong enough during the engine's first miles of operation (open that throttle !!!), then the entire ring will wear into
the cylinder surface, to seal the combustion pressure as well as possible.



The Problem With "Easy Break In" ...
The honed crosshatch pattern in the cylinder bore acts like a file to allow the rings to wear. The rings quickly wear down the "peaks" of this roughness, regardless of how hard the engine is run.

There's a very small window of opportunity to get the rings to seal really well ... the first 20 miles !!
If the rings aren't forced against the walls soon enough, they'll use up the roughness before they fully seat. Once that happens there is no solution but to re hone the cylinders, install new rings and start over again.

Fortunately, most new sportbike owners can't resist the urge to "open it up" once or twice,
which is why more engines don't have this problem !!

An additional factor that you may not have realized, is that the person at the dealership who set up your bike probably blasted your brand new bike pretty hard on the "test run". So, without realizing it, that adrenaline crazed set - up mechanic actually did you a huge favor !!
 

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I also agree that the acceleration and deceleration (engine braking) is what helps seal the piston rings. I've heard this opinion from many mechanics that I respect so it's what I go with.

I don't think you can destroy your engine by going either way so just pick what you believe in.

I've also heard that engine braking while going down a decline in gear is another great way to seat the rings.

Also remember to warm the engine up all the way in idle if breaking in.
 
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