breaking in old low mileage beasts

Is it necessary to continue breaking in an engine that had 200 or less miles put on it a couple decades ago? Somehow it seems sort of funny to break in an engine that was first used 20 - 30 years ago and has just been resting since then. It seems beyond my will...but i would hate to hurt our indian, it only has 7 miles on it, or the magnum with 139, ouch.


Re: breaking in old low mileage beasts


I would run them at no more than 15 mph for the first 300 miles or run them up a little but drop back to 15 mph or half throttle.

Also make sure to use the correct premix per individual mfg. Some recommend a heavy mix of oil for break in and then after 300 miles to a normal 50:1 , 32: 1 or 25:1 depending on the mfg's bike.

Re: breaking in old low mileage beasts

Don Pflueger /

the problem with them sitting that long is that the seals have become dried out. sitting is qorse than being used. so not only do you need to finish the break in, but before you start it you need to relubricate everything.

Re: breaking in old low mileage beasts

Take off the head and look at the cylinder surface. If there is still some cross hatching from the original bore/hone job, some break-in can still happen. If the cylinder face is smooth, the break-in period is over.

The crosshatching is what wears the new rings and reshapes them until they contact the cylinder all the way around.

Some people say you have a very short amount of time before the crosshatching disappears. Once it's gone, it's gone.

So, they also say the engine should be run under high load for at least some period during the early part of the break-in. This forces the rings hard against the bore during the time the most crosshatching exists and so the most metal can be reshaped.

New ring outer face is tapered.. the face is not straight up and down, 90 degrees. This is so the ring wears quickly and can change shape during break-in.

Getting the rings worn to the point where the entire ring circumference touches the cylinder wall is the objective of break-in. Crosshatching must exist for this to happen.

break-in stuff

A cylinder, piston, rings and everything else change shape when they heat up.

A cylinder might be perfectly round when cold but slightly oval when hot. A ring that was broken in on a cold, round cylinder will not seal that cylinder once the engine reaches normal operating temperature. That ring has to be worn to an oval shape too..

So, get the engine hot by idling for a long time so the shape of all the parts is stablized before beginning any breaking-in schedule.


And there are other mechanical forces at work that change with different riding conditions.

In essence, the way you break-in determines under what conditions the rings will provide the best seal.. If you break-in at low engine loads and low speed and mild engine component temperatures, the rings will seal very well at low loads, low speeds and mild temps..

At high temps, speeds and engine load the sealing ability of those same rings is pretty much unpredictable.

Re: break-in stuff

what would happen to brand new piston rings in a cylinder that has already been broken in (no more cross-hatching)? Would the new piston rings not break-in correctly?

Re: break-in stuff

Thankfully, smooth, lubricated cylinder walls don't wear rings very quickly. Without some abrasive action they last virtually forever.

New rings will likely leak badly. Leaks past the ring can and do cause all sorts of problems with cylinder wall lubrication and carbon and glazing and ring groove troubles.

Some accelerated wear will take place right away at any high spots. But without considerable pressure behind the ring forcing it against a rough surface, wear will be very slow. If half of a ring needs to lose 0.0005" before the whole ring can make cylinder contact, it may never happen in a low power engine with smooth cylinder and leaking rings..

Failed break-ins happen all the time.. Some people are very serious about the quality of the job and have the tools and skills to detect it when it happens... like racing teams that rebuild engines regularly and need to get it done right or they don't win and don't get paid. They will start the break-in over and re-hone/crosshatch the cylinder wall and use a new ring set.

Re: break-in stuff

If you have 100-140 or more lbs. of compression,unless you're building a racing engine, don't worry about it.

Honda Expresses and Suzuki FAs and Franco_Morinis have only 7 to 9 :1 compression ratios. It's not a problem for a common moped.

I've never had a problem on break-in as long as I varied the throttle of the ped and didn't try to strain it and lug it,getting it too hot. don-ohio (:^D

Re: break-in stuff

yeah.. we _are_ just talking mopeds here... but it's fun to hash over the finer details as if they really mattered.

The practical problems to avoid when breaking-in are more in the line of gapping the rings or buying the right sized piston.. and taking careful measurements .. perhaps boring the cylinder to fit a piston that is just too big.

Lubricate new parts before firing it up.. take that rag out of the crankcase before bolting the cylinder back on. ;)

Just don't make major miscalculations of forget something that might cause outright piston seizure or other damage.

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