2-stoke engine run in...

[MarshyUK]

Hi all,

Havent been here in a while and its good to see many new members, hopefully a few more from the UK too!

Anyway, just done a piston kit and other small jobs to my gasser, but not comes the time to run it in. I remeber a website posted here a while ago, motoman or something, who tells you to run it hard then leave to sit for 30mins or something like that. Does anyone have the link? ?

[yamaha_rulez_125]

welcome back, ? here you go.

the site is www.moto814.com if thats what your looking for.

if your looking to break it in i think theres an article in there about that.

[HawkGT]

That's not it. It's MOTOTUNEUSA

Don't know if he makes any reference to two strokes or if his methods apply to two strokes. I would guess yes, but IDK...

[kx_rider53]

Do Not do a hard break in for a 2 stroke. Here is the right way.

From Moto814

1) Assemble the engine properly and torque all fasteners to specs.

2) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), shut it off.

3) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.

4) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), shut it off.

5) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.

6) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), take the bike off the stand and put it in gear. Take it for a ride. During this ride you want to keep the engine under a load at all times. Do not coast. Do not let the bike idle. Do not allow the engine to stay at one RPM. Riding on a mild slope is fine for this, as is slightly dragging the rear brake the entire time. Do this for about 15-20 minutes. Then shut the bike off.

7) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.

8 ) Re-torque the head and base nuts.

9) Go ride.

The cool-down steps are crucial to this operation. You must let the engine cool completely for the break in process to work properly.

Also, do the warm up procedure I outline here before EVERY ride. Your top ends will last much longer if you do.

-Steve

[HawkGT]

Why would the break-in procedure (seating the rings) on a two stroke be any different than a four stroke? They might be; I just don't know why...

[JoelH.]

Uh oh. Here we go!

[MarshyUK]

So im guessing with the advice given so far, i should go with the run for 20 mins, leave to cool for an hour, repeat 3 times, then take it out gently for 20 mins, then use normally, or not? ?

[seehenry]

yea this is going to be a painful thread. ive always just run the snot out of the pistons from the word go. warm up the bike and hit it I say.

[The Spanky]

Your break-in (two-stroke or four) largely depends on the type of piston you installed. A cast piston doesn't need any special treatment for break-in beyond the time it takes to seat the rings. Just ride easy for 10-15 minutes and go for it. That's why cast pistons are used as OEM equipment, because the manufacturers know that too many riders won't adhere to a specific break-in procedure.

A forged piston (Wiseco), on the other hand, must be carefully broken in. They require heat-cycles to release the trapped stress left in the metal from the manufacturing process. For a forged piston, that break-in guide that kx_rider53 posted is the correct way.

[STILL_KICKIN]

Your break-in (two-stroke or four) largely depends on the type of piston you installed. A cast piston doesn't need any special treatment for break-in beyond the time it takes to seat the rings. Just ride easy for 10-15 minutes and go for it. That's why cast pistons are used as OEM equipment, because the manufacturers know that too many riders won't adhere to a specific break-in procedure.

A forged piston (Wiseco), on the other hand, must be carefully broken in. They require heat-cycles to release the trapped stress left in the metal from the manufacturing process. For a forged piston, that break-in guide that kx_rider53 posted is the correct way.

? Very well put!

[MarshyUK]

My new pistons a Wiseco so i guess that told me!

Thanks! ?

[HawkGT]

Your break-in (two-stroke or four) largely depends on the type of piston you installed. A cast piston doesn't need any special treatment for break-in beyond the time it takes to seat the rings. Just ride easy for 10-15 minutes and go for it. That's why cast pistons are used as OEM equipment, because the manufacturers know that too many riders won't adhere to a specific break-in procedure.

A forged piston (Wiseco), on the other hand, must be carefully broken in. They require heat-cycles to release the trapped stress left in the metal from the manufacturing process. For a forged piston, that break-in guide that kx_rider53 posted is the correct way.

? Not even close to being well put.

"...doesn't need any special treatment for break-in beyond the time it takes to seat the rings. Just ride easy for 10-15 minutes and go for it..." Are you suggesting that 10-15 minutes of easy riding is for seating the rings? Easy riding is precisely what rings do NOT need for proper seating. They'll never fully seat without high cylinder pressures and the window of opportunity for seating is smaller than ever with todays light hones and coated cylinders.

Regarding the heat treatment: Wiseco pistons are heat treated as one of the last phases of their manufacture. There's no ammount of beneficial heat treating that's going to take place inside your engine that hasn't already been performed by the manufacture of the piston. If you need that confirmed by a reliable source than call Wiseco themselves and ask them...

The use of cast and hypereutectic pistons by OEM has zero to do with break-in procedures. It's pure economics. Cast pistons are almost as good as forged (in stock tuned engines) and cost a lot less to manufacture.

[gunner150]

? Not even close to being well put.

"...doesn't need any special treatment for break-in beyond the time it takes to seat the rings. Just ride easy for 10-15 minutes and go for it..." Are you suggesting that 10-15 minutes of easy riding is for seating the rings? Easy riding is precisely what rings do NOT need for proper seating. They'll never fully seat without high cylinder pressures and the window of opportunity for seating is smaller than ever with todays light hones and coated cylinders.

Regarding the heat treatment: Wiseco pistons are heat treated as one of the last phases of their manufacture. There's no ammount of beneficial heat treating that's going to take place inside your engine that hasn't already been performed by the manufacture of the piston. If you need that confirmed by a reliable source than call Wiseco themselves and ask them...

The use of cast and hypereutectic pistons by OEM has zero to do with break-in procedures. It's pure economics. Cast pistons are almost as good as forged (in stock tuned engines) and cost a lot less to manufacture.

No, you run 4-stokes hard for break in. 2-strokes are ment to be broken in easy.

[HawkGT]

No, you run 4-stokes hard for break in. 2-strokes are ment to be broken in easy.

But why? I'm willing to accept that answer but only if it's supported with reasoning that makes sense.

[The Spanky]

"...doesn't need any special treatment for break-in beyond the time it takes to seat the rings. Just ride easy for 10-15 minutes and go for it..." Are you suggesting that 10-15 minutes of easy riding is for seating the rings?

No, I'm suggesting that cast pistons don't need special break-in procedures. They do not need to be heat-cycled like forged pistons.

Regarding the heat treatment: Wiseco pistons are heat treated as one of the last phases of their manufacture.

Not once did I say "heat treating". Heat treating is a part of the manufacturing process, and is a completely seperate issue than "heat cycling" during break-in. Forged pistons must be heat cycled several times to relieve the internal stress that is left over from the metal being beaten into shape during manufacturing.

The use of cast and hypereutectic pistons by OEM has zero to do with break-in procedures. It's pure economics. Cast pistons are almost as good as forged (in stock tuned engines) and cost a lot less to manufacture.

Break-in procedures most certainly do play a factor in the manufacturers' choice of cast pistons. They are well aware that many new bike owners are just going to jump on the bikes and start reaming away, with no break-in time. If the bikes were equipped with forged pistons, a large number of them would be siezed on the first ride, resulting in massive numbers of owners screaming for repairs that should be covered by the manufacturer, despite the fault ultimately being squarely on the shoulders of the bike owners.

Cast pistons are almost as good as forged

On that we most definitely disagree. Forged pistons are more durable under high-heat, high load conditions than cast pistons will ever be.

Cast pistons don't require much in the way of special break-in, that's part of the reason they come as OEM equipment in two-strokes. Forged pistons, on the other hand, are a different story. A forged piston must be heat-cycled before it can be run hard, or you're playing roulette with your engine.

A new forged piston has to be heat-cycled several times to relieve the internal stresses left over in the metal from the manufacturing process. If this isn't done properly, the piston will distort and become out-of-round, causing it to wedge itself into your cylinder, more commonly known as a "seizure". A seizure with a two-stroke isn't a very dramatic occurance, usually the engine just stops running. You replate the cylinder, rebuild the top-end again, and you're back in action. On a four-stroke, however, a seizure is often catastrophic. The four-stroke has more rotating mass, which creates additional inertia. So, when the piston seizes, the rest of the engine tries to keep spinning. The result is, more often than not, a snapped connecting rod, broken crank, and destroyed cases. A big bill usually follows.

To better understand why forged pistons are more seizure prone, you need to understand what makes a forged piston different than a cast piston.

A cast piston is manufactured by pouring molten metal into a mold. The final shape is machined to it's final exacting tolerances.

A forged piston is made by taking a chunk of metal, and beating it into shape with a die-press under enormous pressure. Like casting, the final shape is achieved through precise machine work.

The main difference between a cast and forged piston is the grain structure. A forged piston is beaten into shape, and as a result the metal stretches and compresses as the piston takes shape. The varied, elongated grain structure is like fiber reinforcing, and it makes for a very strong piston. Microscopic cracks don't readily propogate through the structure of a forged piston due to the high density and the irregularly spaced and sized grains. A cast piston, on the other hand, is made up of grains that are all the same size, because it starts out as a liquid that, after being poured into a mold, undergoes a controlled cool-down process that allows the metal to reach a near-perfect equilibrium right out of the mold. The highly regular grain size and distribution makes them more prone to crack propogation and failure.

The break-in of the two types is very different, because the metal properties are very different. The forging process produces a lot of internal stress from beating the metal into the intended shape. The stress is trapped in the metal of the finished part. A cast piston has lower internal stress, because it was able to seek it’s own internal equilibrium as the liquid metal flowed around inside the mold and then underwent a controlled cool-down. Since a cast piston has lower internal stress, it won’t distort nearly as much as a forged piston will when heated to a high temperature. The forged piston's propensity to distort when heated is the reason they require an elaborate break-in procedure.

To relieve the internal stress, and maintain it's correct shape, the forged piston has to go through a series of heating and cooling cycles. As it heats up, the grain structure will re-distribute itself into alignment to relieve any trapped stress. As it cools, the cylinder will contain and restrain the piston, maintaining it's shape. After a few heat/cool cycles, the internal stress reaches equilibrium, and the piston will no longer distort when heated in the engine. It will maintain it's shape for the rest of it's life.

Forging produces a higher grain density than casting, making the part much more durable under high-heat, high-load conditions. As long as you are patient enough to break a forged piston in correctly, you will have a piston that is more durable under extreme conditions.

Problems with Wiseco pistons are almost always caused by one of these three issues:

1. Improper break-in-This can be a death sentence for a forged piston.

2. Improper warm-up-A great way to cold-seize the engine. This also kills crank and rod bearings, not just forged pistons.

3. Cylinder-to-piston tolerances too tight-You can't just slap a Wiseco piston into a brand new engine with no time on it. Forged pistons require about .002" more cold clearance than a cast piston. Once it's time for the first top-end job, a cylinder will usually have loosened up enough for the forged piston to have enough clearance. Most Japanese two-strokes spec .002"-.004" clearance for the OEM pistons. Wiseco specs .003"-.005" clearance.

Another less common cause of problems with all pistons is when the person doing the top-end work doesn't drill the lube holes in the piston for an engine with a central exhaust bridge. A forged piston will actually tolerate this better than a cast piston.

Anytime you rebuild the top-end, you have to measure the ring end-gap, and file the ring ends if neccessary. I rarely have a set of Wiseco rings that don't need to be relieved slightly. If the end-gap is too tight, the ring ends will hammer the locator pin right out of the piston, with devastating results. Wiseco specs .004" per inch of bore size for their ring end-gap clearance.

All of these problems are caused by the mechanic that does the work, or the rider that's too lazy to perform a proper break-in or proper warm-up. You can't blame the product for your own incompetence (although that's usually what people do).

why don't you call Wiseco and ask them

No, why don't you call Wiseco and ask them. I've been building engines for a long time. I think I know of what I speak...

[HawkGT]

Chokey, I understand the differences between cast and forged--how their manufactured and their differing expansion properties. When I said that cast are almost as good as forged I said that based on (stock) cars and bikes of all types not requireing forged pistons to operate reliably. I did fail to remember that the expansion properties of OEM cast pistons make them more suitable for ham-fisted owners that don't properly warm-up an engine.

What I don't understand is what stresses are left in a forged piston that the manufactures' heat treating does not relieve. How do "heat-cycles" do anything that the heat treating does not? You mentioned stresses left in the piston being beaten into shape. Why doesn't the manufactues' heat treating relieve those stresses? Wiseco indicates that their heat treating is part of their finishing process...

Chokey, I can appreciate your experience in building engines--but with all do respect, that alone does not make you THE authority. There are plenty of experienced builders who's opinions vary considerably on this subject and more...

I'm not trying to be argumentative, I just don't get all of your points.

[MarshyUK]

Good to see ive managed to get a disagreement over a simple(ish) question lol, so what break in procedure should i follow tomorrow morning for a Gas Gas EC200 2-stroke equip with new Wiseco Piston, its been started and ran for around 5 secs before i killed it.

Thanks...

[STILL_KICKIN]

HEY Chokey!!!!

I stand corrected....that was VERY WELL PUT!!!

CAN WE GET A METALERGIST UP IN HERE!!!!

gunner150 "Not even close?

Why are 2 different types of metal used when there is surface to surface friction between the two metals? Why wouldn't I use a steel cylinder and a steel piston? Think about it!

If you can understand that, then you can understand what Chokey has already stated pretty well.

Yes there are alot of people who build engines, and there are engines that last and engines that don't!!!!!

"May every man be my superior, in that I may learn from him"

?

LMAO @ Jimdarkice ?

"Good to see ive managed to get a disagreement over a simple(ish) question lol, so what break in procedure should i follow tomorrow morning for a Gas Gas EC200 2-stroke equip with new Wiseco Piston, its been started and ran for around 5 secs before i killed it."

[The Spanky]

What I don't understand is what stresses are left in a forged piston that the manufactures' heat treating does not relieve. How do "heat-cycles" do anything that the heat treating does not? You mentioned stresses left in the piston being beaten into shape. Why doesn't the manufactues' heat treating relieve those stresses? Wiseco indicates that their heat treating is part of their finishing process...

You are confusing "heat treating" and "heat cycles".

Heat treating, as part of the manufacturing process, is a hardening process. The piston is heated to a target temperature, held there for a specific period of time, and then "quenched", or rapidly cooled. By what method Wiseco uses, I don't know, perhaps oil quenching, as this is the most common method. The sole purpose for doing this is to bring the metal to the desired level of hardness. The heating time, temperature, and cooling rate are all carefuly calculated to achieve a specific degree of hardness. Not hard enough, and the part doesn't hold up. Too hard, and the part breaks. There is a fine line between "hard" and "brittle".

Heat cycling, on the other hand, is the way to relieve the pent-up stress that is still trapped in the metal of the forged piston. When a forged part is quite literally beat into shape, the grain structure is forced into all sorts of random alignments, causing tiny areas of localized stress that can potentially cause warpage and failure if the part isn't "stress relieved" before being put into service. By cycling the piston through several heat-cool cycles, the grain structure will realign itself into a smooth continuous directional grain flow that will yield far greater impact strength and fatigue resistance, greatly increasing the strength of the part and reducing the chances of failure.

[The Spanky]

Good to see ive managed to get a disagreement over a simple(ish) question lol, so what break in procedure should i follow tomorrow morning for a Gas Gas EC200 2-stroke equip with new Wiseco Piston, its been started and ran for around 5 secs before i killed it.

Thanks...

Use the heat-cycle method that has already been posted.