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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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  #31  
Old 09-13-2019, 08:56 PM
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I don't think anyone here is arguing the point that heat can change the structure of metals. . . . .
.
.
Um, yeah I am. Well, beyond normal thermal expansion, which at the temperature involved is, well normal and happens every time you run the bike

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. . . . What I care about is a proper warm up, an adequate cooling system with no leaks, no air leaks etc. From there once I've confirmed the engine is sound after any work my focus moves into generating enough load to sufficiently bed the rings in.
.
And that must be the most sensible thing anyone has said on this entire thread.

I must have run in 100 racing engines and came to the conclusion that it was easiest on the dyno if the fan could push enough air to keep the normal water temperature. Done with some respect to the ring to bore relationship would result in the same power and engine longevity.

In the old days of air cooling, miserable pistons, 1/2 arsed machining, and hard to mix or crap oil, people would over heat their engines by running them at standstill forever or ragging them before the final piston clearances had been scraped off the interface making them viable as a performance engine.


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  #32  
Old 09-14-2019, 01:49 AM
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Originally Posted by (F5) View Post
Um, yeah I am. Well, beyond normal thermal expansion, which at the temperature involved is, well normal and happens every time you run the bike


And that must be the most sensible thing anyone has said on this entire thread.

I must have run in 100 racing engines and came to the conclusion that it was easiest on the dyno if the fan could push enough air to keep the normal water temperature. Done with some respect to the ring to bore relationship would result in the same power and engine longevity.

In the old days of air cooling, miserable pistons, 1/2 arsed machining, and hard to mix or crap oil, people would over heat their engines by running them at standstill forever or ragging them before the final piston clearances had been scraped off the interface making them viable as a performance engine.
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  #33  
Old 09-14-2019, 02:27 PM
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I don't think anyone here is arguing the point that heat can change the structure of metals. More to the point, what question are you asking?
It was a simple question. Do you heat cycle a new engine and if, how?
seriously,what's hard to understand about it?

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A forged piston has seen some heat already, both during forging, during, machining, finishing, etc. And will surely see more in use.
Every piston has seen some heat whether forged or casted.

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Is there a specific break in time which leads to optimal structure? At which point does it go beyond optimal and fatigue?
This is what I am trying to find out. Had the chance to talk to a GG factory team mechanic a few years back and the method he described was rather unusual. As they let the engine cool for 24 hours which I have never heard before. So I asked a guy I know from an oil company, he works in R&D and is specialized in tribology and he said that may make sense.

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How does this matter to us?
I don't know. I never did any heat cycling. I get a brand new bike and ride it. Done. Which leads back to the question, is anyone doing heat cycles before the bike is just ridden normally? And if the answer is yes, how and why?


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How are airplane engines broken in? Some good reading on the matter if you go looking.
I only can say JTD9's from P&W just run on the test stand before delivery. There is no braking in period once the engine is installed. No clue if that is also valid for newer super fan engines aswell, but I'd assume it.
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  #34  
Old 09-14-2019, 05:08 PM
swazi_matt swazi_matt is offline
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I have always heard that the engines are tested in the factory (probably to pretty high revs) anyway so any heat cycling once it is delivered to the customer is probably already too late isn’t it?
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  #35  
Old 09-14-2019, 08:26 PM
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Quote:
Originally Posted by Doc Brown View Post
It was a simple question. Do you heat cycle a new engine and if, how?
seriously,what's hard to understand about it?
All good.

I think the answer is yes, and probably for everyone. No one builds a fresh engine and smashes it hard on it's initial start up.

There will always be a series of heat cycles prior to really putting a heavy load on it.. I don't particularly call it heat cycling in regards to tempering or changing the structure of metals.

It's more so to ensure the engine is sound.. That there are no unexpected issues (oil leaks, fuel leaks, coolant leaks, air leaks, unexpected noises or behaviour).

From there on in, the heat cycles occur every time it is used.

PS. Even buying a new bike from a dealer the engine will have been started/tested in the factory, again at pre delivery, and most of us will give the bike a start or light ride somewhere before really put it to work. Thus, I'm not really concerned with 'heat cycles'. I care about a sound engine with correct tolerances. I care that the fuelling is correct, and the cooling too. Then I focus on bedding the rings.
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  #36  
Old 09-15-2019, 06:52 AM
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Originally Posted by Jakobi View Post
All good.

I think the answer is yes, and probably for everyone. No one builds a fresh engine and smashes it hard on it's initial start up.

There will always be a series of heat cycles prior to really putting a heavy load on it.. I don't particularly call it heat cycling in regards to tempering or changing the structure of metals.

It's more so to ensure the engine is sound.. That there are no unexpected issues (oil leaks, fuel leaks, coolant leaks, air leaks, unexpected noises or behaviour).

From there on in, the heat cycles occur every time it is used.

PS. Even buying a new bike from a dealer the engine will have been started/tested in the factory, again at pre delivery, and most of us will give the bike a start or light ride somewhere before really put it to work. Thus, I'm not really concerned with 'heat cycles'. I care about a sound engine with correct tolerances. I care that the fuelling is correct, and the cooling too. Then I focus on bedding the rings.
No bad feelings Jakobi, always like your posts and enjoy reading them.
I see it like you, I probably do what everyone does when starting a new engine for the first time. I don't heat cycle it nor do I brake it in. For me the most important is to let it completely warm up under low loads. And I use 40:1 premix the first full tank. But other than that I don't do anything special.

The Sapnish guy said, and here is probably the answer for you swazi_matt, that when they have a brand new engine they treat it very special. I assume its either brand new or overhauled (new piston, rings etc.) and hasn't been started, tested or used before.

I never heard that before on simple engines but I know a lot about how multi cylinder race engines are treated. I know that the legendary Judd V8 is broken in in a very special way as I had the chance to talk the tech chief. Any time before its started oil and water are warmed up or it goes west, but that's another story...
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  #37  
Old 09-15-2019, 10:24 PM
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Quote:
Originally Posted by Doc Brown View Post
I never heard that before on simple engines but I know a lot about how multi cylinder race engines are treated. I know that the legendary Judd V8 is broken in in a very special way as I had the chance to talk the tech chief. Any time before its started oil and water are warmed up or it goes west, but that's another story...
It's kind of the same story though.

All to do with tolerances, operating temps, and thermal expansion. Generally speaking bigger parts require bigger tolerances to allow for greater variations. In a race engine with tighter tolerances you need to remove some of the variables.. thus specific start up/warm up procedures.

From my research, it seems to be the same with most of the 2T reading about heat cycles. Usually bigger bores (think jet skis/snow sleds, etc), moving from a cast piston to a forged. Forged by nature expands more and needs more tolerance. Add to that the bathtub curve and infant mortality, and odds are that when you make significant mechanical changes, that if it's going to fail it's going to do so sooner rather than later. If you're going to have a big piston nip up due to thermal expansion you're best chance of avoiding is a slow warm up, and in the event that it does nip it's best on a low load slow idle than wide open down the track.

Factories probably tend to stick to a certain procedure for consistency and fault finding. The less variables you are dealing with the better.
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  #38  
Old 09-16-2019, 12:52 PM
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Originally Posted by Jakobi View Post
It's kind of the same story though.

All to do with tolerances, operating temps, and thermal expansion. Generally speaking bigger parts require bigger tolerances to allow for greater variations. In a race engine with tighter tolerances you need to remove some of the variables.. thus specific start up/warm up procedures.

From my research, it seems to be the same with most of the 2T reading about heat cycles. Usually bigger bores (think jet skis/snow sleds, etc), moving from a cast piston to a forged. Forged by nature expands more and needs more tolerance. Add to that the bathtub curve and infant mortality, and odds are that when you make significant mechanical changes, that if it's going to fail it's going to do so sooner rather than later. If you're going to have a big piston nip up due to thermal expansion you're best chance of avoiding is a slow warm up, and in the event that it does nip it's best on a low load slow idle than wide open down the track.

Factories probably tend to stick to a certain procedure for consistency and fault finding. The less variables you are dealing with the better.
Yes, that sounds very plausible to me. The BMW engineer (it was a BMW with a Judd V8 engine) I talked too said the engine would be destroyed when its started cold and this is due to the very close tolerances. They had a specially designed external pump with a heater unit connected to the car. One tube was lead through the oil pan to warm up the oil.

Here is a little video of the car

https://www.youtube.com/watch?v=84rE2LcwHIw

Unfortunately Georg, the driver died in a horrible accident at a hillclimb race in 2011. It was a great honor for me to know him.
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  #39  
Old 09-16-2019, 03:27 PM
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Here's some food for thought.

Why do we believe that the piston and liner would "wear" to itself in the first hour of operation, but not in the following 100 hours?
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  #40  
Old 09-16-2019, 05:10 PM
swazi_matt swazi_matt is offline
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Quote:
Originally Posted by Doc Brown View Post
Yes, that sounds very plausible to me. The BMW engineer (it was a BMW with a Judd V8 engine) I talked too said the engine would be destroyed when its started cold and this is due to the very close tolerances. They had a specially designed external pump with a heater unit connected to the car. One tube was lead through the oil pan to warm up the oil.

Here is a little video of the car

https://www.youtube.com/watch?v=84rE2LcwHIw

Unfortunately Georg, the driver died in a horrible accident at a hillclimb race in 2011. It was a great honor for me to know him.
That is the same for F1 cars, they have to be heated up before they start and then they also have a very sophisticated clutch that makes sure that it does not stall as that would also trash the engine (I do not have all the facts, but i saw a tv programme where the presenter took about an hour to get out of the pits because he couldn't get the clutch action right)
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