JohnP2

I have a new Savage 4.6 I'm breaking in (believe it is a .28 block). What is the longest amount of time you would feel comfortable between break-in cycles - assuming there is a limit.

This will be my fifth engine to break in,and am considering doing the first two cycles in the evening, and then the final three cycles in the morning. Will waiting 8-14 hours affect the break in?

Thanks!

controlliner

The time the engine is not running, does not effect the break in process. It's all about how much actual running time the engine has on it. Time to cool completely between runs is one of the more important things. Make sure the piston is at bottom dead center when letting the engine cool, it will prevent any possible "stretching" of the top of the cylinder liner.

JohnP2

Thanks. will definitely set piston at BDC between runs, just wanted to ensure that there was no unknown issues with allowing a long ionger than normal interval between methods.

purenitro33

I wouldn't waste a lot of time "heat cycling" as it really doesn't do anything other then cause extra stress on the engine and starting components. Just fire it up and run it as long as possible. The reason I say this is because while running rich, the piston doesn't even get hot enough to cook the oil let alone get hot enough to do any type of heat treating. It is however very hard on the starting system starting it over and over when the engine still has a lot of pinch. IMO heat cycling is just a waste of time, it also better on the engine to run constantly at 200-220F rather then constantly starting cool which adds extra stress again until everything warms up.

HerrSavage

Ideally, when heat cycling anyway, you'd preheat the engine to 200F before each start. Then yeah, let cool at BDC between runs.. The duration of the interval is irrelevant.. Depends on outside temp too of course..

purenitro33

You need at least a temperature of 350*C to properly heat treat silicon impregnated aluminum alloy, that's 662*F.

nitroexpress

Yes, but heat cycling (not heat treatment) is intended to relieve manufactoring stress.

purenitro33

Sure but you need to achieve a certain heat to change the molecular structure (stress) as you put it. Running at 200-220*F will not be enough to do that, it's 1/3 of the temp required to change the structure.

llkoolskillet

When you heat treat aluminum you need to bring it wrought first which is 875f-1000f then you quench, then soak in the furnace for the desired time for the desired strength.

I also dont see how heat cycling can relieve stress on parts. Constantly starting, letting it warm up then cool down and then restarting will relieve stress, IMO it adds to it. Think about your only prolonging the enevidable by heat cycling. Why not run as much fuel as possible which speeds the break in up and NO it wont hurt it cause your not stressing the internal parts out by constantly restarting. I think heat cycling is a joke but this is my opinion and everyone has one!

HerrSavage

Which is why preheating has become such a big deal.. Seems to me the key to "heat cycling" is more the cooling (with piston at bdc), than the warming up from a cold start. Whatever the case, I heat cycle and it works for me.. Though I do run the cycles longer and longer, and generally am less uptight and scientific about it the more engines I break in..

purenitro33

I firmly believe in pre-heating but that has nothing to do with any type of heat cycling/tempering. I'm not saying "not" to heat cycle, I just think it's a total waste of time and accomplishes nothing.

Ttowntoolman

Heat cycling and heat treating way different. The idea is to lap the piston into a perfect fit into the sleeve without putting too much stress on the moving parts (rod and crank). Bringing the engine up to operating temp however you choose and run the piston up and down until it wears in to a perfect fit, that is my theory of how this shizz works. I have never had a nitro engine that I broke in fail in any way shape or form. Everyone seems to do it different.....so be it. Read everyones opinion and form your own and do what works for you = WIN.

JohnP2

Oh I have. Look to your left under my name. ;-) First time ever starting a nitro engine, my knuckle hit the rotary carb putting it at WOT. I did not even know how to stop the engine back then....it ended up stopping itself. ;-(

Anyway, thanks for the responses!

purenitro33

A hot running engine that has a constant supply of fresh lubrication on each stroke has a lot less stress then one just being started. My question is what exactly is accomplished by heat cycling? I'm not looking to argue but I just don't see what is accomplished by the heat cycle method short of extra wear on the starting components from trying to start a tight engine over and over as apposed to just letting it run as much as possible each time until the pinch has been mainly removed.

SLAYERDUDE

This explains it well, and Purenitro is on the money too, I run one of his ERCM Race mod engines and it was a pita to break in his way ( It took some arm twisting to not run super rich and get to 200F) but runs perfect.
Going on 3 gallons now.
Every engine I have broken in still runs good, including my 13 gallon K5.9 "POS", and the O.S. .12 CVR that's well over 10 years old.
All done with different methods...

Our engines are tapered pinch sealed rather than using rings like a dirtbike, weed eater etc.

In laymans terms, you want to get the engine up to operating temps before starting, or as soon as possible.
This expands the sleeve which relieves the tight pinch fit on the piston, and stress the rod and crank encounter trying to push the piston thru the pinch until the sleeve warms up and expands enough to loosen the fit.
Then keep it at that temp so the parts can wear in and mate together.

Not just idling thru tanks of fuel, but running the engine at different RPM's as it will in normal running conditions, but don't beat on it.

Ttowntoolman

I see your point, makes sense to the utmost degree. Instead of letting it cool keep it going until completion because the cool down actually does nothing.....I will try this next time I break in something.

HerrSavage

The cool down does do something.. Or else it wouldn't matter about setting the piston to BDC..

purenitro33

The cool down does nothing, the reason to put the piston at BDC is so when the sleeve contracts, the piston doesn't get stuck in the sleeve.

HerrSavage

You just said it "does something" - the sleeve contracts..

SLAYERDUDE

Lol it's to keep the fit from being distorted, not anything to do with a break in process.
You should put the piston to BDC EVERY time you are done running, including after break in...
Just a good practice to get into.

purenitro33

Right And what does that have to do with "heat cycling"? I think your making things way more complicated then they have to be, the operation of a two stroke engine is a very simple concept unless you make it more then it is.

nitroexpress

Playing the Devil's advocate.

If the piston is kept at TDC during cool down, how can anythingget distorted? Although thepiston and sleeve would tend totightly bindtogether,they would each form a perfectfit.

The_Shark

My way of thinking.

Remove plug, drop a few drops of fuel or after run oil in engine, turn it over a couple times (this will lube it up)prime the engine by blowing the fuel into the carb, idle a tank, choke out the enigne before it leans out from a empty tank (by blocking carb) fill it up immediatly and start it again.

when ever you shut down a engine for the day (or long enough that it cools) put the piston to BDC, this will prevent any deformity on the sleeve.

letting it cool down just makes the sleeve too tight on the piston, causing scouring before its started up again- or thats my grasp on it.

SLAYERDUDE

I wouldn't say "distorted", as in deformed and out of round, but it would keep the sleeve from retracting to it's original size when cooled, possibly loosening the pinch.
As well as having the piston "stuck in the pinch" the next time you try to start it.

HerrSavage