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Running-in a new Bullet:
"A properly run-in machine will have just enough clearance between mating surfaces to permit an unbroken oil-film under normal operating conditions"
After ages and ages of dreaming and lusting, you
have finally taken delivery of your new Bullet.
The manual warns you; the dealer warns you; your friends warn you:
Run it in correctly, they say, or else...
In face of this united chorus, you almost
wilt. But not quite! Bulleteers, as a rule, will not be stubborn, but they won't be pushed into anything willy-nilly, either!
Or else, what? you ask, innocently but firmly. The dealer looks incredulous. But you
won't back out! And he is forced to play his trump-card on the backfoot: The warranty noes not cover misuse. And no, he can't qualify "misuse". It is just about any thing you admit to having done when you
go to report a problem during warranty period.
Your friends don't know either! They were simply passing on what they had heard said, just to be helpful (?) to a friend.
Impasse?
Hardly! For a Bullet-eer it is just a beginning of a fascinating voyage of discovery.
What is this running-in; what is it for; how strict are the guidelines to be followed; indeed, what ARE the guidelines?!!
Really, in this day & age, "don't exeed 50Km/h for first 3000Km; change oil at 500" hardly classifies as a technical guideline! More of a "fatwa": Incomplete, illogical, and arbitrary.
This time we re-wind into History! The history of manufacturing-technology. To us techies swearing by CAD, CAM & CNC it comes as a jolt to realise that not soooo long ago, the mass-production of components
was only a small part of the story. To make a reliable machine, they had to be assembled by highly skilled craftsmen to get the required slackness/tightness of fit !! In short, the parts could not be economically
produced to required tolerances.
The success of several legendary marques of the motoring world is attributed to the skill of these artisans: Some manufacturers went to the extent of engraving the name of the
assembler on each engine, just like a painting or work of art!
Forward now, not to Bullets, but to Guns! Very recently, I came across an interesting article about a prosperous gunsmith firm specialising in
rebuilding NEW handguns for better precision and reliability. This they do by plating/lapping until all the clearances are exactly enough and no more. Their labour-charges were USD500 for a gun costing USD400. And
the gun was manufactured by a reputed company whose logo is a frisky horse.
Whatever the technology, the mechanism can always be improved by manual fitting. But the cost more than doubles with hardly a dozen
parts to be fitted!
Finally, we come back to familiar terrain: Who has not freed a seized door-hinge by liberal application of penetrating-oil and cycling open/shut with gradually increasing amplitude. If the
entire operation was attempted in a single try, something would have bent/broken!
Hmmmm. So here is an alternative! Neither you have to manufacture to space-shuttle tolerances nor you have to hand-fit the
parts. Just aim for interference-fit where running-fit was needed, and it will wear itself to a lovely running-fit if progressively run-in like the hinge!
So that was the run-up to running-in.
Which you have done by "the book":
3000Kms never exceeding 50Kmph, Oil-change on the dot at authorised-dealer's, and all.
Feeling smug?
OK, ride out to the nearest National Highway one sunday
morning (no traffic) and open 'er up! Ten minutes at 120Kmph, and it is even-money that you have a seized engine and misc damage in forks & gearbox.
Oh, really ?!!! But how ?
And why didn't anyone ever mention it ?
Well, I just did, and the reason is not difficult to understand!
First we consider the engine construction:
Piston - Al Alloy; Rings - White Iron;
Cylinder - Grey Iron; Gudgeon,CrankPins - Steel; ConnectingRod - Al Alloy; FloatingBush ....OK, OK, the point is that there are many different materials, which have different co-efficients of thermal expansion. It
stands to reason that the clearance between the components will change as temperature changes. The plot FURTHER thickens, if you believe me (Please do; I am pretty good at Metallurgy) when I say that these materials
are non-homogenous! I'm serious!! For example, Grey Cast Iron is particles of graphite embedded in iron. The size & distribution of the graphite is influenced by so many factors, you really don't want me to list
them here! You'll just take my word for it when I say that in case of a mass production piece, nobody can predict it's EXACT dimension at a given temperature. Nobody but an insurance salesman :-)
Now consider engine temperature:
It depends mainly on the balance between (a) the heat from the burnt fuel, from friction and (b) the heat removed by the exaust gases, by air, by oil. Rises with rising engine RPM.
Back to running-in.
You have run-in your bike at 50Kmph. Which means, at the corresponding temperature T(50), the clearances are ideal. The next step is to make them likewise at T(60) where
T(60) = T(50) + DeltaT
and NOT at T(120) where
T(120) = T(50) + n DeltaT where n>>1 , right ? :-)
Don't like "mathematical" formulae ? , eh ? :-)
OK, try this:
Recall (or
visit) a machine shop. Observe how the machinist removes material from the workpiece to bring it down to the required dimension. He traverses the length repeatedly, advancing the tool SLIGHTLY each time, removing a
LITTLE material each time, obtaining a pretty decent finish too. Try removing the whole lot in one pass, and you'll neither get accuracy nor a good finish! If you were very lucky. If not,
screeeeeeeEEEE-KRAK-crrrruNCHH. Overheat, smoke, toolbreakage, system-seizure.
See any connection ? :-)
In other words, even if you have already "run-in" the engine at 50Kmph, you should
progressively expose it to higher speeds and gradually form the clearances for best finish and fit. If you directly go to 120Kmph, the clearances might suddenly close-up, scrubbing off the oil-film and creating a
rough unstable finish. If you are unluckier, crrrrrruNCHHH!
Now, should you take your chances on that, or should you take Nandan's advise ?
Point One:
Even if your bike has been used for
YEARS in the city, say at 70Kmph max, DON'T try holding 120Kmph steady on the first interstate trip! Run-in the engine to 120Kmph first.
Point Two:
A suggested running-in method. Don't exceed
50Kmph for the first 1000Km. (OK, 3000 if you feel better that way) Then with engine warmed at 50Kmph, go to 60 and hold it for not more than half a minute. Do not repeat for at least 10 minutes (You can guess why,
right ?) Repeat this process atleast 5 times before proceeding to next step, which is the same but holding time is one minute. Then repeat for 2min, 5min, 10min. This may have taken several days or weeks! Repeat
this for 75, 95 and then 120 Kmph. NOW you can say your bike is run-in.
Point Three:
OK, you didn't take Nandan seriously, and chased a car on the NH without looking at speedo nor watch. Your
engine suddenly goes uh-uh-uh-uh-uh and you grab the clutch and coast to a standstill praying it is a case of fuel-starvation, nothing worse. But the kickstarter is like the footrest! Immovable. And the oil-filler
is smoking like a chimney. Curses! Why didn't anybody warn you! Worse, what next! Relax. If it is any consolation, you are not the first person to have this happen to. Nor the last. Not until Nandan writes the
Bullet-manual !!! Relax, because if you have grabbed the clutch in time, the engine will free itself in about 5 to 15 minutes, and the oil would have stopped smoking. First, open the sump-plug (front, not the rear
one, that is the oil-tank plug), and let the oil drain. Gently kick the engine over, with decompressor pulled, listening for any unhealthy noises, feeling for resistances. To be on the safe side wait half an hour,
which you can utilise getting some engine oil if possible. Now start the engine without putting back the plug. Yes, I know that the scavenge-pump and rockers are running "dry", but that is the lesser of
the evils. Oil will start dripping from the sump-plug hole. (Collect it and examine for metal-particles...Always nice to analyse the stable after the horse has run away ! ) Now & then, rev the engine for better
oil-distribution and cleanup. After about five minutes, or after you feel about 250 ml of oil has been lost -in case you could not get more oil- screw in the sump plug and proceed to your destination. Change oil as
soon as possible. Hear a rat-tat-tat-tat from the engine nowadays ? That is because the piston has been "grated" on the dry cylinder wall till it has lost some diameter, and rock/play against the cyl wall
is now possible. Don't worry. It is not an emergency situation, it can be ridden safely for months (Ask me how I know!) before changing the piston.
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