Here we go, something else i also have saved =P
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Here's the item I wrote ages ago.
Nobody else seems to agree with it but...... it served me well over the years! It worked when engines were VASTLY more sensitive than they are now so I doubt VERY much that there is much WRONG with it even if it WERE over-cautious. It'll also explain the bit you have ALL missed..... and that's WHY we run an engine in and what EXACTLY it is supposed to be DOING to our engines!
Running in a standard 100cc or 115cc type engine
All the figure and times are for 2 stroke 100cc or 115cc type engine with cast iron bores and alloy pistons; i.e., the standard TKM type, or Rotary Valve type motor. The world is different for “Nicasil” type bores!
Running in depends on what you've had done.
Just a Hone and Ring is about 20 mins
Piston, ring and rebore about 30 mins
Full bottom end (plus anything else) 45 to 60 mins.
However, I have heard some 'quick boys' (or those who THINK they are quick) just giving about 5 to 10 laps for new rings and honing.
Now, the question seems to be, How Long? However, it SHOULD be WHY do we run-in and then HOW do we run-in?
Your engine is made of parts that differ in hardness. Some are very soft and will 'rub down' (run-in) very quickly, some bits are EXTREMELY hard and will take AGES to rub-down. Luckily, the hardest parts are made to the most accurate tolerances or you'd NEVER get them to run-in!
The process of running-in is that of making sure that two (or more) components that rub together have had a chance to 'rub-off' their raised surfaces and edges. Taking the piston and rings as an example, the bore and the piston SEEM perfectly round and smooth BUT THEY ARE NOT! There will be rough surfaces on both and there will be raised areas on both. If these rub together too hard, they will overheat and weld themselves together. The harder they rub, the hotter they get and the LARGER the 'bump' that gets raised by the heat, which makes it rub harder, get hotter, get larger, harder............ etc..
Running-in is making those areas smooth each other OUT! However, the twist is that as your piston and bore get warm, they DEFORM in shape and thus 'high spots' that were not there originally, start to appear when the engine gets warm/hot. Part of the process of running is making sure all those 'heat raised' high spots are ALSO run in!
So, to run in, you need to make the engine work and you need to get it hot enough to raise the high spots and run those in as well!
To start with, running the engine slowly will rub-off all the 'cool' high or rough spots. BUT, once those are run in, you need to start raising the others that only appear when they are warm or HOT!
So, start by doing the first few laps just giving short, 1 to 2 second FULL POWER bursts, followed by coasting until you are going slowly again. That's full power for 2 secs, coast for 5 seconds, full power for 2, coast for 5, and so on.
That will take off the basic (i.e. cold high spots). As the running in process progresses, make the bursts last LONGER, e.g. 2 to 3 seconds, then 3 to 4 seconds and so on. You'll notice that the coasting period ALSO extends and this is GOOD! The Burst of FULL power (throttle) will put enough heat into the engine to raise the 'warm high spots' and the coasting is the period when they are being rubbed down! To get the warm high spots to rise, you MUST give full throttle, anything less will NOT RAISE them and if you don't raises them during running-in, they will raise in your first race and that will simply cause a seizure!
As the running in procedure continues, increase the period of FULL power, 5 to 6 seconds, 8 to 10 seconds. After a while, you'll start using the pattern of the track to control the BURSTS, e.g., full power out of corner X for 10 seconds etc..
By now you are probably annoyed at me not stating the period of time that you do for each of the 1-2 second or 5 to 6 second bursts. How long do you do the 5 to 6 second bit? Well, you need to think about this 'hardness' lark. If you've just done a hone and rings, the rings are hard enough and slippery enough to need VERY little running in period. However, new main bearings are INCREDIBLY hard and they need MUCH longer to go though all the stages. So, the amount of time in each of the stages (e.g. 2 to 3 second bursts) is dependent on what you are running in! If it's new mains, little end, big end etc. you stretch the period of each of the 'burst' stages to give you the time required to arrive at FULL power (used as you would use in a race) at about the required time at the end of a 45 to 60 minutes running in session! You need to do ALL the stages (in my opinion) for ALL types of running-in, you just make the stages last longer for the types that need more running-in!
Remember, the final stage should be a FULL power lap followed by a choking and a slower lap, then 2 laps at race speed and a choking and slow lap.
Lastly, you don't need to go round for the full 60 mins without a break! Just record the time for your sessions and add them up. Just remember that the engine will require a little extra time to get to working temp if you have had a break for a cup of tea. Take that first lap after a break slowly after the engine has cooled and don't count that lap in your total time!
Also remember, this is JUST my opinion and others will disagree, I am SURE! However, I cannot remember the last seize I/we suffered other than 'old age' failures (e.g., rings breaking at the end of their life, etc..). My memory still goes back over 40 years of karting!
Finally, it seems 'fashionable' to run 'looser' components than we used to run. This WILL reduce the need for LONG run-in times. Even if you do NOT choose to use the times that I choose, I'd STILL recommend the PRINCIPLE! Raised areas still DO exist and the piston (for example) STILL distorts during the heating cycles!
Ian
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100cc Running in by '100ccnational' (19 Nov 2009 @ 21:23)
