Tech Answer: Initial Break-In

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Tech Answer: Initial Break-In

Postby poopShotgun » Mon Apr 09, 2007 7:47 am

After I rebuilt my engine, I asked around and did a little bit of reading on breaking in a new kit. The instructions here have been cobbled together from several sources, including club members, and represent the procedure I used to break-in the new Rally engine. There are other ways to do this and everybody has their own methods, so you may want to do a little research of your own. That being said, this seems to be a good procedure and has worked well.

When should this be done?
New cylinder, after porting a cylinder, new rings, new piston, boring a cylinder (which requires a new piston). Installing a new kit will always require this procedure. If the kit is already broken in (by someone else), I would still suggest a minor break-in period of 120 miles or so because the piston rings may have shifted and will need to get used to their new positions. You can break up the steps below for 120 miles (0~60, 60~100, 100~120).

There are several things to note when breaking-in.
1. DO NOT add extra oil "for luck" or whatever. Stick to the manufacturer's suggested mixture.
1a. If you have a pre-mixer, DO NOT add additional oil to the tank. The pre-mixer is more accurate than you are and will add less or more oil as needed.
2. Use the recommended oil mixture (usually 2% on Vespas, could be as much as 5% on Lambrettas depending on model, check your manual) and non-snythetic oil when breaking-in a new kit. The reasons are a little fuzzy to me, but some have suggested that synthetic oils are too "slippery".
3. The point of the break-in is to temper the rings and smooth out the cylinder walls so that the rings make a near-perfect seal.

Here is the procedure I used for my bike:

Miles 000~300 (Km 000~500) ->
The crucial first steps. Take it easy, don't use more than 2/3 throttle except occasionally before stopping to idle. Town driving is good for this and varying speed will be natural. Do not leave throttle in the same position for more than thirty seconds. Try to get some load on the engine (go up hills, etc...). The idea is to temper the rings in a bath of oil, so you'll want to get them fairly hot.

Miles 300~500 (Km 500~835) ->
As the first 300 miles, but 3/4 throttle max. You may use full throttle occasionally, but never for more than a few seconds.

Miles 500~600 (Km 835~1000) ->
Take the engine up to full throttle often, but never leave it there. You may stop varying speed, but do not go above 3/4 throttle when driving evenly. Continue putting load on the bike and continue letting it cool down after long, even driving.

Miles 600+ (Km 1000+) ->
The bike is broken in. You can now switch to your favorite oil, whether it is synthetic or not. At this point, it is also a good idea to change your gearbox oil and inspect the engine for any leaks or loose nuts.

Working on the engine during break-in:
You can safely take off the cylinder head and also seperate the cylinder from the engine halves if need be, but I would suggest you do not take the cylinder off the engine (and subsequently off the piston) unless absolutely neccesary. The reasoniong here is that the rings should stay inside the cylinder until the break-in is complete. You can crack the case enough to do most minor engine work that requires the fly-side case half removed (replace shift-cross, work on transmission) without removing the cylinder.

Working on the engine after break-in:
You should be able to do everything you need to do, including removing the cylinder from the engine and piston.

Good luck and happy riding!
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