View Full Version : Running in of cylinder?

06-09-2004, 03:52 PM
Hi, I have been reading some posts about "running in" cylinders, and since I have just bought a new one, thought I gain some knowledge. I have once read that running in the cylinder is very important and can determine the speed, reliablity, and life of the engine in the long run. So how exactly should you correctly run it in. I have heard all different speeds from people to keep at and how long for. The other day I was told that 30mph for 200km should be fine, but also 25mph for 150km, so how should I do it?

06-09-2004, 06:55 PM
Well Actually there are many opinions on this subject...

Why Run The Engine In?
First, you have to understand why you should run the engine in... The entire purpose of it is to seat the rings... When a new cylinder, piston and rings are assembled for the first time, the rings are rather coarse, and the cylinder walls are ground rough with a cross sectional pattern. Seating the rings involves "wearing" the rings and cylinder walls... After the running in is completed, the cylinder walls and rings are polished by one another making a tighter seal... If too much strain or rpms is put on the motor before properly running in, you can get "Blow by", which means hot gases from your combustion leaks past the rings. This causes scorching of the cylinder walls, and makes for an ever worse seal... Then things get worse and worse.

Different opinions on ways to run in!
1. WHAT THE BOOK SAYS -- Never go above 3/4 throttle until you have about 300km on the motor.... This is a general run-in procedure. Basically they are saying that if you have 300km on the scoot, the motor has run long enough that the rings should be properly seated.
2. Run the motor for about a half an hour until the motor gets really hot. Let the motor cool entirely, then repeat 4 more times. The heating of the motor expands the piston and rings. Letting it cool and repeating this is supposed to seat the rings into the cylinder quickly.
3. Go on a long trip only using about half throttle... Run the motor for about 2 hours straight, never giving it a chance to cool. This way the piston expands and rubs hard on the cylinder and seats the rings in one easy fast shot.

Diferent Opinions on the entire subject!
Now after having said all of that, this is pure speculation. Many people and mechanics say this is a bunch of bunk! I know many people who feel it is absolutely imperative to run a motor in... While others say and feel the best way to seat the rings is to run the hell out of it as soon as it is put together.... This way if there is a problem, you will find out right away.

One thing I have heard many times is: Have you ever heard a mechanic tell someone that the reason why there motor broke down is because of improper running in?

My opinion!
Myself, I feel it good to run in a bit before getting on the throttle too much. I feel that 300km is a bit much. And the more time on the motor you have, the more you can get on the throttle... But avoid full thottle over long periods of time before several hours are on the motor.

Other things to do!
I recommend using a stone to break the sharp edges on all of your ports... The sharp edges of the ports can wear the rings fast, and slows seating of the rings. If you run your finger down the cylinder wall over the ports, you will feel the sharp edges. Run a stone over the sharp edges and make them smooth.

Also before you put it on, use a dremmel tool to grind the ports.... Make sure not to change the size of the port, and make sure not to gring in the cylinder. Just clean up the ports and make them shiny. The castings are usually quite poor and very rough. Simply clean up the rough spots and make them smooth

06-10-2004, 06:46 AM
Thanks very very much for that, great imformation. Ill follow most of it, but I dont know about gringing the ports with a stone, I think Ill leave that. Anyway cheers. Just wondered did you follow any of them procedures when you run your 70cc kit in scootnfast?

06-10-2004, 12:20 PM
Don't run it in and it will quickly start to go very quickly, but it won't last. Run it in gently and it will take longer to go quick but it will last much much longer. Similarly if you go flat out from turning the motor or allow it to warm up before giving full throttle.

06-10-2004, 02:32 PM
Sorry but I cant understand your post ditechspain, what do you mean? Do you mean that if you run it in properly at low speeds, the engine will last longer, but the scooter wont go as fast as it would if you dont run it in properly?

06-11-2004, 09:56 AM
If you run it in gently, it takes longer for the engine to really free off, but it will then last a long time in my experience. if you go flat out straight from the dealer, you free the piston rings in particular off very quickly but they won't last as long and the eventual rebuild will be sooner. Similarly I wouldn't expect the bearings to last as long.

06-11-2004, 12:53 PM
Oh okay, so it is best to run it.