Forum bmwbike.com

I have come across 2 conflicting recommendations when it comes to putting the cylinders back in with a new set of Pistons and rings.

One expert says: "When reassembling, DO NOT OIL THE RINGS, just LIGHTLY oil the piston skirt and cylinder wall".

The other expert says: "Oil should ONLY BE APPLIED to the piston rings and cylinder walls. From past experience, this is the only method I will ever use. I departed from this procedure several times using dry and semi-dry techniques, as recommended by so-called experts, with costly results."

Anyone care to comment!

Pierre,

I've never heard of the two methods. On initial start up I'd rather have some lubrication there. Anyway what ever oil you put in the bore or on the new piston won't stay there for long. In my opinion it's most important to at least oil the bore so that the microscopic hatch scratches after honing are full of oil to give some lubrication. Though I believe the critical thing is to first turn the engine over without the plugs to make sure all the oil is getting to the right places, and then most critically varying the rev range when the engine has fired so that the rings bed into the cylinder walls correctly.

Ben

I heard someone say that each method has a purpose. For long life, apply oil to everything and break the motor in gradually. But if you are rebuilding a motor that must run in a race tomorrow, use the second harsher method, because you need immediate break-in more than long life.

Allen,
Both of these experts were not referring to racing. I am just wondering why one would only oil the skirt/cylinder and the other rings/cylinder.....I think I'll go with Ben's method and lightly oil everything. I also read that for break-in one could run the engine stationary for 30 minutes at fast idle.....I feel uncomfortable with that one! I wonder what the auto industry does to their cylinder/ring fit. I do not see new owners comming out of the dealer at 30 miles an hour and ever so often sprinting to 50 mph then down to 30 and over and over again for 100 miles!

Modern engines straight out of the factory don't need "running in" because they have already been run in at the factory prior to installation into the body. They are also engineered to more exacting tolerances. They also reach operating temperatures very quickly and therefore less wear in the first few miles.
Initial start and running in are actually two different things
The idea of running the engine at a fast idle for the first 20 minutes or so is to bed in the cam, assuming that you have changed or reground the followers and cam. It should be done with the aid of a molybdenum grease. Don't use the choke for long, as the over rich mixture tends to wash the oil of the cylinder walls which could spoil the break in of the new rings.
After the initial start the engine speed should be varied through the rev range. The short bursts of high revs pushes the rings out against the cylinder walls and aids in the bedding in. On the low revs it has time to cool. Also try to avoid "lugging" the engine, low revs in a high gear.
This is the technique I tried to apply to my cars, I'm not sure if the same applies to motorbikes. Motorbikes are a new animal for me.

Ben

Thanks for the primer Ben. Now I know what breakin proceedure I will be taking.

Regards,

Pierre

PS. What grade oil would you recommend for break-in period?