SOHC.co.uk Forums > The Black Bomber Board
The Dutch 450
K2-K6:
Yes Ash, there's some things on which decisions are made that have such a fundamental impact but look, in the primary consideration phase, to be insignificantly small.
If we open up discussions about it then the route through what really happens should be more clear for others looking in.
As Jensen points out with his posts and tests, sometimes it's going to define that which you don't want to do. It's always going to deliver something of value.
Nigel.
K2-K6:
One of the core reasons for how the engine was to be run in was given as the original fill of oil had to remain in the engine to complete that process.
The projection was that the oil contains small abrasive particals that come from internal wear, which continue to refine the moving components if left in place.
My view is that process is completely wrong, I don't see what basis it has as it also leads to a curious decision regarding honing.
It's worth going through why the the bores are honed to see what should be happening.
When a bore is finished from initial machining it won't necessarily have either a degree of topographical accuracy or surface finish in place to be suitable for an engine.
Primary function of honing with rigid stones is to allow the stones to lay flat on the original bore and by their movement path they will correct any imperfections to bring surface variance to within required tolerance.
Secondary function is to leave that characteristic crosshatch pattern that will, long term, retain some oil during use of the engine to help lubrication.
Thirdly, and this is the most short lived property, it should be left by method and grit size, with the burrs resulting from essentially gouging the metal's surface, in place.
It's this "fault " that is going to cut / lap the new piston rings.
Going to the piston rings, when made ( we'll talk about rings from this era as things are different for much later engines) and as they are fitted to pistons, they, when placed in the bore, are not as round as the new bore. This means they won't seal as required.
Running in is how they are made to fit. Using those burrs left over from honing, the piston rings are, in engineering terms, lapped to fit their own cylinder.
It happens specifically by the burrs breaching the lubricating oil and cutting the ring material. If you hand grind a wood chisel on on a flat oil stone, this is exactly the same process. The oil acts as a soap to allow the abrasion to work, also to remove debris from the lap site.
The practical limitation of this comes as the burrs ultimately break down and dissappear from the bore surface. This would probably be finished by about 300 miles of engine life with normal production materials.
It's this process that defines the running in period of these types of engine. It's probably certain that it's mostly over by the time you get 500 miles and prompts the first oil change to remove any of the byproducts of this event.
What happened here was that based on that first theory of bedding the engine in, it becomes clear right at the end of the thread that he chose to plateu hone for the bores from the outset.
What this means is a much further refinement of the honed surface to closely approximate a perfectly, post running in bore surface that is used in current engine production methods.
It might sound like the best quality that can be achieved but needs to be paired with piston rings prepared for that eventuality.
This though gives a problem with the rings that need the old type hone to be properly brought into service. What the current engines do is to pre-lap the piston rings, and so avoid the initial running in procedure.
It's suggested that it's because the oil is of such film strength that the rings take a long time to seal, when in reality the original hone method is designed to breach any oil film.
It's a fleeting transaction and a fine balance but that is how it takes place.
It's not a surprise that it took 7000miles before he thought the rings were sealing.
UK Pete:
Nicely written Nigel
K2-K6:
Just to expand that theory about abrasive content of oil running within an engine.
In the tested example, every effort is made to filter the oil far in excess of normal running by passing it through external filtration along with replacing the engine's own filter at fairly short interval. You'd have to consider that this would directly oppose the particals theory.
But much more basic than that, the piston rings are the only part you really need to wear any appreciable material from to make them seal as effectively as possible. Oil with abrasive would not be selective in this way and it's correct to make every effort to reduce any real chance of it happening.
A general abrasive in the oil longer term would be highly detrimental to all other bearing tolerances throughout the engine.
Conventional running in period is constructed to take advantage of that hone / lapping effect, distributing the removed material into the oil and filter, then discarding both when the bulk of any change has been reasonably allowed to complete. It's one of the most significant sectors in the engine's life, completed properly it'll be run in a much cleaner status from then onwards.
jensen:
Hi,
Found this post after ashimotok0 pointed out. I thought I was registered to this forum, but it was the other one, the SOHC/4 site. I was active there under the name supersports400. Written one large thread about my CB400F, http://forums.sohc4.net/index.php?topic=65233.0.
Intresting views and comments on my thread here, I will certainly respond when I have a little more time on my hands.
Jensen
btw, this is my SOHC4:
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