AO Platinum Member
Join Date: Feb 2002
Location: The land that Time forgot
Re: castrol oils : magnatec, GTX, GTX magnatec?
Any parts vary in actual size, even if they are nominally "the same size", because of manufacturing and machining tolerances.
Consequently, when they are manufactured they are graded into what "sub-size" they fall in to.
For example, you have a particular sized piston. The piston is supposed to be, say 63mm wide but in actual fact could be anywhere between 62.98 and 63.01mm.
The actual size varies because of manufacturing tolerances.. for example a cutting tool can be at the end of it's life or the machining may take place on a particularly cold or hot day when the metal was marginally a different size. Anyway, variance happens.
The parts are typically grouped into 4 sizes and ideally these are "matched" to the corresponding size bore. Bore is obviously bigger than the piston (0.1mm bigger??) but again it varies. There will be "63.1mm" bores that range from 63.08 to 63.11 etc.
This makes it sound simple - fit a 63.00 piston in a 63.10 bore.. etc. but obviously the parts won't all be a precise size measured to 2 decimal places. You could end up with a 63.099mm bore (classed as a "63.1") which is fitted with a "63.0" piston that is actually 62.950mm. So the difference is 0.104mm.
Next engine along might have a 63.095mm bore (still classed as a "63.1") and is fitted with a "63.0" piston which actually mearures 63.044. So the difference is half the previous one at 0.051mm.
The second engine is obviously tighter than the first one, though each is within manufacturing tolerances. The notion of a "Monday" or "Friday" engine is old tosh.
When someone "blue-prints" an engine what they do is rebuild the engine with closer toerances re. these sizes. If you have that 63.099mmmm bore, they'll get rid of your "loose" pistons and fit "63.0"s that measure 63.048 (clearance of 0.051mm).
Don't quote me on the sizes of pistons and the tolerances I've used.. they're just to show the example.. but that's why some engines are relatively looser than others (and why they may burn more oil).
I didn't even mention the roundness of the bore.. I think though the Japanese generally tend to make engines that are more consistent regarding "precision" (more parts are closer in size).. maybe why they're famously more robust.
Then there's running in.. although a "tight" engine abused will probably then become more "worn" than a "loose" one that is abused..
I dunno. You can also under-do the running in and get glazing. There's a heap of variables.. but the best thing is to get (by good luck or blue-printing) a "good" engine in the first place.
No bullets for Chaingun..
Last edited by Ralf S.; 26-09-07 at 07:53.