So there is an article here http://www.bdkraceeng.co.uk/Bike1.html#Ignition that states: "If you measure csa(cross sectional area) of oil loss at rod ie:area of pin minus area of rod inc shells, times 2 for both sides . Plus oil loss for outer main brg(since these are fed together). This is the total area for oil loss assuming the crank is not moving(no centrifugal pull). A rule of thumb is that the supply csa is at least a third larger than the loss csa. This also assumes no 90 degree bends etc. If you look at the oil feed in the btm case it has an arduous path to the outer main and consequently the big end. The oil rises in a 5mm drilling (where the restrictor jets are) and then horizontally in a 6mm hole and then up again at 6mm to the outer big end. The 5mm drilling has to be because they wanted to put a M6 thread in it for the jet. Anyway, take the 5mm hole out to 6mm and then use a thread repair, Time sert or Helicoil, to restore the thread for the oil jet. The reason the main is OK is because it always has sufficient oil and little centrifugal force, however the big end throws the oil away at a considerable rate .Remove more than you are putting in and bang! I have seen hundreds of FZR's with outer b.ends gone. All modified as above sorted them out without fail. " Here are my corrections to this based on my FZR400RR 3TJ1. If you own an FZR250 then it might be worth checking yours too. The feed to the outer mains is not 6mm. The final hole is 6mm but there is a reamed section below that (shown in red on image) that is 5mm. First the text: The oil rises in a 5mm drilling for main bearings 2 & 5, where the restrictor jets are (2.55mm diameter), and it also branches horizontally in a 6mm hole and then up again at 5mm to the outer main and big end. The 5mm drilling has to be because they wanted to put an M6 thread in it for the restrictor. Anyway, take the 5mm hole out to 6mm all the way to the bottom and then use a thread repair, Timesert or Helicoil, to restore the thread for the restrictor. The 5mm gallery (shown by blue arrows) is not large enough to feed both the 5mm main & big-end, and the 2.55mm restrictor. Mains 2 & 5 have to have restrictors because they are mains only and do not feed big ends. Here is a 5mm drill bit inserted in outer main. It is a very snug fit. Mains 3 & 4, which also feed big-ends are also 5mm or slightly under. I will do this mod when I get some heli-coils. Of course you cannot just enlarge the lower part of that gallery, you have to run a 6mm drill all the way down. Fizzer owners you need to check yours and report to the forum so that owners will know which engines, if any, are affected.
An interesting theory. Personally I've never seen an FZR400 crank with the outer big ends gone - it's always the inners in my experience. When they're looked at closely I've usually found that bad finishing of the oil holes at the crank surface was responsible. Sharp edges are not good... Doing what is suggested couldn't hurt - but if you've got it that far apart, look at the oil holes on the crank too....
Yes, it would be worth checking and that is why I posted it here on the forum. I think BDK have enough of a reputation that we can consider it valid and the maths doesn't lie. The first clue would to be to look if the oil supply galleries look similar and does it have the screw in restrictors like the 400.
I have read elsewhere that this correction is also applicable to any 250's that are going anywhere near a racetrack
Looking at the 3 sets of 250 cases I have here, no mods needed. The transverse passage which feeds the mains via risers is in fact tapered from both ends. The outer ends are around 12mm ID and it tapers to around 8mm ID in the center. Vast spare capacity on the ends....And it's full width - unlike the 400's The choke point is actually the fore and aft passage which brings oil to the center of the transverse one - it's around 7.5mm. To enlarge this would involve retapping the oil union on the front of the cases as it's already the same size as the passage. Given the generous size of these passages already - and the smaller dia of both mains and big ends - I'd doubt if any enlargement is required. Bear in mind I've been enlarging oil passageways in British twins for many years....
I've only ever heard/read of 3LN1's doing an outer big end while racing I recall seeing oil feed stuff & diagrams in the service manual for the 3LN, but as everyone knows it's all in technical Japanese.
I can't find the oil diagram for the 250 but a full width feed pipe as @gregt stated (thanks for that) means no worries for the 250's.
i use the google translate app on my phone for translating the scanned japanese manuals, its dead easy just take a picture of the page and away it goes.
I measured the 2KR cases I have apart at the moment and the outers are 6mm, the centre two are 5mm and the inners have restrictors in them. The two centre bearing lowers were the most worn too.
@Murdo my outers are about 6mm at the opening but 5mm further down as you can see in the diagram. Are yours like that also?
After a second look this morning your right, they are tapered to 5mm about 30mm down. They all go straight into the big gallery that runs across the bottom of the case.
