Joined Nov 2001
17K Posts | 774+
Ely, England
been doing a few engines recently and my 'crank man' and I have been looking at the troubles we have had.
the big end is nigh-on perfect but the bearings are worn, the little end is worn the gudgeon pins are worn and finally the inside of the rods are worn in a hump bridged way. my conclusion was that the rods are oscillating left to right under the piston and tilting onto one edge. this would account for the little ends only wobbling at the ends and not the middle and in the rods flopping left to right wearing a curved surface inside. the big ends aren't worn out in the normal sense of the word but if doing any kind of lateral test are very worn.
the difference is .001" (one thou) .025mm compared to the middle of the rod.
why does this happen?
I think it's because there is a kind of "kick" in the crank at either 3 or 9 o clock. this 'kick' tilts the crank momentarily and makes the rod make a left-righ action?
to hold the rod tighter under the piston axially would make it worse and force wear onto the bottom end.
what can be done? diagnose it first would be a good start! I bet Dale L would know about this already. we've had several like this over the years but without prercise crank pressing (tons) figures and notes made about which models I'm not sure what can be gleaned from it?
of the present crop of cranks I'm doing it is an FE501 that is the worst and not a 650.
regards
Taffy
the big end is nigh-on perfect but the bearings are worn, the little end is worn the gudgeon pins are worn and finally the inside of the rods are worn in a hump bridged way. my conclusion was that the rods are oscillating left to right under the piston and tilting onto one edge. this would account for the little ends only wobbling at the ends and not the middle and in the rods flopping left to right wearing a curved surface inside. the big ends aren't worn out in the normal sense of the word but if doing any kind of lateral test are very worn.
the difference is .001" (one thou) .025mm compared to the middle of the rod.
why does this happen?
I think it's because there is a kind of "kick" in the crank at either 3 or 9 o clock. this 'kick' tilts the crank momentarily and makes the rod make a left-righ action?
to hold the rod tighter under the piston axially would make it worse and force wear onto the bottom end.
what can be done? diagnose it first would be a good start! I bet Dale L would know about this already. we've had several like this over the years but without prercise crank pressing (tons) figures and notes made about which models I'm not sure what can be gleaned from it?
of the present crop of cranks I'm doing it is an FE501 that is the worst and not a 650.
regards
Taffy
