Warped manifolds and exhaust oil leaks.
in 2 Stroke Technical Questions
11 years ago
I have been involved over the years with two stroke Rotax engines and in a former life as a level two (Aus) maintenance holder and as such have noticed a common problem with 582 503 and 447s, it is the black oil leaks comming from the exhaust manifold flange which are all slightly warped or mis aligned, and as a result every engine I do a service on I draw file both the exhaust manifold flanges and in the case of single carby engines the inlet manifold then finish them off on a glass plate with fine paper to get rid of file scratches and confirms a flat finish, this always cures the oil dribble from the exhaust.
Receantly I noticed that one cylinder on my 447 was running hotter than the other both EGT and CHT were higher just outside the acceptable imbalance range and this was on a new engine straight from the box, by raising the needle one notch it lowered the temps but not the imbalance, checked everything and found the inlet manifold had a warp in it the flange surfaces were not true.
Remember the factory tells you to align the cylinders/jugs with a straight edge bar when reassembling or torqing the heads so the port surfaces are straight and true but fit a warped manifold and you have leakage problems.
As mentioned I always file true the exhaust and inlet manifold flanges then use the manifold bolted up to the cylinders without gaskets and lightly torqued up (about 10nm), then I torque down the heads, even if there is the slightest misalignment the cylinders and manifolds will always be true to each other.
Just a note with a single carby 447 503 use the inlet manifold as a straight edge.
So folks don't assume a new engine is without faults.L
Finally this is my opinion and procedure take it on face value.
Receantly I noticed that one cylinder on my 447 was running hotter than the other both EGT and CHT were higher just outside the acceptable imbalance range and this was on a new engine straight from the box, by raising the needle one notch it lowered the temps but not the imbalance, checked everything and found the inlet manifold had a warp in it the flange surfaces were not true.
Remember the factory tells you to align the cylinders/jugs with a straight edge bar when reassembling or torqing the heads so the port surfaces are straight and true but fit a warped manifold and you have leakage problems.
As mentioned I always file true the exhaust and inlet manifold flanges then use the manifold bolted up to the cylinders without gaskets and lightly torqued up (about 10nm), then I torque down the heads, even if there is the slightest misalignment the cylinders and manifolds will always be true to each other.
Just a note with a single carby 447 503 use the inlet manifold as a straight edge.
So folks don't assume a new engine is without faults.L
Finally this is my opinion and procedure take it on face value.
