Looking for alternative ROTAX 912 piston pins for a homebuilt aircraft. Mine were heavily scratched.
The reason – very likely – is because of poor design and bad oil quality. Newer Rotax engine conrod have oil-hole, old ones(left)- do not.
Polishing – did not help, after few hours they got scratched again. I must note, that I have not properly honed crankshaft itself.
The (unfortunate) result is below.
The engine is from year 1989.
Piston pin lenght – 56 mm. It is slightly longer, than new rotax pins, which are 55.3mm. Image below – side-by-side comparison (brand new rotax pin – on the right).
Internal diameter – has been changed as well: new ones (on the left – with the yellow spot image below) is considerable “beefier”.
As the engine is extremely old, has been a subject of many modifications (injection system, different pistons, etc) – I decided to use it as a test bed. Instead of buying OEM parts (150 EUR/each) – decided to look for alternatives.
Closest ones found are from:
- PROX PISTON PIN 20 X 55.5 X 13.0 MM
- WISECO S553 Superfinished Wrist Pin/ Piston Pin 20×55.5mm for XT500/TT500
- JE Pistons
- Namura
- Vertex
As rotax allows generous 0.07 m pin clearance – looks like anything similar would do just fine.
After some wait, I was able to obtain WISECO S553 piston pin.
Left-to-right: old Rotax, New rotax, WISECO:
Side view:
NEW Rotax, WISECO, old Rotax. Both of them have 13mm hole.
Ater honing with the tool ( KS Tools 150.1180 Cylinder hone 2-arm, Ø18-63 )
The end view is below. It is not perfect, but very smooth and does not feel scrached. It is well within tolerances, the piston pin slowly “float” nicely inside.
I will change the oil after ~25 hours to see, how is it doing.
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