After reassembly, the manual shows you the "T" mark on the flywheel through the inspection hole. Set intake valve lash to 0.05mm – 0.08mm and exhaust to 0.08mm – 0.10mm. (Hot vs. cold specs vary; cold is safer for amateurs).
Extracted from the official 253FMM service manual v2.3
| Specification | Value | | --- | --- | | Engine Type | Single Cylinder, 4-Stroke, OHV | | Bore x Stroke | 72mm x 72mm | | Displacement | 249.6cc | | Compression Ratio | 9.0:1 (Standard) | | Spark Plug | NGK D8EA or Denso X24ES-U (Gap: 0.6-0.7mm) | | Idle Speed | 1400 RPM +/- 100 | | Oil Capacity | 1.3 Liters (with filter change) | | Valve Clearance (Cold) | IN: 0.06mm, EX: 0.08mm | | Primary Drive Ratio | 4.055 (73/18) |
Yes, the timing chain and valve clearances are similar, but the 253FMM has unique quirks:
Manual Solution: Turn to "Crankcase Breather System." The 253FMM has a one-way reed valve in the valve cover. The manual shows a simple test: Remove the valve, blow through it. Air should only flow out. If air flows both ways, replace it ($5 part).
