Genuine Tohatsu 0.5mm Oversize Piston 309-00004-0 2.5/3.5HP
309-00004-0
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Tohatsu 0.5mm O/S Piston
Genuine 309-00004-0 | For a correctly machined bore
Genuine Tohatsu 0.5mm oversize piston for rebuilding specified 2.5HP and 3.5HP two-stroke powerheads after the cylinder has been professionally bored and honed to the matching oversize specification.
Key Features
- ✔ Genuine Tohatsu OEM piston
- ✔ 0.5mm oversize service specification
- ✔ For professionally machined cylinders
- ✔ Exact part number 309-00004-0
- ✔ Matches the 302-00014-0 oversize ring family
Technical Specs
| Part type | Piston |
| Size | 0.5mm oversize / O/S |
| Engine cycle | 2-stroke |
| Power family | 2.5HP / 3.5HP |
| Manufacturer number | 309-00004-0 |
| 4Boats SKU | 309-00004-0 |
Compatibility / Fitment Guide
Verified base engine family: Tohatsu M2.5A2, M3.5A2 and M3.5B2 and Nissan Marine NS2.5A2, NS3.5A2 and NS3.5B2 two-stroke outboards, only where the serial-specific piston/crankshaft diagram lists the exact part number in this listing.
Machining requirement: the cylinder must be measured and bored/honed for the 0.5mm oversize piston to the exact Tohatsu piston-to-wall clearance. Use matching 0.5mm oversize rings.
Identification rule: read the model and serial plate, then check the correct internal-engine diagram. Similar-looking 309, 3F0, 302, 361 and other numbered parts are not interchangeable by appearance.
Exclusions: not for an unmachined standard bore; not for 361-00004-0 applications; not for M9.9/M15/M18; and not for MFS four-strokes.
Part Number Cross Reference
| Tohatsu | 309-00004-0 / 309000040M |
| Matching oversize ring | 302-00014-0 / 302000140M |
| Standard piston (not equivalent) | 309-00001-1 |
| 4Boats SKU | 309-00004-0 |
Do not confuse 309-00004-0 with 361-00004-0, which belongs to a different engine family.
Frequently Asked Questions
Can it be fitted to a standard cylinder?
No. It is 0.5mm oversize and requires a correctly machined cylinder.
Which rings are required?
Use the matching 0.5mm oversize ring reference 302-00014-0 after confirming the engine catalogue.
Is this the piston for M9.9/M15/M18?
No. Those engines use different numbered piston families.
Are pin and clips included?
Only the piston is assumed included unless the photographs explicitly show additional components.
Note: A machine shop or qualified marine technician must establish final bore size, clearance, ring gap and piston orientation.
For the products under £150 the shipping is £6.99.
Free delivery for most items over £150.
