"Pulsar" Oversize Piston Kit | Honda CB350 / CL350 / SL350
If your CB350's cylinders are worn beyond service limit, they need to be bored oversize — and that means oversize pistons. Original Honda oversize pistons are obsolete, and the aftermarket alternatives are hit-or-miss on quality. We designed the "Pulsar" series to solve that: cast aluminum pistons with modern coatings and rings, built to match the original Keihin-era engineering with improvements Honda didn't have in the 1960s.
Why You Need This
After decades of service, your Honda CB350 / CL350 / SL350 cylinders will inevitably wear. When you pull the engine apart and measure the bores, you'll know whether a hone and re-ring will do — or if the cylinders need to be bored oversize. If they're over the Honda factory service limit of 64.10 mm (2.5236 in.), boring is the only option.
Before the Pulsar series, your choices were limited: hunt for obsolete NOS Honda oversize pistons (and matching rings, pins, and clips — all sourced separately), pay a premium for racing-grade forged pistons, or gamble on no-name imports with incorrect tolerances. We tested those imports ourselves — wrong weights, bad machining, components that didn't fit. The Pulsars are the complete kit done right.
Features
- Pressure cast aluminum, CNC finish machined for accurate skirt dimensions
- MoS2 (molybdenum disulfide) anti-friction coating on piston skirts — reduces scuffing and wear
- High-temperature hard anodization on piston crown and top ring groove — improves thermal transfer (critical in air-cooled engines) and prevents micro-welding of the top ring
- Gas nitrided forged steel top ring — hard coating on all surfaces for wear resistance and low friction
- Steel phosphate coated 2nd ring
- Modern 3-piece oil ring — far easier to install than the original cast iron one-piece oil rings, with better oil control
- New wrist pins (gudgeon pins) — correct length, weight, and machining. Reverse compatible with factory Honda pistons
- Proper "C" style retaining clips for correct fit
Specifications
| Spec | Detail |
|---|
| Replaces OEM Part Numbers | 13103-312-010, 13103-287-010, 13103-312-000, 13105-312-010, 13105-287-010, 13105-312-000 |
| Fits Models | CB350 K0–K5 (1968–1973), CB350G (1973), CL350 K0–K5 (1968–1973), SL350 K0–K2 (1969–1972) |
| Standard Bore | 64.00 mm (2.5197 in.) — Honda factory spec |
| Factory Service Limit | 64.10 mm (2.5236 in.) — bore oversize if exceeded |
| Available Oversize Options | 0.5 mm over (#4302), 1.0 mm over (#4303) |
| Recommended Piston-to-Wall Clearance | 0.0015" to 0.002" (0.038–0.051 mm) |
| Kit Contents | 2 pistons, 2 ring sets, 2 wrist pins, 4 retaining clips |
| Sold As | Complete kit — two pistons rebuild one engine |
Note: The 0.5 mm and 1.0 mm oversize options work with the stock factory head gasket — no custom gasket needed. Honda also made 0.25 mm and 0.75 mm oversize pistons originally, but in practice most worn cylinders need at least 0.5 mm of material removed to clean up.
Does NOT fit: Honda CB350F (four-cylinder — different engine entirely), CB360, or any other model. The CB350 twin uses a unique bore size not shared with other Honda twins.
Installation
Difficulty: Advanced — requires engine machine shop for cylinder boring
- Measure your cylinders — Use a dial bore gauge to check bore, taper, and out-of-round at top, middle, and bottom in both axes. If any measurement exceeds 64.10 mm, the cylinders need boring.
- Send cylinders to a machine shop — Have the new pistons on hand before dropping off the cylinders. The machinist needs to measure the actual pistons to bore the cylinders to the correct clearance (0.0015"–0.002").
- Wash machined cylinders — Scrub with hot water and dish detergent. Wipe with a white cloth — when the cloth shows no dark residue, the cylinders are clean.
- Install piston rings — Marked side faces up toward the crown. Three-piece oil ring: wavy spacer goes on first, then thin rails on top and bottom. Rotate ring end gaps 120 degrees apart.
- Install wrist pin clips — Put clips on the inner side of each piston (cam chain side) first. Install wrist pins from the outer side. Place rags in the engine case and cam chain hole so you don't drop a clip into the bottom end.
- Install pistons on connecting rods — Arrow on piston crown faces toward the front of the engine. Check connecting rod small end bore for wear before installing. Lubricate pistons and cylinders with motor oil.
Wrist pin clip warning: Make sure each "C" clip seats fully in the circumference of its groove — the end of the clip can catch and not fully engage, which will allow the wrist pin to walk out and score the cylinder wall.
Our Pulsar Pistons introduction video covers the design details, coatings, and ring technology across all supported Honda models.
Frequently Asked Questions
How do I know if my cylinders need to be bored oversize?
Measure the bore with a dial bore gauge at the top, middle, and bottom of each cylinder in both axes. The Honda factory service limit is 64.10 mm (2.5236 in.). If any measurement exceeds that, the cylinders need boring. If they're within limit, a hone and standard re-ring may be all you need.
Do I need a custom head gasket for oversize pistons?
No. Both the 0.5 mm and 1.0 mm oversize options work with the stock Honda head gasket.
Why don't you offer 0.25 mm or 0.75 mm oversize?
Honda originally made those sizes, but in practice most worn cylinders can't be cleaned up with just a 0.25 mm cut — they need at least 0.5 mm to get a clean bore. The half-millimeter increments (0.5 and 1.0) are the most commonly needed sizes.
Will this fit a CB360 or CB450?
No. The CB350 twin has a unique bore size (64 mm) not shared with the CB360 (67 mm) or CB450 (70 mm). We make separate Pulsar pistons for those engines.
Can I already have 0.5 mm oversize pistons in my engine — can I go to 1.0 mm?
Yes, as long as the cylinders still have enough material. Have your machine shop measure the bores and confirm there's sufficient wall thickness to go to 1.0 mm oversize.
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Last updated: March 2026
