A piston and pin set is bought by bore size and by pin fit, not by engine name alone. Two engines sharing a model code can take different oversizes once the block has been rebored, and a pin that is a thousandth of a millimetre out will either seize or knock. This article explains what is in a set, how oversizes are numbered, the two pin types you will meet, and exactly what to measure before you order.
Piston နှင့် Pin ကို bore အရွယ်အစားနှင့် pin အံကိုက်မှုအလိုက် ရွေးရပါသည်။ ဤဆောင်းပါးတွင် တိုင်းတာနည်း၊ oversize နံပါတ်များနှင့် မှာယူရမည့် အချက်များကို ဖော်ပြထားသည်။
In This Article (ဆောင်းပါးအကြောင်းအရာများ)
1. What a piston and pin set contains
2. Bore sizing — standard and oversize
3. Pin types: press-fit and full-floating
4. What to measure before ordering
5. Clearances that decide whether it lasts
6. Fitting mistakes that destroy a new piston
7. How to order from Win Auto Parts
1. What a Piston and Pin Set Contains
Piston နှင့် Pin Set တွင် ပါဝင်သည်များ
A piston assembly is not one part. What arrives depends on how the set was packed, and assuming the wrong contents is the most common reason a rebuild stops halfway.
| Component | What it does | Usually included? |
|---|---|---|
| Piston | Carries combustion pressure to the connecting rod | Always |
| Piston pin (gudgeon pin) | Hinges the piston on the small end of the rod | Usually — confirm on the listing |
| Circlips / retaining rings | Stop the pin walking out into the bore wall | With full-floating pins |
| Piston rings | Seal compression and control oil | Often sold separately — see the piston ring set article |
| မြန်မာ | Piston, pin, circlip များ ပါဝင်နိုင်ပြီး ring များကို သီးခြား ဝယ်ရတတ်သည် | — |
Ring များသည် အများအားဖြင့် သီးခြား ရောင်းချသည် — မှာယူမီ အတည်ပြုပါ။
2. Bore Sizing — Standard and Oversize
Bore အရွယ်အစား — Standard နှင့် Oversize
A new engine runs a standard bore. When a block is rebored to clean up wear or scoring, the bore grows, and the piston must grow with it. Oversize pistons are sold in fixed steps, and the step is stamped on the piston crown.
| Marking | Meaning | When you need it |
|---|---|---|
| STD | Standard bore, as the engine left the factory | First build, or a block that only needed honing |
| 0.25 / +0.25 | 0.25 mm over standard | Light wear, the usual first rebore |
| 0.50 / +0.50 | 0.50 mm over standard | Moderate wear or a light score |
| 0.75 / +0.75 | 0.75 mm over standard | Heavier wear |
| 1.00 / +1.00 | 1.00 mm over standard | Usually the last rebore a block will take |
| မြန်မာ | Oversize ကို 0.25 mm အဆင့်လိုက် ရောင်းသည် | Block ကို rebore လုပ်ပြီးမှ ရွေးပါ |
Order after the rebore, not before
The machine shop decides the final size when it cuts the block. Ordering pistons first commits the shop to a size it may not be able to reach cleanly — and an oversize piston cannot be made smaller.
Block ကို rebore မလုပ်မီ piston မမှာပါနှင့် — အရွယ်အစားကို စက်ရုံမှ ဆုံးဖြတ်ပါသည်။
3. Pin Types: Press-Fit and Full-Floating
Pin အမျိုးအစား နှစ်မျိုး
The pin is what connects the piston to the rod, and there are two ways of holding it. They are not interchangeable, and fitting the wrong one damages either the rod or the piston.
| Type | How it is held | How to recognise it |
|---|---|---|
| Press-fit (interference) | The pin is an interference fit in the connecting rod small end; the piston bosses are the bearing surface | No circlip grooves in the piston bosses. The rod must be heated to fit or remove the pin |
| Full-floating | The pin turns freely in both the rod bush and the piston; circlips hold it in place | Visible circlip grooves at each end of the pin bore |
| မြန်မာ | Press-fit နှင့် Full-floating နှစ်မျိုး ရှိသည် | Circlip အကွင်း ရှိ မရှိ ကြည့်ပါ |
Never press a pin in cold
A press-fit pin is fitted by heating the small end of the rod, not by forcing the pin through. Pressing cold distorts the piston bosses and bends the rod — damage that will not show until the engine is running.
Press-fit pin ကို အအေးဖြင့် ဖိသွင်းခြင်း မပြုပါနှင့် — Connecting rod ကို အပူပေးပြီးမှ တပ်ဆင်ပါ။
4. What to Measure Before Ordering
မှာယူမီ တိုင်းတာရမည့် အချက်များ
Bring these four figures and the order takes one call. Without them we are guessing from a model name, and model names cover several bore sizes.
- Bore diameter after machining — measured by the machine shop, in millimetres to two decimal places.
- Oversize step — STD, 0.25, 0.50, 0.75 or 1.00.
- Pin diameter and length — measure the old pin with a micrometer, not a tape.
- Pin type — press-fit or full-floating (look for circlip grooves).
- Engine code — not the vehicle model. The code is stamped on the block.
Bore အချင်း၊ oversize အဆင့်၊ pin အချင်းနှင့် အရှည်၊ pin အမျိုးအစား နှင့် engine code — ဤငါးချက်ကို ယူဆောင်လာပါ။
5. Clearances That Decide Whether It Lasts
သက်တမ်းကို ဆုံးဖြတ်သော အကွာအဝေးများ
A piston that fits is not the same as a piston that will last. Three clearances matter, and all three are checked at assembly, not at the counter.
| Clearance | Why it matters | Symptom when wrong |
|---|---|---|
| Piston-to-bore | Room for the piston to expand as it heats | Too tight: scuffing and seizure. Too loose: piston slap, a cold knock that fades as the engine warms |
| Ring end gap | Room for the ring to expand in the bore | Too tight: the ends butt and the ring breaks. Too loose: blow-by and oil consumption |
| Pin-to-bush (full-floating) | Oil film between pin and small end bush | Too tight: bush picks up. Too loose: a light double knock at idle |
| မြန်မာ | အကွာအဝေး သုံးမျိုးကို တပ်ဆင်စဉ် စစ်ဆေးပါ | တင်းလွန်းပါက ပွတ်တိုက်မှု၊ လျော့လွန်းပါက အသံထွက်မည် |
A knock that disappears when warm is usually the piston, not the bearing
Piston slap is loudest on a cold start and quietens as the piston expands. A bearing knock does the opposite — it gets worse under load and with heat. Diagnosing the wrong one means stripping the engine twice.
အအေးတွင် အသံကျယ်ပြီး နွေးလာမှ တိတ်သွားပါက piston ဖြစ်နိုင်သည်။ Bearing ဆိုပါက ပူလာမှ ပိုဆိုးသည်။
6. Fitting Mistakes That Destroy a New Piston
Piston အသစ်ကို ပျက်စီးစေသော အမှားများ
- Fitting the piston the wrong way round. Most pistons carry an arrow or a mark that must face the front of the engine. A reversed piston puts the offset on the wrong side and the engine will be noisy from the first minute.
- Reusing old circlips. A circlip that has been sprung once loses tension. If it leaves the groove at speed, the pin scores the bore and the block is finished.
- Filing the ring gap on the wrong ring. Compression and oil rings have different gap specifications. Check both against the manual.
- No oil on the pin and bore at assembly. The first revolutions run dry and pick up metal before the oil pump has pressure.
- Assuming the bore is clean because it looks clean. Honing grit stays in the crosshatch. The block must be washed with hot soapy water and a brush, not blown out with air.
Piston ၏ ရှေ့ဘက်အမှတ်ကို မှန်ကန်စွာ ထားပါ၊ circlip အဟောင်းကို ပြန်မသုံးပါနှင့်၊ တပ်ဆင်စဉ် ဆီလိမ်းပါ။
7. How to Order from Win Auto Parts
Win Auto Parts မှ မှာယူနည်း
Win Auto Parts stocks piston and pin sets across the common Japanese and commercial engine platforms sold in Myanmar. Because sizing depends on machining that has already happened, these are confirmed by part number rather than by vehicle description.
- Call the trade desk on 09 5105768 with the five figures from section 4.
- Or email support@winautoparts.com — send a photograph of the old piston crown showing the size stamp, and of the block if a size is marked on it.
- Or browse the range at winautoparts.com and quote the part number.
- For a workshop rebuilding several engines of the same type, ask for a quotation — quantity pricing applies from five sets.
09 5105768 သို့ ဆက်သွယ်ပါ သို့မဟုတ် support@winautoparts.com သို့ piston အဟောင်း၏ ဓာတ်ပုံနှင့်အတူ ပေးပို့ပါ။
Related Articles
ဆက်စပ်ဆောင်းပါးများ
- Piston Ring Sets — What Is in a Set and How to Select One
- Measuring the Bore and Choosing Oversize Rings
- Piston Rings — What They Do and When to Replace Them
- Fitting Piston Rings — Common Mistakes
- Engine Internals — Frequently Asked Questions
- Crankshaft Thrust Washers, Bearing Shells and Liners — End Float and Undersizes
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