Piston rings are supplied in standard size and in oversizes to match a rebored cylinder. Ordering the wrong size wastes the set, and ordering standard rings for a worn bore wastes the whole rebuild. This article explains what to measure and how to choose the size.
Piston ring ကို standard နှင့် oversize အရွယ်အစားများဖြင့် ရရှိနိုင်သည်။ အရွယ်မှားပါက ring အစုံလုံး အလဟဿ ဖြစ်သည်။
Figure 1 — Where to measure a bore, and how taper and ovality are worked out. ပုံ 1 — Bore ကို မည်သည့်နေရာတွင် တိုင်းရမည်။
Standard and oversize
Ring sets are normally offered as STD (standard) and in oversizes such as 0.25 mm, 0.50 mm, 0.75 mm and 1.00 mm. The oversize refers to how much the cylinder has been bored out. Rings must match the finished bore, so the machining decision comes first and the ring order second.
Bore the cylinder first, then order the rings
Do not order rings before the machine shop has finished. The final bore size is decided by how much damage has to be removed, and it may come out larger than expected. Order to the measured finished bore, not to the intended one.
စက်ရုံမှ ပြီးဆုံးပြီးမှသာ ring မှာယူပါ။ အပြီးသတ် အရွယ်အစားသည် မျှော်မှန်းထားသည်ထက် ကြီးနိုင်သည်။
Measuring the bore
Use a bore gauge, not a vernier caliper. Measure each cylinder in at least three positions down its length and in two directions at right angles, then look for:
- Taper — the bore worn wider at the top than the bottom, because the top of the stroke sees the highest pressure and the least lubrication.
- Out-of-round — the bore worn oval rather than circular.
- Scoring — vertical scratches from debris or seizure.
Compare against the manufacturer's wear limits for that engine. If taper or out-of-round exceeds the limit, new rings alone will not seal — the block must be bored and oversize pistons and rings fitted.
Honing and the crosshatch
A bore that is within limits still needs honing before new rings are fitted. Honing cuts a crosshatch pattern that holds oil and lets the new rings bed in. Fitting new rings into a glazed bore is one of the most common reasons a rebuild still burns oil afterwards.
Ring အသစ်မတပ်မီ bore ကို hone ရမည်။ Hone မလုပ်ဘဲ တပ်ပါက ဆီ ဆက်လောင်နေမည်။
What to tell us when ordering
- Vehicle make, model and year
- Engine code — essential, because one model often used several engines
- Number of cylinders
- The size required: STD or the oversize, taken from the finished bore measurement
Related Articles
- Engine Internals — Frequently Asked Questions
- Fitting Piston Rings — Common Mistakes
- Piston Rings — What They Do and When to Replace Them
- Pistons and Piston Pins — Sizing, Pin Types and Fitting
- Head Gaskets and Engine Gasket Sets — Grades, Bolts and Fitting
- Crankshaft Thrust Washers, Bearing Shells and Liners — End Float and Undersizes
Engine Parts — article 10 of 11
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