Fitting Piston Rings — Common Mistakes

Fitting piston rings incorrectly is the most common reason a freshly rebuilt engine burns oil. This article covers the mistakes that cause it — ring gap, ring orientation, gap stagger and compressor technique — and how to avoid each one.

ပီစတင်ရင်း တပ်ဆင်မှု မှားယွင်းခြင်းသည် အင်ဂျင်ပြန်လည်ပြင်ဆင်ပြီးနောက် ဆီလောင်ရခြင်း၏ အဓိက အကြောင်းရင်း ဖြစ်သည်။ ဤဆောင်းပါးတွင် အဖြစ်များသော အမှားများနှင့် ရှောင်ရှားနည်းများကို ဖော်ပြထားသည်။

A ring set is inexpensive next to the labour of an engine rebuild, and almost every rebuild that burns oil afterwards failed at one of a small number of steps. This article covers those steps.

Ring တပ်ဆင်ရာတွင် အမှားအနည်းငယ်ကြောင့် rebuild တစ်ခုလုံး ပျက်နိုင်သည်။

Check the end gap in the bore

1. Place the ring alone into the cylinder it will run in.
2. Push it square using the crown of a piston, so it sits level in the bore.
3. Measure the gap between the ring ends with a feeler gauge.
4. Compare against the manufacturer's specification for that engine, and check every ring rather than assuming they are all the same.

Too little gap and the ring ends butt together as the engine heats up, which scuffs the bore or breaks the ring. Too much gap and combustion pressure escapes.

ကွာဟချက် နည်းလွန်းပါက အပူတက်သည့်အခါ ring အဆုံးများ ထိမိပြီး bore ပျက်စီးနိုင်သည်။

Fit the rings the right way up

Compression rings are not symmetrical. A mark such as "TOP", a dot or the maker's name identifies the upper face and must face the piston crown. A ring fitted upside down pumps oil up the bore instead of scraping it down, and the engine will burn oil from the first day.

Use a ring expander

Fit rings onto the piston with a proper ring expander tool. Spiralling them on by hand twists the ring, and a twisted compression ring is cracked or distorted even if it looks intact. Expand each ring only as far as needed to clear the piston.

Stagger the ring gaps

Position the ring gaps around the piston according to the engine manufacturer's diagram. Never line the gaps up with one another — aligned gaps give combustion gas a direct path down the piston. Keep gaps away from the piston pin axis and the thrust face unless the manufacturer specifies otherwise.

Ring ကွာဟချက်များကို တစ်တန်းတည်း မထားပါနှင့်။ ထုတ်လုပ်သူ ပုံစံအတိုင်း ခွဲထားပါ။

Fitting the piston into the bore

• Oil the rings and the bore before assembly.
• Use a ring compressor. Never force the piston in — if it resists, a ring has escaped the compressor and will break.
• Check the piston is the correct way round in the bore. Most pistons carry an arrow or mark that must face the front of the engine.

Bedding in

New rings need load against the bore to seat. Follow the engine builder's running-in instructions. Avoid long periods at constant light load in the first hours, and change the oil at the interval the builder specifies, because the initial oil carries the fine debris from bedding in.

Related Articles

• Engine Internals — Frequently Asked Questions
• Measuring the Bore and Choosing Oversize Rings
• Piston Rings — What They Do and When to Replace Them