Cummins/Onan — Cylinder Block Inspection

Testing & diagnosis

From a Cummins/Onan service manual — check it applies to your exact model before use.

Applies to: Cummins/Onan MCCK

Procedure

1. Check for cracks; coat suspected area with 25 percent kerosene and 75 percent light motor oil.
2. Wipe dry and immediately apply coating of zinc oxide (white lead) dissolved in wood alcohol; cracks discolor white coating.
3. Inspect cylinder bore for scoring; check Welsh plugs for tight, even fit and fins for breakage.
4. Check cylinder bore for taper, out of round and wear with cylinder bore gauge, telescope gauge or inside micrometer.
5. Take measurements at four places near top and bottom of piston ring travel.
6. Measure cylinder diameter readings A, B, C, D as described.
7. Compare reading A with B, then C with D to determine cylinder taper.
8. If taper exceeds 0.005 inch (0.127 mm), rebore and hone cylinder for next oversize piston.
9. Compare A with C and B with D to determine out of round.
10. If cylinder is out of round 0.002 inch (0.051 mm), rebore and hone for next oversize piston.
11. Clean cylinder block thoroughly with soap, water and clean rags; white rag should not soil after cleaning.
12. Never use gasoline or commercial cleaners to clean cylinder bores after deglazing or honing.
13. Dry crankcase and coat it with oil.

Full service-parts list: Cummins/Onan MCCK →

Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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