1997-2001 Honda CR250 – Top End Service – Part 7: Cylinder Inspection

How To Inspect The Cylinder On Your 1997 – 2001 Honda CR250.

1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder InspectionThe Tools You Will Need Are:

  • Plastic Scraper
  • Soft Brush
  • Shop Towels
  • Mechanics Straight Edge
  • Feeler Gauges
  • Bore Gauges
  • Calipers
  • Emery Paper
  • WD40
  • Plastic Wrap

If you don’t have them yet, you can get a set of Feeler Gauges HERE, a set of Bore Guages HERE, and your or a Machinist Straight Edge HERE.

Click Here To Open The Top End Specifications Table In A New Window

Cylinder Cleaning

Clean your cylinder as thoroughly as you can without damaging the mating surfaces or bore.1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Clean Cylinder Surfaces 1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Clean Cylinder Mating SurfacesRemove all gasket material with a plastic scraper, and smooth any pits or burs with 600 grit emery paper.1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Smooth With Emery PaperCheck the cylinder head mounting studs.

1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Check Head StudsIf you find a loose stud, re-torque it along with the others when the cylinder is back on the bike.

If you have a seized alignment dowel, the only thing you can do is use PB Blaster (or whatever penetrating oil you prefer) and be patient, otherwise you will need to go to a machine shop to have it removed.

If carbon build up is present in the bore, it will need to be deglazed. There are two methods of deglazing, depending on your cylinder wall material.

Stock, this is an aluminum cylinder with Nikasil plating, and can by carefully deglazed with a scouring pad.

However, your cylinder may have been bored out and fitted with an iron sleeve, which can be deglazed with a ball hone.

The definite way to tell is using a magnet. If it sticks, it’s sleeved.

1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Niksail Or SteelYou can also tell visually.

This is a cylinder off an air cooled ATV, and you can see a distinct difference in color between the cylinder wall and the cylinder body.1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Sleaved Cylinder

With your cylinder cleaned and deglazed, inspect the water jackets, transfer ports, and exhaust valve sub chamber for obstruction, wear, or damage.

Clean the mating surface on the crankcase with a plastic scraper. Check the surface for smoothness, and correct any pits or burs. Check the mounting studs for tightness and thread condition.1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Clean Crankcase Mating Surface

Inspect Cylinder Mating Surfaces For Warp

Lay your straight edge against 2 adjacent studs, and try to fit a feeler gauge underneath.1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Cylinder WarpRecord any found gaps.

If you find any gaps, double check the surface for smoothness and try again.

The warp limit for the cylinder is 0.002 inch.

If your cylinder is out of spec, It will need to be reconditioned at a machine shop.

Cylinder Bore Inspection

Before you measure the cylinder bore, visually inspect it.

If you feel a defined lip at the top of the cylinder bore where the piston rings stop, or if the plating is chipped or damaged around the intake, exhaust, and transfer ports, it needs to be replated.

This cylinder is in excellent condition considering the unusual wear on the piston.  The intake side is slightly marked, but is still smooth, so I’m comfortable with reusing it as long as it’s within spec.

Draw out a chart to keep track of your measurements.

Measure your cylinder in five locations at 10, 30, 80, 100, and 130mm from the top of the cylinder.

Label the locations A, B, C, D, and Bottom.

Locations A and B can be measured front to back and side to side.

Locations C and D can only be measured side to side, and the bottom can only be measured front to back.1997 - 2001 Honda CR250 - Top End Service - Part 9 - Clearance Calculations - Cylinder CalculationsMeasure, then re-measure, and record all measurement for later.

1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Cylinder Bore Guage 1997 - 2001 Honda CR250 - Top End Service - Part 7 - Cylinder Inspection - Cylinder Bore Guage MeasurmentWash your cylinder is hot soapy water with a cylinder brush, then dry with compressed air.

Apply a thin coat of WD-40 to the cylinder walls to inhibit oxidation, and wrap your cylinder in plastic wrap until you are ready for assembly.

Part 6: Cylinder Head Inspection
Part 8: Exhaust Valve Inspection
1997 - 2001 Honda CR250 - Top End Service - Part 6 - Cylinder Head Inspection1997 - 2001 Honda CR250 - Top End Service - Part 8 - Exhaust Valve Inspection

Keep Your ’99-’01 CR250 Running Right!

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