How To Inspect The Piston On Your 1997 – 2001 Honda CR250.
The Tools You Will Need Are:
- 4mm Hex Wrench
- Needle Nose Pliers
- Snap Ring Pliers
- Telescoping Bore Gauges
If you don’t have a set of Telescoping bore Gauges, you can get them HERE.
This piston has perfect carbon build up, meaning the pre-mix ratio is correct, the carburetor is tuned right, and the transfer ports are flowing freely.
This piston did make contact on the intake side of the cylinder, indicating the piston warmed up before the cylinder, and expanded too fast.This is what happens when you don’t let your engine warm up.
I have to replace this piston, but if your piston still looks good, it may still be within spec, and if it is, all you need are new rings.
Your piston must be in perfect condition in order to re-use it, so one thing wrong and it needs to be replaced.
You will however need new wrist pin clips regardless of your piston’s condition.
Expand the rings, and move them straight up off the piston. Do not try to “unwrap” the rings.
Label the top and bottom rings accordingly. You will not re-use these rings, but you will need them later.Clean the carbon from the crown of the piston with parts cleaner and a plastic scraper.Clean the pin bore and ring grooves with a soft brush and a pick. Inspect the piston crown for damage. If you find any, replace the piston.
Inspect the ring grooves and locating pins, if they are damaged, or you have missing pins, replace the piston.
Inspect the piston skirt, if you find any abrasions or cracking, replace the piston.
Inspect the interior of the piston and pin bore for wear or cracks. Guess what you need to do if you find any?
Pin, Needle Bearing & Connecting Rod Inspection
Clean and dry the wrist pin and bearings, then check for excessive wear or damage.
The piston to pin clearance can be no GREATER than 0.0016 inches.
To calculate the piston to pin clearance, subtract the smallest wrist pin measurement from the largest piston bore measurement.
The largest bore measurement for this piston was 0.708 inches, and my smallest pin measurement was 0.707 inches, resulting in a clearance of 0.001 inches, which is within spec.
If the connecting rod is out of spec, you will need to replace the crank assembly.
Even though you will not be re-using your piston rings, we can use them to see what the engine has been up to.
Take the old pistons and roll them around their respective grooves and feel for any snags or binding.
Lubricate the crown and grooves with assembly lube or 2-stroke oil.
And the bottom ring should have a clearance no greater than 0.026 inches.
Repeat this process with the new rings. If the clearance exceeds spec with new rings, the piston must be replaced.
|Part 4: Exhaust Valve Removal||Part 5: Cylinder Head Inspection|
Keep Your ’99-’01 CR250 Running Right!
- Service Specification
- Clutch Replacement
- Carburetor Service
- Engine Top End
- Front Fork Maintenance
- Rear Shock Rebuild
- Wheels & Tires
- Kickstarter Inspection
- External Shift Linkage