Piston Rings help ? - SOHC/4 Owners Club Forums
Jul. 07, 2025
Piston Rings help ? - SOHC/4 Owners Club Forums
Hello, I am trying to get my compression good on my bike along with stoping some smoke from blowing out the pipes
I wantt to change my old piston rings. I went on ebay and was surprised by the choices. Can someone explain?
I see regular rings then I see some that say 2nd Over...3rd Over...4th over
Whats the difference and how will I know what I should get without opening up the eninge first. First you will need to strip the motor to see if it is still the std bore size.
Std bore size is 47.0 - 47.01mm. std piston size is 46.97 - 46.99mm
Bore wear limit = 47.1mm
Piston wear limit = 46.85mm
If after doing the measurements your bore and or pistons are out of spec then you will need to re-bore to the next oversize. sizes that Honda supplied are std, 0.25, 0.50, 0.75 and 1.0 mm oversize.
If your bore and pistons are in the specified specs, then you need to check the piston ring end gaps and the piston ring to piston ring groove clearance. ( Max 0.15mm. if more than this replace pistons and rings)
Ring end gaps:
Top and second ring = 0.1-0.3, (limit 0.7mm)
Oil ring = 0.1-0.3, (limit 0.7) one piece ring
If the pistons/bore are in spec then you can get away with a new set of rings (same size as the pistons that are in your motor), block will need to be honed and then check/set ring gaps etc.
OK saying all that the CB350F piston and rings are all discontinued and very hard to find.
There is another way in that you can fit the CB400F pistons and rings, which also have the better 3 piece oil ring. the std piston is 51mm, to do this you will also need a set of larger OD sleeves as the 350 ones do not have enough meat to bore to this new size.
Some machining will be required, boring the block for the new sleeves (on a milling machine) and enlarging of the upper crankcase (can be done with a dremel)
Kevin
I wantt to change my old piston rings. I went on ebay and was surprised by the choices. Can someone explain?
I see regular rings then I see some that say 2nd Over...3rd Over...4th over
Whats the difference and how will I know what I should get without opening up the eninge first. First you will need to strip the motor to see if it is still the std bore size.
Std bore size is 47.0 - 47.01mm. std piston size is 46.97 - 46.99mm
Bore wear limit = 47.1mm
Piston wear limit = 46.85mm
If after doing the measurements your bore and or pistons are out of spec then you will need to re-bore to the next oversize. sizes that Honda supplied are std, 0.25, 0.50, 0.75 and 1.0 mm oversize.
If your bore and pistons are in the specified specs, then you need to check the piston ring end gaps and the piston ring to piston ring groove clearance. ( Max 0.15mm. if more than this replace pistons and rings)
Ring end gaps:
Top and second ring = 0.1-0.3, (limit 0.7mm)
Oil ring = 0.1-0.3, (limit 0.7) one piece ring
If the pistons/bore are in spec then you can get away with a new set of rings (same size as the pistons that are in your motor), block will need to be honed and then check/set ring gaps etc.
OK saying all that the CB350F piston and rings are all discontinued and very hard to find.
There is another way in that you can fit the CB400F pistons and rings, which also have the better 3 piece oil ring. the std piston is 51mm, to do this you will also need a set of larger OD sleeves as the 350 ones do not have enough meat to bore to this new size.
Some machining will be required, boring the block for the new sleeves (on a milling machine) and enlarging of the upper crankcase (can be done with a dremel)
Kevin
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