cb750k6 piston Rings

[Bitsa (Ralph Wright - RIP)]

Hi All,
Your advice needed please.I have a k6 engine when running was OK but smoked a little,Took it to bits and measured the ring gaps which were out of spec.I have a new set but when on measuring the gaps the first two were within spec but the three piece oil ring the gap was considerably bigger is this the norm or am I missing something?If the speedo is original its done about 35 thou.The reason for this on my k4 my rings were all one piece and all the gaps were the same.
Cheers
Bitsa

[Seamus]

What reference data are you using for the ring gaps? I guess you have measured all  these at top, middle and bottom of the bores to ensure they are true.

[Waggles]

Hi Bitsa,

I don't have any experience specifically with these pistons / rings but in general terms I would not be too concerned IF the oil ring is not 'pegged' into position in its groove. The two compression rings seem to show the bore is OK, if there is no peg in the oil ring groove you would as a matter of course not line up all the gaps in the 3 piece ring anyway.

Remember the job of the oil control ring is not to seal the bore, hence its name 

Am sure someone with direct experience can enlighten us shortly though ........

[Bitsa (Ralph Wright - RIP)]

 Hi Seamus
You guessed right top etc.I am only going on the info in the Haynes book.Maximum gap 28 thou the new rings have a 15 thou gap except as I said the oil ring.
Cheers
Bitsa

[Bitsa (Ralph Wright - RIP)]

Hi Waggles,
Thanks for that but what confuses me if I read it right is Haynes book says oil ring gap should be smaller than the other two.
Cheers
Bitsa

[Waggles]

Hi Bitsa,

Am currently at work so don't have the manual to hand, but are the gaps quoted general? ie really relevant to the one piece oil ring I wonder? can't help but think the 3 piece works in a different way so could have different specs?

Will check my manuals and see what Hondaman has to say when I get home. You are right to be suspicious though, but if they are OEM parts its likely to be OK

[Seamus]

This is for the early K series and I suspect this would not have changed for later bikes. Data taken from the Honda manual (do you have a copy of this?)

The oil ring spec is for a single ring. I cannot find any spec for the 3 piece oil ring except in Hondaman's book where he comments that the ripple ring must be fitted with the ripple up towards the crown and the ends must meet perfectly. A suggestion is also that ring gaps are measured about an inch from the bottom of the bore (least wear?)

Bore 61.01 - 61.02mm    max 61.10mm

Piston dia (measure at right angles to gudgen pin at the skirt) 60.965 - 60.985mm    min 60.85mm

piston to bore clearance 0.01 - 0.04mm   max 0.06mm

End gap for 1st and 2nd ring 0.2 - 0.4mm   max 0.7mm
Oil ring 0.1 - 0.3mm   max 0.7mm

Side clearance of rings
top 0.04 - 0.07  max 0.18mm
mid 0.025 - 0.055  max 0.165mm
oil 0.010 - 0.040   max 0.

Also will you hone the bores (recommended by Hondaman) before reinstalling barrels etc.

Good luck

[Bitsa (Ralph Wright - RIP)]

Hi Waggles.
Thanks mate will look forward to that.In my day they were one piece oil rings  straight forward stuff.Like you say 3 piece may work differently.The new rings are Honda.
Cheers
Bitsa

[Seamus]

A small comment in the Honda manaul states that the oil ring gaps are only for the spacer rings. (Obvious I guess, but worth mentioning)

[Bitsa (Ralph Wright - RIP)]

Hi Seamus,

Thanks mate good stuff yes I will hone the bores and re check gaps and stop worrying about the oil rings.There was not alot of difference between top and bottom of bores.
Cheers
Bitsa