Piston ring gap?

[Conquiztador]

Ok, so Econohonda sent me the rings for my sons chinese dirt bike. They are Honda CT 90 ones. And pretty close.

The two top rings have about 1mm overlap. I have no idea how much to take away. Normally I have the figures, but not for this thingy.

So I recon that for a 50cc 4 stroke, if I make them really close so that not even a c@nt hair fits between I should be OK?

The oil rings (the three of them together) is too thick. wont fit in, so I will have the piston machined tomorrow. Just an additional hassle. But just the way it goes.

Oh and, when comparing the Honda rings to the chinese ones, what a difference in quality! No wonder the chinese bikes are cheap if all bits are done like this.

[Motu]

3 thou per inch was the rule,but as your piston is a metric one you won't be able to use that calculation.....I'll have to try and figure out how you could possibly work that out in metric.They are opposing systems and one won't fit the other...it may not be possible - give me a few days and I'll get back to you.

[Ixion]

Motu is right. You need imperial bores for proper rings gaps. You'll need to get it rebored in inches. Once you've done that come back and tell us the bore in feet and inches and we'll work it out.

[Ocean1]

So I recon that for a 50cc 4 stroke, if I make them really close so that not even a c@nt hair fits between I should be OK?

No. The gap is to compensate for expansion. Too small and you'll break the rings and fuck the bore, too wide and you'll lose compression and burn oil.

3 thou per inch was the rule,but as your piston is a metric one you won't be able to use that calculation.....I'll have to try and figure out how you could possibly work that out in metric.They are opposing systems and one won't fit the other...it may not be possible - give me a few days and I'll get back to you.

Should still work shouldn't it?

Just divide the bore size in mm by 25.4 to get inches, do the arithmetic and (if nescessary) convert it back to mm.

EG: (as long as we're talking cast iron rings) 50mm bore = 1.968" = 5.9 thou.

Near as fuckit to 0.15mm gap.

[Conquiztador]

No. The gap is to compensate for expansion. Too small and you'll break the rings and fuck the bore, too wide and you'll lose compression and burn oil.



Should still work shouldn't it?

Just divide the bore size in mm by 25.4 to get inches, do the arithmetic and (if nescessary) convert it back to mm.

EG: (as long as we're talking cast iron rings) 50mm bore = 1.968" = 5.9 thou.

Near as fuckit to 0.15mm gap.

As I was saying: a c@nt hair!

[Ixion]

No. The gap is to compensate for expansion. Too small and you'll break the rings and fuck the bore, too wide and you'll lose compression and burn oil.



Should still work shouldn't it?

Just divide the bore size in mm by 25.4 to get inches, do the arithmetic and (if nescessary) convert it back to mm.

EG: (as long as we're talking cast iron rings) 50mm bore = 1.968" = 5.9 thou.

Near as fuckit to 0.15mm gap.

No, no, that won't do at all. For one thing it's too simple. And, my bad, I did not read the original post properly and missed the fact that this is a Chinese engine

Now, the Chinese are an old and venerable race, and slow to forsake the good old ways.

Whereas the Japs, who copied everything they have from the Brits (specifically, in this context, BSA),use Imperial, inch ,measures (they just quote them in metrifacted centithingies to confuse people. Inscrutable folk), the Chinese stick with their traditional measures. To wit, the hwank for bore sizes and the fu-quck for gaps.

Now, the really important thing to remember is that the Chinese system works the reverse to the British (and thus Jap) one. In the Brit/Jap system, you adjust the rings gaps to suit the bore. In the Chinese system you adjust the bore to suit the ring gaps. That is why the rings you have overlap. You need to hone the bore until there is a gap of three fu-qucks . The extra clearance will also help stop seizures. If the clearance between piston skirt and bore be too great this can be adjusted by winding a tight spiral of green bamboo round the piston, securing it with a dab of rice paste.

Fitting the piston may also be challenging. That too, is the reverse of the Brit/Jap system. Whereas , in the latter you offer up the gudgeon pin to the piston (sliding the pin into the piston boss, then slipping the piston over the conrod eye and pushing the pin through), in the Chinese system it is the reverse. You must first fit the gudgeon pin into the conrod eye, then slip the piston over the conrod/pin assembly. This requires a degree of dexterity not often found in Westeners.

Good luck

[Ocean1]

As I was saying: a c@nt hair!

No, no, that won't do at all.

Coonts.

Jimmy Whitworth is rotating in his grave.

[Conquiztador]

Thou, there is a trick here for young players: Do NOT use a c@nt hair that is curly!

[pete376403]

And red c*nt hairs are smaller diameter than the regular black ones (Blond ones are general fakes, make by bleachiing black oes)

[Motu]

Ok - I've called in the kids to help,and with a lot guidance for me....they have sorted it ou.......OI!

Looks like it was even more complicated than I thought...I better leave it to the experts.

[Conquiztador]

Ok - I've called in the kids to help,and with a lot guidance for me....they have sorted it ou.......OI!

Looks like it was even more complicated than I thought...I better leave it to the experts.

U just don't wanna help me!