I think the exact number isn't as important as "even". If you have a burnt/bent valve or broken compression ring, then one cylinder will be noticeable lower than the other cylinder(s). I think they say "within 10%" is the goal for all cylinders. Aside - not sure the math works like that. The compression is from BDC to TDC. There is extra volume above the top of the cylinder and the valves may or may not be completely closed when the cylinder starts back towards the top. 14.7 is STP for sea level. The dynamic compression is relative to ambient temp and pressure (the air outside the bike). Static compression is the 9:1 ratio. You have a naturally aspirated bike which means no turbo/super charger. This means that your volumetric efficiency (VE) is most likely < 100 (meaning you don't actually take in exactly 450 cc - more like 350-400. I think that only nascar can get over 100% VE meaning their engine would pump more than total displacement - maybe like 460 in this example.
> On May 30, 2016, at 15:56, jonpalms <[email protected]> wrote: > > I hope someone can enlighten me on this issue. > I tested my wifes 1986 honda cb450sc nighthawk for compression value. I think > its suppose to be 9/1 compression ratio and I guess that should be 9 times > 14,7, wich is 132,3 psi. I`m not sure this is correct though. Some places I > read that the compression is suppose to be 185 psi. The result from my tests > show appr. 120-125 psi and 125-130 psi and when I added some oil in the > cylinder it just raised a few psi. Hot engine and open throttle. > The bike runs pretty good but its running lean I think, since sparkplugs are > pretty white colored. > Is 125 psi too low? If there is some leak, and the wet test only gave a few > more psi, where can it be..... valves? > > Another thing is the lean running engine. We just got this bike from the US, > and I don`t know its history. I figure a good carburator cleaning would fix > the lean problem. Any suggestions? > > Appreciate some good advice :) > > Jon > -- > You received this message because you are subscribed to the Google Groups > "Nighthawk Motorcycle Lovers!" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/nighthawk_lovers. > For more options, visit https://groups.google.com/d/optout. > <IMG_7286.JPG> > <IMG_7496.JPG> > <IMG_7498.JPG> -- You received this message because you are subscribed to the Google Groups "Nighthawk Motorcycle Lovers!" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/nighthawk_lovers. For more options, visit https://groups.google.com/d/optout.
