Compression

[coppersaucepipe]

What should the compression be on a good class B bike? I've got 9 bar on the front and a smidge over 7 on the rear on the engine in the bike. My spare measured at a smidge over 9 on the front and 9.5 on the rear.

[skidlids]

7 bar is to low
where as 9 to 10 bar isn't bad

[milesaway]

What should the compression be on a good class B bike? I've got 9 bar on the front and a smidge over 7 on the rear on the engine in the bike. My spare measured at a smidge over 9 on the front and 9.5 on the rear.
mine gives over 9 on both- is it the cyl you were pouring neat petrol down that's low? check yr valves first but if it's the flooded one you probably washed off oil and damaged rings/bore- shame its not front as 10 times easier to pull off and investigate

[coppersaucepipe]

mine gives over 9 on both- is it the cyl you were pouring neat petrol down that's low? check yr valves first but if it's the flooded one you probably washed off oil and damaged rings/bore- shame its not front as 10 times easier to pull off and investigate

It is the flooded rear cylinder. I'll drop the spare engine in for Anglesey and have the current engine apart on the bench I think. It hydrolic locked at one point, so I'm guessing I may have damaged something then if it wasn't already low.

[bally71]

Measured mine yesterday

6 bar front
6.5 bar rear

LOL .. Think it's time I swapped that engine

[milesaway]

Measured mine yesterday

6 bar front
6.5 bar rear

LOL .. Think it's time I swapped that engine

worth checking valves first- if clearances are out enough can loose compression- if they are its as easy to pull off the heads then you can grind them in before you set clearances and can check state of bores and measure rings at the same time

[mat2hew]

worth checking valves first- if clearances are out enough can loose compression- if they are its as easy to pull off the heads then you can grind them in before you set clearances and can check state of bores and measure rings at the same time

or its even easier to get miles to do it for you.. :)

[milesaway]

or its even easier to get miles to do it for you.. :)

tell you what matt- the money people seem to charge for doing such things i'm beginning to wonder if carpentry isn't the wrong business to be in!

[Ghost]

tell you what matt- the money people seem to charge for doing such things i'm beginning to wonder if carpentry isn't the wrong business to be in!

Its not what people are charging Miles it's the daft buggers paying the elevated prices. One could be busy working for nothing but sensible fees should apply. :D

[bally71]

worth checking valves first- if clearances are out enough can loose compression- if they are its as easy to pull off the heads then you can grind them in before you set clearances and can check state of bores and measure rings at the same time

cheers miles .. but I've planned to change the motor anyway

Nice fresh motor .. should be all up and running ready for Donington

Can't wait .. the old motor was only making 50 odd horses ... I won't be able to control the thing with an extra 10 .... :eek: