Low compression?

[darrenpickup]

Hi all, I am starting to restore my 1983 Rd 125 lc mk1, I have cleaned the carb up, checked the spark plug etc. Done a compression test and only getting 55 psi, I know this is low but is it too low to get her started. Thanks.

[steven]

Hello Darren,
What is the compression ratio for your model of RD125 ?
A quick google and I found a compression radio of 6.8:1, is this the correct CR for your model ?
With a Compression Ratio of 6.8:1, your approx compression pressure should be somewhere in the region of 115 psi to 136 psi, so 55 psi does seem very low.....holed piston? broken/stuck rings ?

I have managed to get small engines running with very low compression, but once started, they "wouldnt pull a solidier off your granny." !

Mabey look down the plug hole with a torch and see if the piston is holed, or poke a piece of brazing rod or someithing down the plug hole to see if it holed ?

Mabey some oil down the plug hole too, to free up the rings incase it has stuck rings ?

But I fear you are just avoiding the inevitable, if the compression pressure is that low, the barrel will need to come off for farther investigation.

Plz let us know how you get on.

cheers,
steven.

[darrenpickup]

Thanks Steven, I will have rummage around and let you know how I get on, I can remember trying to kick it over years ago and it locked solid,but very easy to kick over now, I think I know it needs a top end rebuild but in denial. Cheers.