I've just about finished restoring an old Thwaites dumper with this engine and wonder if anyone has any experience with it, in particular an annoying small oil leak out of the dipstick tube?
Messing around today I've measured the length of the tube and was surprised to find that it is as long as the dipstick itself, thus its bottom end lives submerged below sump oil level. The dispstick has some form of seal within a cup at the top but it's not particularly effective. Therefore as far as I'm concerned it is no surprise that oil gets pumped out of the tube due to crankcase pressure fluctuations caused by the piston.
- The engine seems in sound condition with good compression because starting it up from cold is really easy.
- I've found the crancase breather tube that runs from the rocker box into the inlet track, I've rodded this out and confirmed it's clear. (The engine appears not to have an elaborate breather system like (for instance) a Lister CS.)
So, is this just another fairly poor British design where a little bit more development work was needed or am I (hopefully) missing something obvious?