Crankcase pressure woes!

[Al B]

Right then the story so far......

A few months ago a motor I've got (1600 with a proper breather set up - rocker covers & alt' stand oil filler) decided to build up a bit too much crankcase pressure, and started to spew oil from behind the bottom pulley.

so, I fitted a sandseal pulley kit and that sorted .....it for a while.

I decided to whip off the barrels and pistons to see if anything untoward had gone off, it had, No's 3 & 4 were severly scored on their undersides, hence poor sealing and increased crankcase pressure.
One brand new 1641 kit later ('rings correctly spaced) and all should be tickety boo ........ not so.

Next it started to leak from the head ends of the pushrod tubes, 3 sets of seals and a liberal smearing of sikaflex later and it still leaks a wee bit but it's now leaking from the fuel pump gasket and alt' stand gasket.... 'think the flywheel seal may have gone too

Next up is the replacement of the stock fuel pump, add another breather hose to vent the case some more.


Now it's been put to me today that two things may be contributing to this crankcase pressure buildup,

1. The exhaust is too restrictive causing pressure to build up in the exhaust itself leading to......

2. the valve seals being 'blown by' (or they just could be worn out........ a bit like me!)

Does that sound plausible?


I've got the rocker covers and rocker assembly off at the mo' and when pushing the valve (spring et al) from side to side I can detect a small amount of movement. 'question is, how much movement is there in a new/sound set up?

Could this be the source of all my woes?

Thanks in advance people.

Al B