rear crank leak/crankcase pressure/closed breathing

Side valve, 803, 948, 1098., 1275 and Vizard mods
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rear crank leak/crankcase pressure/closed breathing

Post by ratrodmog »

Wow its been a long time since last posting here (although I have been using the FB MMO page regularly) Warning: this may be a long post so get a brew on ready!

This topic has more than likely been discussed at great length but I feel some clarification is needed.
A quick background on my engine. It's a 1098 that I've fitted a new crank, bearings (making sure to seal the rear scroll as well as possible), oil pump, clutch, rocker shaft (with new springs etc) and it runs an Hs4 carb, alloy inlet and Maniflow exhaust. Cold compression is 155 and all 4 cylinders pretty much the same. The oil pressure holds nicely at around 65 when moving swiftly and 40 at idle (although it's set a little fast currently). The engine was an Ivor Searle recon at some point before I got it and runs pretty well. It's definitely had a rebore and head skim at the point of being reconditioned. I ran this engine for a couple of years before the crank bearings gave out.

Now my issue / issues!
It is leaking from the rear crank into the bellhousing (a drip from the jiggle pin, clutch judder in 1st but no clutch slip when pulling) and I think burning oil. Just did a 300 mile round trip over two days and started on just under the 'max' dipstick mark and now is on just above the 'min' mark.
The current breather arrangement is as follows: vented oil filler cap, rocker cover take-off going directly into the carb body (the Hs4 has a port) and tappet chest breather venting to atmosphere (pointing down to the sump). I think I'm right in thinking this is an open system? My theory is that crank pressure is excessive (why I'm not sure) thus forcing oil out the easiest way, the rear scroll. I've been reading about the later closed breathing systems to controll excess crankcase pressure and remove fumes ect and I think this could be the way to go?
So onto my idea, and please correct me if this is totally wrong, use a tappet cover from a later 1098 with the oil separator (or make my own version of), connect the outlet tube to the carb port ( and possibly run an inline PCV valve), keep the vented filler cap and block off the rocker cover take-off therefore creating a closed circuit crankcase breathing system. This should in theory allow air to be pulled in through the rear scroll (insted of pushing oil out) and in through the vented cap whilst allowing pressure and fumes into the carb and subsiquently burn off.

It's pretty frustrating as I've spent a good bit of time building the engine up and it runs sweet (apart from losing oil obviously) but hopefully there's a simple fix to this problem.

Phewww! And go.......!
engine set-up
DSC_0035.JPG (175.18 KiB) Viewed 396 times
engine set-up
engine set-up

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