Triumph Repair: TR4 ENGINE REBUILD BLOWBY, air fuel mixture, crankcase pressure

Question
JUST REINSTALLED 100% REBUILD FROM GROUND UP. At idle, we see oil blowing out of dipstick. As we accelerate off idle with air cleaners removed, we see some of the air/fuel mixture coming out of the carb throat also. Have new pvc assembly installed, all ports are opened, not plugged. The 1 step up upgraded camshaft was installed. Distributor base plate is free to move, vacuum advance tests good, moves base plate with vacuum applied. Moving distributor to both extremes causes expected results. At idle, vacuum available is very minimal, but increases as you accelerate, this seams backwards to me. Why the pressurized crankcase & air/fuel blowing out of carb throats? Even with oil cap removed, the air/fuel blows outward. Motor appears to run near normal, maybe a little sluggish coming off of idle, starts easy, no overheat.

Answer
Hi David,
There are some basic facts about engines and one is that unless you have a hole in a piston ALL crankcase pressure comes from past the rings. If on a new rebuild you used chrome rings (old new stock) the chrome was probably "hard chrome" and that takes forever to seat. The newer chrome rings are called "soft chrome" which is an alloy of some kind and they seat much easier.
Were the cylinders bored with new pistons etc installed? What kind of finish was put on the cylinder walls? All of this affects blow-by (crank case pressure)

I agree about the vacuum. Max vacuum is on decel and next lower is at idle and as the throttle is opened the manifold vacuum goes down to aprox 5 inches at full throttle and full load. This can vari with a racing cam. Are you sure you are testing MANIFOLD vacuum and not PORTED vacuum? Ported vacuum is taken off of one of the carb bases and manifold vacuum will be off of the intake manifold itself. Ported vacuum will show little to no vacuum at idle and increase as the throttle is opened and then drop as RPM and load is applied.

Even on a modified engine you should start with factory specs on the Ignition timing and then very slowly advance when a cam, high compression, modified exhaust system, intake system and higher grade of fuel is used. This is not hard to achieve at the lower RPM because you can hear the point of detonation (pinging) but high RPM detonation is very difficult to hear and you then need something like an MSD knock sensor display system or such to ID that very dangerous point of ignition advance where high RPM detonation starts.

The lack of torque off of idle can be your cam design, your ignition timing, carbs setting or grade of oil in the carbs dampteners or even the need for a break in period or all of the above.

Did you build the engine or did you have it built? Who timed the cam? and was a cam manufacture cam chart or specs used to time the cam? Fuel and air will blow out of the carbs at and just off idle with some racing cams depending on how radical the cam is. This can also show as low vacuum on a gauge.
Howard