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MG MGB GT V8 Factory Originals Technical - 3.9 Crankcase breather ???

Anyone with a 3.9 Fuel injected V8 fitted a breather ?
R Walker

I don't really understand what you mean. The 3.9, like all engines has breathers already. They are all on the rocker box covers. Can you be more explicit?
Mike Howlett

There really should be a positive breathing system or you can get fumes in the cabin, and it must have an filtered fresh-air inlet and an outlet going into the engine supplying definite suction.

To expand on Mikes there should be a pipe on the back of the right-hand bank of cylinders with what is effectively a fuel filter on it which is the breather inlet. Each rocker cover has a port going via an oil and flame trap to the respective carb. That is how factory MGB V8s (and I suspect engines from other applications of the same era) were, depending on where you got your engine from it may or may not have any or all of these. Later engines with injection and/or Holley etc. carbs may not have the rear inlet, just the rocker cover ports, one of which is filtered for the inlet and the other going to a carb breather port. If the carb or whatever doesn't have a crankcase ventilation port then you should fit a PCV valve between one of the rocker covers and the inlet manifold, and a filter to the other rocker cover.

PaulH Solihull

My 3.9 with EFI taken from a Range Rover has an air inlet on the back of the left hand rocker cover, and the gauze filter outlet that Paul mentions on the front of the right hand rocker cover. The pipe from this outlet goes to a T-piece which has a one way valve in it. The straight through pipe from here goes to the inlet by the throttle butterfly, and the pipe from the T goes to the plenum base.
Mike Howlett

Thanks Mike and Paul. I recognize the arrangement Paul describles - Mine has the same flame trap and breather as the RV8 but it also has the same small hole in the rear valley wall as the MG Factory V8. It has also the same connector pipe but unlike the 3.5 MG which has a filter to air, mine is blocked. It's all a bit Harry Tate.

R
R Walker

This thread was discussed between 04/10/2010 and 05/10/2010

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