Crankcase breather.

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Crankcase breather.

Post by tajman » Thu May 12, 2022 5:42 pm

I have finished the rebuild of the yellow top 1984 "E" engine and re-installed it in my Austin 7 special. I am in the process of piping everything up and realise that the crankcase breather goes from the top of the rocker box cover to a pipe on the side of the SU carb.
Previous engines that I have dealt with that have SU carbs have the breather going to the air filter and the diameter ID of the pipe is at least twice the one on the Reliant engine. I have read some of the previous comments in the forum on the subject and spoken to some "mechanically" minded friends who feel the present pipe is to small. When I stripped the engine , particularly around the rockers area, it was filthy with muck and deposits.
I wonder what other owners would suggest. I have the excess fuel drain pipe on top of the float chamber on the carb and planned to just allow that to drain to ground away form the manifolds and down past the starter motor side. I will also check the oil dip stick is sealing.
Thanks for your attention.

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Re: Crankcase breather.

Post by Wheaters » Fri May 13, 2022 10:45 am

For engine efficiency, the last place the rocker breather should go is back to the carburettor. I put mine to a catch can. The fuel overflow can either go to the factory designed charcoal canister for emissions reasons, or as you suggest, overboard in a safe place. The important thing is to keep any fuel away from the hot exhaust or sparks…as some found to their cost!

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Re: Crankcase breather.

Post by hidunc » Fri May 13, 2022 11:37 am

Bear in mind the needle profile is set to take into account the extra air drawn into the system through that 8mm stub - whether from the 2mm air-balance hole in the overflow bowl's return pipe or the minimal crankcase blowby, so obviously you would need to find some way of tuning at least the middling needle profiles. In power tests at TVR, when finding the easiest / cheapest way to up the bhp output of the 850 for the final batch of firepumps in 2002, the standard breather setup was the most efficient. By far more improvement was gained by cam profile [expensive], mild gas-flow of head [just about cost-effective], and opening tappets up to 18thou using standard cam and 9.5:1 head [free!]. Somewhere I have copies of about 5 combinations of settings printed out from the rolling road results.

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Re: Crankcase breather.

Post by Nitrowing » Fri May 13, 2022 4:57 pm

I use an inline catch can so the oil mist condenses in that rather than getting sucked through the carb.
No wonder we no longer have a motor industry

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