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Post Info TOPIC: Crankcase Breather
DaveC $118

Crankcase Breather

As I get my arms around (literally in some situations) the Peerless, a number of questions arise.


Here is the first.  What solutions have people found for routing the crankcase breather pipe to a convenient location?   Specifically, the car came with hodge-podge of hoses leading from the bottom of the metal pipe to an old bottle up near the windscreen.  However,  because the bottom of the metal pipe is so low, the first loop from the bottom of the pipe had such a large radius that it ended up just 2 inches from the road....


In short, i need a way of keeping any hose from the bottom of the pipe from being too low on that first turn.


Any help gratefully received.





In my case the lower breather pipe is just blanked off with a core plug.   Any crankcase pressure (and associated oil mist) is vented through the rocker cover and into a catch tank. 
And yes, I do have the uprated rear crank seal to stop it venting all over the clutch.

See Moss diagram TR3 Engine external, item 40



PLUG (in place of breather pipe) 
Note:closed circuit breathing
TR2, TR3/3A, TR4/4A£1.90



nigel Cluley


don't want to sound stupid here but....why do you want to catch it?

surly its your god given right to distribute said breather pipe contents for all the world to enjoyimslow.gif

I have a plastic flexy pipe that just takes it a little further back. it still lubricates the chassis but does'nt drift onto the exhaustdisbelief

the rocker cover/top vent I have re-machined/re-directed and now goes into the induction side of the air intake...

mmmm smellless peerless gadget.gif

and the rear seal conversion kit that I had fitted (admittedly back in the 90's) is leaking as bad as the cork ****e!



Thanks, both In California, letting everything blow out on the road would be asking to be locked up forever.... On these suggestions, I'll figure something out that works Dave

Gary Stretton


Hello Dave,

another alternative is to run an outlet hose from the rocker cover into a flame trap and then into the inlet manifold. The Triumph TR6 trap 603330A or TR4A 13H5191 version should be ideal. The TR4A version is a PCV valve, very similar to the Vitesse/GT6 set-up I have on my Spitfire's six-pot. It should be available secondhand for reasonable money, should you not want to sell a kidney buying new.

The relevant Moss catalogues have diagrams/prices.

All the best.


PS Nigel, was that your oil slick I witnessed in your neck of the woods a while back? Now I understand.



This should be so straightforward.

The core plug in the lower breather hole is standard TR4 practice, and means that all the pressure and oil mist comes out the top of the engine.

Yes, you can pass this from the rocker cover through a flame trap/PCV valve and into one of the air filters (again standard TR practice)


Make sure that you have the modified crankshaft rear seal or it will blow oil mist onto the clutch as well.  The TR3 scroll device doesn't really retain pressure.

The Flame trap/PCV valve will need to be regurlarly cleaned/replaced or it will block with condensed oil/moisture/mayonnaise goo and the lump will then leak oil from every seam.

Passing this noxious mix into one of the air filters to burn it off makes the carbs more difficult to balance and can mean that the associated plugs get oiled more often.  At least the mess doesn't end up on the road.

Piping it into a 1-litre catch tank with an exit filter  is standard competition practice and mandatory for race scrutineering in the UK.  Real tightwads (AKA Peerless owners) will then periodically empty the catch tank back into the sump once the oil and water have separated out.



Gary Stretton


Thanks Frank,

it's an issue I'll need to tackle with my engine and I will be doing the oil seal conversion. As for my Spit's PCV/flame trap it has never needed regular cleaning in 15 years, nor did it oil my plugs. I check it every year but it's always been fine. If the engine is run up to temperature for long enough (as in on a run, not idling on the driveway) then any mayonnaise/condensation will be burnt off, so it shouldn't be a problem. Good quality oil is also paramount.

All the best, Gary

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