17 replies to this topic

[P1GLT]

kia ora from Aotearoa New Zealand,

 

I'm after some advice on my recently purchased 1971 Austin Mini that's been through a full resto and a worked engine transplant - ported, blueprinted, a whole lot of internals from the motherland, etc. I've been told its about 100hp but have no proof of this. Pretty sure it was built with a bias to a race engine rather than road engine. 

 

It has a minor leak out the timing chain somewhere which I'm not worried about and will remedy in time, but what’s more concerning is after a decent blat there's signs of oil being forced out the rocker cover screws and occasionally the vented oil cap. While giving it a decent go over this week I noticed a couple of things that seemed odd to me (as a newbie but with some mechanical understanding).

 

1. The transmission breather is connected straight to the rocker cover breather. I've done research and haven’t come across this anywhere else. From what I understand the general intent is to have a negative pressure in the rocker to draw air in through the oil cap not out?

 

2. The crankcase breather is open with a hose wrapping over the engine and down to the bottom of the car, without a catch can. There is a dribble of mayonnaise like mixture coming out of this pretty regularly when the engines cold. I've read this is done for race engines but not really ok for road cars.

 

I understand there are many different approaches to breather setups depending on engine and preference but my concern here is long term damage. Hoping someone may be able to give me some pointers as to whether this setup is common / ok, or if I should look to change it.

 

Thanks

 

 

 

[Ethel]

Doubt it's doing any damage as such, but it's not the best. Race engines run open breathers as much because they wouldn't work as on a road car - they'll be at wide open throttle so much there'd be no manifold vacuum to suck up the fumes.

 

There are enough advantages on a road car to make it worthwhile including fewer oil leaks as the pressure will be trying to get in past the seals, rather than blowing oil out. You're correct drawing fresh air in through the oil filer allows the flow of combustion fumes out, which is good for stopping it contaminate the oil. I expect the pipes were linked "because they are there" most don't have a pipe on the rocker, it would have connected to the air filter casing, but it'd be fine to just block it off if you have a vented filter cap. How you hook the transfer case  & other breathers will depend on your carb(s). If it's a single SU  it likely has a hose connection just upstream of the throttle.

 

Mayo is a classic sign of head gasket failure, BUT burning petrol also produces water, so don't jump to that conclusion without other evidence.

[P1GLT]

Ngā mihi Ethel - you're correct it's an SU carb so easy to connect the lower engine breathers in as is typical. Will give me some plumbing to do over the Christmas break. Nothing else to suggest the gaskets done and its minimal amount of dribble so thinking / hoping its just the condensation mixing while it warms up. 

[Edington]

Not wishing to highjack this particular subject on breathers but my enquiry is relevant. My 1969 cooper has the mushroom shaped housing sitting on top of the inlet manifold of a twin HS2 set up. The diaphragm in side is therefore connected to the inlet vacuum while the other side is connected to the breather from the tappet chest cover. I'd be interested to know what is it's purpose and if the diaphragm is damage what are the consequences. The engine is not running great and I'm thinking of doing away with it.     

[Tornado99]

Ngā mihi Ethel - you're correct it's an SU carb so easy to connect the lower engine breathers in as is typical. Will give me some plumbing to do over the Christmas break. Nothing else to suggest the gaskets done and its minimal amount of dribble so thinking / hoping its just the condensation mixing while it warms up.

Mayo like oil out a breather is not necessarily indicating a problem like coolant contamination. I see similar all the time on my classic Norton Commando motorcycle, which is air cooled. The breather line gets frothy mix of oil and air, moisture will get absorbed from the open end or just from normal engine operation (burning fuel generates water). I'd think most race tracks would have banned open breathers due to oil build up on traction surfaces. The reason most are plumbed back into intake is to reduce volatiles reaching atmosphere/environmental emission concerns.
Later minis have breather "traps" at both tranny and crankcase ends, which feed to intake. I think these large diameter metal cans have a steel gauze within to help condense oil vapour back to liquid and have most drain back down to sump.

Edited by Tornado99, 16 November 2021 - 05:31 PM.

[Spider]

Ngā mihi Ethel - you're correct it's an SU carb so easy to connect the lower engine breathers in as is typical. Will give me some plumbing to do over the Christmas break. Nothing else to suggest the gaskets done and its minimal amount of dribble so thinking / hoping its just the condensation mixing while it warms up. 

 

A few things to check when you re-do the plumbing.

 

A complete closed crankcase ventilation system has an 'air flow' through the crankcase before returning to the CCV (Closed Crankcase Ventilation) Port on the Carb. To this end, Air needs to be able to enter the Crankcase before exiting it, it is the movement of 'air' through the crankcase that removes the moisture from the Oil to stop them Mayo you are seeing.

 

Check that the Oil Filler Cap is a Vented type as there are also sealed ones. Also, the pipe on the Rocker Cover, some of these were open (that that'll be obvious) and there's also a version that has a one way valve in them that lets Air in but not out. These were used on Cars to meet certain emission regulations, depending on the type required. If you are going to run a Vented Filler Cap, I'd suggested blocking off the Rocker Cover Pipe, but be aware that you may still get some Oil around the Filler Cap. You could run a Sealed Cap and then plumb the Rocker Cover Pipe back to the Air Filter and that would be less likely to have the Cap oil stain.

 

 

Not wishing to highjack this particular subject on breathers but my enquiry is relevant. My 1969 cooper has the mushroom shaped housing sitting on top of the inlet manifold of a twin HS2 set up. The diaphragm in side is therefore connected to the inlet vacuum while the other side is connected to the breather from the tappet chest cover. I'd be interested to know what is it's purpose and if the diaphragm is damage what are the consequences. The engine is not running great and I'm thinking of doing away with it.     

 

The Diaphragm is part of a valve and restrictor assembly. It allows a small partial vacuum to be applied to the Crankcase. If the Diaphragm is holed, it can cause a lot of Oil to be drawn in to the Manifold and you'll usually see a Blue Cloud following the car at times (line worn rings) if it's doing this. I was never crazy about these particular set ups, but if you do away with it, you want to replace that Crankcase Ventilation System (PCV in this case) with another type. Open vented crankcases will only likely build up Mayo and develop premature Oil leaks.
 

[Edington]

Many thanks for the comment above which explains my smoky exhaust. I now plan to replace the inlet manifold with one that doesn't have access for this 'restrictor assembly' and connect the PCV to the air filter box. Hopefully this will improve things.

[Ethel]

The air filter housing likely, also hopefully, won't have enough depression to draw fumes out. You could play about with a restrictor in hose to limit the flow capabilties - an inline ball valve would give quick 'n easy proof of concept - or just clamp the hose.

[T.Harper]

Somerfords sell new PCV diaphragms for £6 for anyone looking to repair these.  I did one over the summer and seemed to resurrect it.

 

https://www.somerfor...hragm-pcv-valve

Edited by T.Harper, 17 November 2021 - 10:50 AM.

[Edington]

Inspected the assembly and oil vapor is getting into the inlet manifold. The diaphragm is really a gasket and I can't understand how this arrangement works unless something is missing  

Attached Files

•  inlet oil breather.jpg   85.05K   3 downloads

[Spider]

If you don't have CCV Ports on the Carb Bodies (that's that 5/16" Brass Tube that pokes out near where the Dashpot screws on at a 45⁰ upward angle), then sure ditch the Factory PCV Valve and fit an inline one from another small engined car, eg, these some for Toyotas and Hyundais that are well suited, in the Fuelmiser Range, a PCV014 is perfect as it has a 13 mm dia body on to which you can slide 1/2" Emission hose over (ignoring the barb on the manifold side).

For street cars, and like Ethel mentioned, I do advocate a Crankcase Ventilation System that's plumbed somewhere that has a lower than atmospheric pressure. Returning it to the Airfilter Case will resolve issues of smells and fumes but you'll likely find the Rocker Cover will get a regular build up of Mayo which you'll need to regularly remove and clean the cover.

[sonscar]

I think there should be some sort of valve and spring inside the pcv valve.Steve..

[Ethel]

Looks like it's still sat in the base, under that disc.

 

It's very simple really. Atmospheric pressure is fed to the top side of the diaphragm ( lord knows what's gone on with that one); when  there's a big enough difference with the (manifold) pressure below the diaphragm it'll compress the spring & close the valve. As soon as it closes only the breather hose will be connected to the underside, so it'll open again. In practice it'll average out to equal the spring rate divided by the surface area of the diaphragm.

 

It looks fixable, you'd need a setscrew & washer to plug the hole if you removed it anyway.

[Edington]

Ok it looks like there is no spring under the disc. Just looked on the somerford minis web site which does show a spring! So before I do away with it I'll get a new diaphragm and spring and see if that does the job. 

[Ethel]

Thought it looked low!

 

Have a look at the bit that actually bungs the 'ole too, before you place your order.