My hoses are shot. What are people using to replace these two hoses.
One is on the inlet manifold, about 4 inches long, the other is from rear of block to inlet manifold, even longer. .

I use 1/2” ID heater hose for the breathers. Technically you should use oil resistant hose but I’ve never seen any degradation on mine

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Vacuum hose. Heater hose doesn't like oil or fumes. Or hold shape under vacuum. As on a Cooper S or 1100S with PCV.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

An alternative part number seems to be BAU5065M but can't find one locally.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Do Not use Heater hose or Vacuum Hose, It is Not oil or fuel resistant.
Use 1/2" inside diameter Fuel hose or Smog hose / PCV hose. Easy to buy, just google 1/2" fuel hose etc........
Here is an example but do your own search.

https://www.repco.com.au/parts-service/ ... gL4tfD_BwE

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You can buy pcv hose, type in 13mm pcv hose google is your friend

Has anyone actually experienced any issues with the wrong type of hose?

I can't say I have seen any issues with either heater hose or brake vacuum hose.

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1986 Mayfair (998 auto), 1974 S, 1974 Van, 1972 PMG Van

Too many minis

Got the Repco hose today, see what happens.

There are a number of breather hoses in use and they depend on where the oil separator is. For the part numbers in question, the following dimensions apply.

12G581 (Oil separator to Breather Valve): Length 11 ID 7/16 OD 11/16
12A1052 (Oil separator to Breather Valve): Length 3.5 ID 7/16 OD 11/16
12H1407 (Breather Valve to Manifold): Length 1 7/8 ID 7/16 OD 11/16

The material specified is oil resistant rubber BMR11/C which, apart from the normal requirements for oil resistant rubber, shall have “a high resistance to fuel and hot and cold oil or its vapour. The cover shall have good ageing characteristics in the under-bonnet atmosphere.”

On my 850, as a result of all this discussion on breathers, I discovered to my horror that the side cover pipe (crimped appearance) had the slot covered in paint, and the breather hose from rocker cover to air filter, although original, was in a poor state inside and there was no chance of any suction of vapours through to the air cleaner let alone any inlet of fresh air at the side cover.

I cleaned out the side cover slot (supposed to be about 15 thou slot in the crimp) and obtained some ½ ID hose. This was a tight fit, even though the ID of the original is specified as 7/16. However, I wanted to preserve the appearance of the original hose, and because the original pipe was more or less falling apart, I was able to peel back the outer vinyl covering and slip the new rubber hose inside it, and so from the outside, it looks completely original.

Incidentally, for an early Morris 850, the hose is 2A634 and is specified as 3 ½ inches long. For later models, the hose is 12A52 and 5 ½ inches long. As well, the material specification is BMR11/B which is medium resistance to oil and vapours.

Picture below shows restored hose with original outer covering and new hose inside.

I have also been using good quality, name-brand, heater hose for breather applications for years on my minis, on the premise that if it doesn't cope with oil fumes it will become obvious. I haven't seen any deterioration in the hoses in that time.
But I only use vacuum hose on the brake boosters for safety's sake.