Crankcase breather tube

[A.I.M]

Hi folks,
My 250 scrambler engine crankcase breather tube has seriously degraded (full of holes) over approx. 2000 km. I wonder if this might be due to incompatibility with the synthetic lube oil I have been using after the running-in stage?
Has anyone else had a similar problem and found a solution?
I would prefer to continue using synthetic lube oil long-term, it's my belief that it's much better for the engine internals, after running-in on mineral oil.
Cheers,
Al

[Duccout]

Hi Al,

Is the tube rubber or plastic? I doubt that it is due to the engine oil, it is more likely due to the heat and the emissions from the engine.



Cheers,

Colin

[A.I.M]

Hi Colin, thanks for the quick reply.
It's the original-style rubber tube with spiral wire reinforcing, connecting the crankcase breather to the inlet air filter.

To my eyes it looked more like the synthetic oil eating into the rubber - BUT - the engine has been suffering from burning a lot of oil, so I guess it is possible that combustion gases have also been getting into the crankcase.

Maybe my best bet is a like-for-like replacement and keep a close eye on it.

Cheers,
Al

[themoudie]

Aye A.I.M,

Here is a link to the clear PVC hose that I use as a breather on the 450 MKIII, whilst using Smith & Allan, 15W-50 Fully Synthetic oil, having previously run the engine in using an old school 20W-50 mineral oil, changed at 20, 250 and a 1,000 miles afore filling up with the 15W-50 Fully Synthetic oil.

Clear-unreinforced-pvc-tubing

I have had no apparent "attack" to the structure of the hose in over 14,000 miles of use, over 4 years. Make sure you warm the PVC hose, with boiling water before sliding it over the male crankcase fitting and securing with a Jubilee clip, or hose clamp of suitable diameter. You'll get a shrink fit!

Good health, Bill

[IanHood]

Bill,

Do you use that tube with or without the spiral reinforcement inside? I don’t have the reinforcement so wondering how it performs without.

Regards

Ian

[blethermaskite]

Ian, Same as Bill I have been using pvc breather tubing for years with no spiral reinforcement never any issue's.
Cheers, George

[A.I.M]

That's good to know, thanks Bill / Ian / George.
For my scrambler I would like to keep the original "cake-tin" air filter, and the tube connects to the back-side of it. The tube has to bend 90° to fit, and it's only about 35 cm long, so I might try to recover the spring from the old tube and install it in a new one to prevent kinking.

All the best,
Al

[themoudie]

Aye Al, Ian,

To answer your queries about PVC hose collapse. I have never had problems, with the un-reinforced PVC hose collapsing, providing you keep the radius of the curves greater than 45°. However, the bore required for the MKIII's breather is a "standard" size that I cannot remember off hand, but, moulded straight, "T" pieces, "Y" pieces, 90° elbows and blanking plugs are all available from local DIY suppliers, moulded in nylon that resists most of the chemicals they are likely to encounter in an engine breather.

I found that the nylon mesh reinforced PVC tubing had a thicker wall and with the mesh, made it more difficult to bend to even 65° curves. It also seemed to age harden more quickly than the un-reinforced PVC hose. That was down to the PVC polymer mix used in their manufacture.

I hope this helps.

Good health, Bill

[IanHood]

Many thanks Bill.

Ian

[graeme]

A good auto parts store will have a variety of car heater hoses with various formed bends and sizes. Pick one that has the size and bends you need and cut off the rest.
Just a suggestion,,,
Graeme