Engine breather pipe.

[1577Participant]

Hi All

There is a considerable amount of crankcase pressure on our rebuilt Light 15 engine most of which forces its way out through the unsealed filler ‘cap’ pushing oil out despite a hose connection between it and the oil bath type air filter fitted to our car. The oil breather pipe on the side of the block seems to do very little to alleviate this pressure and may be restricted in some way. Access to one of the bolts fixing the pipe to the block is very difficult and before attempting to remove it, it would be useful to have any info on the construction of the pipe. Where it joins the block, the Jose Franssen  illustration shows two gaskets with something sandwiched between , possibly a screen or mesh of some sort. Any knowledge of this anyone?

 

 

 

[BernieParticipant]

In the middle of the sandwich, between the teo gaskets, there is a plate with a “D” shaped hole, half the size of the hole in the head of the breather – it is effrctively a baffle to precent oil being allowed to drip down the block and out of the breather.

There should be a small lug on it to ensure it can only be fitted the correct way up, i.e. with the hole to the top of the aperture in the breather pipe assembly.

If your engine is newly rebuilt it may be that the rings are not fully bedded in yet but, if that breather was not checked at the time, it will be worth the hassle of removing it to do it now.

B……………

 

[David FaulknerParticipant]

Luckily I have a picture for you as I changed my breather. As Bernie says there is a steel baffle between the breather and block designed to stop the oil coming out but letting air escape. In my case I was getting a lot of oil from the breather pipe so made a new one to point up as per some 11D’s

You can see how the baffle should sit in this image

The reason I subsequently found for my problems was a burnt out exhaust valve (details in another thread) but having oil come to the top of the engine out of the filler seems a bit extreme?

[BernieParticipant]

I have taken the liberty of “enhancing” David’s picture for a little mor clarity ..

B…………

[1577Participant]

Thanks Bernie and David. I shall remove the breather pipe when I can get the car up on a lift. Even then the torsion bar makes access to that second bolt rather difficult. Re the oil filter David , there is a rather unofficial hose connection between the rocker cover and the top of the oil bath type air filter with the purpose I guess of recirculating the breather fumes back into the engine. This does not give any problems but cannot relieve entirely the pressure created. As suggested by Bernie, the situation may improve as the rings bed in. There is quite a difference between a dry and ‘wet’ cylinder pressure test…typically 5 and 8 bar respectively. Thanks again.. Mike and Mary Bromley.

[David FaulknerParticipant]

That is a rather large difference on compression test so hopefully it settles down soon. I’m assuming you did ensure that the ring gaps were not in line went the pistons went back in.

As for the breather, yes room is tight on a small bodied car which is why I got the young apprentice with slim arms and long fingers to change mine whilst on a ramp at a local garage 🙂

Here’s the homemade one that I replaced mine with, no baffle plate and 15mm unrestricted pipe up to the filter to stop dirt ingress. OK doesn’t look original but it’s down the side of the engine and saves the garage floor.

[1577Participant]

Not a stickler for originality myself..it’s all about what works the best. That certainly looks like an interesting option.

I didn’t do the engine overhaul myself which, as it turned out, I wish I had. It was the conclusion of a sorry saga discussed here some time ago involving a complete engine rebuild when in fact the problem was entirely related to a minute hairline crack in the cylinder head which did not show up under a professional test. We eventually found another head from a fellow member of our local French club which I think was from a very early car since there were some strange dimensional differences including the overall height and much taller pedestals for the rocker shaft. Still after much fiddling to fit it to our I’D block, it seems to work and I don’t think it is related in any way to the excessive pressure in the crankcase.

Many thanks for your interest and advice.

 

 

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