Easing crankcase pressure

[david.g.chapman]

My twin Cam engine is running well, but still manages to push a couple of drops of oil out of the rear crankshaft seal on every run.

This is despite having a new rear seal running on a new speedi-sleeve.

I have checked the blowby and just get a gentle puffing from the oil filler hole at idle, which smooths out to a gentle draught at higher revs. The engine doesn't burn oil and I have 160-170 psi on all cylinders.

I've fitted a cam splash guard under the oil filler cap, and have noticed that no oil now comes out of the hole when the engine runs.

I just wonder if anyone has tried to fit a breather outlet in place of the oil filler cap? With no significant oil coming out it might be an opportunity to lower crankcase pressure without having to machine the cam cover?

Dave Chapman.

[mbell]

I don't remember ever seeing any one do it. I think the standard cap would be hard to modify for this.

I am not sure if the cap is Elan only or there might be a source for a different less fancy cap that might fit the neck or not. Anyone know?

This is topic I've been wondering about and will see after resealing my engine if I need to do something. At the minute I tried to redirect the standard breather out to the neck of the air box to see if that improves it.Other location that you might be able to add a breather without modding the cam cover are:
- Head to Block drain tube
- Fuel pump cover, if using elec pump
- Cylinder head D Plugs (small bore only..)

[ericbushby]

Hi mbell,
This type of oil cap works quite well.

It is a cheap and nasty thing but because of it`s multiple small steps it is not so particular about gasket thickness or softness. Unfortunately I do not know the source of these. If you could find one it would be ideal for experimental mods.
This is on my car at the moment because I cannot find a gasket that seals reliably with the correct three eared cap.
Suggestions welcome.
Eric in Burnley
1967 S3SE DHC

[h20hamelan]

Burton makes one for others, but I cant find a similar twin cam offering anywhere. Erics has just a atmospheric vent and no provisions for capture?

https://www.burtonpower.com/alloy-oil-f ... fp641.html

Having the oil go to the intake or a catch can or plum it into the exhaust post o2 with a flame-trap?

[david.g.chapman]

I'll see if I can fabricate something. For an experiment, it just has to fit and lock on over the oil filler port with a reasonable level of sealing and take a hose of some sort.

I'll post when I have something...if others want to have a go, feel free!

Dave Chapman.

[nmauduit]

There should be a breather on the engine (back of the head RHS, near the cast oil separator location) usually routed to the carbs breather box: if your engine is not blowing back (nor developping a head gasket leak) would this be somehow clogged ?

[Frogelan]

Dave,

Here are two ideas:

Many race cars have a breather outlet on the front of the cam cover leading to an oil coalescing collector (with a small air filter).

Another option (idea of the Californian Europa forum (racing section)) is to open up the fuel pump blanking plate with a similar breather. Burton suggest (for the standard blanking plate) that a splash plate is integrated.

I will be doing both but please note that the latter is "experimental": I have not tried it yet!

Andrew

[david.g.chapman]

I've come up with something. Think Homer Simpson/Heath Robinson!

I can't use the fuel pump route as I have a mechanical pump fitted.

It's made from 5 inches of 22mm central heating pipe opened out and hammered flat. The cheapest source of copper plate I know!

I've left it unfinished so you can see how it's made.

Note that there is a deflecting plate inside the cover above the splashy cam.

The pictures below should be self explanatory, apart from:

1. The side view shows the 3mm self adhesive foam sheet I used to seal against the cam cover.

2. The hole at the back. That was to take a bicycle spoke wrapped around the bell housing bolt directly below, to even out the clamping pressure. It looks like it's not needed at the moment.

I have not tried this yet, and there is every chance that it will stink out the bonnet space and gasses will get into the car. I will then extend the filter to the end of a hose under the car, or take the hose somewhere more environmentally friendly.

I'll let you know if it works.....

Dave Chapman.

[Andy8421]

David,

In the spirit of trying to avoid you going down a path that is unlikely to be successful, I applaud you inventiveness, but I think your problems are elsewhere.

For a normal engine that doesn't have large amounts of blowby, the standard breather is fine. A race engine at high revs may need additional breathing, but it is not clear why your standard breather at the back of the engine isn't working. I would suggest you address that before putting a stove pipe chimney on top of the engine.

From a technical perspective, the interior of the engine when running is filled with an oil mist that has the larger droplets separated by the 'velocity drop chamber' cast on the back of the head before the blowby exits the engine. These droplets then drain back into the sump.

With your solution, in the absence of some way of separating the oil droplets it is likely that the oil will soak into the filter, and drip over the engine.

[david.g.chapman]

Yes, Andy. You are probably right. Large droplets of oil are stopped by my internal plate, but oil mist is another matter.
As we know ford engines of the period had a breather cap in the rocker cover with just a bit of wire wool in it. I get the feeling that there is more oil around in the lotus head!
This is also just to see if the modest reduction in crankcase pressure is enough to affect oil getting past my new rear crankshaft seal. One run should be enough.
If it works, then I will be think about refinement to address oil soaking. Otherwise, it was fun to do!

Dave.

[mbell]

The standard breather has a fire trap in it at the engine end, which is a fine wire mesh. It's sugar checking that is clear and not clogged up. If you haven't already.

[ericbushby]

Hi Dave
I say ignore the nay-sayers, there is nothing like a bit of garden shed manufacturing to entertain yourself and learn something. I have just abandoned a project to design and make a phone holder to use as a sat nav. I used a Cad System, that is Cardboard Assisted Design.
The results were just on the good side of useless! but I enjoyed the process.
Eric in Burnley
1967 S3SE DHC

[david.g.chapman]

Well! I have a run in the car up and down the A12 dual carriageway at 70 mph - about 40 mins running.

There is no oil to be seen externally. I took the filter off and have had a look inside. There is a trace of oil mist on the inside of the filter top plate, just at the centre. Otherwise no oil present.

A running time of a few hours may give a significant oil deposit , but I don't think it's anything a bit of steel wool would be bothered with, if the existing filter is replaced with it. I'm going to keep the filter for now.

There is no smell in the cockpit, apart from what was there before.

Now the big test - oil used to drip from the bellhousing at 1 drop every 1 to 2 mins with the engine hot and idling. Under the same conditions it's now more than 5 mins per drop. Not bad!

To top up with oil the filter is removed and you fill through a 15mm pipe. Might take a bit longer but possible.

I've noticed that the idle speed has reduced slightly. I've adjusted to compensate.

I ended up fitting the bicycle spoke, as the plate resonated at 2000 rpm and buzzed. Not any more!

So I'm going to stick with it for now. Remember you need the interior plate in place - it makes a big difference.

One last thing - the existing breather pipe to the air box is clear.

Cheers,

Dave Chapman.