Cylinder head crankcase breather inlet

[mbell]

So it well know that the twincam has some issue with the cranckcase breathing with oil getting into the airbox and it being too restrictive for extended high RPM running or if engine isn’t in tip top condition. These have common work arounds of adding catch can and adding a breather to front of the cam cover.

I am planning to take the opportunity to improve mine while I have the engine out and easy access. As part of this I was looking at the standard setup to try understand what might cause the issues. What I noticed is the cylinder head breather inlet between cylinder 3 and 4 on the inlet side. This is a 7/16” hole that is drill down from a surface level with the cam cover gasket.

It struck me that was more restrictive in diameter than the other parts of the breather setup (& the ford cross flow setup) and it was positioned where it would be easy for oil to enter (flung from the inlet cam or draining down the cam cover).

It seems to me that increasing the size of that inlet hole and doing something to prevent oil easily entering might improve the standard setup. However there not much excess material in that area to widen the hole, so I am not actually planning to do anything in that area.

I was wondering what other people thought and if anyone had done any modifications or seen any modifications in that area of the head?

Thanks,

Mark

[mbell]

Here a photo, of what I assume is standard setup. The breather inlet is the small hole you can see.

[rgh0]

In addition to blowby gases coming up the chain cover along the cam and down the hole shown. The blowby gases also come up the drain tube on the bottom of the oil KO chamber as well as oil draining back down.

With these 2 paths there seems to be enough flow area for a road engine in good condition. Never thought about modifying it but maybe some sort of baffle could reduce the amount of oil going out with the gases

Race engines blowby more with higher revs and higher combustion pressures also their carb setup is often modified so as you say they are generally vented from the cam cover front to a catch tank

cheers
Rohan

[mbell]

The blowby gases also come up the drain tube on the bottom of the oil KO chamber as well as oil draining back down.

Thought this might be the case, likely another reason for the high oil content if the blow by gases in to the air box.

Never thought about modifying it but maybe some sort of baffle could reduce the amount of oil going out with the gases

Complete guess but a simple lip might avoid a lot of oil ingress into the separator. A 90 degree elbow would likely do a good job but probably reduce the hole diameter further which is likely not a good thing.

I am working on adding a separate external separator with additional feed from the fuel pump area. Not modifying the head, so all a bit academic but not an area I've seen discussed on here so thought it was worth asking.

[HCA]

I am interested in anything you come up with as I am about to build a road engine that I want oil and drip tight. For the cc ventilation, I have a catchcan with a low volume scavenger pump drawing from both the rear and front of the head and cam cover.

I do wonder though if one can end up taking too much out..?

[nmauduit]

Here a photo, of what I assume is standard setup. The breather inlet is the small hole you can see.

there are a number of previous threads on this topic. I did have a go at it, too, while trying to maintain a stock look (fully reversible and no front breather): initially I raised this hole with a press fitted alloy tube (not much difference, but retrospectively I also had a head gasket leak developping at the time...), so eventually opted to get the head side oil return plugged from the bottom and used the regular back of the head breather combined with a crossflow style breather from the block joining into a small condensor, the top of it venting in a small catch tank. Even after track days I have not had much in the catch tank since I've done that (couple tea spoon at most). This is a bit messy I must admit, but I like the idea of not burning extra oil via the airbox, esp. more in some cylinders than others.

breather dual route

I did not find a photo of the complete current setup (with the oil condensor), it's all hidden below the carbs but this gives an idea. The condensor is a small alloy box located about above the fuel pump (made of square tubing laying around, something like 2x3x10cm) filled with alloy mesh (I did not want any hard material in the oil circuit in case loose bits start to move around), it returns the condensed oil to the sump from the lowest intake into the block breather (bottom hose on the photo), the next lowest port gets the head breather, the top port is about level with the catch tank and would send overflow there (to be emptied behing the RHD wheel via a small drain tube).

[mbell]

I am interested in anything you come up with as I am about to build a road engine that I want oil and drip tight.

I'll likely post about it once I am done at least making and fitting it.

I do wonder though if one can end up taking too much out..?

I think you can, if you drop the pressure too much you encourage more blow past. Modern cars have PCV system to carefully manage the pressure in the block to keep them is a good range.

I am planning to do some experiments with relocating the connection to the air box to see if it can be made more effective. I am hopefully the brunelli principal can be used on the airbox neck area to improve the removal of gases (and spread them more evenly over the cylinders.)

Testing of that will need to wait for me to complete multiple jobs and get the car back together and running thou.

there are a number of previous threads on this topic.

I found a lot of threads on adding catch cans and the like but not anything on the inlet hole on the cylinder head. So must have missed your thread.

initially I raised this hole with a press fitted alloy tube

Ok thanks. This does suggest a lot of flow and source of oil is up the rubber tube. Rather than down from the top hole.

I did not find a photo of the complete current setup (with the oil condensor), it's all hidden below the carbs but this gives an idea.

Thanks, I am working on something similar but plan to still vent into the airbox. I don't like the idea of venting the gases under the bonnet where they may get into the car. Hopefully with good separation of oil from the gases, the side effects of venting into the airbox will be less.

[nmauduit]

Ok thanks. This does suggest a lot of flow and source of oil is up the rubber tube. Rather than down from the top hole.

I would not quite conclude that ("a lot of flow"), I was investigating and as mentioned found that avenue inconclusive : my main cause of added blow back was the start a head gasket leak. With an engine in good condition there should not be a lot of blow back on road use, I would say only moderate during track use, and monitoring it (level in the catch, oil smell is there is a lot of out venting when hot...) is an crucial point of preventive maitenance imho.

[2cams70]

The problem with the Lotus cylinder head appears to be that the internal cavity (the velocity drop chamber) cast into the head isn't big enough to properly do it's job.
Inside the engine you have gas pressure generated from piston ring leakage and you have microscopic oil droplets suspended in this gas. The microscopic oil droplets are mainly the result of oil leakage from the crankshaft bearings. Increasing either of these factors increases the workload on the velocity drop chamber. Increasing the entry port size to this chamber or placing baffles near these ports are unlikely to have much effect. It's very fine mist type droplets uniformly distributed in the gas stream we are talking about not tap drip sized droplets.

The velocity drop chamber works by providing a reservoir where these gases can gather in an area of relative stillness (i.e low flow). This area of relative stillness gives the oil mist under the action of gravity time to fall out of the gas, collect at the bottom of the chamber, and return to the sump (that's the theory anyway).

To improve the oil separation performance the velocity reducing action must be improved. The oil mist must be given more time to fall out of the gas stream before the gas stream exits the engine. Either that or the gas stream needs to be passed through a large surface area filter (eg a coarse wire gauze). The two methods could be used in combination of course.

I'm sure if you could stuff that velocity drop chamber with some coarse wire gauze a lot of the problems would be solved. You can't of course because it's inaccessible. For reference on the pre-crossflow pushrod engine that adapter on the block that is located in the same position as the rubber oil drain back tube on a LTC is stuffed full of coarse mesh steel gauze. It isn't just an empty conduit.

That's the theory at least. I'm not sure of the solution. It would be interesting to know how the BDA engines is designed in this area.

For your information I'm leaving my engine totally standard in this area. For me personally a few non critical drops of oil here and there don't bother me if I know it's caused by original design rather than a fault!

A PCV valve by the way is only necessary on engines with a closed ventilation system - i.e crankcase gases are fed back into the engine to be reburnt. On these engines the gases are fed back in directly to the inlet manifold -i.e after the carburettor has already determined what the correct fuel/air mixture should be based on airflow. The PCV valve allows the gases to enter the engine in a controlled manner so the fuel/air mixture is not seriously disturbed.

[mbell]

With an engine in good condition there should not be a lot of blow back on road use,

&

The problem with the Lotus cylinder head appears to be that the internal cavity (the velocity drop chamber) cast into the head isn't big enough to properly do it's job.

Yes, its hard to know if the oil in airbox I got was due to volume of blow by being high with average oil content. Or average blow by with high oil content. I've never noticed any significant oil in the air box before, but then I've never put 1,000 miles on the car in 2.5 days or had run any real distance with the redline oil in it. So it is hard to come to a conclusion on what the issue is.

To improve the oil separation performance the velocity reducing action must be improved.

My plan, currently in progress, is to add an additional chamber to the breather setup. This is oil catch can with drain in the bottom. I plan to route the current breather via this and add a second one from fuel pump blanker. I've bought the catch can and modified it slightly to provide a longer flow route from the inlet to the outlet. I also have some copper wire mesh I may add to it.

Next step it to get the pumping fitting and made a bracket to mount it and connect it all together.

I'm sure if you could stuff that velocity drop chamber with some coarse wire gauze a lot of the problems would be solved.

I had wondered about this. It might be possible to roll some up and stuff a few rolls through the hole. The holes is probably 3/4" with grommet removed. So not big, but not tiny either.

For me personally a few non critical drops of oil here and there don't bother me if I know it's caused by original design rather than a fault!

I am also not too worried about a few drops outside the engine, it more needing to top it up often. I pulled the sump yesterday and confirmed it was leaking and likely the major factor in engine oil leakage (relatively small compared to the gearbox...). I've had a go at straightening the bent mounting holes on it and will be re-installing it carefully, with carefully selected and applied sealant.

This won't address the oil in airbox issue, which hopefully my mods will address or maybe I'll have to change oils. As might just be side effect of the redline oil.

Thanks both for the input.

[rgh0]

My understanding is the original flanged metal stub pipe that fitted into the head breather chamber and connected to the rubber pipe to the air box back plate had a metal gauze in its end that stuck into the head. This pipe is often been replaced or the gauze removed because it blocked or maybe at some stage Lotus deleted the gauze to reduce cost.

The chamber size was obviously acceptable to Lotus to serve its purpose as it was added during the development stage of the original prototype heads in the early 60's . With Old twin cams tin old Elans here are many and varied reasons why its effectiveness may not be seen as adequate today.

50 years ago during my engineering degree, my final year project was building a dyno based emissions monitoring test rig and doing testing on the effectiveness of the PCV system which was a newly added regulatory requirement at the time. The engine tested was a new 4 cylinder Holden engine of the time ( I presume a Vauxhall based engine) . Testing showed that overall engine emissions were actually worse as the PCV recycled gases increased tail pipe emissions more than just venting the blowby gases and not upsetting the air fuel mixture so much. Carburetted engines and PCV valve systems were in reality a waste of money to achieve a worse result to comply with poorly thought out regulations. Once fuel injection and feedback from wideband sensors to the ECU became possible all this of course changed

cheers
Rohan

[nmauduit]

My plan, currently in progress, is to add an additional chamber to the breather setup.

my thinking in pursuing the same line was that a cold/air cooled oil condensation chamber would be more effective than the one embedded in the head (which also would lack mesh to initiate condensation) - I then opted to an "all soft metal" version (rather than say, filling it with more efficient stainless sponge for a mesh) when I figured I would try a return to the sump, so as to limit the risk of any hard shards making its way back into the oil pump (if you are not returning the condensate to the circuit you may be more efficient in the condensation mesh). Also I change oil relatively often...

[mbell]

This pipe is often been replaced or the gauze removed because it blocked or maybe at some stage Lotus deleted the gauze to reduce cost.

I made my tube from some Ali tube as it was missing when I got the car. I haven't added the mesh, as couldn't think of good way to secure it. My impression was the mesh was mainly there as a flame trap but also helped remove oil. I suspect it would help my car (I have standard one on order, that I may never fit) but I'd be surprised if it removed all the oil.

my thinking in pursuing the same line was that a cold/air cooled oil condensation chamber would be more effective than the one embedded in the head (which also would lack mesh to initiate condensation)

I'd be quite happy to not add one but my oil usage is higher than I'd like, there certainly a decent amount making it to the air box along with some leaking from the sump gasket. I have no idea how much is staying in the air stream and being burned.

I suspect (hope) the external one is going to be more effective than the Lotus one but time will tell.

[2cams70]

That fine mesh soldered into the block to airbox tube is a flame trap. It's not really designed to separate out the oil. It's made out of copper rather steel because copper has much better thermal properties for flame quenching. That's the reason also why it's a cone shape rather than flat - to present a large cooling surface area to any flame (I used to work for a welding equipment manufacturer and flashback arrestors (as they were called) were a profitable add on).

Being a fine mesh it's a prime candidate for becoming blocked. If that mesh becomes blocked you most certainly will have excessive crankcase pressure. It's quite delicate and easy to damage which is probably why on a lot of engines it's now missing. Although I haven't heard of any cases of crankcase explosions without the mesh Lotus obviously thought it a wise precaution to have it.

My understanding was that it was mainly EGR (Exhaust Gas Recirculation) systems that caused all the angst when the first ADR 27A engine emission regulations were introduced in 1976. PCV and non vented fuel tank systems were mandated a year or two before that and didn't really impact engine driveability to a great extent. This wasn't an engine emission standard as such but rather a strategy to prevent raw fuel vapours escaping into the atmosphere. As with a lot of things it's mainly the calibration that determines whether things operate correctly or not and there was still a lot to learn back them. PCV and EGR systems are still used today of course. By the 1980's they pretty well had the systems sorted even without the assistance of much in the way of electronics.

I remember going through the parts listing and to the wreckers to try and source a replacement EGR valve for a 1980's Falcon. I was amazed at the subtle design variations in each valve. Obviously a lot of work had been done in the calibration to suit each engine variant. EGR valves for the 3.3L engine were different to the 4.1L, M/T was different to A/T and in some case Victoria was different to NSW!! Looking at different valves side by side there were differences in both the control poppet valve shapes and also the diaphragm spring tensions.

GM certainly had some pretty ordinary 4 cylinder engines back then. Who could forget the "Cam in head" engine and the "Starfire 4". GM V8's were much better.

To the OP - don't forget to check the condition of your engine for piston ring sealing. If that's not right then everything else is moot!!

[RichardHawkins]

Twin Cam,

One of my Lotus owning friends has had a backfire ignite the vapour in his sump! He said it made quite a mess.

Richard Hawkins