missing drain tube between head and block

[seniorchristo]

While looking for oil leaks this morning in my 1967 Elan I noticed there is no oil drain tube from head to block on my engine. I can see the cap installed in the block above the fuel pump and can feel one underneath the head. Has anyone had experience with this? My engine is a modified 711M tall block.
Thanks
Chris

[patrics]

Hi Chris
From what I see at race circuits and my own race engine the top engine builders don't fit the drain tube - I have never asked why but at the front of the engine there is obviously a massive hole down to the sump - to me fitting one is just asking for an oil leak?

Regards
Steve

[Fred Talmadge]

It is possible to put one in without removing the head. There is a kit for replacing pushrod tubes on VW when they get a hole in them. You have to cut it down to fit. Need to check the nut to make sure it doesn't come loose.

[seniorchristo]

Thanks Steve,
My engine has a few race mods including the swiveling oilpan pickup. I'm dying to know what's inside I will probably pull the cam cover off to see what cams are installed but the internals will remain a mystery for the time being.
Later
Chris

[billwill]

When you look at pictures of the 711 block on non-twin-cam engines you can see that the big hole above the fuel pump, is in fact the crankcase breather hole. It was fitted with an external pressed steel condensation chamber.

It seems that Lotus decided to have a fume condensation chamber built into the head, which would drain back to the sump through the breather hole and they also needed a new smaller breather hole in that condensation chamber to equalize the crankcase preassure.

So, it seems, you can ignore the chamber in the head and block its holes if you have other means of crankcase breathing.

I haven't checked but it may be that the condensation chamber in the twin cam head is not actually connected to the cam/valve chamber.

[seniorchristo]

Thanks for your reply Bill. You've lost me on the condensation chamber. So if I am only draining oil back to the sump from the front of the head there are no ill effects? Also my cam cover has a breather which runs to the Weber airbox. I've noticed not all engines have this feature. Was this included only on some engines or installed later by car owners.
Later
Chris

[Lyn7]

Hi Chris, the breather from the cam cover is not standard, I do not think any twin cams had this feature on any car as standard.
Regards Lyn..

[billwill]

The breather hole at the back of the head is the one I referred to above as "they also needed a new smaller breather hole in that condensation chamber to equalize the crankcase preassure."

I think all the later Elans had the breather tube from the rear of the head to the air box. I think some egulations came in which prohibited dripping any oil onto the road which the earlier breather tube did a little bit of. The earlier cars had a simple pipe about 2 foot long from that breather hole down the back of the engine over the bell housing with an open end at the bottom.

Inside that breather hole in the head is a chamber, which as I said above, I am not sure if it actually connected to the volume (covered by the cam cover) in which the cams and valves are located. The oil which is pumped up to lubricate the cams and valve pots returns to the sump via the front lip, the timing case, where the timing chain is located. It is easy to think (I did so for years) that the oil returns via that conical rubber drain pipe from head to the hole just above the fuel pump, but that (I believe) is not the case; the only oil that returns that way is oil which came up that drain pipe as fumes and then condensed back to oil inside the chamber at the back of the head and then ran back down the drain pipe as liquid.

[billwill]

Thanks for your reply Bill. You've lost me on the condensation chamber. So if I am only draining oil back to the sump from the front of the head there are no ill effects? Also my cam cover has a breather which runs to the Weber airbox. I've noticed not all engines have this feature. Was this included only on some engines or installed later by car owners.
Later
Chris

You'll notice that I said "So, it seems, you can ignore the chamber in the head and block its holes if you have other means of crankcase breathing."


You DO have an alternative breather in the form of " my cam cover has a breather which runs to the Weber airbox. " So the original breather hole above the fuel pump has been blocked off in your case (probably with a core plug).

[billwill]

There is more description and photos of this breather chamber in this thread:
lotus-twincam-f39/cylinder-head-query-t19564.html

In this picture from that page:

You can see that the breather condensation chamber is actually an add-on to the head casting, it is only present around the two rear air intakes.

This picture shows the usual conical drain tube.

[mbell]

My probably incorrect understanding/memory is that the crank case breather has an oil separator in the head (wire mesh?) to reduce the amount of oil coming out of the breather pipe to the carbs or road. The drain pipe is used to drain the collected oil from that oil separator.

I'd guess no oil drain pipes just means a bit more oil will collect in the sperator and therefore more oil exiting the via the crank case breather.

[billwill]

This photo shows the original ugly breather chamber used on the 711 blocks on Ford crossflow engines. So you can see why Lotus wanted to make a neater solution.



http://www.pistonheads.com/gassing/topic.asp?t=1326632

[billwill]

My probably incorrect understanding/memory is that the crank case breather has an oil separator in the head (wire mesh?) to reduce the amount of oil coming out of the breather pipe to the carbs or road. The drain pipe is used to drain the collected oil from that oil separator.

Yes there is some scrunched up mesh in the final breather pipe. Not clear how effective this is. It's main purpose may be to prevent grit etc from being sucked INTO the engine or to prevent oil explosions.

Quite a good description of crankcase ventilation on Wikipedia.
http://en.wikipedia.org/wiki/Crankcase_ ... ion_system

I'd guess no oil drain pipes just means a bit more oil will collect in the sperator and therefore more oil exiting the via the crank case breather.

Only if there is an air connection through-way between the cam/valve chamber and the condensation/separator chamber, because otherwise if the drain hole is sealed, there will only be air in there anyway, no oil vapour

[mbell]

Yes there is some scrunched up mesh in the final breather pipe.

I thought I'd read there was some mesh in the oil separator within the head not just in the breather pipe. That what i was referring to, probably wrong thou.

Of course this only matters if the standard breather hole is being used. As you say if it isn't used (vented from the cam cover) there will be no air flow through that chamber so the build up of oil (or not with no little air flow) doesn't matter and there is no need to drain the chamber.

If the standard breather hole is used then you need the drain tube to drain the chamber or the oil is likely to be suck/blown out of the breather. Which isn't good.

I've had a oil leak from my drain tube so know some oil does pass through it....

[mini64]

Just to chime in and maybe clarify - my race engines also have the rubber "drain" tube disconnected and both holes plugged (block one and head one), with other means for venting the engine via a port on the front of the cam cover.
----edit ---- As Rohan pointed out below I am wrong about the chamber not being connected to the cam area - just wanted to update this in case someone doesn't read the whole thread. I'd forgotten years ago I blocked this drain by drilling and tapping it and putting in a plug------

The rubber tube is not actually a drain tube but as others have said a connecting tube from the block vent up to the vent chamber lotus put in their heads. the hole in the side of the head, on the side of this chamber, is then often connected to the airbox or left to vent to the ground via a hose. This head chamber is not connected to the cam area. Oil does not drain down from the head to the crank here. However you will often find this tube an oily leaking mess as both the crank and cam throws oil in its general direction, and the more worn your rings are the more pressure will be going up this tube caring the oil with it.