Twin Cam restrictor

[1972Series4]

This is the first time I have worked on a Twin Cam and while chasing an oil leak discovered that my short block does not have an oil restrictor leading to the head which MAY be part

of my leak problem. A friend who has a BDA block sent me a picture of his block with a restrictor that looks exactly like a  carb jet or air corrector. None of my DHLA parts fit (all too small). Can someone enlighten me as to what the restrictor is and where I can acquire one? 

[S1Steve]

We like pictures😀😀

[MoBoost]

Appears to be a non-standard part. I don’t have a photo of my engine with the cylinder removed to show. 
https://forums.lotuselan.net/t/cylinder-head-oil-restrictor/9945/4

[1972Series4]

 

I only have one. It's of my friends block with the aforementioned restrictor that I don't have. My passages, block and head, are a shade over .3 inches diameter.

Looks like a jet of some kind with no threads in the block, a press fit. I could be wrong. If I have to I'll call Dave Bean Mon or Tues. 

 

 

 

 

 

[1972Series4]

MoBoost, thanks for the link. I'll peruse it more fully tonight

[1972Series4]

Looks like I need to call Dave Bean on Monday.

[jbcollier]

Restricting flow to the head is common in racing engines as they spend all their time in the upper rpm range and can suffer from more oil being delivered to the head than can flow back to the sump.  For the street it is not a good idea.

[MV8]

It sounds like your leaks are due to crankcase pressure. A restrictor delays top end pressure on start up and reduces valve train lubrication and cooling. Look at windage, oil weight, smoothing oil returns, and crankcase breather systems that also act as an aux return to the pan.

[Dave W]

I have an old repair manual with the Lotus Twin cam. Looking at the engine exploded view, I can confirm that the oil stricter is not stock. 

[1972Series4]

More info that I didn't think to include; the oil system is a dry sump with a Titan pump that puts out near 80 psi at idle with Torco 40w break-in oil. The pressure reading

is taken at the oil filter adapter just before the oil enters the engine. The lines are all -10 and -12 aeroquip.

[MV8]

Why? The whole story from the beginning please.

[jbcollier]

OK, we are no longer talking a stock engine.  80 psi is a LOT for a Twink.  I would indeed put in a flow restrictor to the head.  Measure the current passage and reduce it by 25% to start.  You are going to have to run the engine without the cam cover and make sure the cams are getting adequate oil flow at idle and not excessive at high rpm.  It's going to be messy but worthwhile.

[panamericano]

Or, you could put a pressure regulator (adjustable) in line with the dry sump plumbing.  Went through that with a 2 L Peugeot mill with a Moroso pump.  Called Moroso and was told the pump was for a small block V8.  I think I got the regulator from Speedway Motors, or some roundy round supplier.

[MV8]

Use the oil weight that will get you a hot idle of 25-35psi. This may be 0w-20. For break in, the best you can do is 30w.

The relief valve should be adjusted to 60-80 psi at 3500 rpm.

Fix the pressure problem leading to the crankcase pressure problem leading to the leaks and you won't need a restrictor.

[wdb]

The twincam in my 7 has a high pressure 2-stage oil pump. I'm not racing it but I have not noticed any issues with oil flow. The recent conversion to dry sump fixed all of the oil leak issues as well. I'd like to see more pictures showing how your dry sump is plumbed, in particular the venting stuff.

[1972Series4]

I'll give the history/specs of this engine that I should have included the first time. I bought the car from the estate of a long time friend who died in Dec 2022. We have known him for almost 40 years and I have driven the car in local San Diego autocrosses some 30 years ago. When I got the car it had no engine or transmission and was in VERY rough condition. It did have a very nice bare head however and all the stuff to assemble it. It also came with a dry sump pan, tank and Titan pump. Another mutual friend had a barely used short block (1660 cc) that he had pulled from his Elan to fit a class-legal engine. It was assembled by the same guy who did my head (Bill Schlossnagel). Now I had the makings of an engine. The combo has about 10 1/2 to 1 compression. The head was originally on a 2.0 liter aluminum block that got sold years ago. 145psi compression on all 4 cylinders. You ask why use the dry sump. 1, Because I already had it. 2, because a wet sump assembly would have to be procured. 3, because the sump would hang below the chassis about 3 inches. 4, because everyone I talked to said it was a good thing. 5, it has a "cool" factor!

So, yes, the engine is not stock. It's sort of a detuned race engine that should be "peppy" on the street. I have not run it more that 20 seconds or so because I have

no coolant in the it. I am going to put a restrictor in it after talking to Ken at Dave Bean. I have attached pics of the ca as-is when I got it, the rear fender and nose cone attached and the engine.

[1972Series4]

To WBD. The sump feeds to the oil pump. through a SHORT 6 inch -12 line. The feed from the pump to the tank goes rearward and across the

bell housing. Oil then goes out the bottom of the tank back across the top of the BH to the pump inlet. These lines are about 2 to 2-1/2 feet long. From the pump, oil travels rear about a foot to a chassis mounted spin-on filter adapter through a -10 line. This is where I tapped the adapter for a 1/8 NPT sender for a Stewart Warner

gauge sender.  The hole for a sender in the block is covered by the right motor mount. From the adapter to the engine through another -10 line which necks down to a 3/8 NPT brass nipple and goes into the engine. It works In the pic of the engine above you can see a -10 vent on the center front of the cam cover and another one

on the top of the tank at the rear. Needs a filter.

[1972Series4]

Follow up to WDB. Annnd it's a right hand drive so everything including the steering shaft is in the way and can't be moved.

[wdb]

More questions!

 

In my case there was crankcase pressure buildup which was causing leaks just about anywhere that couldn't take the pressure. Reading up on twincams, this seems to be a pretty common issue. People do all sorts of things to give the pressure somewhere to go. The dry sump system gave me negative crankcase pressure, i.e. vacuum, which keeps the oil inside instead of pushing it out. Hopefully this explains why I've been asking about the venting of your dry sump and crankcase. But it may not be germane to your issue.

 

First and foremost, what is your oil leak problem? I dug around a bit and couldn't find a clear answer.

 

It looks like you have a vent on the front of the cam cover. Where does that go?

 

There should be another vent at the right rear corner of the cylinder head; where does that go?

 

There are two ports on the top of the oil tank. How are you using them?

 

I have the relative luxury of LH drive. It makes the plumbing runs shorter but also a great deal more densely packed. You can see more pictures and discussion in my build thread. This link should get you to the page with dry sump stuff. 

 

Here are pictures of the top of my oil tank, showing how I vented the engine and tank. As you can see the cylinder head vent goes to the outer tank port, and the center port goes to a catch can which is then vented to atmosphere. (I checked the catch can yesterday and it is dry!) I had considered adding a cam cover vent but so far I don't seem to need it.

 

 

[1972Series4]

First of all where did you get that tiny filter? I think it will work well on my tank. My leak problem is where the block, head and timing case all come together. Even 20 seconds of running (no cooling system) left enough oil that it was hard figuring out where it came from. My first thought on pulling the cam cover was WOW there's a lot of oil up top. Hence my decision to put in a restrictor. On teardown, the timing case gasket looks suspect.

The vent on the front of the cam cover is a -10 AN base fitting welded on the back side by the previous owner. Since it has no evidence of oil flow I take that as a sign that there is good CC vacuum. He also welded a plate over the LR filler hole.

My vent/drain at the RR corner of the head is a rubber assembly that connects the two. It's about 2 inches forward of yours and it looks like in the pic you may have one also. The extreme rear hole that you have used on my head goes nowhere as verified by shining a penlight in the hole and is plugged by a steel insert on the bottom of the head. Alternate drain? Since I don't have a drain with 90 degree vent pipe like you that fitting on my tank is capped. The Lotus cap is used to fill the tank.