Lotus Twin Cam .120" oil orifice...pinging Rod;

[thruthefence]

Examination of the illustrations in the David Bean catalog shows an oil restrictor, #1710 with an orifice of 0.120".

A friend of mine over on the Europa board, is having low oil pressure problems on a fresh Twin Cam overhaul, clutching at straws now; but is anyone familiar with the placement of the orifice, and the likelihood of it's being overlooked during an overhaul? "overlooked" means "left out" of the casting. I would assume it would be removed for cleaning the oil galleries?

 

[ivymike]

...so from a project standpoint, when confronted with such a problem, I'd have a quick brainstorm session to try to identify other possible causes of the problem, then eliminate the easy ones first, then go after the hard ones. You might find that there is no way around another teardown, in which case it doesn't matter whether the orifice was left out or not, because you'll soon be looking for it.

in general, I'd start with whether you can determine adequacy of supply volume (or at least reduce the probability that supply is too low), then go after places where the oil could be escaping too easily (missing or damaged gasket? misplaced cooling jet? bearing with too much clearance? missing orifice?)

 

[patprimmer]

^^^^ plus clogged pickup, pickup to close to floor of sump, air leak on suction side above oil level.

Regards
Pat
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[Tmoose]

And of course double check that gauge/sender, too.

 

[thruthefence]

Yeah, all the easy stuff has been checked, pick up tube reswadged, (seemed a little loose where it was pressed into the block) screen verified clean, a "New" oil pump installed, mechanical direct reading gauge of known servicability installed, NO JOY.

an old moss-back once told me (regarding troubleshooting) if you're out in the Texas panhandle, and you hear the thundering sound of hoof-beats, don't think of zebras right off the bat. Think of horses or cattle.

In this case, the horses & cattle have been ruled out.

I understand that the orifice is in a place that will involve pretty invasive, labor intensive work to access.

thanks for the input!

 

[patprimmer]

evelrod will know this one. Wait for his comments.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[thruthefence]

I need to add that off idle, ( I wouldn't have tried this, myself ) oil pressure builds in a linear fashion with RPM, 60 psi @ 2500 RPM, no load.

 

[ivymike]

so the pump is working and the oil is leaking out somewhere... that orifice might be the culprit.

 

[evelrod]

Never seen a problem with the oil restrictor orifice. Generally, without it the top end would simply be flooded and I would think that would be noticeable. What it may be, and it's happened to me once when I was just learning the twincam Fords, is you may have the wrong main bearings. The factory (god love the British) had some bad block castings and rather than scrap them it was customary to over bore the mains 0.015" and fit oversize bearing shells to compensate. If, like me, you don't notice and put in standard shells, you will have the same problems as you describe. I have heard of it happening to others since then. My mantra is NEVER skip a quick Plastiguage....

Okay, I reread the posts and you mention the oil pickup. That is definitely something to consider. The early wet sumps had threaded blocks and the later Kent blocks had pressed in. I have had similar oil problems (air sucked into the pickup) and resultant bearing failure from improperly installed oil pickup. I don't use the stock oil pump or pickup so I had not thought of that. Also, the early pumps had the ck valve spring come loose when mechanics put a washer behind it to boost oil pressure. Stock twincams live quite well with 55psi hot and our race engines at 95psi hot (not attainable with a stock pump) but people still try by 'shimming' the ck valve. If you want a bit higher pressure, change the spring.

One other problem I encountered due to replacing the rear main oil gallery inspection plug with one that was a bit too long thus covering the secondary oil drilling to the main bearings...That was another dumb move on my part...low oil pressure to the mains and subsequent failure...There is a lot to learn AND a lot to forget. I hope some of this helps.

Rod

 

[BrianGar]

Having worked on one a long time ago, reaching into the corner of my head tells me the restrictor was pressed into block deck, before placing head. It was a so called aftermarket part as such, as the heads took far too much oil than was needed at high rpm. This lead to flooding, and failure to return to sump fast enough which meant the breathers took a hammering as did the priority journals/drillings.

My point is, its a simple test to see what is happening. Measure oil pressure at block, and then at head. If you have no pressure to head, its blocked. Or gasket could be fitted incorrectly(can you place these upsidedown?)
The engine should work fine without said flow restrictor since it was a sort of after thought. Which then leads me to believe its either blocked(If you have block pressure, but not head) or that your problems lie with the pressure bypass stuck open on the oiling circuit.
I have two links here on said issue which may interest you also,

http://www.lotuselan.net/forums/elan-f15/cylinder-head-oil-restrictor-t16875.html

See other link, on that link.
Its a long time ago since I built one of these, so maybe the links will provide more use than I can, but I do know It not being there will not matter. If its blocked, it will matter, do a block, and head pressure test and see if they are the same. If they are both low, suspect oil bypass. And also know that a new, dealer pump can have a faulty bypass as I found out, 3 times in 12 years. When you have to start doubting new genuine parts, engine building quickly becomes not fun anymore...

BG

 

[BrianGar]

Rod beat me to it, hes fast for an old guy ;P!

 

[evelrod]

Ole Rod...

 

[Ross0684]

Dumb question-what oil pressure is he getting?
I am happy to defer to the experts above, but "normal" oil pressure for the standard Kent engine is 40 psi.
My twin cam runs 35/45 psi and talking to more knowledgable persons than I, the consensus is volume is more important than pressure.
Chasing pressure gives a reduction in motor HP, when it may not be required.
Ross

 

[thruthefence]

a cut & paste from the original post:

"My rebuilt twin cam filled with 20W-50 has no oil pressure at start-up, but builds pressure at higher RPM. At engine speeds above about 1500 RPM, the oil pressure fluctuates. At idle, the oil pressure drops to near zero. I've verified the symptoms with a mechanical oil pressure gauge."

He's plastigaged the bearings, last post I saw,

NO JOY

 

[evelrod]

Yeah, would be nice to have a followup, TTF.
My money is still on the oversize main bearing bore.

Ross, back in the day, we would replace the ck valve spring to get a small boost in pressure and about 55psi hot was all the 'high volume' pump would do (that's 85+ cold and you had to be very careful not to rev the engine above 3000 until the oil warmed). Today we use a multistage dry sump pump suitably plumbed into the wet sump to achieve the 95psi hot pressures and still maintain less than 100psi cold...still using caution with revs until the oil warms.
We also now have an accumulator plumbed into the system (55psi release pressure) where back in the day we did not. It's all about leaving no stone unturned. If it saves ONE engine it will pay for it's expense. My engines in the late 60's made about 165hp, the same engine in the late 70's, 185hp...Today our David Vegher tuned engine is 197hp@8400rpm and he, as well as other vintage Lotus twincam tuners, are making in excess of 200hp from 1600cc on a regular, reliable basis. In order to make these high hp engines live at 9000+ rpm, it takes high flow and high pressure oil systems.

There is a world of difference in racing and street preparation. What will work reliably on the street often will end in catastrophic failure on the track...AND VICE-VERSA!

Rod

 

[thruthefence]

"mains have huge clearances" (speaking of axial movement on the crankshaft)

QUOTE FROM THE POOR GUY DEALING WITH THIS ISSUE.

Now, "Huge" is a pretty subjective measurement.

What sets crankshaft end play? Clearance on a thrust bearing, I suppose.

Is there a "plus-or-minus" limit called out?

 

[evelrod]

TTF, I don't have a book in hand, but typically something like 0.005"-0.009" would work. However, I really don't think that would account for the oil pressure problem. At least not totally or to the extremes you posted.

Perhaps this chap should take his engine to a qualified mechanic that knows what to look for. The bottom end of a Lotus is not much different than that of any English Ford (or Toyota clone, for than matter)!

Rod

 

[BrianGar]

Just to add another bit,
Ive taken vw inline 4s apart with 2.0mm of crank axial float, and they were perfect when running.

BG

 

[thruthefence]

Rod, I think he put an indicator on the crank, and got .007" which is nuts-on your 'ball park' figures.

The owner apparently bought this engine, overhauled by a local "experienced Lotus Twin cam mechanic", but never run.

I have no idea where he's located.

Everyone is about 'out-of-bullets' on this deal.

 

[evelrod]

TTF---Hey, what the heck is an experienced Lotus mechanic if it's not ME? I said at the outset of this thread that in the beginning all those many years ago (That's kinda like 'once upon a time'---I should have been a novelist ) I did exactly as I suggest is his problem...I had no idea that there was such a thing as a 0.015" oversize shell available or that the folks at Ford UK would produce such an overbored main bearing bore. Live and learn...I did. Since that engine (around 1968 or so) I have seen this done on several engines of UK origin. No where else, though. Like I said, ya just gotta love the British!

Bottom line---If it can happen to me, etc---:-(

Rod