Lotus Twin Cam .120" oil orifice...pinging Rod;
Lotus Twin Cam .120" oil orifice...pinging Rod;
(OP)
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?
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?





RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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?)
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Regards
Pat
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RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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!
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Regards
Pat
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RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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,
h
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
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Ole Rod...
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
"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
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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?
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Ive taken vw inline 4s apart with 2.0mm of crank axial float, and they were perfect when running.
BG
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
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.
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Bottom line---If it can happen to me, etc---
Rod
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Being an experienced air cooled VW boxer engine guy, I can absolutely verify that over boreing the main bearing bores in the crankcase is std operating procedure on the VWs when overhauling as the bearing shells inevitably pound into the aluminium or magnesium crankcase and lose bearing crush.
Regards
Pat
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RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Of course, at the time I learned about it (the hard way, of course), in my 'group', "VW" was used in the pejorative mostly. I love ya, babe...I'm just not a bug person!
Rod
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Regards
Pat
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RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
Here's the cut'n'paste from the long suffering Lotus Europa Twin Cam operator:
"I finally got the engine installed, and on start-up, the oil pressure is
60PSI. The problem was that the oil pickup tube was too close to the bottom
of the pan, which "strangled" the oil pump. I cut off 3/8" and now I have
great oil pressure."
Apparently someone suggested a wad of modeling clay under the oil pick up screen when dry fitting the pan, and then measuring the clearance!
"All's well that ends well"
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
I'm curious, and you may have already told us this way back somewhere .
#1 Is this engine based on a 711m or 771m "tall" block ?
#2 would it be "does it have a Lotus or Kent/Cortina pan on it ?"
I fear light is dawning on Marble head over here ...
RE: Lotus Twin Cam .120" oil orifice...pinging Rod;
For intent and purpose, save the rear seal, both pans are identical.
Rod