Lotus Elan

Advice - carbs airbox clogged with oil!

PostPost by: seaandmoor » Sat Aug 19, 2006 4:46 pm

Hi all,
Did random checks to-day after the plus two was not running well. You know the oil fumes breather pipe which is connected off the rear right hand side of the engine onto the back of the airfilter box? Well oil has been coming from the engine along this pipe and has completely saturated/clogged the airfilter in about 500 miles.

I haven't experienced this on any other cars before but suspect it has been a problem on this one from the day I purchased it. Any ideas as to causes, better still any cures?
Thanks Seaandmoor
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PostPost by: john.p.clegg » Sat Aug 19, 2006 5:39 pm

Just a couple of guesses

1 Check your oil level,it may be too high and being chopped up by the swirling crank/big ends...

2 Do a dry/wet compression check to see if gasses are passing by the piston into the bottom end...

Others on here well give more accurate reasons/ideas no doubt

John :wink:
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PostPost by: Foxie » Sat Aug 19, 2006 5:50 pm

The good news:

Very probably your piston rings are worn allowing gas to blow crankcase oil mist into the airbox.

Run the engine with the dipstick out and check for gas blowing out.

Immediate action: Reroute the vent pipe to an oil catch can. It is not environmentally or road user friendly to vent it on the public road !

It helps if you have a threaded nipple fitted to the head opening to take a breather tube. Threadcutting not to be done in situ !

Future action: Fit new rings or a do complete rebore.

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PostPost by: seaandmoor » Sun Aug 20, 2006 10:31 am

Thanks for thoughts on that John and Sean.
The type of answers I was expecting really but (I'll probably be wrong) I somehow think there is another contributory cause.
I'll see what happens with the dipstick out and do the oil catch can temporary fix. (Oil level is between low and full and isn't overfilled)

The compression is up without leakdown, there's no puffs of white smoke out of the exhaust to suggest excessive wear and the rings/bores together all the valves/guides/springs etc in the head were only done about 2000 miles ago when converting to unleaded.
What next?

In the mean time I'll see if there are any other clues or pointers and let you know.
Regards, Seaandmoor.
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PostPost by: ElliottN » Sun Aug 20, 2006 12:45 pm

As an option for a catch tank instead of drilling/tapping your head or camcover - cliveyboy does a t-piece pipe which you can fit in place of the breather tube that blanks off the path to the airbox - you just have to engineer a catch tank off the bottom of the T.

Check http://www.cliveyboy.com/lotus.html
Elliott - 70 S4 dhc
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PostPost by: cliveyboy » Mon Aug 21, 2006 7:18 am

Seaandmoor
Are we talking about clogging up an air filter thats located in the nose cone, because that is pretty severe.
Usually the air breather is just for a small bit of mist which gets sucked back into number 4 cylinder, hence number 4 spark plug usually being oily.
Couple of suggestions:-
Is the engine normal size or is it a larger 1700cc conversion. the bigger volume engines have problems with oil breathing and chuck out lots of oil especially through the breather.

Also the airbox tends to get a slight oil/fuel mix in it normally, are your carbs set up correct (not spitting back) or could it be more fuel based than oil that is clogging up the filter. (You did not mention that you are using excessive amounts of oil).

When checking the blow back up the dipstick, you will always get a small amount which is normal.

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PostPost by: seaandmoor » Mon Aug 21, 2006 10:30 am

Hello Clive,
Thanks for that. For clarification... the air filter box in the nose cone is fine, it's the back half of the standard airbox that goes over the carbs air inlets that's clogged with oil and leaking out onto engine bay, not a lot but what a mess.
When I bought the car it had sponges over the carb air intakes which I was told was a fire risk if the carbs spat back. There was an upturned breather pipe off the back of the engine and I was getting a nasty smell of oil fumes in the car which made me feel sick.
Solution - fit original type airbox for the carbs air intake and reconnect the breather to the back of the airbox so that the original method of dealing with the 'crankcase blow-by gases' (page 62 Fig 27 of the workshop manual) is re-instated.
As regards losing oil, it started on the full line and after 2000mls it's 9mm below full, that's not much is it. No significant pressure out of the dipstick hole. You are right though about the rear plug on cylinder 4 being dirtier than the others.
So, do you think your 'T' piece gadget will stop the oil mist getting into the carbs airbox and still prevent the smell of hot oil getting inside the car?
Any others had experience of this problem? (whenever I take a car to the garage with a problem they always suck their teeth, scratch everywhere of their anatomy and say "very odd, never come across that before" :roll:
Thanks again, Seaandmoor
Attachments
Engine to airbox blow-by gas pipe.JPG and
engine blow-by gases to carbs airbox breather pipe
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PostPost by: cliveyboy » Mon Aug 21, 2006 12:42 pm

One of those Tee pieces would certainly stop oil getting into the carbs/airbox. You will also have to run a piece of hose from the tee piece to outside the engine bay preferably as Sean suggests via a catch tank.
Mine vents to underneath the car.
I know what you mean about the fumes, initially I did not use a long enough piece of hose to reach right under the car and fumes got into the cabin, (made the head spin abit)

Clive
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PostPost by: iain.hamlton » Mon Aug 21, 2006 2:35 pm

Seaandmoor,

I have a similar experience to you, but approached it slighly differently from Cliveyboy.

You can get a breather elbow to replace the breather connection to the airbox from Paul Matty, CN, ebay etc. I fitted one of these and connected to a catch tank. I find it works best if the catch tank is mounted lower than the head, and the elbow points downwards.

best regards, iain
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PostPost by: cliveyboy » Mon Aug 21, 2006 7:28 pm

I believe the rubber elbows are a standard Ford part used on their non twincam engines that use the same engine block
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PostPost by: poiuyt » Wed Aug 30, 2006 12:30 am

I connected a long section of radiator hose (5/8 or 3/4") to the connector at the head and ran ii past the engine and through a hole on the floor of the body ahead of the radiator. The head is vented and the junk doesn't wind up in the carbs.

Considering the oil that always seems to leak from the twin cam what little oil may come from this hose is minor
Steve B.<br>1969 Elan S4
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PostPost by: sk178ta » Thu Aug 31, 2006 8:00 am

I had a similar problem before I had my engine rebuilt. A rubber cork in the hole in the airbox and a longer tube from the breather hole into a catch bottle, actually a bike drinks bottle fitted under the carbs. It transformed the previously rough running at low revs.
Jim
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PostPost by: elansprint71 » Thu Aug 31, 2006 10:15 pm

"A rubber cork": I'm sure that is an oxymoron, or something similar! A rubber bung, perhaps. :twisted:

Pete.
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PostPost by: M100 » Thu Aug 31, 2006 10:26 pm

A rubber bung? Sort of what Bernie Ecclestone paid to the Labour party?
Martin
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PostPost by: mastijo » Fri Nov 17, 2006 10:06 pm

Seaandmoor,

Did you ever sort out your problem with the oil through the breather. I just finished restoring my 64 Elan and am experiencing the same problem.

I only have 300 miles on it. The engine was completely rebuilt. I have read that the blow by may be caused by the rings not being bedded in yet.

I plan to try the catch tank and monitor to see how it goes

John
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