Lotus Elan

Dancing oil filler cap

PostPost by: JonB » Sun Mar 25, 2018 10:45 am

Hi

I've been considering the oil leaks in my engine (in another thread about engine removal) and one of the things I was going to do was look at the crankcase breather situation. I started the engine and carefully undid the oil filler cap. I was very surprised when the cap, now loose, started dancing about on top of the oil filler. This is caused by the air pressure in the crank case varying as the engine turns, but it seemed a bit excessive to me. I put the palm of my hand over it and could really feel it.

This is normally a symptom of excessive blow by or maybe the breather tube that goes to the air box is constricted (usually by the pipe swelling due to oil contamination, I guess). However, I have extremely good compression figures - all cylinders are over 190 PSI - so I think blow by isn't the problem. I'm not sure - anyone care to advise?

Thanks
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PostPost by: MarkDa » Sun Mar 25, 2018 2:36 pm

You do need the crankcase breather to be working - so that's the first thing to check.
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PostPost by: steve.thomas » Sun Mar 25, 2018 5:49 pm

John
There is a wire mesh filter inside the metal part of the breather pipe which can easily get blocked. I don?t know if it?s removable but I cleaned mine by spraying in some carb cleaner.
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PostPost by: JonB » Mon Mar 26, 2018 8:26 am

I pulled the air box cover, ran the engine and put my finger over the breather pipe to feel for pressure gradients. There's hardly any air flow there. From the looks of the oil cap it should be chuffing like a steam engine! I took a borescope and slid it into the breather pipe. I couldn't get it right into the metal part (there seems to be a constriction or lip in the pipe that was too narrow for the camera) and couldn't quite make out the mesh thanks to the camera's limited focal length, but I expect it is at least partially blocked. I mean, it must be. Carbs off job to fix it, but not enough time before Peterborough. That'll be job #1 next weekend!
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PostPost by: billwill » Mon Mar 26, 2018 5:38 pm

I don't think it needs Carbs off, but Airbox off certainly. Then wash out the breather pipe & its internal mesh with petrol ?
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PostPost by: JonB » Mon Mar 26, 2018 6:37 pm

Can't get to it... the rubber pipe is 6" long.
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PostPost by: billwill » Tue Mar 27, 2018 12:13 am

Odd? On my S3 you have to undo one end, (usually the airbox end) in order to get the back of the airbox off the carbs; then the head end was just a push fit (I seem to remember).

I now have a copper pipe with a short rubber chunk just as a mounting, so current arrangement definitely not the same as yours.
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PostPost by: JonB » Tue Mar 27, 2018 8:14 am

Oh right, yes. Air box back removed, carbs left in place. That?d work.

Sorry. Normal service will be resumed as soon as possible!
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PostPost by: elanfan1 » Tue Mar 27, 2018 9:09 am

That's a job you could do whilst Spyder work on the other end?
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PostPost by: JonB » Tue Mar 27, 2018 9:38 am

They don?t seem to want me in their garage. Kill joys.. :D

Probably ?elf n safety innit?
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PostPost by: JonB » Fri Apr 13, 2018 9:07 pm

To report back on this, briefly.

I took the rubber pipe off with its bit of fuel pipe bodged up connector, and removed the fuel pipe, then found a piece of copper pipe that fits in the breather hole on the head. It's about 13.5mm diameter. This after examining the parts list to see what the proper pipe looks like. Fitted it to the head and slid the rubber breather pipe over it, all good.

There appears to be much less oil leakeage from the timing chest and the oil filler cap isn't jumping about so much when resting on the filler neck. Result.
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