Lotus Elan

Sudden big end noise?

PostPost by: Mr.Gale » Mon Jan 29, 2018 12:57 am

types26/36 wrote:
Mr.Gale wrote:Drop a valve? Mr.G


NIGELAN wrote: Pulled each plug lead in turn, no change in noise.and same drop in revs so assume that all cylinders are firing .


Unlikely to be a dropped valve if all cylinders are firing equally.


Yes, you are right. I wrote my comment before I realized there was a second page.

I dropped a valve in my Lotus Cortina once and what happen is the piston came up and bent the valve and pushed it up in the combustion chamber. The other bad new is it was a intake valve so it was firing out the carburetor and started a fire in the air box. The good news is it only put a mark on the piston and combustion chamber.

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PostPost by: Elan45 » Mon Jan 29, 2018 3:27 pm

I have the SE fabricated headers and back in the 70s when I drove my Elan everyday in the summer, I came home from the office one day sure I had a failed big end from the noise it made. A little investigative work that evening had eliminated the noise by tightening the header bolts.

Turns out that there was enough flex in the headers that when #4 loosened slightly, it would blow the header off the head slightly and then slam it back to the head when the pressure was released. This was a single cylinder sound that was very scary.

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PostPost by: Chancer » Mon Jan 29, 2018 3:44 pm

But not at tickover I would venture?
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PostPost by: NIGELAN » Mon Jan 29, 2018 5:05 pm

Embarrassed :oops: and need to apologise for leading you all astray.

I was certain it was firing on all four, but it wasn't!

No compression on no.1, spark plug has no gap, boroscope shows damage and possible chunk of metal in cylinder. :shock:

Did not look any further, depressed and also got flu now.

Will report back when engine stripped and taken to expert to determine what may be salvaged.

Thank you all, sorry to have misled.
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PostPost by: Chancer » Mon Jan 29, 2018 5:39 pm

Thats bad luck but it may not be terminal, check the valve clearances on that cylinder, you may have a collet adrift.

Fingers crossed!

Its random unstressed failures like this (might be) that put a whole new perspective on the discussion about using a Zetec engine.
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PostPost by: NIGELAN » Mon Jan 29, 2018 5:59 pm

Thanks Chancer, I spent time and money removing a zetec and replacing it with the original TC in my S4 (which is now a brilliant drve). It would be sad to have to put a zetec into the +2!

I will not give in without a fight. If nothing else it is all a learning experience :D
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PostPost by: MarkDa » Mon Jan 29, 2018 6:32 pm

Being optimistic and positive, it was running - therefore it's repairable.
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PostPost by: nmauduit » Mon Jan 29, 2018 6:39 pm

NIGELAN wrote:No compression on no.1, spark plug has no gap, boroscope shows damage and possible chunk of metal in cylinder.


sorry to read that... You may want to fiddle and look into that cylinder a bit more to check what kind of lose piece would be there (moving around a piece of copper wire to see what moves...)
Then if not in a rush and depending on engine condition before the problem, you may opt to remove the head first, in case it is a broken valve (I'm assuming there is no way something could have been swallowed by the carb...) then decide from what you uncover.

Good luck !
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PostPost by: NIGELAN » Mon Jan 29, 2018 7:30 pm

Having just looked at Miles Wilkins book page 102, he has a picture of part of a valve seat sitting in the cylinder. My piece of metal looks to be identical!

Miles captions this picture as .........."valve seat fell out making this cylinder head scrap".......

Mind you, what does he know about Lotus TCs....... :roll: :wink:
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PostPost by: rgh0 » Mon Jan 29, 2018 7:48 pm

I have had the same happen. Dropped a valve at 8000 rpm. it demolished the top of the combustion chamber totally so nothing was left but the water jacket hole. But it was still rebuildable.

cheers
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PostPost by: nmauduit » Mon Jan 29, 2018 8:00 pm

NIGELAN wrote:Having just looked at Miles Wilkins book page 102, he has a picture of part of a valve seat sitting in the cylinder. My piece of metal looks to be identical!

Miles captions this picture as .........."valve seat fell out making this cylinder head scrap".......


nowadays TIG welding to fill up a combustion chamber damage offers more options than back in the days... a careful assessment of the damage (and of the probable cause: if fallen seat was because of inadequate tolerance during a previous rebuild, you may want to change all seats... ) will lead you to a repair cost estimate as a basis for decision.
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PostPost by: denicholls2 » Mon Jan 29, 2018 11:59 pm

A failed crank isn't going to maintain oil pressure. Even a spun bearing won't maintain oil pressure. If you have oil pressure, unless it's a flywheel bolt failure it's unlikely to be a crank problem.

Crank failures rap twice as fast as top-end or jackshaft failures. Even at idle it's a pretty fast rap. rap-rap-rap-rap-rap instead of rap -- rap -- rap.

Very unlikely a big-end failure lets the engine run at idle, particularly if it's sudden. Too much friction. Failed bearings are the exception, but they come on slowly and always show low oil pressure.

With the cost of a Weber head, not sure which I'd rather have.

Are all of your airbox and carb-related bolts accounted for? Swallowing one of those can be the worst of both worlds. And makes a crank-speed noise if it gets past the valve.
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PostPost by: alan.barker » Tue Jan 30, 2018 6:36 am

If the problem is a Valve Seat i would only change the problem Seat. If the other Seats haven't moved leave them alone.
I hope the damage is not too bad.
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PostPost by: NIGELAN » Tue Jan 30, 2018 6:34 pm

This afternoon I removed the head.

Top of no.1 piston now pebbledashed with a couple of deeper gouges
Head combustion chamber now missing an exhaust seat and is extensively pebbledashed as well.
Bore has lost its honing marks when compared to the other cylinders but no scoring or gouge marks.
Have not checked big end yet for damage.

Will post some photos when I learn how.

Nothing more depressing than seeing an engine in bits :(
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PostPost by: NIGELAN » Tue Jan 30, 2018 6:54 pm

Some sad pics.

Any opinions from those of you who know?

Any suggestions as to repair experts near Buckinghamshire would be appreciated.
6.jpg and

5.jpg and

4.jpg and

3.jpg and

2.jpg and
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