It's not happened...but what if? Has anyone had this happen to them? What mileage had it done, what mods did it have and what caused it? What did you do and more importantly how much did it cost?

Reason I ask is I have a 115K totally original 20vt which cost me £1k and although I have spent more than that again getting it all sorted, I haven't budgeted for an engine rebuild! Unless is was relatively cheap (under £1k) or possible to fix it myself without removing the engine that would be game over for the car basically.

Also would it be a good idea to replace the shells after a certain mileage, regardless of oil pressure etc.

It seems every second coupe for sale has had an engine replacement.

Yes^^ I've noticed that too. The cost of an engine replacement is also a question worth asking.

I've rebuilt 2 engines with spun shells.

The main thing is crank condition because the shells are soft, crank is hard so shells will assume the shape of the crank very quickly.

So in both cases I replaced the crank and while I was at it, and did a total strip down / rebuild.

The 2 I did were both Alfas that hadn't been topped up with oil.

What I didn't account for was paranoia. The thought of all my hard work coming to nothing was too much - the next time I just bought a second hand engine and did a swap and it worked out cheaper and took about 5x less time.

There is no 100% rule to what you can do if a shell has spun, you need to measure the components that will have been affected. If the crank is out of tolerance it needs replacing of grinding. No ifs or buts that the answer.

Note that the crank measurements must be taken with a micrometer and I'd recommend that they be taken in at least 6 places, 120 degrees apart and at each end of the journal. This will tell you wear, ovality and taper. Any measurements out of tolerance and the crank will need work or replacement.

Also, when you replace the shells, check for bearing crush.

When people just whack a set of shells in, they are basically a bunch of jokers that should have their tools confiscated.

Rudidudi, that all makes sense. And a new set of shells is a perhaps £200ish from what I have read on here. But that's only an option if the crank journals are okay. If they are not okay then you're basically looking at a bottom end rebuild with the engine out or a replacement engine, both very expensive.

In terms of preventing it happening, I imagine the main thing to watch is oil level. One thing that confuses me though. On this forum people mentioning oil pressure dropping and then a knocking sound and then they diagnose a spun shell. But which comes first, the spun shell or the drop in oil pressure? If the drop in oil pressure causes the shell to spin, what causes the drop in oil pressure?

They'll basically come at the same time.

Once the shell clearance is out of tolerance it'll leak oil out of the crankshaft (the big end bearings are lubricated at high pressure by oilways inside the crankshaft) right into the sump which will cause the drop in oil pressure.

The oil pressure drop will then cause more wear on the out of tolerance shell and it'll start knocking relatively soon after.

AFAIK that's what happens anyway, but I'm no expert on that stuff.

Graham is right, wear is certainly a factor that can impact oil lubrication.

I suspect that causes are multiple, some pressure losses due to spun bearings and others due to oil pump wear.

I'd love to pull apart and inspect a block that failed catastrophically due to oil pressure, there is far too much speculation on this issue without any substantial research. Of course bearing spinning is one outcome but why...?

I say it again, wear or bearing crush or oil starvation/pressure. Which causes which though?

If anyone has a failed engine they want to donate I'll do the analysis in the spring /summer...

The ones I did had progressively worse damage on multiple shells further from the supply but that's on engines that had total oil starvation.

Our VW Camper (which was just high mileage but had a good supply of oil) went within a minute or 2 of startup so I reckon the hot crank/shell bonded when the engine was turned off, then whatever was picked up destroyed the rest of the shell as it started. This leads me to think it was heat caused by lack of flow around the failing journal rather than a total lack of oil.

I don't have numbers or measurements to back it up but by observation it's almost always the big ends that expire, not the mains. Often when the big ends have gone, the mains and thrust washers will be fine, and unless there are metal parts moving in the oil the rest of the engine is fine - though I'd prefer a complete strip and clearing of all oil ways.

What do people mean when they say 'spun' a bearing? I've never seen one where the bearing has moved in its housing and while it is certainly possible for it to bend or break the locating tabs I think mostly we're looking at situations where the bearing stays in the right place in the big end but it running with inadequate lubrication.

I think the big ends are more susceptible to wear than the mains because they suffer asymmetric loads and have much smaller surface area (whichever big end is under thrust has two mains to support it) - I would postulate a mechanism where the oil flow is reduced leading to collapse of the laminar film between bearing and journal, leading to local contact and heating, leading to wear and eventually scoring of the journal.

If the bearing has marked the crank no point of trying to save it just bin it and buy a replace crank you don't want all your hard work going down the drain . You can't grind the crank down on the 20v turbo it is coated you will lose oil pressure .

What is it coated with out of curiosity?

You *can* regrind the crank but you *must* have the hardening replaced. This is usually the expensive part... a quick google finds an informative site in the Midlands: http://www.longwear-nitriding.co.uk/index.html

Whether it's financially viable is another question, but we're close to the point where it's going to be the only option for a scored crank.

Mind you, there's no great financial sense in pretty much anything we do to a coupe... doesn't stop us doing it!

So would an upgraded oil pump be a good option.

Not really - the standard pump is more than up to the job, but it does wear out eventually

When my oil pressure wandered near 1 bar on hot idle, I had the oil pump replaced and it went back up to about 1.75 bar straight away. Engine had done around 220,000 miles at that point

Back to the OP's question - if an engine spins a shell, the most expedient solution (and probably the cheapest too) is to swap the whole engine with a known-good secondhand replacement

But for how much longer? Not too many good engines out there.

I think the failing in the bottom end is the end float in the crank. I stripped a na motor a while back and it seemed huge. It seems to me that alongside good oil and frequent changes things like not sitting with the clutch pressed for long periods at traffic lights. That along with not heavily loading/labouring the engine all the time should work wonders for longevity.

There will come a time when a good engine is hard to source. Even the best serviced coupes can suddenly fail.

Roughly, how much would it cost to rebuild the bottom end in terms of preventative maintainence.

Cost of shells, a regrind and hardening

Probably 400 for the crank end of business

Then whilst you're there...

You can buy a new crank from fiat 600 I think ... You have a regrind and coated cost nearly 600 from what iv read .. If you your handy with a tool set and can read a book you can rebuild your own engine you can pick up forged pistons and rods for less then 800 then head set and bearing worst way 1200

Didn't think new cranks were available anymore, not even from Fiat?

I thought the club bought the last of the 20vt cranks from Fiat? Not sure if they've all been sold now though.

http://www.ebay.it/itm/Kurbelwelle-Fiat-...=item53d574f16d

Cranks aren't cheap

http://www.ebay.it/itm/Kurbelwelle-coupe...=item1c36437211

Found a cheaper one 499 euro, don't know why there is such a big difference in cost. Can't read German (or Italian) lol

These cranks need to be double checked they are right for our 20vt Blocks as I supplied one for FC's engine builder and he sent it back saying the design was different.

Yes because it's for a 2.4 stroke kit from cutaro racing who does the the hole kit for the fiat coupe

Wow, this question has produced some very interesting discussion. It appears to be a potential ‘coupe-killer’ particularly as good second hand engines become thin on the ground.

It makes me think that unless a spare engine of known pedigree is available, more effort will have to go into the bottom end rebuilds. As someone with a bit of metallurgical knowledge I do understand the issue of removing the hardened nitrided layer. The key to saving the engine must be to stop as soon as you hear a knock and pray the crank isn’t too badly damaged. Otherwise it’s hope for a better engine or try a reground and re-nitrided crank.

Not only to save the crank from further damage but also to reduce the amount of white metal being circulated around the engines oil ways. This is why I say don't run or drive the car until it's been diagnosed fully.

If you spin a shell you talk to a friendly coupe specialist, get a price for a fancy engine then lie to your wife, family and friends until you have paid for it

Can we get a laymans version of what happens?

There are lots of talk of the coupe spinning a shell, but from what I can see they don't actually spins a shell. What does happen and what causes the noise?

Is it something hitting something it shouldn't or is it something rotating without a coating of oil like it should?

Would it be something that has broken?

Can you visually see what has caused the problem by removing the sump?

I can see its shell and crank related but it gets confusing as people have replaced the bottom shells, but its more likely to be the main ones?

Causes seem to be lack of oil, either from the oil level being low or oil starvation from a blockage, but are there any more suspect pipes on the car, that are more likely to block than others?

It is exactly that, the shell bearing becomes hot, expands and gets picked up by the rotating crank so that it's then squashed against the other half shell. Other times it'll just be worn thin, either way the rattle is the excessive gap between big end and crank journal as the rod goes up and down commonly known as a death rattle.

With the sump and rod caps removed you'll see the issue, these failures are mainly big end because of the oscillating movement and force of the rod/crank.
Mains do fail mainly down wear/mileage, contamination or lack of oil, but my money is on big end number 3 as they seem to be the ones that fail the most.