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What do you do if you spin a shell?!
#1463774
15/12/2013 22:23
15/12/2013 22:23
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The_Doc
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The_Doc
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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.
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Re: What do you do if you spin a shell?!
[Re: ]
#1463778
15/12/2013 22:30
15/12/2013 22:30
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jonofitzer
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jonofitzer
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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.
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Re: What do you do if you spin a shell?!
[Re: ]
#1463781
15/12/2013 22:41
15/12/2013 22:41
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The_Doc
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The_Doc
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Yes^^ I've noticed that too. The cost of an engine replacement is also a question worth asking.
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Re: What do you do if you spin a shell?!
[Re: ]
#1463810
16/12/2013 00:44
16/12/2013 00:44
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The_Doc
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The_Doc
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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?
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Re: What do you do if you spin a shell?!
[Re: ]
#1463815
16/12/2013 00:59
16/12/2013 00:59
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GrahamL
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GrahamL
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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.
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Re: What do you do if you spin a shell?!
[Re: lenzoferrari]
#1463852
16/12/2013 11:16
16/12/2013 11:16
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Craig1989
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Craig1989
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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?
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Re: What do you do if you spin a shell?!
[Re: ]
#1463853
16/12/2013 11:18
16/12/2013 11:18
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Joined: Dec 2005
Posts: 33,568 Berlin
barnacle
Club Member 18 - ex-Minister without Portfolio
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Club Member 18 - ex-Minister without Portfolio
Forum Demigod
Joined: Dec 2005
Posts: 33,568
Berlin
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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.htmlWhether 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!
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Re: What do you do if you spin a shell?!
[Re: ]
#1463855
16/12/2013 11:53
16/12/2013 11:53
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jonofitzer
Unregistered
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jonofitzer
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So would an upgraded oil pump be a good option.
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Re: What do you do if you spin a shell?!
[Re: ]
#1463856
16/12/2013 12:16
16/12/2013 12:16
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Joined: Dec 2005
Posts: 17,367 Staffordshire
Nigel
Forum veteran
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Forum veteran
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Posts: 17,367
Staffordshire
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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
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Re: What do you do if you spin a shell?!
[Re: ]
#1463870
16/12/2013 13:49
16/12/2013 13:49
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jonofitzer
Unregistered
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jonofitzer
Unregistered
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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.
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Re: What do you do if you spin a shell?!
[Re: ]
#1463958
16/12/2013 20:11
16/12/2013 20:11
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GrahamL
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GrahamL
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I thought the club bought the last of the 20vt cranks from Fiat? Not sure if they've all been sold now though.
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Re: What do you do if you spin a shell?!
[Re: ]
#1464073
17/12/2013 14:21
17/12/2013 14:21
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marcus300zx
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marcus300zx
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Re: What do you do if you spin a shell?!
[Re: ]
#1464114
17/12/2013 18:13
17/12/2013 18:13
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The_Doc
Unregistered
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The_Doc
Unregistered
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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.
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Re: What do you do if you spin a shell?!
[Re: ]
#1464116
17/12/2013 18:17
17/12/2013 18:17
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Joined: Sep 2006
Posts: 17,227 FCSS 01684 593187
Countrycruising
Club Rep Europe, member 914
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Club Rep Europe, member 914
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Posts: 17,227
FCSS 01684 593187
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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. 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.
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Re: What do you do if you spin a shell?!
[Re: ]
#1464117
17/12/2013 18:17
17/12/2013 18:17
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Big_Muzzie
Unregistered
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Big_Muzzie
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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
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Re: What do you do if you spin a shell?!
[Re: ]
#1464397
19/12/2013 10:10
19/12/2013 10:10
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marcus300zx
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marcus300zx
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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?
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Re: What do you do if you spin a shell?!
[Re: ]
#1464400
19/12/2013 10:25
19/12/2013 10:25
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Joined: Sep 2006
Posts: 17,227 FCSS 01684 593187
Countrycruising
Club Rep Europe, member 914
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Club Rep Europe, member 914
Forum veteran
Joined: Sep 2006
Posts: 17,227
FCSS 01684 593187
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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.
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Re: What do you do if you spin a shell?!
[Re: lenzoferrari]
#1464477
19/12/2013 18:05
19/12/2013 18:05
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Joined: Dec 2007
Posts: 2,252 Windsor/ Reading
knight7660
Competition Level
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Competition Level
Joined: Dec 2007
Posts: 2,252
Windsor/ Reading
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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 . You can get them regarded and like what has been said already. It will be the only option soon unless you buy a brand new one
Last edited by knight7660; 19/12/2013 18:09.
LE53 (452BHp & 389ftlb's with Quaife) Wine red VIS FOOFY Audi RS4 B7
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Re: What do you do if you spin a shell?!
[Re: ]
#1464479
19/12/2013 18:18
19/12/2013 18:18
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GrahamL
Unregistered
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GrahamL
Unregistered
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Has anyone actually had a 20vt crank reground and treated successfully and had it last a reasonable length of time?
I remember a few stories of unsuccessful attempts over the last decade or so but can't remember anyone saying they'd done it 100% successfully.
Obviously getting a new crank was almost always the preferred option until recently (due to cost/availability) so there are probably very few who have even attempted a repair.
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Re: What do you do if you spin a shell?!
[Re: ]
#1464481
19/12/2013 18:45
19/12/2013 18:45
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GrahamL
Unregistered
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GrahamL
Unregistered
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^^ Interesting, thanks.
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Re: What do you do if you spin a shell?!
[Re: ]
#1464489
19/12/2013 19:08
19/12/2013 19:08
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jonofitzer
Unregistered
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jonofitzer
Unregistered
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Some good info here.
Is it safe to say damage to the crank only happens when the knock first starts? And if a low oil pressure engine but not knocking would benefit greatly from a new set of shells that's if the crank measures ok?
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Re: What do you do if you spin a shell?!
[Re: ]
#1464493
19/12/2013 19:38
19/12/2013 19:38
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Pigman
Unregistered
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Pigman
Unregistered
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Some good info here.
Is it safe to say damage to the crank only happens when the knock first starts? And if a low oil pressure engine but not knocking would benefit greatly from a new set of shells that's if the crank measures ok? In reality, bearing damage occurs long before you can hear it. In this case the bearing being the interface between white metal bearing surface and hardened ground crank. It's just that the crank is so much harder than the white metal bearing surface that you can often get away with clean up/polish and replace white metal bearings (shells). The key to the bearings success is the layer of oil molecules between the two bearing surfaces. Once and if this is compromised damage starts to occur. You may not hear or notice it for a long time. Having spent 20 years in the bearing industry, the last five of those with SKF, I know a little about bearings. As for polishing a crankshaft and refitting it; it's often done and gives fairly good service, but with bearings often the ground surface is used to hold oil molecules in the microscopic valleys. A polished surface prevents this, so I would not expect a polished crank to last as long as a ground crank. Regrinding a crank, if done to the original manufacturers spec in terms of accuracy, concentricity, parallel and surface finish, should be as good as a new crank, again assuming that the nitriding is done properly. Of course, we find that sometimes the manufacturer's spec can be improved upon, but this is a specialist job and advice should only be taken from specialists in this field with a very good reputation. Nitriding is by no means a new treatment. It's been around for ages and I would have no hesitation in using a nitride and reground crank, with two caveats. 1.) The aforementioned trust in the quality of the machinist/workshop. 2.) An acceptance that by grinding the crank I have reduced the diameter of the bearing and therefore the crank will have less strength than previously. Knowing that these cranks can be used with much more than the 220BHP standard power, means that this wouldn't worry me too much, but I wouldn't use it in a 600BHP monster Coupe. It's only a little less strength and wouldn't be an issue in a standard Coupe. That said, Joe has such a crank in his track car and that's got a few horses.
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Re: What do you do if you spin a shell?!
[Re: ]
#1464495
19/12/2013 19:56
19/12/2013 19:56
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Joined: Sep 2006
Posts: 17,227 FCSS 01684 593187
Countrycruising
Club Rep Europe, member 914
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Club Rep Europe, member 914
Forum veteran
Joined: Sep 2006
Posts: 17,227
FCSS 01684 593187
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What is the typical cost of getting a crank re-nitrate joe? Their price is based on a minimum weight of 100kg, I'll find out the costs after Xmas as the paperwork was 2011 so it's with the accountant. Some good info here.
Is it safe to say damage to the crank only happens when the knock first starts? And if a low oil pressure engine but not knocking would benefit greatly from a new set of shells that's if the crank measures ok? Heat damages the crank so damage can occurs before the shell actually spins but it is however possible to salvage a crank if it knocks and is caught early, ie not driven/started. Low oil pressure engines aren't always down to excessive clearance with shell bearings. As Simon's showed a knackered turbo will also reduce the pressure, then there's the pump, oil ways to the cam buckets etc etc.
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