Bottom end problems...
Discussion
All I know is that the recommended weight/force/inertia/stresses of the pistons at high rpm..7000+.. should not according to safety/manufacturing guidelines exceed 2.5 tonnes. Pistons in the speed 6 exceed 3.5 tonnes under such stresses, apparently. Hence why Craft are replacing mine and a couple of others with lighter weight pistons. Hope this makes sense - I'm not sure I've explained it well.
Al.
Al.
TUSC-AL said:
All I know is that the recommended weight/force/inertia/stresses of the pistons at high rpm..7000+.. should not according to safety/manufacturing guidelines exceed 2.5 tonnes. Pistons in the speed 6 exceed 3.5 tonnes under such stresses, apparently. Hence why Craft are replacing mine and a couple of others with lighter weight pistons. Hope this makes sense - I'm not sure I've explained it well.
Al.
Thats essentially as I understand it. Also I have been informed that the high rpm loads are causing the main caps to move around. They are single bolts either side of the cap and are dowel located. TVRCraft offer a solution to this which involves fairly intensive block rework around the block mains and making up billet end caps dual bolted either side. If anyone has the Sprint mag where TVRCraft were interviewed you can see a block with these caps done... shame they wont be on display they look lervely. Along with the lighter pistons and rods the crank will be tuffrided for additional strength.
I made my descision based on:
It would be a real pain in the ass to get to a decent mileage and the top end is fine only to find the bottom end suddenly lets go...
Rgds
G
TUSC-AL said:
All I know is that the recommended weight/force/inertia/stresses of the pistons at high rpm..7000+.. should not according to safety/manufacturing guidelines exceed 2.5 tonnes. Pistons in the speed 6 exceed 3.5 tonnes under such stresses, apparently. Hence why Craft are replacing mine and a couple of others with lighter weight pistons. Hope this makes sense - I'm not sure I've explained it well.
Al.
From what I remember from the talk, that was a fair chunk of it. Another item, IIRC, was a change in the conrod shaping which left more material at the smaller end and hence shifted the centre of gravity for the rod. I guess that doesn't help with the balacing at high RPMs.
MarkoTVR said:
From what I remember from the talk, that was a fair chunk of it. Another item, IIRC, was a change in the conrod shaping which left more material at the smaller end and hence shifted the centre of gravity for the rod. I guess that doesn't help with the balacing at high RPMs.
Similarly a change of shape in the crank.
Truckosaurus said:
It was reported that one of the LNT racecars "put a rod through the block" at the recent Istanbul LMES race.
It could have been any number of things that caused this (eg. engine seizure due to cooling/oil pressure failure) and without more info we'll never know. IIRC these engines are far from stock and operate in a race environment anyway so imo not a valid indicator.
I still haven't heard of any cases where the bottom end fails in the mode described by Melling in an S6 used for the road (someone prove me wrong!).
If you did a careful dynamic analysis of any engine, you would find ways of improving its balance so it could comfortably rev higher than its standard design limit. No machine is ever perfect....just good enough for the job it needs to do.
I'm not knocking the guys who've decided to go for the whole hog rebuild, but until Melling mentioned this theoretical problem, nobody knew anything about it because it's not something that's manifested itself.
>> Edited by dvs_dave on Tuesday 22 November 10:45
I think the implication is that the re-designed melling/craft head will expose the design flaws in the bottom end, as previously the head would be the first area to fail before any bottom end problems occurred. So, it's more of an issue if you opt for the Craft top end rebuild I guess. I went intending only for a top end rebuild, but when the engineering problem was explained to me it seemed prudent to go the whole hog and complete all the Melling recommended modifications. I want to hold onto my Tuscan for a while and missed any depreciation by buying at rock bottom second hand so to me the economics made sense, but i understand it won't to many people.
Cheers
Al.
Cheers
Al.
Hi Folks, heres some pictures of some speed six parts for discussion here.
Standard 4.0L engine components from a 2000 year car.
Below the rare and beter Farndon Billet Crankshaft.
Below Speed six with a hole in the block from Sebring 05.
A very worn (soft) finger follower
>> Edited by justinbaker on Tuesday 22 November 15:48
Standard 4.0L engine components from a 2000 year car.
Below the rare and beter Farndon Billet Crankshaft.
Below Speed six with a hole in the block from Sebring 05.
A very worn (soft) finger follower
>> Edited by justinbaker on Tuesday 22 November 15:48
JR said:
I'm not knocking the guys who've decided to go for the whole hog rebuild, but until Melling mentioned this theoretical problem, nobody knew anything about it because it's not something that's manifested itself.
How did Ocean1's engine fail?
Dunno....he just says in a post almost 12 months ago that his S6 engine had siezed after it sounded like it wasn't running an all 6 cylinders for a few miles? No more details so it could be anything.
Great pics Justin...very interesting to see these "ignored" components.
A few questions:
Does the Melling bottom end rebuild replace the crankshaft? I would have thought it would need to be replaced if you're putting in different mass pistons and conrods.
Does the engine still require the crank damper after this mod?
Will the fully rebuilt engines have a higher rev limit?
Will the engines be silky smoooooooooooth :smile: ?
>> Edited by dvs_dave on Thursday 24th November 15:37
A few questions:
Does the Melling bottom end rebuild replace the crankshaft? I would have thought it would need to be replaced if you're putting in different mass pistons and conrods.
Does the engine still require the crank damper after this mod?
Will the fully rebuilt engines have a higher rev limit?
Will the engines be silky smoooooooooooth :smile: ?
>> Edited by dvs_dave on Thursday 24th November 15:37
dvs_dave said:
A few questions:
Does the Melling bottom end rebuild replace the crankshaft? I would have thought it would need to be replaced if you're putting in different mass pistons and conrods.
Does the engine still require the crank damper after this mod?
Will the fully rebuilt engines have a higher rev limit?
Will the engines be silky smoooooooooooth :-) ?
For £11.5K I'd expect a warp factor 10 thrust option too!!!
justinbaker said:
Below the rare and beter Farndon Billet Crankshaft.
>> Edited by justinbaker on Tuesday 22 November 15:48
Hi Justin,
I'm not sure if this is a Farndon crank.
It is the one from my car (photographed at Autocraft). It is not marked "Farndon" and MCD identified it as being from one of their original development engines. We have no idea how it ended up in my car (which is otherwise a standard TVR speed 6 - not one of the development engines).
Does anyone know if Farndon made the development cranks for MCD, or if they were done in house ?
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