Rover V8 good for only 100k miles ?
Discussion
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This being the case, why did my Griff need a full engine rebuild after 21,000 miles, and why do we hear of so many V8's going pop before 100,000 miles?
Also it seems to me that far more of the Griff 500 engines suffer than the 400. If this isn't caused by the excessive stress the engine is placed under, what is it caused by?
(Disclaimer: Don't ask silly questions did you keep it serviced, full of oil, drive @ 7000 rpm all the time? etc. etc.)
I have not heard or read of many of the Rover V8 engined TVRs going pop, where do you get this idea from? I see from your profile you had a Griff500 and remember some of your comments from other threads. Your Griff was second-hand, how do you know what the previous owner(s) did, or did not do? Any tuned engine that is thrashed from cold (for example) is highly likely to go pop at some point, used properly and maintained properly the Rover V8 is as reliable as any other engine.
OK leaving aside the silly questions which IMO account for a large majority of problems, and widespread use of Mobil 1 (which most V8 specialists I've spoken to regard as unsuitable for the engine), I can think of some reasons the 500 engines might not be as durable as the smaller ones: a longer stroke puts more side loads on the pistons, shorter pistons are less stable and damage the bores more, and a wilder cam puts greater stresses on the valve train.
Here are some figures for those of you who are inclined to be overly curious about what actually is happining inside your engine. Comparisons are for a 3.5 and a 5.0 engine. Piston speeds (PSN SP ), rated in inches a minute. 2000 rpm 933/1180, 3000 1400/1770, 4000 1867/2360, 5000 2333/2950, 6000 2800/3540.As you can see, the longer stroke engines have much higher speed than the 3.5. Want to feed you head some more ? Piston G's (PSN Gs ), acceleration in G's taken at TDC, which is the highest rating. Same engines, same speeds. 2000 rpm 203/257, 3000 457/578, 4000 813/1028, 5000 1270/1606, 6000 1829/2313. This is the part that tears your beloved engine apart ! Take the average weight of a cast/forged piston, multiply by the G's, and see exactly how much weight is being thrown around inside the motor. NOW add in the piston speed this weight is traveling at, and you will be amazed at how they can keep everything together ! Play with the figures a little bit, and you will see that in some instances the pistons are actually traveling farther than the vehicle, given time/gear/rpm. Mr. Green V8S, how about those G figures ? Now if we could only do this on a skidpad, eh ! Hope this helps some, rather than muddling up the picture.
I think I'd better start by saying I'm no guru on this, or any subject for that matter 
, however I do have a good general understanding of most things, electrical and mechanical.
So if the 500 has much greater piston speeds by virtue of the longer stroke, surely the fact that it also has lightened and balanced con rods and pistons counters this effect as the amount of energy being thrown around is directly proportional to the speed and weight of the moving parts?
I haven't got a clue as to how much lighter the moving parts are, but I would expect them, along with the higher speeds to equal out, so that the stresses are pretty even?
I'll go along with Peter H on the side loads though, as with the longer stroke comes a greater sideways movement of the con rods on the crank and hence on the bore.
Anyone who strips these down noticed any greater bore wear on the 500 as against the 400??
Harry
, however I do have a good general understanding of most things, electrical and mechanical. So if the 500 has much greater piston speeds by virtue of the longer stroke, surely the fact that it also has lightened and balanced con rods and pistons counters this effect as the amount of energy being thrown around is directly proportional to the speed and weight of the moving parts?
I haven't got a clue as to how much lighter the moving parts are, but I would expect them, along with the higher speeds to equal out, so that the stresses are pretty even?
I'll go along with Peter H on the side loads though, as with the longer stroke comes a greater sideways movement of the con rods on the crank and hence on the bore.
Anyone who strips these down noticed any greater bore wear on the 500 as against the 400??
Harry
Piston speeds (only ): actually I was only trying to show the difference in piston speeds for the examples shown. All things being equal, the internal parts are moving faster in the 5.0 engine-regardless of the amount of weight involved, thus adding to the wear internally. Frictional horsepower losses increase also. I'm sure you will agree, that if two identical weight reciprocating assemblies are spun at different speeds-the higher speed one stress the engine more. Now to G's: Any increase in load "must" be counteracted by an increase in strength-or the damned thing will blow apart ! What are the weight of the parts being examined ? Beats me, maybe some of our more knowledgeable readers could add to this. Peter H is correct about the side loads-but I was trying to explain why (maybe ), the engines go "pop", rather than just wearing out. After all, just run around a while without your air filter, and see what this does to the "normal " average wear factor. While we are on the subject of side loads-ever think of what happens everytime you slam the clutch out-drive the crankshaft forward-that's what end play and thrust is for. Talk about connecting rod misalignment...at 6 grand ! Through how many gears-how many times. Again my intent was only to show what was happening "inside" the engine, not to confuse or muddle up the picture, nor did I intend to make this some kind of major thesis. Thanks......
Concur that this is just a shallow look at the engines, any deeper and I'll drown . As stated the 500 does have lightened, balanced rods and pistons, so perhaps it's just to help reduce the effects. Just curious really for someone that strips these to comment on whether they've noticed any marked difference in the wear patterns?
Rest assured that any work of this magnitude required on my toy it will straight to man that knows, talking's one thing doings another
Harry
. As stated the 500 does have lightened, balanced rods and pistons, so perhaps it's just to help reduce the effects. Just curious really for someone that strips these to comment on whether they've noticed any marked difference in the wear patterns? Rest assured that any work of this magnitude required on my toy it will straight to man that knows, talking's one thing doings another
Harry
My goodness, shame on me for even getting someones feet wet, let alone drowning them ! Please accept my apologies, it was not my intent to carry subject matter beyond anyones capabilities. Oh yes, you are quite correct, as anyone who should desire work of this caliber/magnatude should definately consult a professional in this field. Talking is one thing as you stated....at least 339 times, it states in your profile, which beats my total replies by a whopping 304 ! Very nice car by the way, I envy you !
quote:
Here are some figures for those of you who are inclined to be overly curious about what actually is happining inside your engine. Comparisons are for a 3.5 and a 5.0 engine. Piston speeds (PSN SP ), rated in inches a minute. 2000 rpm 933/1180, 3000 1400/1770, 4000 1867/2360, 5000 2333/2950, 6000 2800/3540.As you can see, the longer stroke engines have much higher speed than the 3.5. Want to feed you head some more ? Piston G's (PSN Gs ), acceleration in G's taken at TDC, which is the highest rating. Same engines, same speeds. 2000 rpm 203/257, 3000 457/578, 4000 813/1028, 5000 1270/1606, 6000 1829/2313. This is the part that tears your beloved engine apart ! Take the average weight of a cast/forged piston, multiply by the G's, and see exactly how much weight is being thrown around inside the motor. NOW add in the piston speed this weight is traveling at, and you will be amazed at how they can keep everything together ! Play with the figures a little bit, and you will see that in some instances the pistons are actually traveling farther than the vehicle, given time/gear/rpm.
Good point, the extra inertial loads caused by increased piston speed will probably dwarf the effects I mentioned. Makes you wonder how these things survive at all?
Cheers,
Peter Humphries (and a green V8S)
quote:
... widespread use of Mobil 1 (which most V8 specialists I've spoken to regard as unsuitable for the engine) ...
Why and what's better?
On piston speeds: The energy involved increases with mass and with speed squared [E(k)=(m.v^2)/2 - sorry!]
The upshot of which is that if you double the piston speed and half its weight it will still have twice as much energy to dissipate as it did before. Double the speed, same weight: four times the energy. Double the speed, quarter the weight: same energy.
And you couldn't reduce the weight much for a speed double as it would have to be stronger: it might even be heavier. Hope this doesn't deepen the waters further.
I've always been struck by that fact that at 6000 rpm, say, each piston is belting up and down 100 times per second - I'm impressed they stay together at all
Peter and John....thank you ! Was beginning to think I couldn't explain something any longer. Tried to do it without the math, for those who might not be the worlds greatest mathematicians...just giving a general idea, without the headaches, so to say. Anyone know of a good scuba sales outfit, for those that may have drowned ? I have a feeling they might need it. Thanks again.....
Thanxs for the 'O' level revision John perfectly clear now , so when I assumed that speed and weight were direct proportional it wasn't quite the whole story with the speed component being squared 
happy now. Moral lighten to your hearts content, but it won't fully overcome the problems associated with increased internal component velocity.
I may well be self depreciating but don't assume that means I'm beyond educating
Harry
, so when I assumed that speed and weight were direct proportional it wasn't quite the whole story with the speed component being squared happy now. Moral lighten to your hearts content, but it won't fully overcome the problems associated with increased internal component velocity. I may well be self depreciating but don't assume that means I'm beyond educating
Harry
I think (?), that at one time or another we are all self depreciating, to one degree or another, and as far as being able to increase our intel level that's why we are here isn't it ? My learnig curve has been rather rocky, that's why on one wall of the garage I display all the broken parts, from mistakes in calculations or just plain old brain farts. Beleive me it's a LONG wall, and it's rather full ! A lot of stories hang there, some good, others not. The object is to pick up all your marbles and keep on going, and learn to tell and laugh at yourself, for all the stupid shit I did ! Have fun, ask questions and learn, and share your information with someone....even if it's only on how to apply wax, the proper way.
LOL haven't even learnt the waxing bit properly yet Just hope nobody has to put this theory to the test on my lump in the foreseeable future. An old saying that is often used, but is very true, is that a day when you do not learn something, is a boring day (that or you've been asleep all day!)
Happy motoring.
Harry
Just hope nobody has to put this theory to the test on my lump in the foreseeable future. An old saying that is often used, but is very true, is that a day when you do not learn something, is a boring day (that or you've been asleep all day!) Happy motoring.
Harry
I always thought it was 'deprecating' rather than 'depreciating', however....;-)
As far as the mass/wear/weight discussions go: my 390 has just acquired new pistons (standard Rover cast jobs) that are heavier than the old forged ones. They also have deeper skirts, so will perhaps cause less bore wear. Having said that, at 102,000 miles, the bore wear was negligible, and the pistons scarcely worn at all (i.e hardly elliptical!).
I recall that ? Cosworth published some figures suggesting that a typical piston, at high revs, effectively exerts a tension of >7 tons on the conrod as the crank goes over TDC. One reason why I've fitted new conrod bolts during my rebuild!
W.
As far as the mass/wear/weight discussions go: my 390 has just acquired new pistons (standard Rover cast jobs) that are heavier than the old forged ones. They also have deeper skirts, so will perhaps cause less bore wear. Having said that, at 102,000 miles, the bore wear was negligible, and the pistons scarcely worn at all (i.e hardly elliptical!).
I recall that ? Cosworth published some figures suggesting that a typical piston, at high revs, effectively exerts a tension of >7 tons on the conrod as the crank goes over TDC. One reason why I've fitted new conrod bolts during my rebuild!
W.
message. OK here goes again. This time I’m being sensible and composing in Word to cut and paste later. I was lying awake last night worrying about this and I had to get it off my chest ...
And I’ve done most of my thinking while typing before, so this should be shorter If you’re worried about drowning, skip to the end 
What I said above about calculating energy is correct but is certainly not the full picture on wear in the engine.
The kinetic energy in the pistons will be transferred to the crankshaft, making the car go.
The energy in the exploding fuel will:
overcome friction between the pistons and cylinder walls;
overcome friction in the crankshaft;
supply energy to push the pistons up to expel exhaust or compress fuel/air and drag them down to suck in fuel/air;
drive the crankshaft round;
and other minor stuff.
The crankshaft is resisted by the transmission, friction between the wheels and tyres, air resistance, etc.
Inside the cylinder, wear is caused by friction between the piston and cylinder liner. The amount of that friction depends on how fast the piston is moving and how hard it is being pushed (thrust). It does not depend on the weght of the piston.
The downwards thrust from the exploding petrol is more or less evenly spread across the pistonhead () so it’s in line with the cylinder. The upwards thrust will be in line with the connecting rod between the piston and the crankshaft – so it is almost never directly in line with the cylinder. The greater the eccentricity of the crankshaft (due to a longer stroke cylinder) the more this thrust pushes the piston against the side of the cylinder, and so the more the friction increases. This friction generates heat and also wears away the side of the cylinder and piston. This friction is reduced by the engine oil.
The thrust downwards acts on the crankshaft (making it turn), and is resisted by the crankshaft bearings (stopping the crankshaft from being shoved out the bottom of the engine). The downwards thrusts on the crankshaft are due to the force of the exploding fuel (in two cylinders at any one time) the momentum in the pistons (in four cylinders at any one time), the resistance to the exhaust gases being vented (in two cylinders) and the fuel/air mix being compressed (in two cylinders). There are upwards thrusts due to the momentum in the other four pistons, and the fuel air mix being sucked in. (That last may not entirely accurate as I’m not sure how fuel injection works).
(Momentum = mass x velocity)
The thrust in the crankshaft bearings will increase friction in the bearings at the bottom, and will tend to deform the bearings themselves. The friction generates heat and will tend to wear the bearings away over time.
The friction is reduced by the engine oil (which loses its lubricating properties with both time and use), and the deformation is resisted by the hardness of the materials used to make the bearings.
The wear will be more evenly distributed with a V engine than a comparable inline one (straight 8?), and more evenly still with a boxer engine. In fact a boxer layout must be a lot more efficient than a V or straight.
Engines that are modified to deliver higher performance often have different crankshafts fitted even if the stroke isn’t changed (eg TVR 390SE) – the thrust the bearings have to deal with will be greater.
And all this friction is why you have to CHANGE YOUR ENGINE OIL!
If you’ve read this far, thanks for your patience and I hope you haven’t drowned. If you think I’m wrong, please say so, this is a bit off my specialist subject.
If you’ve skipped to the end, I don’t blame you – just read the bit in capitals above.
John
.
PS I train engineers!!!
PPS OK civil engineers.
>> Edited by JohnLow on Thursday 9th May 13:02
And I’ve done most of my thinking while typing before, so this should be shorter
If you’re worried about drowning, skip to the end What I said above about calculating energy is correct but is certainly not the full picture on wear in the engine.
The kinetic energy in the pistons will be transferred to the crankshaft, making the car go.
The energy in the exploding fuel will:
overcome friction between the pistons and cylinder walls;
overcome friction in the crankshaft;
supply energy to push the pistons up to expel exhaust or compress fuel/air and drag them down to suck in fuel/air;
drive the crankshaft round;
and other minor stuff.
The crankshaft is resisted by the transmission, friction between the wheels and tyres, air resistance, etc.
Inside the cylinder, wear is caused by friction between the piston and cylinder liner. The amount of that friction depends on how fast the piston is moving and how hard it is being pushed (thrust). It does not depend on the weght of the piston.
The downwards thrust from the exploding petrol is more or less evenly spread across the pistonhead (
) so it’s in line with the cylinder. The upwards thrust will be in line with the connecting rod between the piston and the crankshaft – so it is almost never directly in line with the cylinder. The greater the eccentricity of the crankshaft (due to a longer stroke cylinder) the more this thrust pushes the piston against the side of the cylinder, and so the more the friction increases. This friction generates heat and also wears away the side of the cylinder and piston. This friction is reduced by the engine oil. The thrust downwards acts on the crankshaft (making it turn), and is resisted by the crankshaft bearings (stopping the crankshaft from being shoved out the bottom of the engine). The downwards thrusts on the crankshaft are due to the force of the exploding fuel (in two cylinders at any one time) the momentum in the pistons (in four cylinders at any one time), the resistance to the exhaust gases being vented (in two cylinders) and the fuel/air mix being compressed (in two cylinders). There are upwards thrusts due to the momentum in the other four pistons, and the fuel air mix being sucked in. (That last may not entirely accurate as I’m not sure how fuel injection works).
(Momentum = mass x velocity)
The thrust in the crankshaft bearings will increase friction in the bearings at the bottom, and will tend to deform the bearings themselves. The friction generates heat and will tend to wear the bearings away over time.
The friction is reduced by the engine oil (which loses its lubricating properties with both time and use), and the deformation is resisted by the hardness of the materials used to make the bearings.
The wear will be more evenly distributed with a V engine than a comparable inline one (straight 8?), and more evenly still with a boxer engine. In fact a boxer layout must be a lot more efficient than a V or straight.
Engines that are modified to deliver higher performance often have different crankshafts fitted even if the stroke isn’t changed (eg TVR 390SE) – the thrust the bearings have to deal with will be greater.
And all this friction is why you have to CHANGE YOUR ENGINE OIL!
If you’ve read this far, thanks for your patience and I hope you haven’t drowned. If you think I’m wrong, please say so, this is a bit off my specialist subject.
If you’ve skipped to the end, I don’t blame you – just read the bit in capitals above
. John
. PS I train engineers!!!
PPS OK civil engineers.
>> Edited by JohnLow on Thursday 9th May 13:02
quote:
Inside the cylinder, wear is caused by friction between the piston and cylinder liner. The amount of that friction depends on how fast the piston is moving and how hard it is being pushed (thrust). It does not depend on the weght of the piston.
Just to prove I did read your post (which I think was pretty well spot on) I'll just make one minor quibble ...
Never looked inside a running engine to check, but I wouldn't expect the bore wear to vary with piston speed. Piston wear probably would, though.
The reciprocating mass (piston, little end, part of the con rod) is accelerated vertically by the con rod, this causes a vertical load on the con rod which increases with revs and with reciprocating mass.
Since the con rod is at an angle when these loads are present, this introduces a corresponding side load between the piston and the cylinder wall. My guess is that because of this side load, heavier pistons and increased revs would each increase bore and piston wear.
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