sorry about anotheerrrrr thread haha but good for the future when people search ;)
Anyway, just removed my sump and the crank seems fine.. no play in it what so ever.
BUT the conrods have movent side to side about 2mm im assuming this aint normal!?
There is no movment up and down though.. so im have no idea.
So you're saying that when you grab the big end it moves 2mm side to side in each direction??
I'm certainly no expert with this, but as the pistons&rings have a small gap between them and the cylinder...could the movement of the conrods not be due to this gap?
no not when i grab tyhe big end. When i grab the bottom of the conrod.
And i always thought the piston moved on the gudean pin or whatever its called.
The big end is the bottom of the conrod.
ohh i always thought the big end was the crank bearings? or is that the main bearings haha.
Anyway yeahh back on track.. any ideas people :)?
How much oil are they ment to hold?
If it has a small amount of play side to side on the crank (and therefore gudgeon pin) this is nothing to worry about.
hello youth , the movment is aboutttt 2mmm either side and if i move it really quick i can hear it taping the sides.. so im thinking if a engine is running while its doing this will it not make a noise?
But there is no movement up and which make me think there fine!
You'll see this play of this amount on most engines. It allows for crankshaft flex if I remember rightly.
ahh ok then sound. Ive been woried these past few days that its fucked haha. Ill put the sump and and fill her back up with oil.
Just out of curiosity what amount of oil do they hold?
Quote from: scotsjohn on May 10, 2010, 05:02:08 PM
You'll see this play of this amount on most engines. It allows for crankshaft flex if I remember rightly.
Endfloat... I'd be worried if you managed to get a crank to flex ;)
Basic physics Yoofy;anything that takes explosive forces flexes. A couple of thousand explosions a minute spread over the length of the crank has an effect. You can minimize it with attention to balance and tolerances but it wan't dissappear entirely. Conrods shimmy to and froe on the journals for that reason.
Thanks for the lesson.
I don't suppose it's something that folk consider any more. I'm from the era of the four cylinder,three bearing crank which says it all. As for lessons,I'm pretty sure if I need to know something about G's then you're the man.
The 'flex' as you call it of a crankshaft is minimal- especially in a Polo Block, granted on A series engines of old you'll have issues, this isn't why a con-rod is allowed movement on the crank thought is it.
The real reason is to allow a clearance for the oil film to be expelled and thus have oil flow, besides the fact that engine built without endfloat is siezed solid, ergo to have endfloat you also need clearance on the rod laterally- imagine it as a self centre with the gudgeon pin (also floating).
The reason for the movment isn't to allow for 'crank flex'.
I can confirm that Yoof is unfortuantly right in this case.
The sideways movement of the rods is there for a few reasons rather than just one, and no its not because of the flexing of the crank.
Not only does the big end move from side to side but it also moves side to side on the grudgen pin. Without this movement the rod would either seize on the crank or grudgen pin.
Flexing of the crank is absolutely minimal, with a short crank like the G40 one i would expect to see very very little if any flexing under load.
I'll second that.lol!
No, to be frank I see what Yoof's saying and can take it on board. But 2mm play either way isn't end float, it's a rattling good fit, much more than you'd need in a perfect world. Under normal loading the conrod will track pretty consistently, but that all changes if you do something like selecting fifth gear instead of third at low speed. Loading on the crankshaft becomes massive and no matter how well supported it is, it will deform. It's difficult to visualise, but it's like microscopic wave passing up and down the crank that the conrod has to ride. That's the way it was described to me at the National Engineering Laboratory and i believed it. Silly old John.
I never said the endfloat was 2mm...
I understand completely what you're trying to say- but your principle and reasoning is wrong behind conrod movement.
John- if you're talking about elastic deformation causing lateral oscillations in the crank, then I'm well versed, having sat through hours of advanced engine technology lectures... if you want to understand and be able to calculate and appreciate it's impact then Heinz Heislers Advanced Engine Technology is a good place to start, saw me through a HND and most of the final year of my degree.
If you really want to know about crank flex (and it does happen in extreme cases/ poorly designed ones) then research top fuel methanol big blocks, several thousand horsepower, that use deformation of the main bearing (width) to measure det- an obvious case for 'crank flex' and extreme cylinder pressures causing an excessive force to be placed on the bearing shell. Considering most headgaskets would pop at 90bar cylinder pressure you need to got alot further to get an explosion with a large enough force to 'flex' a crank properly. I understand you're taking about harmonics and a movement of microns (it has to be circa <15 microns to retain a decent oil film on the bearing) but to me 'flexing' is big boy top fuel talk.
Robin, it's a gudgeon pin.... retard :P
ah man, My head's hurting. I didnt mean to start this argument :D
stupid HP engines have cranks made twisted so they 'strighten' up when you bosh a few hundred Nm through it.
Been away for a wee bit so just had a look at this tonight; thanks for the lesson Yoof ( not tongue in cheek). The mention of harmonics was interesting though. Ex workmate's doing an odd Skyline project; looking for 700 horses. He's just acquired a crankshaft pulley fitted with a harmonic damper; his crankshaft nose is eating bearings.