Conrod movment...

[Robin]

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.

[scotsjohn]

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.

[Yoof]

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 

[jake_smith]

ah man, My head's hurting. I didnt mean to start this argument 

[giorgio]

stupid HP engines have cranks made twisted so they 'strighten' up when you bosh a few hundred Nm through it.

[scotsjohn]

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.