Quote:
but with a gas engine there is less soot in the oil..
yup true
Quote:
the compression is less so the force is less from the fuel ignition..
uhhh no.
The higher compression and the fact that it's a diesel makes it easier on the rod bolts.
When the piston goes down, and switches direction to go up, there are compressive forces on the rod and rod bearings
When the piston goes up, and switches directions to go down, there are tensile loads on the rod (and therefore the rod bolts)
On the compression stroke, these tensile loads are offset by force required to compress the intake charge.
On the exhaust stroke however, there is nothing to offset this tensile load, so therefore the exhaust stroke is by far the worst for tensile loading on the rod and rod bolts.
Because the forces on the rod during the exhaust stroke have no real bearing on what the compression ratio is, the compression ratio is really irrelevant here. (having said that, a component of the compression ratio is the stroke, and stroke DOES have a impact on rod tensile loading because it effects piston speed)
Basically however fast your pistons and rods are moving, and however heavy they are is how strong your rod bolts have to be.
Quote:
from the fuel ignition
I think you're trying to reference the difference between gas and diesel engines here in terms of compressive loading on the rods.
Diesels in fact put much LESS force on the connecting rods during the power stroke.
Gas engines ignite with a "boom" and put a momentary surge of force on the piston/rod/crank.
Diesel engines burn with a "PUSH" that puts consistent pressure on the piston/rod/crank.
the "peak" pressure in a gas motor is much greater than the peak pressure in a diesel.
Quote:
so we have a larger mass compressing the fuel and a larger force pushing the piston back..
True, higher compression does equal more compressive forces on the rod, but were talking about the bolts failing.
Higher compression = more force pushing against the piston
more force pushing against the piston = less force required to stop the piston and turn it around (top of compression stroke)
As I said before, there is virtually no load on the bolts on the compression stroke, and the higher the compression ratio, the lower the load on the bolts.
Quote:
all this must be handled but the rods, rod bearings and the crank..
while speed might not be as high a a V8 the extra mass is not a linear function.
sudden changes in RPM increase the forces.
All things being equal, a diesel has way less throttle response than a gas engine. Any "sudden change in rpm" would be much greater on a gas engine than a diesel.
and again, were talking about throwing rods, which means were talking about rod bolts failing.
Quote:
lets not forget about harmonics..an inline 4 has more/different that a V8..both are more than a flat 6(Gold Wing 1500), inline 6(cummins) or a V12..
harmonics and engine balancing is a very complicated subject. it's true that different engines have different harmonic/balances...
This does however have very little to do with even crank shaft bearing loading, and virtually nothing to do with rod bearing loading.
I referenced a v8 because of it's stroke, bore and redline....
a 6.2L V8 is common, a 3.1L 4 banger is not.
We could talk about 2.5L gas engines though....... do the math and there will be way more tensile loading on the rod bolts at their redline than ours...
Any rod bolt will fail once the clearances in the rod bearing get too high.
long story short. these motors aren't throwing rods because the bolts are under designed. They throwing rods because the lubrication in north american jeep liberty CRD's sucks for various reasons.
Go call George at the vm specialists in the UK... these motors go 500,000 kms routinely in the UK, and are bomb-proof in boats....
Login
Register
FAQ
Search
4/11)..Bus gone to Scarp 8/23/11 
