what kills con rods?

That looks like no Dellorto I've ever clapped eyes on!

It appears to have two independent floats on vertical guide rails. I assume the pivoting bit that actuates the float valve just sits across the tops of the two floats like a bridge. How do you set the float levels?

Cam
 
Hi Cam - There are two thin brass arms attached to the original style pivot that two pegs on the floats push onto to close the float needle valve like normal - you can just make one arm out in photo - not seen this type before either - Regards - Phil
 
That float setup is just like the flatslide Mikunis and most of the VM series. It is more accurate on rough terrain and likely at more severe angles of lean. Adjustment is easy, bending the tabs on the arm and the tab at the float needle.
 
It looks like the post year 2000 bowl that came on the Delordo fitted to 610 Huskys,I retro fitted one to my 1992 350 Husky.More stable fuel level over rough ground but the big plus was not flooding the engine when you crashed making restarting easer.
 
How do you set the float levels?
Click to expand...

Hmmm - Just beginning to wonder that myself as I can't see a way as yet to set the level with the floatbowl removed. The floats remain in the bowl and to rely on the little pegs attached to the floats that operate the float valve shutoff arm being always exactly in the same place isn't too reliable. Maybe - adjust until it leaks out of bowl breather and then back off a tad? - Not keen on that really though! - Regards - Phil
 
Here I start the topic again.
:) :) :) :) :) :) :) :) :) :) :) :) :) :) :)

Here you have discussed of two different types of conrod failures.
1) Failure during riding, mostly about 4000 RPM
2) Failure on start when the starter is rotating the engine.

On the type 1 failure, what actually failed first? Did the rod snapped or the lower end bearing get stuck?

I have a couple of other ideas which could fail a rod:

-Fatiguing on con rods if misfiring, knocking, hydraulic lock etc.

-Cracks on BTZ units, see mine on photo below. These units mostly worked but gave misfires and no sparks then and then, mostly the rider even don't notice these if happens seldomly. Later those get even worser, randomly on rain or even riding in a fog cloud did the engine to make banging noises on the exhaust system.

-Poor oil if lower end bearing fails first. The factory says that Total Bol d'Or or equivalent should be used, any worser should not be used. Many of you say here that the engine has problems with breathing, not meaning now the pressure pumping effect but the excessive evaporated oil from the breather hose. I think that indicates that you have a too worse oil for the engine, still of course not making alone a provement of a good oil if this doesn't happen. For instance on my SFC has a standard breathing system and you could open the air filter cover, get the air filter out from it and put your finger inside to the breather hose not getting any oil, dirt or even colour to your finger.
 

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I rebuild probably 18 to 20 Laverda cranks pre year on average
from approx. 10 cranks that I have seen over the years that had broken conrods not one of them had a seized big end

 
I wonder how many were damaged due to hydraulic lock and then broke some time later when they finally succumbed to fatigue.
 
In my experience, whatever the rod or it's history, the triggering event for the eventual breakage is a load reversal of some kind. I have seen roller bearing big end breakups both where the rod has broken as a result and where the rod was still in one piece and salvageable. I've seen plain bearing rods where again, there's been a breakage without damage to the big end shells - and ones where the big end has seized first. There's no hard and fast rule...

lately I've had two splendid examples of load reversal breakage through the workshop.
A late 1400 Kawasaki motor in a race car - and turbo'd...The new owner went the wrong way in the sequential shift at the top of 2nd gear - and put a Carillo out the front as a result.
An F3 kawasaki 400 four racebike which snapped a rod due to the (hard riding) owner leaving it in 3rd instead of changing up between corners, then dropping a gear and overrevving it entering the next corner. A rev limiter doesn't protect against stupidity. All big end shells are reusable...
 
Not sure exactly what you mean by load reversal Greg. The load on a con-rod is reversing all the time. It's cyclic and goes from compression to tension every revolution.

if you mean load on the engine going from power to over-run, they you may be right. An engine in over-run (engine braking) mode would generally put higher average tensile stresses on the rod, which might pull it apart if there's a flaw waiting to fail.
 
Dellortoman said:
The load on a con-rod is reversing all the time. It's cyclic and goes from compression to tension every revolution.
Click to expand...
At inlet stroke: tension
At compression stroke: compression
At power stroke: compression
At exhaust stroke: compression

Not very shure of conditions on engine breaking. I think that's a calculatory question.
 
For me, it's all about the F word.

Alternating load of any kind (compression-compression, tension-tension, or worst of all compression-tension) is neatly captured by the engineering/materials nightmare fatigue.

If our conrods do not have an inbuilt large fault (which causes almost immediate failure) then the fatigue life of the part will come into play and govern durability.

Parts usualy go pop during a tension phase.

The conrods have a pretty rough surface, and surface irregularities cause stress concentration, this area reaches its own localised fatigue life and.... bang, bye bye crankcase.
 
MotoJouni said:
At inlet stroke: tension
At compression stroke: compression
At power stroke: compression
At exhaust stroke: compression

Not very shure of conditions on engine breaking. I think that's a calculatory question.
Click to expand...

You're missing out inertia of piston and conrod which is of considerable figures, and I'd guess especially at higher revs and small throttle openings not fully compensated by gas pressures.
 
Old school engine building theory was when assembling an engine never-never let the connecting rods bang on the engine case.  Don't let a piston bang on a connecting rod. When installing the barrel on the piston(s) to never-never ever let the skirt of the piston rock..knock..or otherwise make firm contact with the connecting rod, once installed. The thinking is the piston skirt or engine case (even though it is soft) can mark..crease..or ding the surface of the connecting rod. That dinged area becomes a fatigue-stress point..even though it is only a surface mark..and in service, over time and heavy operation the connecting rod can fail beginning exactly at that dinged location. Some of the broken connecting rod pictures may lend some support to the theory.
crank-4%20jpg.jpg


The picture above (Yamaha engine..you get the idea) shows how easily the connecting rods could be nicely dinged by the engine case, if your not careful.
 
Avoiding the rod contacting the engine cases was pretty important when you were using alloy rods - Norton, Triumph, BSA etc..Modern steel rods against alloy cases, not so much IMO. Your chances of marking a steel rod in those circumstances are pretty slim. Doesn't hurt to be careful though.
Wish i had a dollar for every alloy rod i've carefully polished marks out of before bead blasting...
 
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