https://www.sciencedirect.com/topics/engineering/connecting-rods
Um, thanks for the link but I dont see the relevance here.
Model engines use a single overhung crank with a mist of fuel entering from one side and as such are highly assymmetrical.
Every example in the link seems to use a double overhung crank with a pressurised feed and is highly symmetrical. Taking example of that is fraught with misconception, and again every example (except for the rifle drilling) shows that slots and holes are exit not entry points.
The only way we are ever going to resolve an argument like this is with wear patterns.
This is my logic, with an assymmetrical system oil entry is undoubtably the same, one side will simply allow more flow to enter and similarly the other more flow to exit. Witness a standard conrods big end with no added holes or slots to confuse the issue.
It works, it allows oil to enter the eye and oil to exit but in which direction?
From a fluid dynamic point of view you could argue that it is from the direction that the oil is presented to it, so in a typical front induction model engine that is from front to back and thus the front of the eye receives higher pressure and conversely the rear is a lower pressure area being further away.
From a mechanical point of view a single overhung crank flexs the further away you apply force from the supporting bearing and thus the load bearing crank pin angles away from that load. This allows the rod that applies the force to migrate away from the support, in other words part of the rods mission in life is to walk off the big end and collide with the backplate. No matter how much running clearance you allow between the rods big end to the static backplate and driven crank bearing it will always tend to be assymerical also and a bigger oil entry point presented at the supported end. (There are of course ways to limit this by capturing the little end PAW style to centralise the rod, under cutting the crank pin and the use of hardend disks to lower friction and control damage) but all of these methods recognise what I have just outlined.)
Also holes and slots introduce points of failure and with a model two stroke the big end is the most critical part of the engine.
Circling back to fluid flow the greatest gain is to be found in enlarging the exit as you can only get an amount of oil into a bearing that is matched or exceeded by its exit. It makes no sense in claiming the extra provision of entry points gives benefit when there is no matched oil exit.
Attempts to enlarge the entry points have included cutting a cross in the front of eye that effectively enlarges catchment area but even that seems to be in effective and it was last seen in production engines with ETA.
So if you accept that lets look wear patterns, I have seen Super Tigre speed engines, the same model used and developed year by year using different rods, and every time a drill hole was used in the lower eye it resulted in greater wear on the backplate and it was concluded that the oil hole was allowing the oil out of the bearing before it had time to do its job and lubricate the entire length.
All the evidence that I have seen points to bearing perforation allowing oil to escape and the flow is away from mechanical support.
Now the fact that oil holes in this application seem to be of benefit leads me to believe that they are exit not entry points. In a different application where both ends are supported or double hung as in little ends it still appears to be the same, the only difference being that both eyes equally support the entry and this system really does need a dedicated exit point.
Why does all of this matter? If it understood then progress can be made all the better.
If I am wrong then I look forward to a refutation on the above.
Chris.
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