Discussion and questions related to the course Practical Engine Building
We are currently assembling an RB20DET using RB26 crank and rods. We are only boring out the bores to 78.5mm to keep the strong walls etc. However, we need to machine down the rods to allow them to fit through the bore when inserting the pistons.
In the attached photo you can see the excess extrusion between where the rod and cap connect. Is it possible for this to be machined down flush with the sidewall?
We have tried going through the bottom
I have removed material to do this kind of a job but i was very careful in how hot i got the rod doing it and checked the rod for any damage after you will need to check the rod does have a good 2.5 mm clearance to the bottom of the bore also when it rotates
it is not recommended to remove any material by the manufacturers
To clarify, the full width of the connecting rod big end is too wide to go down the bore and you wish to remove material from the outside edge?
As Ross said, it is NOT good practice as that outer edge is in compression when the rod is loaded in tensile, and removing material will increase both the bending and tensile loading on the big end bolts/ studs and reduce the resistance to 'ovalling'.
However, it will make little, or no, difference under compressive loading - if you don't use a lot of rom and make the power with higher boost, you 'should' be OK removing a small amount of material.
Also, as Ross said, you may need to notch the bottom of the bores for connecting rod clearance, as it's reduced with a smaller bore - DO NOT remove it from the rod as that area is one of the higher loaded parts of the rod.