Connecting rod question TDI IDI

[scopefrfd]

are the connecting rods dimensionally the same for a 1.9td aaz and 1.9tdi AHU engines.

[QuickTD]

Yes and no. The rods are dimensionally the same and will interchange, but the AAZ rods have a counterweight on the rod cap. This is to counterbalance the weight of the "long end" of the rod. A fair number of engines use this technique to avoid inertial loading of the piston skirt as the rod swings past TDC/BDC. The TDI does not have the counterbalance, I don't know why. A few people have removed the counterbalance pad from AAZ rods with no apparent ill effects, I think Dr diesel has done it. "dieselmeken" has used TDI rods without the balance pad as well.

[scopefrfd]

that's great, I picked up a set of 81mm 1,9td pistons and I'm going to put them in a 1,9tdi ahu block.  Almost a 2,1L idi. :lol:  thanks for the help

[scopefrfd]

Actually there 80.5mm pistons.

[vwmike]

that's great, I picked up a set of 81mm 1,9td pistons and I'm going to put them in a 1,9tdi ahu block.  Almost a 2,1L idi. :lol:  thanks for the help

You want to put TD pistons in a TDI? That's not going to work. On the TDI, the combustion (swirl) chamber is in the piston, but on a TD there is a prechamber in the head. Or was your plan to drop an AAZ head on top of this? Might I ask where you found these pistons?

[QuickTD]

What is the purpose behind removing the counterbalances? They would seem like a good idea in any engine.

Less reciprocating mass and quicker revving.

[malone]

*edit

[scopefrfd]

I'm installing an AAZ head on the block.  Pistons are from germany and were $400 with rings, pins and clips.

[QuickTD]

Has anyone tried removing the counterbalances from the crankshafts?

That would be awfully hard on the crank and main bearings. A 4 cylinder engine has acceptable balance, other than the second order due to reciprocating mass speed variations near TDC and BDC. This balance depends on the outer 2 cylinders cancelling the imbalance of the inner 2 cylinders. If this is the only form of balancing used, all the forces must be carried through the crank to cancel the individual cylinder imbalances. This works up to a point. Lots of old 4cyl engines have a crank that looks like a bent piece of rod (no counterweights) and run quite smoothly. They don't rev very high though. At high speeds, the opposing forces of the inner and outer reciprocating masses attempt to bend the crank about its centre, fatigue sets in and breaks the crank or the centre main pounds out, neither is pretty.

 The counterweights used on most high speed automotive engines partially cancel individual cylinder imbalances directly at the source. The mass of the counterweights is usually limited to cancelling the big end mass and a possibly a minor amount of the reciprocating mass, much more and they would begin to add another force to the crank in the 90/270º plane.

[scopefrfd]

the old vw type 1 bug and type 4 bus engines had crankshafts that were not counter weighted...they were good to approx 5500rpm.  After that they started to pound the main bearings, especially in the magnesium cased type 1 engines.

[QuickTD]

It was actually a bit of humor, thus the laughing smiley face.

I did catch that, but went on to explain as a pre-emptive strike against the inevitable "why not?".   Imagine the disappointment of the amateur grinder operator if he actually went ahead...

[935racer]

scopefrfd, where did you get those pistons from in germany? Ebay? What was shipping and taxes like on those? 1.9 pistons are expensive I would love to find a cheaper source.