Low Oil Pressure at Warm Idle
By Bob Donalds
     I have had more than one 2.1 water boxer engine brought in for rebuilding with symptoms of low oil pressure. Despite having put in the longest spring the customer could find for the pressure relief and adding thicker oil, the engine still had low oil pressure at a warm idle. These findings had been confirmed with a gauge. So as I disassembled these engines I was very careful to check for excessive clearances. It turns out the clearance between the rod bearing and the crankshaft rod journal had gotten to the point that it allowed the oil light to come on at warm idle. Unfortunately the more common results of this problem in the 2.1 is that the rod winds up hanging out of a new vent hole its has created in the top of the crankcase. The 1.9 on the other hand is not known for throwing rods unless it was run low of coolant or oil.

     The one thing that has been consistent in all the 2.1 engines I have stripped and measured is that the large end of the connecting rods are no longer round. With this problem in mind I started paying more attention to the big ends of all the water boxer con rods that came into the shop. The first thing I found was that the 1.9 and the 2.1 con rods are the same size and length. In fact they are the same rods. My inspections showed the 2.1 rods had consistently more distortion at the big end. What is the difference between the two applications of the same con rod? The stroke is longer in the 2.1 engine so the rod angle is greater, plus the 2.1 make more power witch puts more strain on the rods. Itâs clear to me from my days at the race track that nothing distorts con rods faster than exceeding the power curve but the fuel injection has a nifty rev limiter built right in. This doesnât explain why we see rod distortion in one engine and not the other. Next I went to the Bentley book to compare the torque specs. The 1.9 rod has a reusable rod bolt that call for a torque of 33-ft. lb. and the 2.1 has torque of 22-ft. lb. plus ¸ turn. The manual also says not to reuse bolts on the 2.1 engines.

The conclusions:
1) Never reuse the rods without having the big ends rebuilt ever!
2) Never rely on Plastagauge alone it does not always show if itâs out of round
     or if the cap is shifted.
3) Consider rebuilding the engine when the heads start to leak if it has got a hundred thousand
    or more miles on it. Keep in mind the core may not be rebuildable if you wait longer. There is
    no doubt the rods are the major reason for the catastrophic engine failures.

     More than one person that has told me that they only got six thousand mile from a rebuilt 2.1 long block before a rod blew through the case. They also told me the big ends of the rods had not been measured or rebuilt. The facts speak for themselves. I see this problem on a daily basis and thought I should pass on my observations.

~Boston Bob



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