High Performance Diesel Engines

Bruce Mallinson
July 2016

What do you think about this; we just ordered 6 cylinder packs from Caterpillar for a NXS Acert Cat engine and as most of you know the cylinder packs come pre-assembled. Most mechanics just clean the block and slide in the 6 cylinder packs, not knowing what is hiding in the liner. At Pittsburgh Power, we balance all of the connecting rods and pistons for the engines we build so we have to disassemble the Caterpillar cylinder packs. Well today, June 8, 2016 we were shocked at what we found; 3 different pistons in 6 cylinder packs. 1 piston had brass bushings installed in the wrist pin bore and the other 5 did not! 3 pistons were identical, 3 pistons were of a different style. According to the spec sheet from Caterpillar, the pistons can be interchanged. I personally would NOT have this in my engine, to me the piston is a very important part of the engine and I want them to all be the same design and weigh the same. So now, we have the 6 pistons off the connecting rods and we weighed them on scale that weighs to the gram that we use for balancing pistons and connecting rods. What we found is the lightest piston is 4076.0 grams and the heaviest is 4194.5 that is 118.5 grams difference. Now to make this more visual so you can see how much 118 grams is we weighed several Snap-On 3/8” drive sockets and the 15/16” socket came out to 118 grams. That is the difference in the weight between the lightest and heaviest piston out of the 6. If we were not going to balance the pistons and would have left the cylinder packs assembled, we would not have seen the 3 different pistons and the difference in weights and the engine would have been a vibrator. These cylinder packs are going into a good friend of mine’s engine and I started building engines for him when he was 17 years old, he is now 52 years old and purchased his 2007 W900-L Kenworth new and it has vibrated ever since. The vibration actually broke the head off of the #1 main bearing cap bolt out west and so he had the Cat dealer rebuild the engine and it still vibrated. Now with 412,000 miles on an in-chassis rebuild, the crankshaft broke. He is pulling the engine from the truck at his home in Tennessee and bringing it to our shop. After the out-of-chassis rebuild and balancing of the rotating parts, this engine will be smooooth! A word to the wise: If you are rebuilding your 1995 through 2009 Caterpillar engine, you just may want to remove the pistons from the liners and connecting rods and see if you have matching pistons and take them to a good speed shop and have them balance them. Please don’t think I’m picking on the Caterpillar engine, I love the 425-B up through the NXS 2007 Acert engine: Most of them are very smooth; I just don’t like engines that vibrate. There are plenty of Detroits and Cummins that vibrate also, so it’s a good practice to balance all of the connecting rods and pistons when rebuilding an engine. Sometimes we have to use 18 Detroit connecting rods to get 6 that are close enough to balance.

2012 through 2016 Cummins ISX engines emissions tune up. Yesterday we had a beautiful 2015 386 Peterbilt powered by an ISX Cummins EGR-DPF-DEF in for an emissions tune up and horsepower upgrade. This truck only had 188,000 miles on it and we found coagulated diesel particulate fluid in the exhaust system. Please notice the picture, some of these pieces are large! We also found a plugged turbo boost sensor, 2 exhaust pressure sensors, and EGR differential pressure sensor. The horsepower was increased to 630 to the ground or 741 flywheel and the torque to 2000 foot-pounds. Strangely, the engine stock produced 556 horsepower to the ground and the torque was only 1400 foot-pounds. So we only increased the horsepower by 84 to the ground, however, by making the emissions work properly and cleaning out the soot in the intake the torque increased by 600 foot pounds. That, my friends, is a shocking increase in torque and the owner of this truck will be ecstatic with the pulling power.

Today we are tuning another ISX-EGR-DPF-DEF (2011 & newer) Cummins and found similar problems: The decomposition tube where the DEF doser is located was just about plugged with crystallized diesel particulate fluid. To remove this tube we had to remove the driveshaft from the truck to gain access to the decomposition tube. This engine has 389,000 miles and is a 2012 -587 Peterbilt. For the doser to work properly and atomize the DEF fluid, it must be clean and be able to spray. The emission systems on the new engines DO run and work properly, however, they DO NEED to be tuned and cleaned, at least every 250,000 miles.

Written By Bruce Mallinson, Pittsburgh Power Inc., 3600 S. Noah Dr., Saxonburg, Pa. 16056. Phone 724-360-4080.