1985/11/01 Caterpillar

3406, 3406B, 3408 Truck Engines

The 3400 Series Engines have been using a plasma coated top ring in pistons for almost three years. These rings are 5/32" (3.97 mm) wide. Compared to the former 1/8" (3.18 mm) chrome plated top rings, the plasmacoated rings do not break and have handled horsepower increases without ring scuffing.

As with many product improvements, there is a trade-off for these improvements - an increase in the wear step at the top of the liner. Field experience shows that fewer liners will be reusable at overhaul based on current Caterpillar Reusability Guidelines. But, field experience also shows that engines are running through mid-life with significantly better reliability (no ring, head, or bearing failures) and that life to overhaul is as good or better than ever.

The change in liner reusability should not cause any problems because of the availability of the Remanufactured Cylinder Kit (piston and rings with rod and liner assembled, and ready for installation). Liners returned for cores have no wear limits. If liners returned as cores are not reusable due to the top wear step, Caterpillar will use new liners in the Remanufactured Cylinder Kit.

Some customers have replaced liners during a mid-life repair solely because of an unexpected wear step area at the top of the liner. This replacement may have been premature depending on the extent of the repair and the mileage at the time of repair. Replacement of liners at mid-life should not be based on the wear at the liner top wear step, but rather on the amount of crosshatch wear or lack of oil control. The liner wear step that is normal for these engines occurs only over the top 19 mm (.75 " of top ring travel and, consequently, will have very little effect on oil consumption. Liner wear below this wear ridge is approximately the same as that produced by the former 1/8" chrome rings. In fact, anywhere that the crosshatch is visible, liner wear is much less than 0.03 mm (.001 ""). See illustration.

Spots where the crosshatch is polished away at mid-stroke indicate that a liner has worn to an out-of-round condition, and can be the cause of an oil consumption complaint. These polished spots are NOT caused by plasma coated rings, but rather by piston deposits. These deposits are a function of oil and fuel quality, oil and fuel usage rates, maintenance and application.

Summary

... Piston, ring and liner reliability are significantly increased.

... Total engine life to overhaul is maintained.

... The wear ridge area at the top of the liner is not a factor for the acceptance of liner cores.

... Piston deposits, which are controllable, wear off the liner crosshatch, which can cause excessive oil consumption.

... The Remanufactured Cylinder Kit comes with the rod and piston assembled in the liner. Use the 6V9448 Cylinder Liner Puller Group to quickly pull out the former liner, piston and rod as a unit, and to prevent broken rings. Using this tool and the kit make a significant reduction in repair time.

... Liner reusability at overhaul is decreased.

Typical mid-life wear pattern of liner caused by plasma top piston ring. Note that the original factory crosshatching is still quite visible except for the slight wear step area at the extreme top.