This article is going to be about the basics of engine building, liner protrusion, upper and lower counter bores, and what we are seeing with the 60 Series 12.7 and 3406 Caterpillar blocks that are 18 to 23 years old. Many of these engines could have in excess of 2 million miles an it’s time for the engine block to be reconditioned at a good reliable machine shop that is capable of making lower counter repair sleeves. The lower counter bore repair sleeves for the Big Cam Cummins, and the 3406 and C-15 series of Caterpillar engines are available from the engine manufacturer. The lower counter bore is the section of the block where the liner O-rings or liner packing seals the cylinder liner to the engine block to keep the antifreeze from entering the oil pan. This is a very critical part of engine rebuilding and often overlooked by mechanics performing an in-chassis rebuild. The 60 Series Detroit engine block has 2 lower counter bores per cylinder with a coolant passage between the two sealing areas. Detroit does NOT manufacture the repair sleeve for this repair; my understanding is they scrap the engine block. The machine shop that Pittsburgh Power has been working with for the past 40 years will make and install the two repair sleeves to salvage the engine block. It’s never welcomed news to an owner-operator when he gets the phone call that his in-chassis rebuild will now be an out of chassis and the price is about $10,000 more because of the lower counter bores. When money is an object, and so is the time it takes to perform the out of chassis rebuild a quick fix for the lower counter bore if the corrosion isn’t too bad and is JB Weld or Liquid Steel. Clean the cavitation with a wire wheel, blow out the dust with an air gun, and wipe the area with lacquer thinner or brake clean. With your fingertip fill the cavitation with the JB Weld or Liquid Steel, allow to dry overnight, and sand it to the contour of the counter bore. THIS IS NOT a permanent repair; and should only be performed if the cavitation is smaller than the size of a dime. However, this will get the engine back together at minimal expense and the owner can get back to work. If the engine block needs to be resurfaced and line bored, then by all means repair the lower counter bores the proper way with new inserts.
Upper counter bores and liner protrusion; we have talked about this many times over the past years and to this day we keep getting phone calls from owner-operators with blown head gaskets shortly after an in-frame rebuild. We ask the question, “What was the liner protrusion set to when the engine was rebuilt?” The answer we always get is “I don’t know or it’s with-in spec.” I’m sorry to say the factory specs are too low to hold a head gasket for 500,000 miles. You want your liner protrusion to be .001 higher than what the book calls for. So, if the spec is .003 to .006, you should have the protrusion set for .007, some of the engine manufactures will say zero to .003, then the protrusion should be at .004. If you are having your engine rebuilt by someone and they do not now the spec, it’s up to the rebuilding mechanic to look it up in the engine manual or online. You, as the owner of the truck, should tell the mechanic you want to know the liner protrusion of each cylinder and it should be written down as the mechanic is cutting and installing the liner shim and checking the protrusion. It’s more time consuming on a Caterpillar because of the deck plate. The gasket under the deck plate must be installed under the plate and the plate must be torqued down to 70-foot pounds. The same goes for all engines. The liners have to be torqued down to 100-foot pounds to obtain a true measurement. If the engine has 400,000 miles since the last rebuild and the head gasket blows, some mechanics will remove the head and gasket, clean the block and check the liner protrusion with a dial indicator, and say the protrusion is off by .003 from side to side, this is because he DID NOT install the proper liner hold down bolts and torque the liners down to 100 foot-pounds. Always ask the mechanic the right questions when he gives you the spec, if he can give you the spec. The proper dial indicator tool used for checking liner protrusion has a base that is about 10 inches long so it takes irregularities along the block into account. A standard magnetic dial indicator base will NOT give you the proper reading.
The tool for cutting the upper counter bores is several thousand dollars and most mechanics will NOT have the tool or the cutting plate for all the engines he has to work on. You should ask him if he has the proper tools to perform the task before he starts rebuilding your engine.
Written by Bruce Mallinson
Pittsburgh Power Inc.
3600 South Noah Dr. Saxonburg, Pa. 16056