COUNTERBORING

Do the job right and stop costly comebacks!! If customers counterbores are worn down and they are hesitant to spend a few extra dollars to do it right, do not warranty the repairs. Too many jobs I do were recent overhauls or have had multiple head gasket repairs, the customer is unhappy and in many cases has taken the engine to different shops to “have it done right”.

Counterbore wear is a growing problem. Engines that never had an issue are now failing. I believe the main reason is that horsepower levels are being increased in the same engine design. For example, a John Deere 400 series engine originally was 95-horsepower. Now the same liner sleeve will support 250-horse power or a Cummins L10 originally was a 300-horse power engine and now an ISM with the same liner is an easy 420-horse power. This is a 40% increase!! Also the coolant being used has been changed. I don’t know if this is part of the problem or not but counterbore erosion in a growing concern.

For more information, contact Mike Hennes at 320.974.8090.

 

 

 

 

 




COUNTERBORE INSPECTIONS & MEASUREMENTS

There are several methods to measure liner protrusion but only one is accurate. Unfortunately, the one taught by most OEM and Technical colleges is to install new liners, clamp with bolts and washers and then measure liner protrusion to specification.

This works ONLY with new fresh cut counterbores.

After many years of machining blocks, I have learned that decks and counterbores do not wear evenly. The deck surface next to the counterbore ledge or especially between cylinders may be worn .002-.003. This is ok since no sealing is done in this area. This will give a false protrusion to specification if simply using a dial indicator to measure liners to block height next to each other. The second problem is that the most worn and eroded counterbores will clean up at .001-.003 or 80% of the contact surface but can require .005-.020 removal to get 100% flat bores. You can see that when checking liner protrusion with liner in block that liner will sit on high spot and give a false reading. A liner flange will not support the compression of the fire ring with head torqued on without distorting. Thus, giving you a comeback job with a compression leak.

The only accurate way is to use proper tool and method.

  1. Clean deck thoroughly and head bolt holes. Tap all holes that have rust or carbon deposits in them.
  2. Use a fine file to knock off nicks and dings on deck and edges of the block.
  3. Using a fine India stone, go over the deck lightly to get all the very fine high spots. This will also show the high and low spots, (Use solvent with stone to keep it from loading up) You will be surprised by how uneven this looks but that is normal.
  4. Using the dial indicator tool check the counter bore.
    • Place the dial indicator so the swing arm can teach over the counterbore easily.
    • Move took over flat part of deck to zero indicator.
    • Slide tool over the bore without moving the swing arm and measure the depth of bore. Also measure for taper.
    • Remember liner will sit on high spots but will push down when installed.
    • Now measure 8 spots around the circumference of the bore. Remembering that every time you adjust swing arm to also zero indicator on deck.

Additional Notes:
When measuring engine blocks like MACK E-7 or Cummins Ml l- ISM. 8.3C- Series with counter bores 3-4 inches down in block will require depth micrometer.

Long-range dial indicators (over 1 inch) are subject to accuracy errors due to cosine error (a mounting problem) and gear train error (over the long distance).