CFR Cylinder Overhaul Service

Mark's Knock Engine Service's accepts complete cylinder head units for overhaul shipped to our shop. We accept the entire unit including the valve gear, clamping sleeve, worm wheel, worm gear, and CR Box still assembled together. This allows our technicians to check tolerances and wear on the apparatus ensuring long, dependable use.

After running an engine for some time it becomes more difficult to temperature tune with toluene and have the intake air temperature come with spec for the prevailing air pressure. This is because the valves, valve seat inserts, and piston rings wear during the normal life of the engine. Over time, or if some particulate is introduced, the valves will start to loose their seal to the valve seat inserts. Also some pressure in the compression chamber can escape past the piston rings. Irregular heat and pressure patterns due to leakage causes problems in rating an engine. In addition the valves, ports, piston and cylinder bore accumulate a coating of carbon. This carbon glows cherry-red and will produce more heat in the chamber necessitating a lower intake-air or intake manifold temperature to properly certify an engine fit to use. A cylinder overhaul is necessary at regular intervals.


We disassemble and carefully clean every part of the cylinder apparatus taking special attention to removing all carbon from the bore, intake and exhaust ports, and pickup and spark plug holes of the cylinder. The valves and piston are cleaned with glass beads as well as any parts that need re-painting. All other parts are cleaned of oil and particulate thoroughly.

We make a detailed cylinder report which notes any existing conditions of the valves, valve seat inserts, valve guides, and of the bore itself. Upon inspection MKES determines what new parts are necessary, and reassembles the cylinder. Cylinder service points include:

  • Valve concentricity and wear checked
  • Valves are ground or replaced if necessary
  • Valve seat insert concentricity and wear checked
  • Valve seat inserts are ground using high-speed stone with proper double cut
  • Valve guide wear is checked and valve guides replaced if necessary
  • Careful inspection of the bore for wear or damage and precise measurements are recorded. When a cylinder's bore becomes worn and needs to be re-bored we recommend and arrange for it to be machined
  • Piston is cleaned, inspected, and measured for wear
  • Piston ring gaps are measured for old and new rings
  • Piston land measurement
  • Valve springs checked and replaced if necessary

We leak check both the intake and exhaust valves before the cylinder leaves the shop.

Clamping Sleeve

They cylinder is reassembled with clean clamping sleeve, worm wheel, and worm shaft, and CR box.

  • Worm shaft is properly fitted with shims to the clamping sleeve
  • Worm wheel and clamping sleeve wear tolerance checked
  • Springs polished, checked, and replaced if necessary
  • Clamping sleeve fittings and bolts are updated if necessary
  • Cylinder is set to a standard height
  • If you still have a hand crank that's all right we'll fix that up too!

Valve gear

The valve gear is inspected, thoroughly cleaned, and rebuilt with attention to:

  • polishing of shafts and replacement if necessary,
  • rocker arm bearing quality,
  • valve lifter cups wear
  • valve adjusting screw wear
  • proper yoke height set

MKES will only sell you parts if they are necessary because of damage or wear beyond the mechanical tolerances of the ASTM specification. This can save your company hundreds of dollars per overhaul.

Dependable functioning of the cylinder and its ability for consistent rating is our number one priority.