Dry Liners
This article is in response to confusion often arising over the fitting of these dry liners.
All early David Brown engines, until the introduction of the three cylinder engines in 1965 were fitted with wet liners. This includes the 4/47 engine as used in the 990 Implematic, which carried over into the 990 Selectamatic until 1968.
Two versions of the three-cylinder engine were introduced in 1965, both using dry liners with a bore of 3 13/16 inches (3.8125 inches; 96.83 mm). The AD3/30, fitted to the red 770, had a 4-inch (102 mm) stroke and produced 36 hp. The longer-stroke AD3/40 replaced the AD4/40 in the 880 Implematic. This produced 42.5hp from a 4.5 inch (114.3) stroke. Both engines were only produced for about a year, 1965, and were the only David Brown engines to have ever been fitted from new with dry liners. As with the earlier wet liners, there was a rim on the top which protruded slightly above the top surface of the cylinder block to effect better sealing. The rim also prevented the liner from slipping down the bore. See the drawing below.
Because both engines had short production runs, relatively few were made, and replacement pistons and liners were discontinued many years ago. However, the engines can be converted to later specifications: the 770 effectively becomes an AD3/49, and the 880 an AD3/55. These later engines did not use liners; their 100 mm pistons ran directly in the block’s parent bores. Although the dry liners can sometimes be removed by hand, doing so requires used fire rings—new ones are unavailable—to fill the spaces left by the liner rims. Therefore, the preferred method is to strip the block and have an engine machine shop bore out the liners, our part number 964857, while leaving their rims in place.
A further complication is that some early three-cylinder engines have thin cylinder walls, which may become porous after the liners are removed. This risk should be considered before proceeding. The alternative is to bore the parent cylinders to take semi-finished liners, which are readily available. They are pressed into place, then bored to 100mm. However, they aren’t available with a rim; the external diameter is parallel from top to bottom. This means that they need to be a really tight fit, to prevent downward movement. Then the relevant (later type) 100mm. piston assemblies can be fitted; our part numbers are E2092 for the 770, E2094 for the 880.
The engine power was slightly increased on these later engines by the increased bore size and a revised fuel pump delivery; the latter won’t matter, though if you are also getting it overhauled you may like to get it set to the later specification.
Later three, four and six cylinder engines.
This category includes all white and Case IH tractors, except white 990 Selectamatic models built up to 1968 with a combined dipstick and oil-filler cap on the starter-motor side; these used the AD4/47 wet-liner engine. In all other
engines, the pistons run directly in the engine block. In the event of excessive wear, the engine block will again need to be stripped bare and taken to an engine machine shop to be bored. However, these engine blocks have thick enough cylinder walls to allow them to be bored oversize; we have oversize versions of E2092 and E2094 pistons assemblies available in +20thou. inch and +40 thou. inch, also the same oversizes for the E3593 piston assemblies for turbocharged engines.
The same 964857 dry liners can be fitted in the event of severe bore wear or damage, but the risk of them slipping downwards remains, as previously mentioned.
Rebuild kits - Please note that other suppliers routinely supply engine rebuild kits containing dry liners; they do this so that they can take a ‘one size fits all’ approach. They don’t mention the extra cost of having the liners fitted or the risk of them slipping.
Fire rings – following removal of the cylinder head, many customers see the tops of these and assume that the engine is fitted with liners. This is not the case with any of these later engines. Note that the rings must remain in place so that they are bored too; new ones aren’t available in any size. They were discontinued in the late 1970’s, therefore no 90 or 94 series tractors, or slightly earlier ones, were fitted with them; there is no recess at the top of the cylinders. See the drawing below.
Comments