Accuracy is essential when line boring cylinder blocks.
With the unique design of Aston Martin cylinder blocks, failure to accurately machine the main bearing tunnel to the very close tolerances required can seriously shorten the life of an engine.
The 3.7 and 4.0 litre engines in particular suffer with oil pressure problems if the main tunnel bore is not true and within the tight tolerances stated by Aston Martin.
We have seen on many occasions how the oil pressure significantly reduces as the engine temperature rises, and also the the dreaded oil leaks from the “mechanical” rear main oil seal. To rectify these faults the engine requires a complete strip and re-build.
The DB2 & DB2 MKIII engines have different issues regarding main bearing tunnel alignment. It is imperative that the bores are round and in line with the front main bush, if this is not adhered to, the crankshaft will be tight when fitted and prone to seizure and wear on the bearings and crank will increase, lowering oil pressure.
The V8 engines tend to be more reliable and line boring is not always required, however we have seen many instances of the “scroll” on the rear of the crankshaft causing damage to the rear main seal. Due to only the lower half of the seal being removable (the upper half is part of the block casting) the crankshaft centre line must be moved slightly, and the whole of the “tunnel” line bored. We have also seen instances of the main bearing caps becoming loose on the doweled studs, this can create movement of the cap and bearings. Again line boring would be required after the re-sizing of the dowel locations within the main bearing cap.
Most line bore machines rely on a rotating, central bar which is held between a mandrel. The tooling is set to size and moved accordingly. Alternatively a Line-Hone machine can be used, this type of machine uses the same sort of set up, but instead of a single point cutter it has a stone which can be adjusted and the bar/stone moves laterally along the main tunnel.
After much research, Aston Workshop decided to invest in the very best line-boring machine available, with bespoke manufactured 90 degree boring heads to suit the unique requirements of Aston Martin engines.
With this machine we can set the cylinder blocks up to exacting tolerances for checking alignment, and machine well within the .0005” tolerance stated by Aston Martin. We usually find that we are within .0001” (one tenth of a thousands of an inch) in both size and trueness across a 6 cylinder block.
The machine is also equipped with a CNC machining cycle. Once the block is manually set up the machine will run through a programme, boring each individual bore. This reduces both cost and operator time.
Another unique feature is that when the block has been line bored, we can remove the 90 degree head and machine the sump sealing face exactly true to the main bearing tunnel, without moving the cylinder block. Then rotating the block (on the same machine), we can proceed to machine the cylinder head sealing face and liner locations as required, perfectly aligned to the crankshaft.
We regularly machine blocks for customers all over the world, and also carry out the finish line boring for suppliers of new cylinder blocks.
Please contact us to discuss your machining requirements.