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Repairing a Valuable Holden XU1 Engine Block

Our customer presented us with an old 186 Holden engine for reconditioning, asking that we achieve the XU1 performance specifications running on premium unleaded fuel. The engine was from his original Holden XU1 that he was restoring.

When the engine was being inspected we identified a sleeve repair that could be a risk. We removed the old repair sleeve to find a large hole caused, most likely, from a blown piston. In normal circumstances we would recommend and use a replacement block that does not have serious damage.

The crankshaft tunnels were all over the place and it had loose main bearing caps. These are the signs of a tuning problem that had the engine running into detonation. Possibly the same issue led to the blow up when a piston or con rod went through the wall of the cylinder. The loose caps were rectified by a line bore and line hone.

Because the block had the right number for this vehicle, it was no use suggesting another block. This one just had to be recovered.

The normal material in common repair sleeves is a soft cast iron. That is suitable for standard engines. But considering the performance expected, we went for a made-to-order, semi-finished, Darton sleeve blank and finish-machined it in our shop. This product is made from ductile iron which is a far stronger material for our purposes.

To get the finished sizes for the sleeve, we first machined the block to establish a sound positioning for the new sleeve and for effective head gasket sealing. For accuracy we did the block machining on our HAAS CNC mill.
These photos show the new sleeve ready to be installed, fitted and tested, and ready to be machined to suit the new piston.

valuable holden xui block 1

valuable holden xui block 2

With the sleeve fitted into the block, sealed, and pressure tested, we finished off the engine work and presented a fully assembled engine with the triple carbs and exhaust system to the dyno cell.

The engine is now ready to go to the dyno cell for tuning.

valuable holden xui block 3

valuable holden xui block 4

The dyno sheet doesn’t really show what work and know-how went into getting this engine running correctly. The triple carburettors, and the distributor, had been reconditioned and set up as best the contractors could for what was expected to be needed. The only real change was the shift from leaded to unleaded fuel. But we knew that this change could be significant after the experiences that we have had on the track with similar old-technology engines going to the unleaded fuel.

What the guys did at the dyno cell involved changes to the graphing of the distributor, and filing the carburettor needles to match what the dyno was telling them this engine needed. This is skilled work that we appreciated, understood, and we never hesitate to recommend the dyno work when such an engine comes through our shop. Like us, the owner was very pleased with the result. The dyno sheet tells the story.

This type of repair is very costly and only justified when vehicle restoration involves a valuable engine block. The value, of course, is the engine number that verified the block belonged to this XU1 when it was built at General Motors Holden.