Question on Engine Building

[Blueflash]

Hi. I have a question relating to engine building.

A customer has a 4-stroke motorcycle, fitted with high lift cams, uprated carbs, and free flowing pipe.

They purchase an off-the shelf big bore kit, consisting of slightly bored out block, and high compression pistons. Compressiom ration will increase from 10:1 to 13:1.

They contract an engine builder to install the kit, and drop the bike, barrels, and piston off with them.

The engine builder suggests that it might also be worth uprating the cylinder head, so the customer goes back to the supplier and purchases a custom machined stage 3 head with +1mm larger valves (intake and exhaust), and uprated followers. This purchase is made several weeks after the supply of the big bore kit, and takes a few more weeks to ship. The supplier did not have the head, barrels, and pistons at the same time, and is never in possession of the customer’s camshafts, although they do stock and supply that same item.

The customer’s existing high lift cams are to be transplanted into this cylinder head.

The high compression piston kit, can accommodate +1mm larger valves as standard, leaving 2mm of clearance within the piston pockets.

Both the supplied block and cylinder head are measured, with flat mating surfaces, no angle introduced, and if there’s been any skim then it’s undetectable.

When the engine builder assembles this engine, would it be reasonable for the customer to assume that the builder will check the piston to vale clearances?

Would turning the finished assembled engine over by hand be sufficient to check the piston to valve clearances, or should the engine builder dry build the engine and actually measure the actual piston to valve clearances?

If the engine builder does not explicitly measure the piston to valve clearances, and some piston to valve contact occurs during the break-in period (because these was insufficient clearance to account for heat expansion, rather than any timing issues)… then would this be the fault/lability of the engine builder, the parts supplier, or the customer?

Would it be fair and reasonable of the enginer builder to refuse to remedy this, and tell the customer to come and collect their bike, engine still broken and disassembled, or should they be offering to remedy it at no extra charge?

[maxwedge]

Any time an engine is modified away from stock, particularly changing the cam and pistons, an actual measurement of piston to valve clearance is standard practice, at home or in a shop. Now some court jurisdictions may want to see specific instructions given to the shop. An expert witness would probably state that the measurement is standard practice in the industry.