29 June 2016

“Rebuilt” is a relative term when it comes to engines

Buying a classic car can be an uncertain proposition, especially when it comes to words like “restored” or “rebuilt.” “Restored” can refer to any number of finish levels, with terms like “body-off,” “concours” or “rotisserie” tossed around with abandon. The same sort of ambiguity applies to the term “rebuilt,” particularly when it comes to an engine, and it can mean anything from a newspaper-masked rattle-can paint job to a completely remanufactured long block engine assembly.

The difference between rebuilt and remanufactured — if sellers are using them correctly — is that rebuilt implies some engine components and parts were replaced as needed, while remanufactured means that the engine was completely torn down, cleaned, inspected and machined back to original or better tolerances than when it left the factory. The terms “balanced” and “blueprinted” are often associated with this type of work. Rebuilt engines run in scope from the aforementioned rattle-can job to complete remanufacture. It’s in your best interest to determine exactly what’s been done, and by whom, to an engine in any car you’re looking at. Following are a few varying degrees of “rebuilt.”

Top-End Rebuild
As the cylinder head or heads comprise the top end of an engine, this remove, rebuild and replace procedure is known as a top-end rebuild. An overheated engine can blow the head gaskets. Clouds of white coolant or blue oil smoke might mean it's time for a top-end rebuild or valve job. The sort of heat that breaches head gaskets usually warps cylinder heads in the process. Replacing the head gasket after an overheat involves removing the cylinder head and either sending it out for machine work and a valve job or swapping it as a core for a remanufactured head. A fresh cylinder head can breathe new life into an engine.

Re-ring and Bearing
If the engine is out of the bay for something like a top-end rebuild, a re-ring can be considered depending on the condition of the engine, bearings and clearances — and if the deck on the block is true. Pulling the crankshaft and pistons for a good look at the connecting rod and main bearings is another way to gauge engine condition. A fresh set of piston rings and/or bearings in an otherwise untouched engine is known as a re-ring, which is not so much an engine rebuild as a refresh to restore proper compression and should be considered as a temporary lease on engine life.

Short Block
If the cylinder walls are scored, the crankshaft and bearings are shot, pistons holed or the deck is warped, then it's time to send the rotating assembly and block out to your favorite machine shop. The block is decked, bored and honed for new pistons. The connecting rods are resized with new rod bolts installed. Camshafts are reground or replaced. The crankshaft is either polished or cut and then polished. Timing chains or belts are renewed. The finished rotating assembly minus the cylinder head (or heads) is known as a short block. A short block can mean sending the original to the machine shop or exchanging your rebuildable core for a like remanufactured short block.

Long Block
The long block assembly is a remanufactured engine from short block to cylinder head — the top and bottom end together. Like a short block, the long block can mean an exchange-for-core job or sending the entire engine out to the machine shop to keep the powertrain original and numbers-matching. Crate engines are a relatively modern version of a long block, which can comprise anything from a remanufactured engine to a factory-fresh, ready-to-install package complete from induction to crank pulley. Another sort of long block engine swap comes in the form of a complete low-mileage used engine salvaged from a wreck — a popular choice for engine swappers.

Supporting Systems
Dropping in a freshly sorted engine and connecting it to a rotten radiator or transmission backed by a spent driveline is an exercise fraught with danger. A great time to get the radiator re-cored or to send the driveline out for new, fresh U-joints and balancing is while the engine is out at the machine shop. The latter procedure is an especially good idea if added horsepower is hanging on the end of the engine hoist. Twisting up a marginal driveline and turning a new exhaust and freshly installed floor pans into scrap metal is an expensive path to engine repairs.

Whether an engine is claimed to be rebuilt, remanufactured or some other term of the seller’s choosing, always ask for proof in the form of receipts and spec sheets, so that you know exactly what it is powering your next car.

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