Car Engine Rebuilding

That was an odd sound I thought. There was a knocking sound coming from the engine. My friends car was quite old and the high mileage was making itself known by alerting us with this knocking sound. The bearings were worn out allowing the rods to move excessively..and making this noise.

I told him the bad news...the engine was finished. When asked my advice on what to do next I had a few questions to ask him. Do you have the cash funds to purchase a new or used car? If not,in addition to paying a monthly car payment on a loan can you also afford full coverage auto insurance? The answer led me to advise my friend to either repair this engine or replace with a rebuild from a reputable dealer.

I also wanted him to know that installation would take hours and hours and cost several hundreds of dollars. I knew my friend could not afford a quick and easy replacement engine so I helpfully volunteered to help him remove, rebuild and reinstall this engine.

Getting the engine out proved no more difficult than any other engine and soon were were tearing the engine down into it's component parts. Taking a motor apart is fairly easy but you still want to take care and do no damage to reusable parts.

Once disassembled we arranged the parts in a manner that would facilitate their reassembly and looked at repairing the damage that had caused the engine to fail in the first place. The is where we took a close look at the crank shaft. The crank sits in a cradle formed by the engine block itself. The crank is supported at 4 points and at each of these cradle points is a bearing insert. A half moon shaped piece of soft metal with an oil hole drilled into it and a drain groove running throughout it's length. The crank shaft sit directly on this bearing insert. It is one half of a complete bearing surface.

The crank is held in place by bearing caps. This is a heavy, half moon shaped piece of steel formed to perfectly fit over the crank once a matching bearing insert is placed in the cap. Between the bearing cap, and it's bearing insert and the underlying bearing insert placed in the cradle formed by the engine block itself, the crank rides on a layer of oil when the engine is running. The bearing surfaces provide a perfectly smooth environment for the crank to spin and be oiled and protected at the same time. This protection comes from the nature of the bearing surfaces..they are soft and able to wear away enabling the spinning crank to "wear" into the new bearings for maximum life.

As time goes by and mileage increases this wearing away can reach a point where there is now too much metal having been worn away, and movement between the crankshaft and its bearings or the rods and their bearings causes an actual impact...or...a knock. Usually, this knock occurs between the rapidly moving up and down motion of the rod impacting against the crank.

I told my friend I knew how to cure this problem and we lifted the heavy crank, into the bed of my truck along with the engine block, the intake manifold and the heads. We were going to a machine shop where accurate measurements would be taken of the crank. While there we would also swap the heads for a reconditioned pair and have the block and manifold professionally cleaned, degreased and painted.

At the machinist shop the technician used his measuring instruments on the crank and informed us that by removing a total of ten thousands of an inch of metal from the bearing journals of the crankshaft he could return the crank to perfect roundness and that this would require us to purchase new bearings that were ten thousands of an inch to large to compensate for the missing metal. This was no surprise to me as I knew that crankshafts do suffer some wear and that turning them down by means of a metal lathe would be needed. The cylinder bores were within specifications so new pistons would not be required.

We returned the next day to pick up the reconditioned crank, the cleaned and freshly painted block, and intake manifold and heads. These were not the original heads but were exact replacements that had been reconditioned with new valves, properly ground mating surfaces and then compression tested. On the way back we stopped in at the auto parts store and picked up some new rings for the pistons, a gasket set for this engine, gasket sealer, engine oil and filter and of course, the over size bearings. After a few more odds and ends had been added to our shopping list we returned to the garage and began the reassembly process.

Reassembly of an engine is actually quite easy. Its a good idea to coat each bearing with oil during assembly. You drop in the new bearings being careful to orient them correctly. Then the crank and then the bearing caps with their inserts. Now is not the time to torque it all down however. Now you want to re-ring your cleaned pistons and pop them into their cylinder bores. One at a time and carefully...tap them down the bore until the new bearing on the rod comes into contact with the crankshaft. You do this for each piston and then..and only then...do you want to start torquing the bolts to specification. The large dollop of oil you placed on each bearing insert will help out a lot here.

With a newly refinished crank, new oversize bearings and reconditioned heads and all the right gaskets in all the right places and several other assembly "watch out fors" we had the engine put back together and got it dropped back into the car.

The newly rebuilt engine started with no problems and I cautioned my friend to simply drive it like he normally would, but to change the oil about three times in the next five thousand miles. A new engine is tight, and there is going to be a certain amount of "wear in"...and this means tiny metal shaving...changing the oil would remove these and prevent them from causing harm in the long run. I knew I had saved him a boat load of money. The cost of pulling the old motor and replacing with a new engine alone would have been about a third of the cost of a new engine. Plus there was the core charge on the old block. Rebuilding it ourselves saved him a lot of money, and he got first hand experience at rebuilding an engine and lots of knowledge of how engines work the way they do.