Closer Look at an Engine

An internal combustion engine is the most common form of power on the road today. The firing chamber can use diesel, gasoline, propane, and natural gas to produce the power, but whether the vehicle is a tractor-trailer highway rig or a small subcompact, most of them share the same basic principles to operate the engine and drive chain components.

Various other methods to harness energy to do work have been tried or are in use now. The Mazda-Wankel rotary is an internal combustion engine variation and so is a steam boiler as used in a vintage Stanley Steamer. A hydrogen fuel cell may someday power our transportation, and there are presently more electric and hybrid vehicles seen on a daily basis. Regardless, the simple mechanical principals of internal combustion engines will apply to today’s muscle cars forever. For a concise and simplified explanation on the function of an internal combustion engine just watch any or all of the hand-picked video clips below. There are how to video experts to help perform any checks suggested that are at the end of this chapter.

Horsepower and torque. How do they relate to an automobile engine? One horsepower, according to the Encyclopedia Britannica is “the amount of work that’s required to lift 33,000 pounds one foot in one minute ( 1 hp= 33,000 ft.-lbs. of work).” Torque is how much weight-moving potential that engine can deliver to the wheels.. Note well: accessories that depend on the engine to function such as the oil pump, water pump, power steering, power brakes, air conditioning, and alternator drop the horsepower available for performance.

Prior to 1972, SAE (Society of American Engineers) standards ratings were used. The SAE standard HP rating was calculated with a finely tuned engine on a stand without any accessories and equipped with free-flowing headers rather than an exhaust/muffler system to achieve the highest horsepower rating possible. The SAE rating is a gross horsepower figure and is not an accurate  indication of the actual hp available from an engine in a passenger vehicle.

To further complicate the scenario, engineers would manipulate the hp rating, upwards or downwards, to suit the needs of marketing perceptions and trends. No names mentioned, but why is there a low hp rating on the less expensive car, but the high-performance model was rated 15 percent higher, even though identically equipped. I’m not certain, but I have a theory. The hp rating was inflated to attract the MCF crowd in the pre-1960s, but a lower than actual rating was often applied from the mid-1960s for the most powerful machinery to reduce inflated insurance premiums on high-performance cars and to help pacify a growing traffic safety lobby.

In 1971, to comply with new EPA-mandated pollution controls, engines had a lower compression to accommodate unleaded low octane gasoline and hp ratings dropped accordingly. Manufacturers also began a switch to the SAE “net horsepower” rating system in 1971. This is a more accurate figure as the engines hp is now tested with all the basic equipment needed for a passenger vehicle in place. Brake horsepower (bhp) is a way to measure an engines output without any needed accessories, a smoke and mirror system; but similar to the net SAE  rating.

© Dutchscenery | Dreamstime.com Vintage classic car engine

If your car is burning oil too quickly (you can see a cloud of bluish-colored smoke in your rear view mirror on rapid acceleration), it indicates too much oil has reached the combustion chamber and is burning along with the fuel. This is a sign of a serious engine problem; however, I wouldn’t decide to completely rebuild an engine until  I performed a few checks, each, progressively more invasive.

The first thing to do is a compression test of each cylinder. Whether the compression is low on all the cylinders or one or more cylinders is something easily checked at home with an inexpensive cylinder pressure gauge. Make certain to disable the power to the spark plugs (remove distributor/coil wire) and then the spark plugs.  Mark the plug wire’s original location with tape or some other way to replace them exactly as removed or you will change the spark plug firing order, causing the engine to misfire. This, with other hints and precautions are thoroughly outlined in the web links at the end of the chapter, hand-picked to help make this a quick and easy job.

Insert the gauge into the spark plug hole, then turn the engine over with help from a second person, manipulating the ignition key. One person will turn the engine over, while the other firmly seats and holds the gauge in the plug hole. The reading will vary according to every manufacturer’s specifications although a higher performance vehicle will give a higher reading. You’re looking for one or more “weak” cylinders with a reading of roughly around 180 PSI a likely starting point. Refer to each manufacturer’s specification book for an exact figure. Ten PSI below the manufacturer’s suggested specifications is normal for a used engine and acceptable if all cylinders are close to equal for most applications. If one cylinder is much lower than the rest , 10 percent or more, this would indicate that you have to remove the head or heads for a closer inspection. Recheck if one or two cylinders have a low compression reading, possibly more than once, to be certain the figure is accurate. The decision for needing a complete engine rebuild is not yet justified.

You’ll have to remove the intake and exhaust manifolds as well as fuel delivery systems, plus other engine add-ons like the water pump, hoses, and timing chain (belt) before you can lift the head or heads from the block. Removing the valve covers will expose the bolts holding the head firmly to the block.  All cast (iron, aluminum) parts, including the block can be thoroughly checked by Magnaflux testing (non-destructive) for cracks. You also have to check the heads for warping where they meet the block. Poor compression is very often the failure of the head gasket to seal the combustion chamber and replacing the muli-layered gasket will fix it. You’ll see evidence of blow-by on the gasket-marks caused by unused fuel and exhaust gases escaping. The head(s) can then be taken to a professional.

This is a good time to have a close look at the tops of the pistons and sides of the firing chamber, now exposed in the block. Scrutinize the cylinder walls  individually and ensure all are smooth and free of scoring, without a deep ridge at the top of the piston’s travel. Use a cylinder bore gauge to measure how much the hole is out of round. Under the engine, still in its compartment, you can drain the oil pan and  remove it. Check the interior for bits of metal. The main bearings, crankshaft connecting rods and pistons are accessible and can even be  removed from the bottom, in most rear-wheel-drive vehicles. If all things show a green light and check out according to manufacturer specifications, restoring the head may solve the problem.

After making the checks and the needed repairs, replace the heads onto the block with a new head gasket between them to help seal tiny gaps or discrepancies. To reinstall the heads, you need a torque wrench, as well as a new head gasket plus additional gaskets for both intake and exhaust manifolds. All the gaskets needed will be in a prepackaged gasket set. The bolts must go through the head into the block and snugged in equally, starting from the center bolts and working your way to each end of the block, then repeat the procedure using a torque wrench and tighten precisely to specifications. Reset the torque after the head gasket seats-in and compresses after no more than a few thousand miles. You can remove and replace the heads in less than four hours at each end, totaling eight hours, if there are no problems.

If you had to read this, then invoke option number two and take the head(s) to your favorite engine shop where they can check all the functions/specifications thoroughly. Test the cylinders for PSI again once the engine is back together and functional. If you’ e not pleased with the results so far, then it’s time to move on to the bottom end.

A good drive chain overview in less than six minutes “How Car Transmission System works”:

https://www.youtube.com/watch?v=QPaUJfA1KsY

Four stroke engine-how it works (2 ¾ minutes)

https://www.youtube.com/watch?v=OGj8OneMjek

Internal Combustion Engine- How It’s Assembled And Works? ( 5 minutes)

https://www.youtube.com/watch?v=v0PUhxFJYBI

Compression test guides:

https://www.youtube.com/watch?v=0W0kQeTvURU

http://www.dummies.com/how-to/content/how-to-check-an-engines-cylinder-compression.html

 

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