When the top of the rocker (the part that pushes on the valve stem) is out toward you, the valve is closed.

Because 2-stroke engines are designed to run at a higher RPM, they also tend to wear out faster; a 4-stroke engine is generally more durable. That being said, 2-stroke engines are more powerful. Two-stroke engines are a much simpler design, making them easier to fix. They do not have valves, but rather ports.

Power stroke. The piston is at top dead center, intake and exhaust valves are both closed and the spark plug has just fired. The exhaust valve opens fully and starts to go closed. Before the piston reaches TDC, the intake valve starts to open and the exhaust valve is still partially open.

If a piston is at top dead center on the compression stroke, both the intake and exhaust valves should be closed. When at top dead center on the exhaust stroke, the exhaust valve should be open. Either both or none, depending on whether the piston is beginning the intake stroke or the power stroke respectively.

Briggs & Stratton Compression Review

If you have car engine compression problems, your car will either misfire when you start the engine, perform poorly or, if you have low or no compression in all cylinders, won’t start at all. You can’t drive your car for long, if at all, with low compression.

Here are some symptoms of a bad valve seal that may need to be replaced:

• Performing the Cold Engine Test. One sure-fire way to tell if you have a faulty valve seal is to perform a cold engine test.
• Idling.
• High Levels of Oil Consumption.
• High Levels of Smoke.
• Engine Braking Test.
• Acceleration Power is Compromised.

A bad rod bearing won’t last much longer. the close clearance of the rod bearing will greatly open up. but even that won’t measurably impact actual compression. Leaky valves , bad rings , broken pistion , blown head gasket are more likely cause of low compression.

Yes it can have good compression and bad bearings (or oil pump).

You usually cannot hear rod knock while idling because the engine isn’t under a load. However, rod knock is usually the loudest when you rev the engine and then let off the gas and listen. The rods will knock when the engine is decreasing rpms rapidly. The only way to fix rod knock is to change out the rod bearings.

Rod knock is a serious issue with your engine—it means the engine is not functioning properly. If you start to notice rod knock, this isn’t a problem that will just resolve itself—you must take immediate action and replace the rod bearing while also fixing any other parts associated with the sound.

A rod knock will only sound worse (louder) as the engine heats up. It will not go away as the engine gets warmer. If it does, it is probably something like an exhaust leak which closes itself as the engine manifolds get warm.

Rod knocking noises are loudest at higher speeds (over 2500 RPM). So, feathering the gas pedal, may result in a distinctive back rattle, between 2500 and 3500 RPMs. As a result, the piston will whack the cylinder head. In addition to the big end of the connecting rod, banging on the crankshaft rod journal.

Some of the ways in which you can fix engine knocking include: Upgrading the fuel that you put into your car and going with something that has a much higher octane rating. Putting additives into your car that are designed to clean carbon buildups.

If you start up your car and hear knocking noises, this usually means the fuel of the car was not ignited properly. This could be due to low-quality fuel, bad spark plugs, or another reason above. But for many high compression or high performance vehicles, 91 or even 93 octane fuel is necessary.

The most common cause of all of these knocking problems is loss of oil pressure from a clogged filter and oil pickup screen causing oil pump failure or just running the engine low on oil from oil loss through oil burning, oil leaks, and lack of maintenance oil and filter changes.

When you have low oil volume or low oil pressure, you’ll commonly hear a “clattering noise” coming from the engine’s valves. Adding more oil will make the noise go away, but it won’t solve the underlying cause of the noisy engine – the oil leak.

Knocking occurs when fuel burns unevenly in your engine’s cylinders. When cylinders have the correct balance of air and fuel, fuel will burn in small, regulated pockets instead of all at once. Engine knocking happens when fuel burns unevenly and those shocks go off at the wrong time.

Below are the top oil additives to stop car engine knocking, especially for older engines.

• 1) Sea Foam SF16.
• 2) Archoil AR9100.
• 3) Liqui Moly Cera Tec Friction Modifier.
• 4) Lucas Heavy Duty Oil Stabilizer.
• 5) Red Line Break-In Oil.
• 6) BG MOA Oil Supplement.
• 7) Rev X Fix Oil Treatment.
• 8) Lucas Engine Oil Stop Leak.

Knocking can damage the surface of the piston, the cylinder walls or the crankshaft bearings, all of which are expensive to repair. Modern computer-controlled injection systems can correct your fuel mixture to prevent knocking, but at the cost of engine performance.

A clattering noise from the engine can be an indication of low oil pressure. Particularly if it gets worse at lower engine speeds. In the case of even lower oil pressure, the sounds can be more like clanging or knocking.

A failed rod bearing will end up producing a metallic knocking or rumbling noise from the engine, especially during cold starts. This is known as ‘rod knock’, and it sounds like striking a tin or aluminum surface, which is low at idle and increases in degree with acceleration.

If it’s spun and damaged the crank you will need to remove the crank have it either machined or replaced then replace the bearings. Prices could range from $500 to $3000.