MST Outboard Engine Service & Gearcase Flashcards
6 cards from real MST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 MST Outboard Engine Service & Gearcase flashcards as text
What is the purpose of the sacrificial anode (zinc) mounted on the outboard's lower unit?
Answer: To protect the engine's metal components from galvanic corrosion by corroding preferentially
Zinc (or aluminum in salt water) sacrificial anodes corrode in place of the engine's more valuable metal parts when dissimilar metals are present in an electrolyte.
When flushing a saltwater outboard engine after use, what is the correct procedure?
Answer: Attach a flush muff to the water intakes with the engine running in neutral and flush with fresh water for 5–10 minutes
Running the engine with a flush muff circulates fresh water through the entire cooling system to remove salt deposits that cause corrosion and blockage.
What type of propeller material is generally most susceptible to corrosion in a saltwater environment?
Answer: Aluminum
Aluminum propellers corrode much more rapidly than stainless or bronze in salt water, especially when the sacrificial anode is depleted.
After a complete lower unit rebuild, the gearcase must be pressure-tested to check for leaks at what specification?
Answer: 3–5 psi held for several minutes with no pressure drop
A low-pressure air test (typically 3–5 psi per OEM spec) held for several minutes verifies all seals are intact before the lower unit is filled with oil and reinstalled.
What is the most common reason an outboard engine's tell-tale (water stream) has low or no flow but the engine temperature is normal?
Answer: A blocked or pinched tell-tale tube or fitting — not necessarily a pump problem
The tell-tale tube can become blocked by debris or a wasp nest without affecting actual cooling flow, so normal temperature with no tell-tale requires checking the tube first.
What is the recommended propeller shaft seal replacement procedure to prevent water intrusion after a prop strike?
Answer: Remove the lower unit, replace both the driveshaft and prop shaft seals, and pressure-test before reinstalling
After a prop strike, both seals should be replaced as a precaution and the lower unit pressure-tested to confirm integrity before returning the engine to service.