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Low Compression on One Side of 454

D

drseth

New member
Hi,

I bought this 1979 Pacemaker 33 Sportfish with twin 454 Crusaders recently. The starboard engine's starter would not engage, and the port engine had the heat exchanger off, so I could not test drive it not compression test it.

I compression tested it today and here it is: 1- 110, 3-115, 5-110, 7-110, and the other side 2-75, 4-15, 6-35, 8-85. All of the pressures held up and were run after the engine was run for 15 minutes. I had just replaced the points distributor with the Delco Voyager EST Distributor Kit, and now, what to do? The engine is original and has 1377 hours.

Could the head gasket need replacing, or should i just get a long block or repower? There are so many variations of 454's, with peanut, oval, and rectangular port heads, as well as Mark IV, and Gen V and VI blocks. I like the idea of a roller cam/lifter/rocker drivetrain for the free horsepower. I also see 502's available, but I want dependability and economy, with a cruise of 18-22 knots. I have just replaced the heat exchangers/risers/elbows, and had the oil coolers acid washed and pressure tested, so I would like to stay with the log manifold system.

What are the specs of the 1979 vintage Crusader 454 350HP? What are the shape of the ports on the heads?

Which way is the most economical way to go?

Seth Anderson
Moon, VA
 
If you can spin the wrenches, getting your heads reworked would likely be the most economical route. You need to make sure the issue is with the top end and not anything below the deck (pistons or rings). Another compression test with oil or a leakdown test would be a step in making that determination.

Your stuff is Mark IV flavored and all the 'production' marine engines use the "peanut port" styled heads. There is NO benefit to going to the larger ports without major changes thruout the rest of the engine.

I'd suspect the most likely scenario is the heads are just worn out but without any history on the engines, its just a WAG. A GOOD machine shop should be able to assess the condition of the current heads and their components. If the RH head is bad, it may be cheaper to buy a complete set, already reconditioned.

You can always retrofit a roller valvetrain (full or partial) but it isn't just changing parts to get it to work. You may also want to assess the condition of the cam before you order any parts.

As far as the specs go, Crusader used the default GM Marine blocks. The list is about a dozen pages so being specific makes it easier.
 
I agree with Makomark, a wet test is the easiest way to determine if lower or upper issue. Having said that, you just bought this thing so you probably don't know the PO's maintenance habbits or the way the engines were run, AND it's a '79!! If I were going to keep the boat for a while and the wallet allowed, I'd go long blocks and the worries about the bottom end will end there.
 
Another thing I forgot to mention. The engine has a lot of blow-by coming out of the rocker arm covers. At idle, there is more smoke exiting the hoses than the flame arrestor can suck back into the engine. Would that indicate an intake valve leaking?

Also, with cylinder 4 and 6 having low compression (15 and 35 psi, respectively), would that indicate a bad head gasket, even if the oil and antifreeze aren't mixing?

If it is leaking intake valves, could it be a carbon buildup, a weak valve spring, bad valve guides, or something else that could be fixed without removing the head?
 
THe classic, fast, poor man's test for bad rings is to squirt 2 tablespoons of oil into the low pressure cylinders. If the pressure reading go up significantly, then you are facing a ring job. That would explain both low readings and excesssive blowby. Without either that test or a leak down, everyone here will be guessing.
 
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