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Old 03-14-2021, 04:16 PM
wagner wagner is offline
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New member - A-4 in a 1974 Sabre 28

Hello everyone!

New member here, but have been "lurking" here and there on this forum for a few years as I became the owner of "Bubble" a 1974 Sabre 28 Mk1 with an original raw water cooled A-4. Believe it is a direct drive late model A-4.

Bubble was an inexpensive vessel because the owner didn't have any one to sail with any more and the motor was "tired" (meaning not running, unknown whether it would run).

Being resourceful and optimistic, I said, motors aren't "tired"--they have something "wrong" with them that needs to be fixed. Armed with the boat owners manual, the MMI A-4 manual, a pile of parts from MMI, a multimeter and a heat-shrink connector kit, I somehow got the A-4 running with some semblance of regularity and even maybe some smooth-ness.

In the initial season, I replaced the following and had only one occasion of total engine failure (apparent corrosion on the points...):
-plugs
-wires
-cap
-rotor
-condenser
-points
-wire between alternator and coil

The A-4 ran remarkably well (shifter was nearly seized...but liberal application of some kind of oil and elbow grease freed it up) until late in the season when a sudden loss of power nearly caused a collision with beautiful Hinkley in Manchester, MA Harbor in 15-20kts of breeze. (This is only part of the story of a very long day...the dinghy motor was also not running that day).

The power loss appeared to be periodic and attempts to diagnose were limited to diving to examine the prop (brrrrr....no wet suit!). Had something hung up? NO. Stuffing box too tight? NO.

Not to worry...it IS a sail boat primarily and we sailed on and off the mooring mostly. Our home harbor has a lot of room to maneuver.

But the problem nagged at us (three of us own the boat) and we intended to "check things out" in the off-season (2019-2020). Well, 2020 turned out to be not so great. We did not launch at all, but DID determine that the rhythmic tapping sound while the engine was running was a stuck valve. A thumb test showed no compression on cylinder 3. A foray into the valve spring gallery showed a stuck exhaust valve on #3. No amount of Marvel Mystery oil and gentle taps availed any movement of the recalcitrant valve.

With winter looming and no break in my professional life (residential construction), we decided to lay her up for the winter again. I put the valve gallery cover back on with the used gasket and ran the engine. Some gallons of RV antifreeze and a few minutes of run time and we put her to bed. Fingers crossed that the coolant made it into all the nooks and crannies....

Which brings us to today! Clearly the head had to come off to unstick the valve...

Head is off. Thermostat is caked in black gunk. Cylinder three is cased in black gunk. Cylinder three exhaust valve is stuck way open and caked in black gunk.

The goal is put the engine back together and running for the season, knowing our mooring is easy to sail on and off and having a small outboard on board as a backup. We only do very close coastal sailing. No offshore work. Like everyone else, we are trying to avoid a full overhaul at this juncture. Time will tell!

The plan:
-knock the valve down carefully
-(probably) pull all the valves, clean and lap
-clean up head, block
-new head studs
-new head gasket
-new thermostat
-new temp sensor
-new oil pressure sending unit (none of the gauges work)
-rebuild carb
-new impeller in water pump
-Oil change
-fuel filter change
-plugs, points
-test motor on the hard for water in the oil etc
-Go sailing

Thoughts on the plan?
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