Low A4 Power and Low Compression Test

[jracine]

Hi all.

I am a third-season owner of a Pearson 28-1 with original A4 engine from early 1970's.

This season a noticed a sudden drop in power - cannot get above 4 MPH under load, no acceleration and struggling in any waves or head winds.

Compression test (dry) as follows: 100, 50, 75, 100. I do not have information on any previous compression readings prior to my ownership.

I have added MMO to the gas to try to clear stuck valves.

Drained the carb and fuel filter (which is changed every season).

Oil pressure and temp is all good.

Idles well and throttle responds well in neutral. But no power beyond an easy 4 MPH in gear.

Any suggestions other than valve job or possible head gasket replacement (noting cylinder 3 and 4)?

I am a newbie at all this.

Thanks.

[JOHN COOKSON]

A big welcome to the forum.

Has the prop been checked for growth and fouling?
What RPM is the engine turning when the power maxes out?

Others members will also be along with ideas.

TRUE GRIT

[joe_db]

With 50 PSI, you have a 3 cylinder engine. That low compression cylinder is essentially just along for the ride.

[jracine]

Thanks for the replies. I did check the prop in the water -- looked fine. It has only been on the water 8 weeks so far this season. I also take it out of the water every year and clean it up.

I have no tac on the engine, so I have no way to measure the RPM at this point.

Thanks!

[Al Schober]

Those two cylinders (2 & 3) with low compression do suggest a head gasket problem. Although I suspect no change, I'd suggest you add a bit of oil to each cylinder and do the compression test again. This will verify that it's not rings. Whether it's valves or a head gasket doesn't matter at this point - the head has to come off for corrective action.
When is up to you (make it through the season?). Difficulty depends on access. Some boats are easy (Tartan 30), others are hard verging on impossible.
Two things you need: First is the Moyer Manual - it's the starting point for info on taking care of and repairing the Atomic 4. Also suggest you visit your auto parts store and get a clip-on tachometer - good thing to have.

[Dave Neptune]

j, your "sudden" drop in power does not indicate a wear problem like the rings. You probably have stuck valves. Do a compression check again and then do another with a bit of oil sprayed into the cylinders like Al suggested.

Be sure the choke is open, the throttle is wide open, spark plugs removed and the ignition lead disconnected for a proper compression check.

Dave Neptune

[tmcdonagh]

Please do not discount this advice!

A big welcome to the forum.

Has the prop been checked for growth and fouling?
What RPM is the engine turning when the power maxes out?

Others members will also be along with ideas.

TRUE GRIT

I was running into a similar problem. Only real change was locale for me and low and behold?, my prop was covered with barnacles. I have about 4 of those little things per square inch. Totally destroyed my ability to reach a reasonable cruising speed and forget about backing up! The engine was running so hard she was beginning to overheat. Grab a mask and fins and check it out! Best advice I have received since “check the wiring order! It’s 1243 not 1234”.

Thanks True Grit!

[joe_db]

I was running into a similar problem. Only real change was locale for me and low and behold?, my prop was covered with barnacles. I have about 4 of those little things per square inch. Totally destroyed my ability to reach a reasonable cruising speed and forget about backing up! The engine was running so hard she was beginning to overheat. Grab a mask and fins and check it out! Best advice I have received since “check the wiring order! It’s 1243 not 1234”.

Thanks True Grit!

A vacuum gauge will instantly make you aware of this issue

[cptinhook]

I replaced a valve on #4 cylinder on my 1978 (later 70's are a little different)P-28-1. It's not too difficult. Access is pretty good on top and PORT side where you need it. If you decide to replace the head gasket after a wet test, I suggest removing the entire face of the ladderway for easiest access.
Lou

[capnward]

Make sure you have bad compression before pulling off the head. When you do another compression test with oil sprayed into the cylinders, you might put some MMO in there too. It might free up stuck valves quicker than adding it to the gas. I don't understand why the head needs to come off to unstick the valves. I should state that in 20 years and 2700 hours of using MMO in the gas and the oil, I have never had to remove either head or valve cover. If you hadn't reported low compression, I would have said it was fuel related, and to check the carb jets and replace filters.

[tenders]

With an Allen wrench and a flexible light, you can see and work sticking valves up and down a few dozen times by hand to try to loosen them up - only removal necessary is the spark plugs.