Low compression - next steps?

[rkohl44]

Hi All,

My engine has never been "peppy" and it usually hesitates as I increase throttle. I finally completed the 2 stage compression test with the following results. Both were with a cold engine. Test 2 was done after a Tbsp of motor oil was inserted into each cylinder.

Test 1: Cylinder 1: 65 2: 50 3: 60 4: 25
Test 2: Cylinder 1: 90 2: 90 3: 80 4: 50

Remarkably higher results, which indicates "worn rings or valve guides."

More info:

I completed the block pressure test and it held 15 psi for 30 minutes. It dropped to 14 psi after about 45 minutes. I'm not convinced my test equipment (the HD pressure gauge, hose barb and plug) wasn't the source of the leak.

Spark is pale yellow, but the coil checks out fine. I do have an ammeter on the original wiring. The boat is a 1982 Catalina 30, so you know how nasty the wiring is. Batteries are new, EI and a new alternator were installed 3 years ago. Carburetor was rebuilt a month ago. Exhaust was rebuilt 2 years ago. It usually starts without too much difficulty when cold. When hot, it often needs starter fluid to convince it to go.

Here is a clip of the mighty beast running (and dying): Engine running

Since I have owned the boat (4 years now), I have been religious about 1. MMO in the fuel, 2. Running the engine for 10-15 minutes at least monthly.



Questions:
Should I repeat the block pressure test?

Would removing the ammeter get me to the desired "snappy blue spark"? (and would this have any influence on the lack of peppiness?)

How does the engine sound? Is the air sucking sound normal as throttle increases? (My A-4 is the only one I've heard run in person.)

Next steps? (Call Ken and order a short block? Pull it out and fix it? Fix it in place?)

How much overhaul can I do on a Catalina 30 in place? I've seen a lot done, but not sure if rings would be possible with the boat in the water.

I feel like I'm stepping up to the big leagues. Thanks for any/all guidance!

[Ando]

Did you get the correct carb rebuild kit? I ask bc I ordered the rebuild kit for an early model carb when I should’ve ordered the rebuild kit for the late model carb. The valves are very different (as well as the gasket) but thankfully the threads are the same for all the valves. My two cents. How long since you replaced the fuel filter, btw?

[ronstory]

IMO, not great but not horrible either... and some questions.

Q1: how often a year do you get out and drive the motor pretty hard?

Q2: Any blue smoke do you get out the exhaust?

Q3: Do you have any blowby in the engine compartment after running for 20-30 mins while cruising.

That said, we need to figure out why your spark is not a good blue spark.

[Dreadnaughty13]

Sounds like a couple of problems

Lack of throttle response may be due to one of the carburetor jets being plugged. They have released a good video of this on youtube. I would definately start here before chasing down something else

https://youtu.be/kHuemGC_PHA

As for the compression, if it's running I'm not sure I'd mess with it but there are a couple of things you could do:

1) If you've already removed the carburetor, you can pull off the valve cover on the side. Check the clearances on you valves to make sure the valves on #4 is seating all the way.
2) If there is access, you can pull the head. If the motor hasn't been broken down for several years this is going to be really hard to get off but is possible. You will need new head gaskets if you pull this off.

[JOHN COOKSON]

That said, we need to figure out why your spark is not a good blue spark.

The first thing I would do is take a voltage reading at coil +.

ex TRUE GRIT

[tenders]

The engine doesn't sound horrible in the video. Well, except for the dying part. Which could be due to a less-than-optimal air/fuel mixture, an idle speed that's too low, or a clog/dirty jets in the carb - basically the FUEL part of the FUEL/COMPRESSION/SPARK triad of necessity.

On the COMPRESSION part, when it's running, put some rubber gloves on and pull off one spark plug boot at a time. The engine's RPMs should diminish in an obvious way, indicating that each cylinder is firing more or less correctly. (Then put the boot back on and pull off the next one.) If #4 doesn't change, you have a pretty good indication that cylinder's low compression is problematic.

Re: SPARK, agree, get us some voltage readings across that coil. This isn't a great time to surgically remove the ammeter, but once this gets cured I would do that. It just doesn't give you enough useful information to justify the long path it makes all the juice follow.

[ronstory]

The engine doesn't sound horrible in the video. Well, except for the dying part.

This made me smile. Thank-you.

[rkohl44]

Ando: Yes, correct carb kit was installed. New fuel filter this year.

ronstory: Q1: motor not not frequently driven hard for extended periods. New marina only takes 10-15 minutes to get to sailing conditions.
Q2: no blue smoke
Q3: haven't noticed any blowby in engine compartment

Dreadnaughty13: carb was just rebuilt. looks like there are other steps before checking valves

John Cookson: I took a voltage reading at the coil within the last 2 months and wrote it down in my logbook. Unfortunately, it's on the boat. Will report back next time I'm there. As I recall, it was what it was supposed to be but can't be 100% certain.

tenders: carb was just rebuilt and I have a polishing filter. I'll perform the rubber glove spark plug boot removal test next time I'm at the boat. I don't have a tachometer installed, but I'd imagine you would suggest I at least get a handheld one. I'll leave the ammeter in place.

Thanks all. More testing to be done and will report back when complete.

[ronstory]

Points for closing out the homework, in a home schooling environment.

As for the compression, you would need to preform a leakdown test to try and discern the cause or causes. But the fact that adding oil substantially increased the compression likely means your rings that are not doing their job effectively.

IMO, if engine is not run much you can get a lot gunk on rings over time. My 2nd A4 was from from a fresh water lake that was only run for very short periods to and from the slip. It needed several MMO treatments of an ounce or so in each cylinder when I left the boat to unstick the rings so it soaked the couple of weeks we were away from the boat.

It's *much* better now. When I first ran it under load high load to test the repitch of the prop... I complete filled the cabin with blowby. Now with MMO treatment and running the motor, very little blowby. Now if it only had oil consistent oil pressure when hot, the motor would be great.

Give the MMO treatment a try and then retest compression in a month or two.

[rkohl44]

ronstory: in this case, the MMO treatment is exactly what? I believe it to be squirt MMO into each low compression cylinder(s) and let it soak. Repeat. Repeat. Repeat...

correct?

[rkohl44]

The first thing I would do is take a voltage reading at coil +.

ex TRUE GRIT

coil + reads 13.8

[rkohl44]

On the COMPRESSION part, when it's running, put some rubber gloves on and pull off one spark plug boot at a time. The engine's RPMs should diminish in an obvious way, indicating that each cylinder is firing more or less correctly. (Then put the boot back on and pull off the next one.) If #4 doesn't change, you have a pretty good indication that cylinder's low compression is problematic.

RPM decreased dramatically when #1 #2 and #3 were removed.
RPM did not change at all when #4 was removed.

[ronstory]

ronstory: in this case, the MMO treatment is exactly what? I believe it to be squirt MMO into each low compression cylinder(s) and let it soak. Repeat. Repeat. Repeat...

correct?

Correct. Just let it sit and longer is better.

[rkohl44]

more info: sometimes oil pools around the top of #4 spark plug

does this indicate worn rings, or valve issues? both? neither?

[JOHN COOKSON]

RPM decreased dramatically when #1 #2 and #3 were removed.
RPM did not change at all when #4 was removed.

How does #4 plug look? Is it not firing because it is oil fouled or because no electricity is getting to it?
Could always try a new plug in #4 and see if it fires.

ex TRUE GRIT