Rebuild does not deliver power of original A4

[richardcmarsh]

Two years ago I bought a re-built A4 from Moyer Marine. Engine runs well, but never exceeds 1700 RPM under load and the boat (1981 Catalina 30) never exceeds 5.0 knots in the water. The old A4 would go to at least 2000 RPM (though I rarely exceeded 1800) and would move the boat at 6.0 knots. Same propeller, clean bottom, exhaust hose replaced this past winter. It was 5 kts/1700 rpm from the day it was put into service mid season after crankshaft died on old A4. The hull speed calculation for a boat with 25' waterline is 6.5 kts. Any thoughts?

[Skywalker]

Have your checked compression?

Are you sure you are getting spark to all four cylinders?

I have no doubt the MMI will make it right.

I bought a rebuilt MMI years back for my C&C 34. After a couple of hours, I heard some kind of knocking. It ran well, but the sound bothered me. I called Don. He asked me to pull it, bring it back. His guys tore it down, checked all the specs, put it back together, no charge. I put her back in, sound was gone. So, I don't know what changed, neither did they, but it worked. Pushed her to nearly 7 kts. Good temp and pressure.

Currently, my 1966 vintage A4 can push my Tartan 27 to 6 kts. It has 100 lbs compression in each, runs at 160 degrees, 40 lbs pressure.

So, if the very wise people on this site don't help you find a solution, call Don.

Good luck.

Chris
Skywalker

[67c&ccorv]

How did the marrying up of the direct drive coupling with the prop shaft go?

What prop are you running?

Did the rebuild include new carb and fuel pump?

[Marian Claire]

Welcome to the forum. What RPM do you reach in neutral? One thing that has to be changed during an engine swap is the throttle linkage connection. Being as this was an instant change I wonder if the linkage is problem.
Interesting.
Dan S/V Marian Claire

[richardcmarsh]

Thanks for thoughtful responses. Carb and fuel pump are relatively new. I cleaned and reassembled carb this spring. Pump delivers plenty of fuel. Same prop which is standard, I think 12 x 9. There is no vibration in shaft. I think the lingo is a "short block swap" done within a month - nothing but the block was changed. I have tried manually controlling the throttle and have adjusted the cable. It revs close to 3000 in neutral if I am not careful. All plugs are dry. I have not checked compression.

I am constantly promoting Moyer Marine after nearly 20 years acquaintance.

[Mo]

Thanks for thoughtful responses. Carb and fuel pump are relatively new. I cleaned and reassembled carb this spring. Pump delivers plenty of fuel. Same prop which is standard, I think 12 x 9. There is no vibration in shaft. I think the lingo is a "short block swap" done within a month - nothing but the block was changed. I have tried manually controlling the throttle and have adjusted the cable. It revs close to 3000 in neutral if I am not careful. All plugs are dry. I have not checked compression.

I am constantly promoting Moyer Marine after nearly 20 years acquaintance.

Compression check would be a good start. I find 6.2 is the fastest I can get my C&C 30 going is calm water with a clean bottom. Prop cleanliness and condition of the bottom of the boat mean so much as well.

Good luck.

[ndutton]

The 9 inch pitch on your 12 inch prop is awfully aggressive. For a 12 inch prop you'd be happier around 6 or 7 inches on the pitch. The A-4 powered Catalina 30 (thousands of them?) had a 12x7 prop.

I believe those who like the Indigo prop do so because of the performance difference with a reduced diameter (10") and 7.7" pitch more than the winglet concept. In fact, Indigo discusses just that in their product description (interesting how their numbers mirror yours):

The vast majority of Direct Drive Atomic 4 yachts were originally equipped with a 2 blade, 12" diameter by about 9" pitch propeller. This application allows the vessel to achieve a respectable cruise speed in calm waters at about 1400 RPM. However, wide open throttle is only about 1700 RPM which leaves very little reserve for foul weather or bottom fouling. Furthermore, at 1400 RPM, the engine is working very hard (near maximum cylinder pressure) which leads to high loads on rings, pistons, and bearings.

[67c&ccorv]

I realize this does not address your question but the 9 inch pitch on your 12 inch prop is awfully aggressive. For a 12 inch prop you'd be happier around 6 or 7 inches on the pitch. The A-4 powered Catalina 30 (thousands of them?) had a 12x7 prop.

I believe those who like the Indigo prop do so because of the performance difference with a reduced diameter (10") and 7.7" pitch more than the winglet concept. In fact, Indigo discusses just that in their product description (interesting how their numbers mirror yours):

That's how it went when I changed the old two-blade "sailor prop" for an Indigo on my vessel Neil...1967 C&C Corvette.

[Dave Neptune]

Hmmm

Richard, the performance should be the same if all else is clean and the "same". As you did a short block, my first check would be the timing and the c-advance. Once confirmed fine I would look to the exhaust for a blockage. If it was about to plug up, it may now be plugged up enough to compromise performance.

Your prop does sound a bit aggressive for your boat as far as pitch is concerned.

Also you may want to check the tach wiries too.

Dave Neptune

[joe_db]

My "new" A4, while a thousand times better in every way than the old one that had myriad issues, is a bit slower. The old one - when it was working right - could be roused to a bit more power until something went wrong with it. There is some variation between engines apparently. I would also agree that 12x9 should be switched for 12x7 or an Indigo. I can hit about 6.2-6.5 knots with a clean bottom with a 35 foot boat. With a clean prop I can hit 2300-2400 RPM.

[tenders]

I find it hard to believe that a rebuilt engine can categorically be said to have less power than the original. These engines never get close to their maximum output to begin with, and there are hundreds of variables associated with the process of removing and reinstalling an engine.

I would wager that in a controlled environment, carburetor settings, condition of prop/hull, engine alignment, and possibly deteriorating condition of unchanged components (like the exhaust system or fuel supply) would account for almost all of the perceived differences between new and old.

[richardcmarsh]

Compression

Compression - none in 4th cylinder. With coaching from Don, I replaced the aft most valve in March. Went on to have a great 2014 season. Since I never before had the full power I expected, it appears mechanic who installed the re-built engine must have had trouble starting it and backed up water into the engine. He did a few other really stupid things - like not connect the alternator. That was 7 or 8 years ago. The circumstances at the time did not permit me to do the work myself. Another reminder that it is best to do the work yourself if at all possible.
Thanks for all the forum suggestions - huge motivation.

[Mo]

Compression check would be a good start. I find 6.2 is the fastest I can get my C&C 30 going is calm water with a clean bottom. Prop cleanliness and condition of the bottom of the boat mean so much as well.

Good luck.

My prop is 12/6 pitch. Michigan 3 blade. It does it for me. Once I leave the dock I have just over a mile and I'm on open ocean. I find the 3 blade prop good in chop sea and keeps the boat moving into it....something to consider if you are wondering if you should have a 2 or 3 blade.

[gregsails]

I am wondering. As it happens,I have my prop and new shaft and cutlass in my basement awaiting spring. I see the 12 in the prop measurement, but where does the 6-7-9 number come from and how do I tell which prop I have?
Thanks
Greg Cat 30 hull 696

[sastanley]

Greg, The pitch should be stamped right after the 12 on the prop hub somewhere..Mine was on the end I think..With marine growth it can be hard to read..Sometimes you need to burnish the area for the stamping to show up.

C-30's of our vintage with Atomic 4s came with a 2-blade 12" diameter x 7" pitch prop.