Rebuild or no?

[Brimikeg]

Good morning everyone,
I have a late model atomic 4 that I recently got running after is sat for a while. From what I understand it was rebuilt in the early 2000's and meticulously cared for by that owner. Then the boat was sold to someone that wanted a diesel so they pulled the motor. I suspect the set it on a pallet at the boat yard and covered it with a tarp and left it there until I picked it up. After some troubleshooting with the cooling system I got it running well with no water intrusion. When the boat is not in gear the motor will rev up as it is supposed to and behaves normally. However when in gear it will not exceed 1500 rpm. It reaches 1500 at about half throttle and stays at 1500 all the way to full throttle. I did a pressure test and got the following results:
1- 0psi
2- 65psi
3- 65psi
4- 75psi
My immediate assumption is that I need to rebuild the engine. I'm going to pull off the head and check to make sure I have no stuck valves or carbon buildup that's preventing them from sealing properly. So my question is, is there anything else I should look at before continuing with a rebuild? I have already pressure tested the water jacket in the block and manifold (and installed a new manifold because that was the root of my previous problem) and everything there checks out. As I am relatively new to this world of atomic 4's I just don't know if I'm missing something obvious that could solve my problem, but in what knowledge I do have of similar engines, I suspect worn piston rings possibly from sitting on the pallet in the boat yard for who knows how long. Any help or advice would be appreciated!

[Dave Neptune]

No rebuild yet! A stuck or sticky valve is probably causing the zero cylinder~~no biggie. The low numbers are not that bad and could easily be sticky rings from sitting or the results of a poor test.

I would add some TCW-3 (synthetic 2 stroke oil) or MMO to fresh fuel at around 100:1 mix.

SPRAY some penetrating oil or lubricant of some sort into each cylinder and let it sit for a day or two. Leave the plugs out and kick her over with the starter once in a while to mix and shake thing up.

Check the centrifugal advance for smooth operation, especially since she has been sitting.

After a few days and/or even some trying to loosen the offending valve with an Allen wrench gently.

Now start her up again and let her run for a bit at various RPM's and stay below 2,000. She may just shake the stuck valve loose and the added oil to the fuel will get in a begin lubricating. Once done let her cool for a few hours and do a compression check.

The compression check should be done with the throttle at full, the choke open, all plugs removed and fully charged batteries.
First do the dry test and record the numbers. Now do a wet test by spraying some oil into the cylinders one at a time and conduct the "wet" test again recording the numbers. Get those numbers back to us for further evaluation.

No need to rebuild unless something is broke or a knocking bearing journal.

Dave Neptune

[joe_db]

^ what he said.
I would bet that nothing is going on other than stuck rings and valves. You can also do a "MMO Tuneup". Get the engine warmed up and start pouring MMO in the carb slowly. When the engine starts to bog down shut her off. Come back in an hour and fire back it back up, once the smoke clears you may have unstuck what needs unsticking At the very least you'll annoy the neighbors with a big cloud of smoke

[Brimikeg]

Sounds good, I've had it running for a while now while trying to figure out what to do with it. Every time I go out to the boat I run it for anywhere from 30mins to an hour to make sure everything is moving properly. I'll give some of these ideas a try and do the tests and post the numbers.

[Brimikeg]

So I went out today and tried first the mmo trick pouring it in the carb, after waiting a while and starting her again it sounded better but still not exceeding 1500-2000 rpm in forward gear. Before leaving the boat I sprayed some penatrating oil into the cylinders, aimed at the valves mainly. I'm letting that sit till tomorrow where I'll give her another start and do the wet and dry compression test. I'll post those results here tomorrow.

[joe_db]

1500 and 2000 are not the same thing. Plenty of boats that are somewhat over-propped or have dirty props don't get much past 2000.
I would try a compression test again soon and see where you are.

[Surcouf]

compression test will confirm if valve is free
many many threads in the past months on stuck valves, a classic. Such as this one

https://www.moyermarineforum.com/forums/showthread.php?t=11680

Patience is key. Good luck

once compression is good, getting into the max RPM, type of prop, hulls, max speed, pro and dirty props... is one of the most debated subject, as it is at the corner of having a good working engine (without ignition grimlins, lack of fuel of air), no shaft line issue, clean hull, the right prop etc... Once again, I can only advice to read manny threads here, and keep an open mind: many owners realize the PO installed a large 3 blades prop that could never go above 2000 rpm.

[Brimikeg]

I know that I have a 2 blade prop on there, however I do believe that it may need to be cleaned so I'm gonna go under to do that soon, I'm working on putting a hookah rig together to clean the whole bottom.

[Brimikeg]

I also have had a running engine on the boat before and we moved much faster than the last time I tried. I was able to motor through about 4' seas, the last time I tried a light current was to strong for the motor to move against.

[Brimikeg]

So yesterday was an unfortunate day, I tried to start the engine and realized the starter went bad, and when trying to do the compression test with the hand crank I realized that my pressure tester was broken. So, I have a spare starter but I won't be able to go back out to the boat until at least next weekend. So I'll pick up a new pressure tester and I sprayed some penatrating oil into the no compression cylinder to let it sit for the week. While cranking I was feeling no compression out of cylinder 1 still so I'm hoping that letting it sit for a week in the penatrating oil will loosen things up a bit.

[Brimikeg]

Hello everyone, so sorry for the long wait since my last post. I finally got to do the compression test after running all of the suggested solutions and here were the results.
Dry:
#1 - 0
#2 - 80
#3 - 80
#4 - 90

Wet:
#1 - 0
#2 - 80
#3 - 70
#4 - 80

Despite the 0 reading on the pressure tester I can now feel some compression coming out of cylinder #1. So far Ive run MMO and sea foam through it in the same manner as described earlier in the thread along with trying to unstick the suspect valve with PB Blaster. I am running more MMO through it now and plan to let some PB Blaster soak in there for the next week or so to hopefully get some more compression out of it. At least the rest of my numbers improved!

[scratchee]

Brimikeg,

That was my thread that was linked in an earlier reply. I'm not any kind of expert, but I did have a similar problem and was able to fix it (with plenty of help from this forum, of course!) I have one question and one suggestion:

Do you hear a loud ticking sound when the engine is running? That sound is what clued me in that I had a problem.

After several days of penetrating oil applications (though the sparkplug hole), what finally freed up my valve was spraying Seafoam into the air intake (also called the flame arrestor, at the front of the carb) while the engine was running. I would spray until the engine started to die, then stop spraying until it smoothed out again, then start spraying again. At some point the engine became much smoother and the RPM jumped noticeably: my valve was free! This approach might work for you too.

[tenders]

A valve stuck the up position can be poked down with a bit of prodding with an Allen wrench of suitable length. The valve is off to the outboard side of the spark plug hole - not directly underneath it. You can't both see in the hole and do the poking at the same time - you have to use The Force to do the poking.

Once you've gotten the valve moving up and down a few (dozen?) times, lubricating with MMO between pokes, very often the valve will start working again of its own volition.

(The theory behind this is that rust or carbon is causing the valve to hang up, and getting it moving knocks the schmutz off.)

(You might want to snake a small USB camera down into the plug hole of the sticking valve to see what's going on in there.)

(Also, just as a public service announcement, double/triple/quadruple check that your plug wires are in 1-2-4-3 order! It is incredibly easy to get them mixed up. I have little masking tape labels on my distributor cap and on the plug wires themselves.)

[Brimikeg]

Scratchee,

Yes I do hear a loud ticking from the front cylinder, that is also what clued me into something not functioning right. I then looked and saw that the spark plug looked completely unused compared to the rest, despite them all having been replaced at the same time. The sea foam treatment you suggested is what helped bring the compression up in the rest of the cylinders and get the troublesome one to be blowing a little. My suspicion is that the valve is now opening a very small amount, here is why. Previously (before the sea foam treatment) I felt no air being blown out of the #1 cylinder whatsoever, and a compression check confirmed that. Also when I would fill the cylinder with either MMO or sea foam or penatrating oil, all would pool up when the exhaust valve was supposed to be open. Now however, after the sea foam treatment, I can deal some air being blown out the spark plug hole when cranking. Despite being able to feel it it seems to be not enough to read on the compression tester, also no liquid will pool up when the exhaust valve is supposed to be in the open position. However I cannot feel with the penatrating oil straw, that the valve opens fully. I will run more sea foam through it once I am back at the boat this weekend.

[Brimikeg]

Tenders,
I will see about getting a small camera to look at the valves, I'll also see about trying to move the valve up and down with an Allen wrench. Thank you!