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post #1 of 24 Old 09-15-2011 Thread Starter
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Atomic 4 compression

Been having engine trouble and just was "informed" by the marina that I have lost close to half of the compression in all 4 cylinders. They were pretty vague about the possible causes and related repair costs. They did warn about sinking too much $ trying to trouble shoot.

Any body have any suggestions?

Not really thrilled about the prospect of buying and installing a refurb for what I understand could be upwards of $5K.

New to the whole arena and could use any help I can get.

Thanks.
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post #2 of 24 Old 09-15-2011
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First of all, a 'compression test' without a dry reading versus a 'wet' (a wee bit of oil dumped into the combustion chamber) is next to worthless .... WHAT were the compression values or does this require an additional charge for such an answer? WHAT was the engine temperature when the 'readings' were taken? When was the compression gage last 'calibrated' ???????
A 'dry' reading will indicate the integrity of the head/valves; a 'wet' reading will show the integrity of the piston rings, etc.
That your marina didnt report such would make me VERY suspicious that they are simply looking to do a 'replacement' ($$$$$$$$).

If the cylinder pressure are 'equal', the engine is still 'operable'.
Id strongly suggest that you get yourself a compression gage and learn to do such simple testing. yourself .... (wet and dry). NAPA and other national, etc. 'auto stores' sell compression gages at very reasonable cost ... and they come with 'instructions'.

Go to Moyer Marine Atomic 4 Engine Rebuilding and Parts and join the forum there. Also you can purchase Don Moyer's "Atomic-4 ... Rebuild and Maintenance Manual" ... and save yourself a fortune when dealing with 'marinas' looking to do unneeded work at well beyond outrageous prices- and to better guard yourself from unscrupulous 'shysters'.
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post #3 of 24 Old 09-15-2011 Thread Starter
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I did not know enough to ask these questions.
They did indicate the cylinder readings were between 30 and 50 (not all the same) and that 90 is what I should be getting.
The motor worked perfectly about6 weeks ago, and then again about two weeks ago for about 15 minutes.
I will check out Moyermarine.
Thanks.
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post #4 of 24 Old 09-15-2011
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What RichH said times 10.

The Atomic 4 is a great auxiliary engine for most purposes. Most marinas can't or will not work on them and will charge you around $80/hour if they do. They are much more likely to tell you it is 'done' to get you to install a diesel which they will likely service as well. You can do most (if not all) of the service on this engine yourself and save a boatload of bucks in the process.
When we got our boat with A4 about 8 years ago I knew almost nothing about the engine. I have learned quite a lot since then and I am now moderately capable of doing all or most of the work it needs. The Moyer Marine forums even Don Moyer himself are great resources to help get you through any 'challenges' you might encounter.
At a minimum you should know how to replace the ignition components (spark plugs, wires, distributor, rotor etc.), change the oil, clean the carburetor, change water pump impeller etc. If I had to pay a mechanic to do these items I could not afford my boat.

Post your question over at the Moyer website for additional encouragement.
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post #5 of 24 Old 09-15-2011
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If the motor was working perfectly both six and two weeks ago, what trouble were you having and when?

edit: in other words, its hard to advise you to buy a tester and do a compression test at all.


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post #6 of 24 Old 09-15-2011
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Additionally, there are a few good mechanics who will work on these engines but since your profile does not indicate your location it would be difficult to make a recommendation.
Most marinas just see you as their next cash cow and will tell you anything to get you to go for a diesel conversion (try more like $12k - $16K).
I have seen working (replacement) A4's listed for sale for <= $2K (about $4K if you get a rebuilt engine from Moyer).

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post #7 of 24 Old 09-15-2011
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Quote:
Originally Posted by RichH View Post
First of all, a 'compression test' without a dry reading versus a 'wet' (a wee bit of oil dumped into the combustion chamber) is next to worthless .... WHAT were the compression values or does this require an additional charge for such an answer? WHAT was the engine temperature when the 'readings' were taken? When was the compression gage last 'calibrated' ???????
A 'dry' reading will indicate the integrity of the head/valves; a 'wet' reading will show the integrity of the piston rings, etc.
That your marina didnt report such would make me VERY suspicious that they are simply looking to do a 'replacement' ($$$$$$$$).

If the cylinder pressure are 'equal', the engine is still 'operable'.
Id strongly suggest that you get yourself a compression gage and learn to do such simple testing. yourself .... (wet and dry). NAPA and other national, etc. 'auto stores' sell compression gages at very reasonable cost ... and they come with 'instructions'.

Go to Moyer Marine Atomic 4 Engine Rebuilding and Parts and join the forum there. Also you can purchase Don Moyer's "Atomic-4 ... Rebuild and Maintenance Manual" ... and save yourself a fortune when dealing with 'marinas' looking to do unneeded work at well beyond outrageous prices- and to better guard yourself from unscrupulous 'shysters'.
The above is truth. A steel sleeve has a different expansion coefficient than the aluminum piston contained within. Aluminum takes on heat initially much faster. If the compression is even all of the way across and it ran last week. It shall run again! I think MacArthur said that when coming back to the PI.
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post #8 of 24 Old 09-15-2011
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Well

The correct thing to do is a leak-down test as you will find the extent and location of the problem cranking speed alone has a huge influence on compression tests

Engine Leakdown Test

Hearing Problems
Beyond getting an overall picture of engine condition, the leakdown test is an excellent way to pinpoint where engine problems are before tearing down the engine. Listening for where the air is escaping by ear can isolate the problem.

Intake Valve: Air whistling out of the intake, carburetor, or throttle body indicates leak at the intake valve.

Exhaust Valve: Air heard hissing out of the tailpipe, turbocharger, or exhaust manifold means an exhaust valve leak.

Piston Rings: Whistling or hissing out of the PCV valve, oil filler cap hole, or dipstick tube means the air is pushing past the rings. Suspect ring or cylinder wall wear.

Head Gasket: Air bubbles in engine coolant seen at the radiator filler cap could mean air escaping into the coolant past the head gasket.

Cracked Cylinder Head: Bubbles in coolant or coolant being pushed up out of the radiator neck can also indicate cracks in the cylinder head or cylinder wall


From what i have seen and A4 can be run pretty far into the ground and more or less just reach a its NOT gonna run anymore point as for example mine came with a 40 year old distributor cap

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post #9 of 24 Old 09-15-2011
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"Been having engine trouble" What kind of trouble? Could be fuel delivery or ignition problems which would have no relation to compression. Unless you have a blown or leaky head gasket compression loss would probably happen over a fairly long time. As the engine was running fine before the trouble I suggest you go slowly and check the small items carefully before you open it up. Let us know what you find.

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post #10 of 24 Old 09-15-2011
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Hackettsan -
Perhaps you could itemize the signs and symptoms of your 'problem' ... and we can collectively brainstorm from there.
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