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Old 09-01-2010, 18:42   #1
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Let's Talk Atomic 4s...

I am at the point in disassembly where I decide whether or not to take the block apart. Head is off, valves are all pulled.

The main reason I did this was because I was getting a TON of smoke at operating temperature just POURING out of the oil fill cap (and my temporary fix involved getting a rubber stopper and about 15' of 1" hose, and just ran it out the port side head porthole while running the engine, so all the smoke wouldn't fill up the cabin). It was one of two things: cylinder blowby or valve guide blowby.

The first thing I did was a compression test, at operating temperature, even before the engine came out of the boat.

Results were basically 90-90-90-90 for each cylinder dry. (that is good - I think)

then I did a wet compression test and got approximately 97-110 for them.

But the smoke kept coming. Coming and coming and coming. I got fed up with it and decided that I was going to start taking the thing apart to try and see if there was any obvious maladies with the engine (scratched cylinders or something). So I took the head off and looked at each cylinder wall - they looked pretty darn good except for the following:



The red areas are barely visible in just the right angle of light and not even feelable unless you REALLY focus and use your fingernail to scratch it... light vertical scratches.

I am also able to wiggle the piston around in the cylinder at TDC, so I know for a fact that the rings are not frozen.



These things are telling me that maybe I was wrong all along? maybe its NOT the cylinders that are the problem?? Could it be the valve guides? and if so - then how hard is it to size/install new ones? What about lapping the valves and the seats?

I guess my main question is: how do I know for CERTAIN that the blowby is occurring at the valve guides OR the cylinders? I've done basically everything test-wise to determine, and this thing is just sitting on my bench, mocking me - telling me "yesssss, take me completely apart and spend 3 thousand dollars fixing meeeeee"

(I'm not rich by the way)

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Old 09-01-2010, 19:17   #2
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I've got a 42 year old A4 on my Tartan 27' that has been well maintained and runs well but can be a bit smokey at start up. Once warm it is just the smell of exhaust I try to avoid while motoring downwind (exhaust from transom). Diesel exhaust is not that pleasant to breath either.
I haven't had the head off our engine (yet) so I can't comment much about your situation. What I can say is that you should post the same well thought out question over at the Moyer Marine forums where many of the members have completely rebuilt their A4 engines: Moyer Marine Atomic 4 Community - Powered by vBulletin
The only comment that comes to mind that MIGHT be applicable to your situation is that IF there is a restriction in your exhaust system your engine may be forced to push the exhaust gases out of the oil fill cap. I would check your exhaust systems hoses and muffler (if you have one).
Good luck.
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Old 09-01-2010, 20:05   #3
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Since you have great compression.....I wouldn't have pulled the head off.

It is either overfilled with oil, or has worn valve guide seals.

Os your breather tube stopped up (it goes into the carburetor)
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Old 09-01-2010, 20:49   #4
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Since you have great compression.....I wouldn't have pulled the head off.

It is either overfilled with oil, or has worn valve guide seals.

Os your breather tube stopped up (it goes into the carburetor)
1) oh well... kinda sucks... but SOMETHING had to be done

2) oil level was perfect, and if its the valve guide seals... how the heck do I fix that?

3) breather tube is fine



see.... the problem was not a little bit of smoke... it would POUR out of the OIL FILL CAP and could fill the entire cabin of my catalina 30 in a couple minutes - to the point where you couldnt even see your hand in front of your face. This happened at operating temperature, so when I first cranked it, it was just fine.

And there is no way for any problem with the carb to cause smoke out of the oil fill cap.

I suppose if there was excessive backpressure in the exhaust, there might be something FORCING the smoke back into the combustion chamber / valves / valve guides... or something.... except exaust fumes and cooling water was coming out of the rear of the boat just fine in my opinion
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Old 09-01-2010, 21:13   #5
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Run that problem by Don at www.moyermarine.com or check out their forum.

I looked it up.....go to Don's response about halway down .pdf
http://www.moyermarine.com/forums/sh...light=Breather
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Old 10-01-2010, 15:42   #6
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Blow by

Redirecting the excessive smoke doesn't fix the problem, it just hides the symptom, and if you only use your engine to get out of the marina and back that will buy you time before you have to do something serious about it, and hopefully you don't get stranded. But the fact that it is burning that much oil (if it is smoke from burning oil) means that there is probably excess carbon building up on the pistons and plugs and rings too. I have a GrayMarine 4-112 that was getting tired and rebuilt it last winter for around 800 clams. I did the machanical work and farmed out the machine work (reground the crank journals, resurfaced the cam). I honed the cylinders myself and replaced all bearings, pistons and rings, seals etc. Relaped the valves, the whole enchilada. I also took the opportunity to strip all the iron parts down to bare, primered and painted. Cured the paint in the admirals kitchen oven (she loves the boat so she put up with it.

I guess my whole point is a rebuild doesn't have to be prohibitivley expensive, and as long as you are happy with the older style gearbox, it will give you a vertualy new engine. Speaking of the gearbox, after the rebuild my engine ran sufficiantly stronger that the clutch slipped if I gave it full power so consider a rebuild on that too. I don't know what prices are on A4 parts but the Gray was very resonable. They are simple engines and should not be scary.

My $.02
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