Port idle conking out

I would say that the "cover" mentioned here is the Valve Cover not the Cylinder Head at this stage.

If compression testing the non firing cylinder is posing problems owing to access I imagine replacing the valve springs with the head on will not be easy either if its even possible

Problem?? The tech replaced the plug..

You are right, valve cover makes much more sense in this context. Working on them in such an restricted environment sounds interesting in the Chinese sense. Still trying to think of an obstruction where I can change spark plugs but not fit a compression tester. Unless its a rigid one.

Always the case if you remember the warranty. =)

It is quite possible that something got lost while playing the telephone game.
[Cue the usual presentation about communication issues. What I actually need, what I think that I want, what I think I've said, what I did say, what someone has heard, what someone has understood, ....]

Maybe there was an obvious sign for a fault and the working cylinder compression test was used to rule out a global problem. Maybe there is an access problem I can't visualize.

So there there is a moment that makes one pause and feel doubt about the situation. (Here while reading about it second hand, which does not help either.) That does not instantly mean that the mechanic is wrong, usually just that some piece of information is missing.

UH?

Leak down on a SBC?

I guess that could be done. Keeps that clock going..

Lets hope again that's a broke valve spring. If the valve fell in and struck the piston (ouch), it all comes out. Could explain where the oil went.

Maybe I'm missing something here, but how does a leak down test determine if there is fuel reaching the cylinder? If it's a failed valve there is no leak down because there is nothing to leak down because there is no compression.

Bob

If you allow anyone to talk you into machining one head and not the other, you need to run the other way.

That would be so noticeable in engine noise alone, a deaf-mute could hear it.

Find a new mechanic.

Your answers make no sense and the mechanic is taking you for a wild ride. If you cannot even screw a compression tester in the cylinder, how do you screw virtually the same fitting into the spark plug hole to perform a leak down test? In order to do a leak down test, if you cannot confirm you are at TDC through the spark plug hole, which is what I'd imagine because you can't even screw a compression tester in there, you'd have to yank the valve cover to confirm TDC. If you yank the valve cover, you should be able to see a dropped valve from a mile away and it would make an aweful racket as someone else mentioned. My guess based upon what you've described is that your mechanic set the ignition timing too high and you have a hole burned in your piston or burnt exhaust valve and that's why it's one of the 2 last cylinders. Usually when you melt something from too high of ignition (or poor quality gas) it's one of the two last cylinders. I agree also, both heads should be rebuilt.

Hi,

Either things are not beig explained properly by the mechanic or there is a complete lack of knowledge about the problem.

Pull the valve cover and see if one of the springs is broken, if the collets had popped out and the valve dropped into the cylinder keep going and pull the cylinder head off.

Do not service one head do both, if any doubt as to valve train components viability replace them all, the component cost is not huge compared to the damage that can be done by a failure and the inconvenience of this in the short summer cruising season.

AFTER, you find a new mechanic. The piston cannot lift any higher than it is normally supposed to. What it sounds like is that you had valve float due to a weak valve spring (or over-revving it) and the valves didn't close as fast as they normally should and the piston hit them.

This^^^

It sounds like you are getting bad info. Whether from the marina manager or the mechanic, you choose. That piston is NOT going to "lift" too high. It goes up and down within the cylinder on a rod. Undoubtedly, you have "dropped" a valve somewhere along the way.

Another thing...

If you are paying marina rates for mechanic labor, you are paying waaay too much for parts and labor. A 350 Chevrolet is nearly bulletproof. Even though you stated this motor is out of warranty, I would go back to Grooms or Jasper, or wherever you got it and plead your case. Maybe date wise you are out of warranty, but actual hours, there is no way you could have accrued enough wear on this motor to drop a valve. While they may not honor 100% of the warranty, perhaps they will give you 50% or so off on the next purchase. Any ASE Certified technician can change it out in his off time.

Here's a for instance...

Shop labor rates here (non dealer) for auto mechanics are in the $100 per hour range. I have a tech that works on my cars for $40 an hr in his off time. Marine labor rates are in the same range. I just moved to a new marina last month. I backed into the slip and was greeted by one of the full-time residents at the slip. When he asked about my cruise to get there, I told him I had an engine running warm. He immediately replied that the guy who lived three slips down is an auto mechanic (working for a reputable shop) and he could get me straightened out. Sure enough, when the guy came in that afternoon from work, we discussed the problem and he agreed to work for $50 an hour. Sometimes, you just have to ask around. I assure you that your fellow boaters are not paying full freight to keep their boats afloat.

It's all relative though. To me, a 50-60 dollar an hour savings is significant. Your income bracket might be higher, or you can manage to write it off. My marina charges 120 an hr plus tax (9%) based on a flat rate manual. They tell you that they are backed up 3 weeks and this is their busy season. My neighbor mechanic guesstimates the actual time involved and does it for less than half of their labor rate, within a day or two.

ETA: Please understand, I am not picking on you in any way. I'm new to all of this, and just feeling my way around. Sometimes you have to do what you can. It just galls me to pay full retail price for anything.

Where did the rest of the valve go? Damage to the liner or piston? You believe a loose part is going to bounce around and not damage anything?
Even if you spun a rod bearing, that could only lift the piston up about .0015 inch. the piston would hit the head before hitting a valve. Nothing wrong on the bottom, unless there is after damage; Yep, you floated a valve. Rebuilt / reused valve spring. Pressed valve stem guides, Rusted valve stem from sea (SALT) air coming up the exhaust system. How many shims were under that spring? Any punk can build a car engine. Mostly it works. Nobody seems to grasp a marine engine runs in a different environment.

How hard and far is it to the next dock? The next mechanic?

Elvis has left the building.

The exhaust valve cannot let sea water in. If you have seawater in there, your exhaust riser or manifold is bad. If you don't find the real cause of the seawater than the same exact thing will happen. The valve doesn't just snap off and disappear. So if the valve is not 100% intact, the motor needs to be rebuilt. But you can find that out the hard way. The other head was rebuilt by the same guy with the same quality as this head, meaning it's probably junk also. Everyone here has given you the same advice, yet you persist, so. I can tell you from my desk chair that you have a mechanic that is not experienced enough with marine engines to properly diagnose and do the work.

Sounds like a typical wobbly warranty, if the time had not expired there would have no doubt been some other reason to decline.

Did your "mechanic" tell you that? Sea Water can only get into the engine if there is sea water in the exhaust between the exhaust valves and the injection point, not the best way to find things and as Capt J says you should check the exhaust system risers and elbows.

The Crankcase is not normally a term associated with a SBC or any automotive engine. If you mean the cylinder block and oil pan you need to be aware that there is a lot more to this and any engine than the non moving parts. If I found an engine of unknown provenance had dropped a valve I would be checking the rest of the supposedly "rebuilt" engine very carefully indeed.

Ignoring the other head will also add to the cost if you do not determine the actual cause of the failure.

Did the valve hit the piston? Have you got any photos of the piston and valve you could share wit the group?

You might be in the clutches of one right now.

Where was your boat during Sandy?

While word of mouth is normally a great reference tool, the messages you post here and the advice you seem to be getting would lead myself and others to wonder just how well you are being taken care of by those you seek out for assistance.