Waking up a sleeping Chevy 350.

[rs2k]

I'm getting ready to try and fire up (again) an OMC 260 HP Chevy 350, but there are a few things that bother me about it. This engine has a brother on the starboard side that I was able to get running long enough to find out the carb needed to be rebuilt. I have a slight suspicion that the port engine may have a cracked block, but so far the evidence is not conclusive.

The first time I tried to fire up both engines I found that they weren't getting fuel. As a precursor to purchasing the boat we tried to use starting fluid. Both engine cranked over with no problem, the starboard engine sounded nice and even when cranking while the port had an obvious exhaust leak sound and feel to it. The oil in both engines looked great, but the port engine was showing it had way too much oil which lead me too believe there may be water underneath the oil.

When the engines fired up on the starting fluid, the starboard engine seem to run fine for about 3 seconds. The port engine on the other hand backfired and caught the carb on fire a couple times. When the port engine finally did run it, was obvious that it had a loud exhaust leak and was backfiring.

When I brought the boat home, I was able to restore fuel flow to the starboard engine and got it running and idling right away without a touch of starting fluid. The port engine's carb however, was leaking too much to start it.

There are no external cracks large enough to be seen in or around the port engine. All spark plugs also appear to be installed and intact. Both intakes had a little rust directly under where the carbs sat, but both engines are in far better visual shape then my 1971 OMC 305 on my other boat. The inside of the intake and valve covers looked freshly rebuilt.

Does anyone have any idea what might be wrong with the port engine? Could an out of adjustment distributor cause backfiring and loud exhaust noise? How about a stuck valve? What about a rusty piston or stuck ring? Any ideas would be greatly appreciated.

Thanks!

 

[danond]

Re: Waking up a sleeping Chevy 350.

Why bother starting an engine with a leaking carb? That just sounds like a good way to blow up or turn crispy.

Run a full diagnostic since it's a "black box" engine to you. Pressure-test the cooling system, do a compression test on the cylinders, and a leak-down if you have the tool. That'll give you a baseline to start from and might save you lots of time fiddling with a carb on an engine with a cracked block, holed piston or otherwise.

 

[180shabah]

Re: Waking up a sleeping Chevy 350.

Ditto, find out what you have before you waste time repairing something that can't be fixed/

Also, get rid of the starting fluid, if the engine is in good shape now, it won't be for long if you keep hittin' it with the ether.

 

[J. Mark]

Re: Waking up a sleeping Chevy 350.

While you are doing a compression check, verify the timing. With your thumb or finger plugging the #1 spark plug hole turn the engine over by hand until you feel compression coming up and then keep turning until the timing mark is at "0" on the timing tab. Remove the distributor cap and note where the rotor is pointing. If that is not where your #1 plug wire was (then it is probably half way around) the distributor may have been installed 180 degrees out and that will definitely make an engine backfire through the carb as it is igniting the mixture while the intake valves are open (by firing the wrong cylinder)

You can turn over an engine with the plugs in it, but it is much easier when they are out.

 

[bruceb58]

Re: Waking up a sleeping Chevy 350.

Just as a test, since you know the one carb is good, move it to the other engine to test that engine out.

 

[rs2k]

Re: Waking up a sleeping Chevy 350.

Both carbs are now sitting in a cleaning solution. I'll go pickup the rebuild kits tomorrow and put them back on the engines. I hope to know more tomorrow afternoon.

They both cleaned up very well, they are edelbrocks. The one on the port engine had obvious signs of water in the port float bowl. You could actually see where the fuel varnished and created a flaky layer of crust that was holding the float which made the needle stick open on the port side. I was really amazed at how well it did clean up with just a brass wire brush.

 

[rs2k]

Re: Waking up a sleeping Chevy 350.

I got both 350s purring running today. The starboard engine purrs like a kitten and has a very nice smooth sound while revving. I do believe this engine is the best running vehicle engine I own at the moment. (Out of 6)

The starboard engine on the other hand ran okay, but it had a lopey sound to it. I went ahead and used the same carb on both engines to remove that factor. I didn't rev it much because the intent was only to warm up the engine oil. It sounded pretty good at 1500 RPM, but it did sound like it was out of tune at 700 RPM. The water temp was stable at 155. During that run I removed each spark plug wire one at a time. I found that removing plug number three did not make a very large difference.

After I shut down the engine and let it rest for a little while first noted that the engine oil was bit milky, but had not noticeably changed in dipstick height I removed the spark plug and drained the oil. The blackened platinum plug had fresh oil on it and the removed oil definitely had water and/or air in it. It was a very thick dark chocolate milkshake. I will let the oil sit over night to see if any water goes to the bottom. I might get lucky and only have air in it.

I then poured a gallon of fresh 30 weight and started the engine back up. It ran rough for about 5 - 10 seconds, but then started to run similar to how the port engine ran. I revved it and noticed a similar (but not as good) smooth, almost electrical motor-like sounding rev to the port engine. I could not let the engine run much more than two or three minutes to see if it had a cracked block or not, it was 930 PM and I was afraid to wake the neighbors.

I am convinced that the back firing and loping sound was the result of hydro lock caused by too much oil added during winterization. Assuming I didn't bend a rod or break a ring, which I highly doubt, I think I may have two good engines.

Not bad considering I bought this boat with the thought of needing to rebuild or replace two engines.