Bad Compression

I recently bought a 1966 33HP Johnson. It hadn't run for about a year or two. My neighbor and I got it started and drove it about 500 yards to my dock. It wasn't running very well and wouldn't start after we got it to my dock. I figured the gas in the carb had gummed up so I rebuilt the carb. Still wouldn't start. It turns over and hits on one cylinder right away but then nothing. I bought a compression tester and one cylinder is at 75 psi and the other is at 50 psi. I put a small amount of motor oil in each cylinder and they went to 100 and 75 psi respectively. I dumped some Sea Foam down each cylinder and let it sit for a while but no change. I have a service manual and am fairly mechanical but have never taken apart an engine before. What would be my best course of action?<br /><br />Thank in advance.

Re: Bad Compression

If you're convinced more seafoam treatments won't help, then your next step is to pull the head to investigate. That's usually a fairly simple task on your 33hp depending on how much salt exposure it's seen. Just remove the 10 bolts that hold it on, not any of the screws.<br />Closely examine the cylinders for scoring, and the head gasket for signs of blowing.<br />To re-install the head, you have to clean and surface the head, and install it using a new head-gasket and an inch-lb reading torque wrench. The gasket sells for around $10-$20

Re: Bad Compression

Kevin - Mandatory reading:<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000033

Re: Bad Compression

Sea Foam needs to be run through the engine, not dumped in not running. Put a can of Sea Foam in a portable tank with a gallon of gas or premix. Run the engine at a fast idle (1500 RPM is fine) until all fuel is gone. Let sit for an hour or so, the take the motor out and run it, fast idle at first, the at planing speed. If it hasn't be done before, repeat with another can of Sea Foam, etc.

Re: Bad Compression

pull the head for a look<br /> no amount of seafoam or oil is going to help. <br /> can ya explain why you retested with oil in thecyl ?

Re: Bad Compression

SoLittle - I wish I would of known of this forum prior to having the engine troubles. Following those steps might have saved me some headaches. <br /><br />WildOne - The problem is that I can't get it started. Should I be able to start the engine with the compression I have? (given that gas and spark are there which I think they are)<br /><br />rodbolt - The compression testing kit I bought had as part of the instructions a diagnosing section. With low compression it suggested that a 1/4 oz of motor oil be put into each cylinder and retested. If the compression went up, it would point to a problems with the rings. I suppose the oil for a short while would help seal the rings.<br /><br />If I pull the head and the cylinder walls look good, is there anything I can do to a motor that won't start to free ring(s) if they might be frozen?<br /><br />Thanks.

Re: Bad Compression

Ah, those instructions are for a 4-stroke auto engine. The idea being that gravity will lead the oil to the rings and away from other possible sorces (namely valves and head gasket).<br />The test is rather meaningless on a 2-stroke, vertical shaft engine.<br /><br />If the cylinder walls & head gasket look(ed) good, the next thing I would do is to pop off the bypass covers on the port side of the engine and prod at the rings through the intake ports. You can get a real good idea if they're stuck or broken by how springy they are. Prod with plastic.

Re: Bad Compression

Thank you everyone for your input.<br /><br />I pulled the head and the cyclinders were a bit scored. I replaced the head gasket and reset the gap on the points (they were a little off) and it started up and ran pretty good after I adjusted the carbs per J. Reeves instructions. I have not retested the compression yet.<br /><br />I have a couple more questions now but will post them in a separate message <br /><br />Thanks again!

Re: Bad Compression

Kevin, You're in good hands already, regarding your motor's compression issues. Please try to keep additional questions in this thread, it's much easier to follow your progress if everything is in one place.<br /><br />Good Luck!

Re: Bad Compression

Sounds good.<br /><br />I adjusted the carb per J. Reeves instructions. After running it around the lake varying my speed, shifting into neutral, reverse etc, when I shut it down, it continued to run/diesel for a good 5 seconds or so. <br /><br />The second problem is that the starter will get very hot and refuse to turn over anymore if I am not able to get it started within 30 seconds or so. The connections at the battery and the terminal of the starter are clean and tight. <br /><br />Thanks.

Re: Bad Compression

What spark plugs have you got in it?<br /><br />The starter will overheat if you crank it for more than about 30 seconds. Give it five minutes to cool down after cranking so long. Those starter motors are not designed to be cranked continuously.

Re: Bad Compression

Champion J4C.