Low Compression on middle two cylinders

[GMcK106]

Engine has been laid up for a year. Could the engine stop at a point where one valve is open on each of these cylinders? Engine was winterized before storage. Couldn't get the engine running and a cold compression test yielded 115 in both 1 and 4 and around 70 in the middle two. Wondering if rust formed on the open valve seat. Motor had been a bear to get started for the first time.

[Mo]

Same general compression on two adjacent cylinders. My first thought would be head gasket. That said, if there was no previous indication of problems, water in oil etc, might very well be sticking valves. An effort to free up the valves could be done. Spray a good penetrating oil /mmo ..whatever you have and try moving with an Allen key...can also remove valve side cover. Turning over engine you will see if they have full travel or are sticking. If they cannot be freed easily, remove the head. Take some pics and we will see where you are with it.

[GMcK106]

low middle compression

This engine was re-built in 2002. My original troughts were warped head or blown gasket. Am I correct to rule this out if there is no evidence of water in the oil?

[Dave Neptune]

Take a close look!

GM, I'd first make sure that it is not just some stuck rings as it has sat for a bit. Toss a bit of oil in the 2 low compression cylinders and see if it comes up! If it does I'd first try to start and warm it up a bit, them do a warm recheck first dry then with oil in the cylinders. If the compression stays low with oil it's the valves and could be as simple as an adjustment. If the compression comes up I'd run a bit with some top oil MMO/2stroke for a few hours and then take another set of readings
If indeed it is a head gasket nothing will change with the oil and the compression between the two cylinders will remain even.
I think it may be worth checking before tearing apart.

Dave Neptune

[GMcK106]

Thanks

Thanks, sounds like a good way to either eliminate or confirm the rings are the problem. Still wondering if #2 and #3 could each have a valve open at some point. That would let air in thru the carb and exhaust.

[Mo]

I would do as Dave suggested first...it's easy. If that doesn't pan out I would remove valve cover on side under manifold and check valves. Worst case scenario is that you may end up taking the head off. There could be more serious problem other than valves or head gasket...but in circumstances such as yours it, s not usually the case.

...excuse brevity of answer...laptop hard drive failure and am using tablet.

[tenders]

70 psi on a cold laid-up engine is not a reason to suspect anything's wrong in those cylinders. The engine will start with that situation. If it won't, I'd look at fuel supply and condition, timing/ignition components, and carb cleanliness and adjustment, in that order.

[JOHN COOKSON]

Roger This

70 psi on a cold laid-up engine is not a reason to suspect anything's wrong in those cylinders. The engine will start with that situation. If it won't, I'd look at fuel supply and condition, timing/ignition components, and carb cleanliness and adjustment, in that order.

Going one step further.........
Get the engine to start. Maybe the (alleged) stuck rings\valves might just unstick. If not try some of the magic additives.
What is the status of fuel and spark?
Are the spark plugs wet with fuel after a period of no start cranking? Does the carb bowel have fuel in it?
Pull a spark lead off a plug and put it on a plug and hold it near the engine to ground. Do you see a nice healthy spark when you crank? Is the choke closing all the way? Is the timing right?

TRUE GRIT

PS I don't know your level of experience - hope this isn't insulting. If so then sorry.

[GMcK106]

Thanks. For All The Help

Round 2 starts next week. I'm going to try harder to start the engine using the advice that was posted. The boat has electronic ignition. The fuel and carb are suspect. At least the fuel did not smell too bad.

Thanks for the help, I'll keep you posted.

[romantic comedy]

You can use starting fluid to check if it is not getting gas. Just spray some in the flame arrested and give it a spin. If it starts for a second, then you know that you have spark and compression, but no fuel from the carb.

[tenders]

Starting fluid, ie "engine crack," in an enclosed space, ie a boat, is really dangerous. I learned this the hard way and almost blew myself and my boat partner out of the water whilst troubleshooting an engine that wouldn't start. In case you're curious, it burns deep blue, like Sterno, and OMFG do fire extinguishers make a mess.

If you have compression and spark, which you don't need ether to discover, are the plugs wet with fuel? If not, and if you're getting fuel out of the fuel pump, the carb needs to come off, end of story.

[TomG]

Starting fluid, ie "engine crack," in an enclosed space, ie a boat, is really dangerous. I learned this the hard way and almost blew myself and my boat partner out of the water whilst troubleshooting an engine that wouldn't start. In case you're curious, it burns deep blue, like Sterno, and OMFG do fire extinguishers make a mess.

This story sounds very exciting!

[roadnsky]

This story sounds very exciting!

AND... remember, we like pictures on this site!

[romantic comedy]

I like blue flames for toasting marshmallows. Thanks for the info, I will take some starting fluid when I have a camp fire.

Sometimes I use propane instead of starting fluid. I just hole the torch head at the carb, then turn it on.

[GMcK106]

low middle compression

Thanks for the advice on starting fluid. This stuff should NEVER be used in an enclosed space.

On round 2 I plan on cleaning out the carb and checking the fuel. There is an electric fuel pump which is working correctly and checking for spark.

I'll keep everyone posted and get some pics.