3.0L OMC Cobra - rough at low end, pinging at high end

[Striper Blues]

Here I go again, different issue. LOW END PROBLEM - I thought I had a timing problem but after several attempts I learned that I have one cylinder that doesn't seem to be firing properly. When I pull the plug wire off one cylinder at a time three of the four drop the rpms significantly the number 3 cylinder does not. I have recently tuned and I put in another new plug to eliminate that. I have a new rotor,points and cap. I'm guessing it might actually be a bad wire. It is old and seems to have been under stress, so I'm going to replace the wires next. <br /><br />HIGH END PROBLEM - at WOT I'm getting a ping after a minute or so even when engine is hot. I'm thinking I may not have adjusted the valves properly when I had the head off end of last season. The head was off for gasket after water pump caused overheat and small gasket leak. My manual says tighten to 0 clearance at top of compression stroke, then one full turn. Is it possible that one cylinder (maybe #3 above?)is too loose and slapping around under heavy load?<br /><br />Sorry for the long post, appreciate your suggestions!! <br /><br />Thanks,<br />Pat

 

[cobra 3.0]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

I would gues the two problems are related. Get new wires and see if it still does it. <br /><br />Alos, are you running at least 89 octane gas? Regular 87 octane will make it ping.

 

[Northern Eclipse]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

The manual is correct but that is a static setup and does not compensate for old lifters and such,you need to aleast do a compression/leakdown test and determine the health of that cylinder your problem could be as simple has a bad plug wire I would swap the wire with one from a good cylinder and see if problem follows that suspect wire, if not do compression/leakdown if you determine valve leakage, then remove valve cover, run engine at low idle and loosen rocker stud until rocker clacks, then slowly turn back down until clacking stops then another 1/2 turn to preload lifter. Keep some rags on the pushrod side of the rockers, because this method is messey, but since you have already done static setup, this procedure is quick and you won't need to run very long. Hopefully your overheat issue did not damage the head or warp it.

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Guys,<br />I replaced all plug wires and spark plugs, no improvement. I'm burning super gas must be at least 89 octane. I'm guessing that the number 3 cylinder valve adjustment is bad. I will remove valve cover and adjust again. Northern, I will take your advise and do when running as described. Is it going to spray oil or only dribble it all over. Can i use towels or something to keep it from running down the block etc?<br /><br />thanks again, Pat

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

What is the likelihood that I have a bad lifter? Is it common?

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

bump<br /><br />

 

[MrDumb]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Pbburke, I do not know about your low end problem,but on the high end i have alittle info. Last year I blew a head gasket therefore I replaced it and went through the same procedure as you. At WOT I have a slight ping or tapping noise (4400 rpm), I have not been able to correct it. But at normal cruising @ 3600-3800 rpm everything is chiming along so I just do not run my motor that hard anymore , I mean the motor is the orginal 1992 OMC Cobra 3.0 so it has put in some time on the water. And it my be possible it did that before but now I am in tune to all of the motor sounds!!! Right or wrong I just baby my BABY alittle more that I use to? She still runs strong, I had her out this weekend and she ran great all weekend. I guess what I am saying is that I accept her for her age!!

 

[Bondo]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Your High Speed Problem is that It's running Lean And/Or the Timing is Too Advanced..............<br />This Possibly applies to both of your boats.........

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Bondo, I just changed my carb and have tried timing adjustments using various recommended approaches. I think in my case when I replaced the head and adjusted the valves the number 3 cylinder was adjusted incorrectly. I'm guessing I either thought I had it at tdc on compression and didn't or the lifter was sticky and slacked up since... I'll find out tomorrow when I pull the valve cover and adust with the engine running.

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Bondo et al,<br /><br />Yikes, the saga continues. I decided to start by resetting the valves cold using the procedure recommended. Starting with rotor pointing to #1 plug wire with points open (i'm guessing points open is to assure you're just past tdc?). When the mark is dead on TDC the points are closed?<br /> Anyway, i followed the sequence for adjusting both #1's the the various 2, 3, 4 (I don't remember the valve right now, it was as described in the link provided). Then rotated to similar position with rotor pointing to #4 etc. The result is difficulty starting the engine. I didn't warm it up prior as it said cold in the procedure. It comes close to running but won't start. Obviously I've don't have it right, in spite of the fact that I've repeated the procedure 5 or 6 times to be dead certain I'm doing what is required. One question I have is, It seems the point where I eliminate slack in push rod varies (perhaps based on the amount of oil in lifter?) Meaning if I back the rocker nut way off then come down from the top, the point at which there is zero lash (so to speak) seems higher that if I had the valve tight (one full turn) then loosen until there is lash. Another example, I adjust them cold, try to start it sputters what not, then I check and at one or two valves the push rod is not loose, but will spin by hand suggesting its not tight enough. Is there a way to gaurantee lifters are fully collapsed before adjusting? My understanding is they need to be fully collapsed, or am I wrong about this? In hind sight, I wish I'd run it till hot and adjusted when running. It used to start easily. DOHHHHH????!!!!

 

[akriverrat]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

since no one else has replied... NO, if you adjust them collapsed they will never close.

 

[Bondo]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Well, First off,<br />Quit using the Rotor for reference...........<br />Use the Timing Marks..........<br />Their on the front of the motor for This Reason............<br />As akriverrat says, They got to be Pumped...... <br /><br />Loosen them All up......<br />Crank the motor over,+ Hopefully they'll pump up.........<br />Then readjust using the timing marks....<br />In the proper order......<br />Once you get it running........<br />ReAdjust Again............................... <br />Good Luck.......

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

I went through the process again using a remote starter switch and timing marks. Got her running then warmed her up for 30 minutes and adjusted again running. I loosened until clattered then tightened just till it stopped then one full turn. The problem I'm having now is that the boat runs fine for about 3 or 4 minutes at cruise speed, say 4000 rpm at which point I start to hear valve noise again, like lifter knock. It almost sounds like they're too loose, although I was very precise in the above adjustment. It only happens when it has been running for a few minutes at higher speed..??? Should i readjust using something other than one full turn after zero lash???

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

bump

 

[Stings]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

i had the same thing on mine. when i would get up in rpms i could hear a ping, i took it in and had it checked out and they couldn't find it. i just pulled it out to play with it this season and discovered it was the gear on my starter, it wasn't disengaging and it would hit my flywheel. ....just a thought

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Holy Smoly....could it be? I noticed my starter growling the other day after starting. I have suspected the solenoid might be hanging...yikes. I'm going to change it ($100 on ebay) just to be sure....

 

[Boatist]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Pbburke<br />First thing you should do is a compression check. I do not know how you can use timing marks to adjust any valves other than for cylinder 1. <br />Pull all the pluggs and do a quick compression check. If you have low compression on any cylinder then loosen the valves on that cylinder to point they will be at zero lash. Now check compression in that cylinder again. If it comes up you are very lucky. If you have been running the motor on the water with a valve open likely have a burnt valve now and it will need to be replaced. If compression still very low put in some oil and check compression again. If it comes up to near normal (130psi) then probably have bad rings. If it stays low then likely have a burnt or warped valve in that cylinder.<br />For static adjustment leave the pluggs out and put a wrench on the front of the engine to turn. With the pluggs out should turn very easy. Start with number one. Watch the valves for #1 while you turn the engine. The exhaust should open and start to close then the intake should open and close. This is the start of the compression stroke, keep turning until near top dead center on the timing mark. The rotor cap should point to # 1 and the points will open. At this point can adust both valves on # 1. Next cylinder to line up will be # 3. You can find the top in many ways. Turn slowly and watch the points. The next lobe is for # 3, when points open should be lined up. You can stick your thum in the # 3 spark plug hole and turn engine slowly. It will blow your thum out until you reach top dead center and then try and suck it in. The points should be on the lobe and open. This will be about one half turn from where you adjusted #1. Next time the points come up on a lobe you can adjust # 4. Then the next lobe will be for # 2. You can always watch the valves. Turning the correct way after the intake valve closes a little less than 1/2 turn and you will be on top dead center. Another is to take an old spark plug and bust out the center make sure have nothing loose then get a big balloon and put it over the plug Put a rubber band around it to hold baloon on. Screw it into the cylinder you want to adjust. Turn the motor foward when you get to the compression stroke the balloon will blow up. When you pass TDC it will start to deflate and you can adjust both valves for that cylinder.<br /><br />I like to leave it at zero lash and start and warn the engine. Put the cover on loose. This lets the lifter fill with oil. I then pull the cover and with the engine running I slowly turn the adjustment down about 2 turns until the engine starts to miss. Must go slow as takes time for the oil in the lifter to get out. Keep track on how many turns down. When it starts to miss I loosen slowly until miss is gone and then turn out one turn. This also center the lifter same as going to zero lash and turning in one turn. The difference is if you have a lifter that is sticking or does not have full travel then the valve will end up a little loose instead of too tight and open where it will burn up. With brand new good lifters can do either way, but with old lifter I feel safer knowing they get closed if I have a bad lifter.<br /><br />Working on a running engine must be careful not to get your fingers in the wrong place and not to drop anything into the engine. Kind of messy and you will spill some oil. I use a old valve cover with the top cut out and spill very little oil. Do the compression check first. When done do compression check again with engine hot to be sure all valves are closing.<br />Good Luck and be carefull.

 

[Striper Blues]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

Stings called it. The starter was slipping back and bouncing on the flywheel after operating at high speed for a few minutes. I replaced the starter and no more pinging at high end.... <br /><br />Thanks Stinger! you the man....

 

[Ski-King]

Re: 3.0L OMC Cobra - rough at low end, pinging at high end

sounds like you might have a warn cam shaft lobe on #3 <br /><br /><br /> good luck