low compression 3.0 cobra (new)

[Randy stoner]

I had a brand new remanufactured 3.0 cobra (chev) engine installed last September in my 17 foot sunbird bow rider and its never been as good as the 130 i had previously. This one is a 140. I have had issues with it since day one and currently there is not 15 hours running time on it not including the intial 5 hour breakin the marina did initially. I just cant seem to get the revs high where they shoudl be. At best i might hit 3900 rpm and the motor is rated for 4850 rpms. I have tried different props, pitches diameters etc without any noticeable difference. Up to 3/4 throttle is seems ok but the last 1/4 has nothing, no difference in motor sound or rpms. Its as if there is nothing there except this long drawn out sound that sounds like a cow mooing. I have checked the linkage and it is correct as well and there is fuel squirting down the throats. Today i took a compression check in each cylinder. 108, 110,100 and 104 psi in cylinders 1 to 4 respectively. Im not happy. This is an out of the box crate rebuild from a reputable remanufacturing company. I installed the compression tester in earch hole. Started the engine up; blipped the throttle then shut it down and went on to the next. Idealy you want to have the throttle wide open when testing but i cant roll the motor over with the key with the throttle wide open as it will not signal the started if not in neutral. I ve done compression tests on other engines, outbord and inboards and never seen such low numbers. Im contacting the marina that installed this on Monday. Somthing is wrong here and ive wasted most of the summer waiting for them to decide what to do.

randy

 

[CaptnKingfisher]

If youre using the rpm gauge on the dash try verifying the rpms with a tiny tach, multimeter or timing light. Your gauge could be wrong. First thing I would do to address this is check timing and dwell are set correctly, then verify idle speed. Check that plugs are the ones recommended by your service manual. Throttle linkages as you have already done.

 

[Scott Danforth]

You are testing compression wrong

You dont start the motor

You pull all plugs, screw in gauge, crank 5 or 6 revolutions (until gauge stops moving) and read gauge, then reset gauge and move to next cylinder

 

[hugh g]

Who told you to check compression with the engine running & throttle wide open? Check it the right way & post back with numbers. I may be wrong but I've never heard of an installer doing the break in period, especially a 5 hour one.

 

[Randy stoner]

I guess there are a lot of opinions on breakins, compression checking etc. I build old Harleys and the way to check compression is to have the throttle wide open when rolling the motor over. In the past i have double checked doing it that way and starting the engine for a few seconds (not WOT) when it starts. Both numbers are within a pound or two but thats with a bike. As far as the marina doing the breakin, when i picked the boat up with the new motor i asked about break-in and was told they tie the boat down and start it up and let it run at 1500 rpm with the prop running for five hours. I dont know if this is true or not but thats what they said. I have seen other boats at that facility docked in a mooring jig running like that so who knows. Im open for suggestions and will take all of them and try it. Thats why i asked. Im looking for wisdom that i dont have. Pulling the plugs, #2 and #4 had heavy rust on them. They were put in brand new last time out just in case. They are Marine plugs. To me that seems like a leak somewhere however the inside of the plugs all were burning good and looked like new as they were. Could be condensation dripping down.

AT WOT it really sounds like an old cow "mooing" you know that long low deep drone sound? You can sometimes hear a slight girgle as well at the top of the rpms as if its breaking up. I have checked the ignition which is new, wires with a tester as well, distrubuter cap and rotor. Everything is as if its fresh out of the box. The engine idles perfect, starts on half a roll without choke even after three weeks of sitting and right on up to 3/4 bore its not too bad but after that, the last 1/4 of the throttle there is no sound difference, nor rpm gain or drop. I have checked and double checked the linkage and it is as it should be. Im almost thinking it could be a carb issue with jetting as the secondary jets may not work at WOT. Just throwing that out there.

I await the wisdom of you fellas.

Thanks, Randy

 

[kenny nunez]

It almost appears that you may have an exhaust blockage. Sometimes the exhaust shutters break loose and restrict the exhaust.

 

[Keyboardman]

Yup, check if the exhaust flap hasn't fallen down inside the pipe and is partially blocking it.

 

[Bondo]

Today i took a compression check in each cylinder. 108, 110,100 and 104 psi in cylinders 1 to 4 respectively. Im not happy.

Ayuh,..... Typically, when a new motor sees such low compression, who ever set it up, over-tightened the valves,....

 

[Scott Danforth]

Ayuh,..... Typically, when a new motor sees such low compression, who ever set it up, over-tightened the valves,....

Bondo, read how he took the compression readings

 

[Bondo]

Bondo, read how he took the compression readings

Ayuh,.... Did,.... but that still doesn't account for the low numbers,.....

 

[jerryjerry05]

RUSTY PLUGS: the manifold and riser is probably leaking water into the motor???
Check the valve lash??
Compression: if all 4 are that close?? then the gauge is faulty or the procedure used is wrong or the valves are staying open too long??

 

[Randy stoner]

What should be the compression in a remanufactured 3.0 litre chev engine if it was done properly?

 

[Bondo]

Ayuh,..... 'bout 150 psi,.....

 

[Randy stoner]

Update to this issue. The marina that installed the new engine finally got back to me after almost 4 months of not responding and replying to the phone calls or emails. I was told to bring the boat back and they will replace the engine. When speaking to them they seem to think it is a blown head gasket. I've had that on other types of motors but generally you can hear it. This engine was quiet, started up fine, idled fine and had really nothing past 3/4 throttle. Max rpm was never over 3600 give or take when it should have been 1000 more. I tried lower pitch props, weight distribution, trim tabs etc. without a lot of luck. My old 130 hp would out perform this new engine hands down. I have been around engines all my life and I do know when one is not up to snuff. A compression test resulted in lower numbers than expected and after comments from some on here and suggestions as to how to take it a proper way, no real differences showed on the gauge. About 2 psi discrepancy from my numbers so this of course told me something was wrong. On two of the cylinders there was considerable rust on the outside of the plug where it thread into the engine after sitting two days from the last time out. This was not condensation accumulating on them as the it would have shown on the others, but only two and after changing plugs the same two showed as much again after just one run. (proper marine plugs were installed).

So I will keep you all updated on this. I'm not expecting to get out much on the water more this season unless I get it back in a timely manner as i was told it will take a week or two to get an new engine then to have it in but here's hoping. Thankyou all for your suggestions and comments. There is a wealth of knowledge on these forums and I thank you for that.

randy

 

[jerryjerry05]

I had a brand new remanufactured 3.0 cobra (chev) engine installed last September in my 17 foot sunbird bow rider and its never been as good as the 130 i had previously. This one is a 140. I have had issues with it since day one and currently there is not 15 hours running time on it not including the intial 5 hour breakin the marina did initially. I just cant seem to get the revs high where they shoudl be. At best i might hit 3900 rpm and the motor is rated for 4850 rpms. I have tried different props, pitches diameters etc without any noticeable difference. Up to 3/4 throttle is seems ok but the last 1/4 has nothing, no difference in motor sound or rpms. Its as if there is nothing there except this long drawn out sound that sounds like a cow mooing. I have checked the linkage and it is correct as well and there is fuel squirting down the throats. Today i took a compression check in each cylinder. 108, 110,100 and 104 psi in cylinders 1 to 4 respectively. Im not happy. This is an out of the box crate rebuild from a reputable remanufacturing company. I installed the compression tester in earch hole. Started the engine up; blipped the throttle then shut it down and went on to the next. Idealy you want to have the throttle wide open when testing but i cant roll the motor over with the key with the throttle wide open as it will not signal the started if not in neutral. I ve done compression tests on other engines, outbord and inboards and never seen such low numbers. Im contacting the marina that installed this on Monday. Somthing is wrong here and ive wasted most of the summer waiting for them to decide what to do.

randy

This a new tester?

 

[Grub54891]

Had a buddy who asked to use my compression tester. His had broken. Brought mine back broken. Said when he puts it in, and starts the motor it pegs the needle and then stops working. UGH> Never did replace it for me.

 

[Randy stoner]

Update: After a lot of phone calls and finally a major B*tching message on the marinas answering machine, they contacted me and told me to bring in the boat and they would replace the motor. Well that was back in mid August. Today i got it back. Of course i havent had a chance to put it in the water but i did do a compression test and the numbers were 136, 132.5,136 and 139.5 in cylinders 1,2 3&4. By the way i took them by rolling the motor over four or five times. So its a whole lot better. I have no idea how it will run in the water but the compression is a lot better than the old (new) engine i had. The tach now doesnt work. I sits at 2000 and doesnt move, Key on or off. Not sure what thats about. Any idea where to check?

Anyway i hope there are a few days yet i can try it.

randy

 

[Bondo]

Ayuh,..... That's certainly much better than before,.... Good Luck,....

 

[Randy stoner]

Been a year or so since i last posted on here. As per earlier posts, my issues I thought were solved. I had a new replacement motor put in and the compression numbers were good. The first of the season 2022 prior to putting it in the first time, i took a compression test only to find out all cylinders were down to 105-111 after sitting all winter. The motor had not gone in the water since the new install, however I took it to a local shop to have it winterized. As i waited i noticed they started the engine and let it run without water for a minute at about 2500 rpms. They said this is how they do it to get the thermostat open. I was appauled at this and I guess something happened because the numbers now are low. Head Gasket perhaps? Also just for gits and shiggles, what should the timeing be on this motor. Although it did run last summer on all four, it seem down on power. I may advance it slightly. What have i got to loose now?

Randy

 

[markhodges78]

Been a year or so since i last posted on here. As per earlier posts, my issues I thought were solved. I had a new replacement motor put in and the compression numbers were good. The first of the season 2022 prior to putting it in the first time, i took a compression test only to find out all cylinders were down to 105-111 after sitting all winter. The motor had not gone in the water since the new install, however I took it to a local shop to have it winterized. As i waited i noticed they started the engine and let it run without water for a minute at about 2500 rpms. They said this is how they do it to get the thermostat open. I was appauled at this and I guess something happened because the numbers now are low. Head Gasket perhaps? Also just for gits and shiggles, what should the timeing be on this motor. Although it did run last summer on all four, it seem down on power. I may advance it slightly. What have i got to loose now?

Randy

No Reputable shop that I know would start an engine more less let it run without water . It would take time to run the engine hot and do damage without water but the water pump is fried