**Update 8/28** Bad Compression in one Cylinder

[Jmorrell588]

90HP VRO 1989 with 1 year old powerhead. I completed a compression check on all 4 cylinders. 3 Cyl. read 120 and 1 Cyl reads 90. I added a tablespoon of Oil to the low reading Cyl. and it jumped up to 120. So, according to the manual and what I have read, this could mean a worn piston ring in that cylinder. (reason for the test! Boat was a little slow getting out of the hole and felt a lose of power as well). <br /> So the question is this!!! me being somewhat ok with working with engines, would a person like myself be able to change the Piston ring myself? NOTE: if this means I have to take the flywheel off, I am not all too sure I could complete the task. <br /> How, and how would go about changing the piston ring for that cylinder? ( I do have the manual ) but it does not have many pictures that I like to look at. Well, maybe someone will have some sites I could go to see how this might be done to a degree. <br /> I do thank you for any input you might have on this Post.<br /><br /> Jimmy

 

[mrc]

Re: **Update 8/28** Bad Compression in one Cylinder

It involves taking the flywheel and just about everything else off <br /><br />I suppose if you where one of those guys who makes those "ship in a bottle" things<br />one MIGHT be able get by with pulling the intake manifold and the head. Disconnect<br />the rod from crank via the access through the intake manifold. Push out the piston,<br />re-ring, deglaze, and reassemble (including all those blasted needle bearings).<br /><br />But I doubt it <br /><br />Anybody tried a re-ring via that method? I suppose it depends on the access<br />you could get through the intake manifold.<br /><br />Basically to replace the ring, you need to remove the piston from the cylinder.<br />Normally this means a complete teardown of the motor. <br />Mike

 

[Terry H]

Re: **Update 8/28** Bad Compression in one Cylinder

Jmorrell...I would first make sure that the carburator for that cylinder is functioning properly...If there is no fuel from the carb to the cylinder you will lose power from that cyl. and that would explain your loss of power. With no fuel mixture to lubricate cylinder walls and piston rings you would have the slightly lower compression. Piston rings in outboards are very long lasting when run on a proper fuel mixture...always lubed you know...Mix yourself up some fuel and put in a squirt bottle, start motor and squeeze some into the aflicted carb and see if you increase rpms slightly. Remember there are 4 cylinders so the increase won't be great, but it will increase. Since you checked compression, you should also check for proper spark. if you do find it's a fuel related problem (my first thought)fix it fast before you do lose a piston...just some Thoughts

 

[sho305]

Re: **Update 8/28** Bad Compression in one Cylinder

Most OBs have a block that splits in the center; at the crank. The cylinders do not come off like, say a dirt bike or a chainsaw would. So, you have to pull the whole crank out to get the piston out and put the new rings on, then you should hone the cylinder to fit the new rings while empty. this can be a pain if not familiar with this kind of work, and supplied with the needed tools as well. Unless yours is not that way, it depends on if you like to do that kind of thing.

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Mr. MRC, Thought and Sho, thank you for your input.<br /> That being the case, will I be okay using the motor for this weekend with low compression in that one cylinder?

 

[Hooty]

Re: **Update 8/28** Bad Compression in one Cylinder

You might try a de-carb. That one cylinder could be suffering a stuck ring.<br /><br />c/6<br /><br />Hooty

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Hooty, thank you for your Reply. I did think of something about what might have caused this Low Compression. I had some water come in through the gas vent twice from waves this season from those huge boat's that belong in the ocean and not on a lake. The motor stalled and the only way to run it out was to keep trying to crank it and run it out as fast as I could while still on the lake. Could the water that got in from the gas vent cause damage to this cylinder? I do know that it can be a number of things. But a post I read from researching in this site, said that I should find the cause. So that I can correct the cause. <br /><br /> Jimmy

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

will I get a correct compression check if I did this cold and not with a warm engine? Note! I have not yet done the decarb yet. Was just thinking while I drink my coffee.

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Bump... Not being rude all. Just want a little more input before I make a decision tonight.

 

[Dhadley]

Re: **Update 8/28** Bad Compression in one Cylinder

Follow Hooty's lead. It's the easiest, cheapest thing to do and may very well unstick your ring. Especially if the motor is propped out at less than 5800.<br /><br />Follow the directions on the can of decarb and concentrate on the low cylinder. I use Engine Tuner from Evin/John.<br /><br />Good luck!

 

[jobassing]

Re: **Update 8/28** Bad Compression in one Cylinder

i just did a compleate rebuild on the same moter it's not that hard to pull apart but i did have to pull the power head to seperate the moter

 

[ratss]

Re: **Update 8/28** Bad Compression in one Cylinder

take motor apart take piston out of hole deglaze cylinder put together, if you're lucky. if you have to ask, don't try this procedure. unless it's junk anyway. lol.

 

[BKool68]

Re: **Update 8/28** Bad Compression in one Cylinder

Your compression reading is not far off, did you have the throttle open while doing it? A dry cylinder will read lower. Try the check using your warm up throttle. I see no need to rip a motor down that has good compression. Are you having any power problems? Waht RPM's does the motor turn under load?

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Bk , thank you for you response and the rest of you guys. Mr. BK, I did a dry compression test. 3 Cyl. read 120 lbs., and the 4th Cyl. (Standing from the back looking from rear, top right)reading was 90. Note, I did add oil (small amount) to the low reading Cyl. and the reading went up to 120 lbs for that low Cyl. <br /> Now, what I cannot understand is how can I start the engine for the test with the Trottle wide open. The motor will only turn over in nuetral. Now I can raise the warm up handle and raise the RPM's that way. When the motor is in the water, at idle, at crank up it will run at 900 RPM's at idle.<br /> I am now Decarbing at this very moment and will let it sit over night and run it in the morning hooked to the hose for 10 minutes. I was told that maybe that one Cyl. might have some gumming, has stated from the above postings from others. <br /><br /> Jimmy

 

[Hooty]

Re: **Update 8/28** Bad Compression in one Cylinder

It doesn't make any difference where the throttle is, just so it's the same for all cylinders. <br /><br />c/6<br /><br />Hooty

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Thank you Mr. Hooty, will keep that in mind when I run the de-carb out in the morning.

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Okay Shipmates, I did the decarb last night and ran the motor this morning to burn it out. I checked the compression in that low Cyl. and it was still low and did not move up at all. I added some oil in that Cyl. just for the heck of it and got good compression that amounted to the same level as the other Cyl.<br /> I called my local mechanic at Smyrna Marine and he has been updated on this issue.<br /> <br />**Question**<br /><br /> He told me to change the head gasket for that Cyl. and see what happens then before I attempt to think about having it taken apart. Have any of you guys come across this?<br /><br />Jimmy

 

[Dhadley]

Re: **Update 8/28** Bad Compression in one Cylinder

That would be the next logical step. Once you get the head off pay attention to what the top of the piston looks like. If you find little pieces in there its most likely a ring and we then know its time to rebuild.<br /><br />Keep us informed!

 

[Jmorrell588]

Re: **Update 8/28** Bad Compression in one Cylinder

Mr. Dhadley and all, I took the head gasket off the right side Cyl's. I have a bad piston with two dents on the tip of the pistons that scratched the walls of the cylinder. <br /> So, with that said, I have the good fortune of a old (Exact same Power head) power head that went on that motor that I can take apart and play with it for a day before I take the power head apart on the current motor. I hope to save a lot of money by doing this and then taking it to the Marine Shop for them to re-bore. I will put it back together, then take it back to the Marine Shop and let them adjust and fine tune the rest. <br /> I do have a manual to do this with and feel okay with it, providing that I am okay when I take the old powerhead off to see if I can do this. <br /> Question??? I am having a heck of a hard time getting the flywheel off the powerhead. Does anyone have any thoughts on this? I was thinking of running the boat by a machine shop and let them pull it off since they have the big power tools. I do have a puller, but I am not sure how much longer I can do this before I take a hammer to this thing.<br /><br /> Jimmy

 

[Hooty]

Re: **Update 8/28** Bad Compression in one Cylinder

Hey J,<br />Go ahead and take the hammer to it. The bigger the hammer, the better. Tighten your puller down real tight and give the head of the puller bolt ( that's the one in the center of the flywheel ) a good, hard lick or two with a good heavy hammer. Tighten the puller bolt down real tight again and hit it another lick. Keep this up and it WILL come off.<br /><br />g'lick & c/6<br /><br />Hooty