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Author Topic:   Assessing Used Outboard Motors

jimh posted 02-11-2006 10:54 AM ET (US)
Many outboard motors are purchased used. A quick procedure for checking the condition of a used outboard motor is presented in the Reference Section article:
Assessing Used Outboard Motors
http://continuouswave.com/whaler/reference/outboardCheck.html
Additional advice and suggestions may be appended to this thread.
bsmotril posted 02-11-2006 07:21 PM ET (US)
If the engine is new technology with an Engine Control Computer, you may also be able to dump the fault codes stored in the motor. Some motors require a visit to the dealer where a special hand held diagnostic terminal is used to perform this task. In the case of Optimax motors, you can get a count of overheat events, and the total amount of time in minutes that the motor was run while overheated. If any of the motors sensors have problems, or if the injectors are generating faults, you would see the fault in the diagnostic data dump. You can also dump a Histogram of RPM versus hours run in increments of 1000 rpm. Finally, you can get a count of the number of times the motor bumped up against the rev limiter. This is all good information to tell you what kind of abuse a motor may have suffered at the hands of the previous owner.
One other thing to do when you run the compression check is to carefully examin and compare the spark plugs to each other. They should all look nearly the same with equal amounts of deposits, and about the same color on the ceramic tip inside the plug that surrounds the center electrode. Variances in the plugs' color can be a sign of lean running which can damage a motor. Excessive oil or carbon deposits on one plug versus the other can be a symptom of a faulty ignition coil or plug wire. And, a plug that is extemely clean compared to the others is almost certainly in a cylinder wear the head gasket is leaking water into the cylinder. Worst of all is a plug that looks as if it has droplets or spatters of aluminum metal on the electrode or tip. That indicates that engine damage has already occured due to overheating or running with an extremely lean fuel air mixture.
BillS
aja posted 02-16-2006 11:49 AM ET (US)
JimH
This is a good article, and something else that a friend on the market recently asked me for might be a similar listing for folks looking for used BW hulls. Of course the list would be different as hulls grew in both size and complexity, but it would seem to be a fairly easy and useful tool to have a checklist which reminded folks to look at issues on any boat, but expecially items specific to whaler hulls. Just a thought...
kglinz posted 02-16-2006 12:18 PM ET (US)
My experence with compression on 2 strokes, is that a loss of compression is due to damage caused by something being caught in a port, when the piston comes up. Wear, with a small loss of compression is not as common as damage with a major loss. You usually have enough compression to run smoothly or very low compression and a "dead" cylinder.
bsmotril posted 02-16-2006 04:42 PM ET (US)
That's true. My dad has a mid 60s vintage Evinrde 40HP big twin with 68 and 74 psi compression on its' two cylinders. It runs fine. BillS
wwbach posted 02-16-2006 10:36 PM ET (US)
I noticed there was nothing covering checking the trim and tilt. A family member had a trim and tilt on a 40 yamaha go on him and it was a $1400 fix (he probably was taken advantage of). I'm not sure what to look for -- make sure it works, check for leaking oil, check for corrosion -- anything else?
-- Bud
LHG posted 02-17-2006 03:09 PM ET (US)
Bud - you are correct. I had that same experience with the Mercury 150 that came on my 21 Outrage. After a few hours of use, all the hydraulic seals went (probably from sitting unused for several years) , oil pouring out all over the place. Also cost $1400!
I think visual inspection is most important, as shallow as it sounds. A cosmetically beautiful engine tells you the owner took good care of it, was a perfectionist. This would most likely apply to it's internals also. Conversely, a corroded out, paint peeling exterior indicates total neglect and "drive it 'til it drops" mentality.
If you are buying a carbureted 2-stroke or 4-stroke, JUST ASSUME you will be in for a $600-800 carb removal, dismantling, cleaning and adjusting job. They all get crudded up and need this to perform properly, and a seller, knowing he is going to sell, just won't put this money into it beforehand. If you can do it yourself, so much the saving.
Also, be sure to run a couple of bottles of QuickClean or RingFree through it immediately. The engine will most likely have some carbon build-up.
WM26 posted 03-18-2006 07:33 PM ET (US)
Has anyone ever been told of a 'leak down' test performed in addition to performing a compression test on an outboard engine.
I was always under the impression that the compression test was the 'tell all' test - but a guy looking to purchase a boat from me keeps asking about a leak down test, using compressed air pumped into each cylinder.
Thanks,
Mark
The Machinery Killer posted 03-22-2006 11:37 PM ET (US)
Hey Mark,
A leak down test in this case would be a bit of a crap shoot since you would need to be absolute in the exact position of the engine. Top dead center is always used for reference in number one cylinder for rebuilds in many engines. The compression test is the good old fashioned direct to the point solution and I have got to agree with the differences not to exceed 15 psi. With a leak down you have got to make sure the cylinder is sealed 100% and in the end you may find one cylinder lower or higher then the others. End result would be removal of the head and the repair so in this case I would not press the issue. Make life simple and smile :)
The $1400 crooks are just that and it makes life harder for the rest of us in the repair industry. I find it very difficult to undersand how any type of seal material to be so high to contribute to a price like that.
Semper Paratus
sosmerc posted 03-24-2006 12:53 AM ET (US)
I have been in the outboard repair business for over 15 years and "evaluate" engines almost daily. If I had to choose between a compression check and a leakdown test, I would choose the leakdown test hands down. Both tests are important, but from experience (primarily on 2 strokes) very high percentage blowby or leakdown almost always indicates a serious problem brewing...and I have seen this even with engines that showed normal compression.
Just one example: I had a 1987 Merc 3 cylinder 90hp that ran ok, but was internally noisey to my ear. After running the engine for awhile to get it up to temperature I then checked compression. All cylinders were between 125-130 psi. I then performed a leakdown test. One of the cylinders had over 38% blowby. The others were around 20%.
I then pulled the exhaust cover and divider plate off so that I could examine the pistons visually through the exhaust ports. What did I find? Severely scored piston skirts and partially stuck rings. The cylinder walls were scored as well. The engine was in need of an overhaul, though it still ran. On this particular engine I determined that the engine was badly "coked" with carbon...especially behind the ring lands...this forces the rings out hard against the cylinder walls causing scoring and my guess is the noise was from the excessive scraping. Poor quality oil, or gas or improper engine temp or excessive prop loading were the most likely culprits.
Don't ask me how that engine was able to produce such normal looking compression numbers...I guess at least one ring on each piston was doing something. But that motor was not going to last much longer.
By carefully moving the piston down the cylinder wall while doing a leakdown test you can get an idea if the cylinder is egg shaped and no long round...the guage will show an increase in pressure drop as you get into a bad area in the cylinder. A compression check cannot show that.
The Machinery Killer posted 03-24-2006 10:21 PM ET (US)
Sosmerc,
What is the part number of either the snap-on or mac tool that insures a proper seal at the plug port in order to get a legit reading. Or what tool group part number and from who are you using for the leak down test?
sosmerc posted 03-24-2006 10:30 PM ET (US)
The tool that I have used for many years came from Precision MFG. & Sales Co., INc.
1-800-237-5947
Their part number is CL 36 and sells for about $80

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Author	Topic: Assessing Used Outboard Motors
jimh	posted 02-11-2006 10:54 AM ET (US) Many outboard motors are purchased used. A quick procedure for checking the condition of a used outboard motor is presented in the Reference Section article: Assessing Used Outboard Motors http://continuouswave.com/whaler/reference/outboardCheck.html Additional advice and suggestions may be appended to this thread.
bsmotril	posted 02-11-2006 07:21 PM ET (US) If the engine is new technology with an Engine Control Computer, you may also be able to dump the fault codes stored in the motor. Some motors require a visit to the dealer where a special hand held diagnostic terminal is used to perform this task. In the case of Optimax motors, you can get a count of overheat events, and the total amount of time in minutes that the motor was run while overheated. If any of the motors sensors have problems, or if the injectors are generating faults, you would see the fault in the diagnostic data dump. You can also dump a Histogram of RPM versus hours run in increments of 1000 rpm. Finally, you can get a count of the number of times the motor bumped up against the rev limiter. This is all good information to tell you what kind of abuse a motor may have suffered at the hands of the previous owner. One other thing to do when you run the compression check is to carefully examin and compare the spark plugs to each other. They should all look nearly the same with equal amounts of deposits, and about the same color on the ceramic tip inside the plug that surrounds the center electrode. Variances in the plugs' color can be a sign of lean running which can damage a motor. Excessive oil or carbon deposits on one plug versus the other can be a symptom of a faulty ignition coil or plug wire. And, a plug that is extemely clean compared to the others is almost certainly in a cylinder wear the head gasket is leaking water into the cylinder. Worst of all is a plug that looks as if it has droplets or spatters of aluminum metal on the electrode or tip. That indicates that engine damage has already occured due to overheating or running with an extremely lean fuel air mixture. BillS
aja	posted 02-16-2006 11:49 AM ET (US) JimH This is a good article, and something else that a friend on the market recently asked me for might be a similar listing for folks looking for used BW hulls. Of course the list would be different as hulls grew in both size and complexity, but it would seem to be a fairly easy and useful tool to have a checklist which reminded folks to look at issues on any boat, but expecially items specific to whaler hulls. Just a thought...
kglinz	posted 02-16-2006 12:18 PM ET (US) My experence with compression on 2 strokes, is that a loss of compression is due to damage caused by something being caught in a port, when the piston comes up. Wear, with a small loss of compression is not as common as damage with a major loss. You usually have enough compression to run smoothly or very low compression and a "dead" cylinder.
bsmotril	posted 02-16-2006 04:42 PM ET (US) That's true. My dad has a mid 60s vintage Evinrde 40HP big twin with 68 and 74 psi compression on its' two cylinders. It runs fine. BillS
wwbach	posted 02-16-2006 10:36 PM ET (US) I noticed there was nothing covering checking the trim and tilt. A family member had a trim and tilt on a 40 yamaha go on him and it was a $1400 fix (he probably was taken advantage of). I'm not sure what to look for -- make sure it works, check for leaking oil, check for corrosion -- anything else? -- Bud
LHG	posted 02-17-2006 03:09 PM ET (US) Bud - you are correct. I had that same experience with the Mercury 150 that came on my 21 Outrage. After a few hours of use, all the hydraulic seals went (probably from sitting unused for several years) , oil pouring out all over the place. Also cost $1400! I think visual inspection is most important, as shallow as it sounds. A cosmetically beautiful engine tells you the owner took good care of it, was a perfectionist. This would most likely apply to it's internals also. Conversely, a corroded out, paint peeling exterior indicates total neglect and "drive it 'til it drops" mentality. If you are buying a carbureted 2-stroke or 4-stroke, JUST ASSUME you will be in for a $600-800 carb removal, dismantling, cleaning and adjusting job. They all get crudded up and need this to perform properly, and a seller, knowing he is going to sell, just won't put this money into it beforehand. If you can do it yourself, so much the saving. Also, be sure to run a couple of bottles of QuickClean or RingFree through it immediately. The engine will most likely have some carbon build-up.
WM26	posted 03-18-2006 07:33 PM ET (US) Has anyone ever been told of a 'leak down' test performed in addition to performing a compression test on an outboard engine. I was always under the impression that the compression test was the 'tell all' test - but a guy looking to purchase a boat from me keeps asking about a leak down test, using compressed air pumped into each cylinder. Thanks, Mark
The Machinery Killer	posted 03-22-2006 11:37 PM ET (US) Hey Mark, A leak down test in this case would be a bit of a crap shoot since you would need to be absolute in the exact position of the engine. Top dead center is always used for reference in number one cylinder for rebuilds in many engines. The compression test is the good old fashioned direct to the point solution and I have got to agree with the differences not to exceed 15 psi. With a leak down you have got to make sure the cylinder is sealed 100% and in the end you may find one cylinder lower or higher then the others. End result would be removal of the head and the repair so in this case I would not press the issue. Make life simple and smile :) The $1400 crooks are just that and it makes life harder for the rest of us in the repair industry. I find it very difficult to undersand how any type of seal material to be so high to contribute to a price like that. Semper Paratus
sosmerc	posted 03-24-2006 12:53 AM ET (US) I have been in the outboard repair business for over 15 years and "evaluate" engines almost daily. If I had to choose between a compression check and a leakdown test, I would choose the leakdown test hands down. Both tests are important, but from experience (primarily on 2 strokes) very high percentage blowby or leakdown almost always indicates a serious problem brewing...and I have seen this even with engines that showed normal compression. Just one example: I had a 1987 Merc 3 cylinder 90hp that ran ok, but was internally noisey to my ear. After running the engine for awhile to get it up to temperature I then checked compression. All cylinders were between 125-130 psi. I then performed a leakdown test. One of the cylinders had over 38% blowby. The others were around 20%. I then pulled the exhaust cover and divider plate off so that I could examine the pistons visually through the exhaust ports. What did I find? Severely scored piston skirts and partially stuck rings. The cylinder walls were scored as well. The engine was in need of an overhaul, though it still ran. On this particular engine I determined that the engine was badly "coked" with carbon...especially behind the ring lands...this forces the rings out hard against the cylinder walls causing scoring and my guess is the noise was from the excessive scraping. Poor quality oil, or gas or improper engine temp or excessive prop loading were the most likely culprits. Don't ask me how that engine was able to produce such normal looking compression numbers...I guess at least one ring on each piston was doing something. But that motor was not going to last much longer. By carefully moving the piston down the cylinder wall while doing a leakdown test you can get an idea if the cylinder is egg shaped and no long round...the guage will show an increase in pressure drop as you get into a bad area in the cylinder. A compression check cannot show that.
The Machinery Killer	posted 03-24-2006 10:21 PM ET (US) Sosmerc, What is the part number of either the snap-on or mac tool that insures a proper seal at the plug port in order to get a legit reading. Or what tool group part number and from who are you using for the leak down test?
sosmerc	posted 03-24-2006 10:30 PM ET (US) The tool that I have used for many years came from Precision MFG. & Sales Co., INc. 1-800-237-5947 Their part number is CL 36 and sells for about $80