Engine Diagnostic

[Charlie]

Okay I'm trying to catch up with Kai about the number of boats that he has. I'm looking at a boat in Mexico. I've talked to the broker and there is no real engine surveyor in San Carlos. In the past I've had an engine survey done before the full survey b/c if the engine was bad I wan't interested.

The broker told me that one of the regular surveyors has a laser temperature guage and takes the temperature of different places on the engine:

The injectors
the exhaust
the cylynders

and a few other places the broker didn't know where. The broker said that the surveyor told him that if there were low compresion in any of the cylynders than there would be a difference in temp. Do you guys buy that?

The engine is a 35 hp Universal diesel with less than 1000 hours. Chances are it should be good but will the temperature guage tell me enough?

I am also looking at Nigel Calder's book and there is a pretty good section on a non invasive engine survey. look at the impeller, check for leaks feel around the oil filler and see if the oil is gritty, check the exhaust elbow, and a few other things.

Any thoughts on how to check the boat over. I'm pretty handy with a wrench but don't want to take apart someone elses boat.

Charlie

In general, yes. THat is what kills VW's. If one cylinder has SUBSTANTIALLY lower compression, it will generally run cooler than the other cylinders. I will talk to you more about it when I see you tomorrow.

[Charlie]

Thanks Kai:

I can't make it to the boat show. Work is catching up. We've had so much rain of late I thought it would be wet all week and I'd be able to go to the show. Since it is sunny I need to get the siding done on the house.

Charlie

[never monday]

It's a Universal, they don't up and die. IF it starts easily cold then go for it. All the other stuff is easily replaced/repaired as needed. Worst case scenerio is about 9K and a few days of your time to repower.

[Alan Wheeler]

There is more to it than just an accurate temp reading with a laser. It simply can't accurately be used as an engine diagnostic tool. A difference in temp could tell you something is not quite right, but you can't tell what exactly. The only real way to use temp is with an infrared camera. And a damn expensive one. It will show not only the temperature but more importantly, the heat patterns. It is almost like looking at the internals of the engine.
The easiest and most accurate way of testing an engine is still to use basic diagnostic tools. A leakdown tester is still the most important tool to have and eyes and ears the second most important tool. Cold starting, smoke and sound are what you look for in a Deisel.

[Charlie]

Thanks Wheels and Never Monday:

Wheels could you explain what a leak down tester is/does? I'm hoping the engine is fine and the fact that it has so few hours on it leads me to believe it is but repowering would be money down the drain. I'm hoping to only have the boat for a couple of years and then to sell it for as little a loss as possible. If I had to repower that money would be gone and it will be too short a time frame to amortize a new engine. If I planned on keeping the boat for 10 years or so then repowering would make sense. I'll email them and ask for copies of the maintenance logs. If the oil has been changed on a regular basis that will be a good sign.

Chalrie

[Richhh]

Here a URL that briefly explains building your own and using a leak down test rig. http://www.xs11.com/tips/misc/misc3.shtml

Its a VERY good way of monitoring engine performance and condition. But like all 'instruments' and techniques its quite dependent on the 'expertise' of the user. Its a very useful method of isolating 'whats the problem' when diagnosing engine problems.

Not only can you assay the rate of leak down but you can isolate what is wrong by 'listening' or otherwise determining where the air is 'exiting' from the combustion chambers: a leaky intake valve will show air coming out the air intake; an exhaust valve - out the exhaust manifold; rings - out the crankcase breather; blown head gasket - soap bubbles developing at the margins of the head, etc. or into the water cooling jacket, etc.

Before I do a leak down test I usually soak (and run at no-load) the internals with either Automatic Transmission fluid or (a USA available) product called "Marvel Mystery Oil" ... just a light weight oil with lots of Mineral Spirits, Chlorinated and Napthenic fractions, etc. What these do is to help remove carbon deposits and crud from the piston ring grooves, valve stems, etc. (a great way to 'restore' compression in old engines). I fill the crankcase with 75%MMO and 25% regular oil, slowly bring the engine up to temp then run at NO LOAD for about an hour, shut down, let soak for 1-2 days then repeat and drain. In petrol/gasoline fueled engines I add a bit of MMO to the fuel so I lubricate the 'top' of the engine.

Hope this helps

[hellosailor]

Charlie, the laser testing is an interesting idea in that local hot spots could be caused by a problem. But unless you knew the particular engine, I'm not sure it is a reliable one. Depending on the cooling passages and other "can't see it" design factors, the temp may not be uniform all over. Some engines are known to run one cylinder hotter than others--at least, in the world of car/truck engines.

So a standard leakdown and compression test would be more reliable, at least to most of us. A compression test requires a guage (in the US available at most auto repair stores and present in most engine shops) and an engine in good health will show uniform compression across all cylinders, and a uniform pattern of buildup and release in each cylinder.

A leakdown down can be as simple as filling each cylinder with kerosene, oil, or diesel and coming back to see if they are all still full the next day. It tests to see if any fluid can get down past the piston rings, which in turn tells you if the rings and cylinder wall are sealing properly, a good sign of engine wear.

You should find both procedures documented in any "shop" manual and plenty of internet sites. If you have time, a very good way to check engine condition is to send a couple of ounces of the engine oil off for analysis. About $25 in the US, and routine maintenance for commercial fleets and large engine (industrial) operators. The oil will show traces of coolant, fuel, silicon, salt, trace metals, and most of the time the report you get back will indicate what they mean, i.e. if there is bearing metal in the oil, you need to replace the bearings before they fail. This is extremely valuable--if you can wait a week or three, or get a rush put on it. Useless if the oil has just been changed, however.

An engine with low hours isn't always a good thing, sometimes it means theengine was run for an hour here and there at the dock, at idle speed, and there will be carbon buildups in the cylinders and the exhaust. If you can't get a satisfactory engine survey fast enough, the other alternative is to put aside some escrow money. i.e. A mutually acceptable third party (broker, bank or attorney, etc.) holds $xxxx of the purchase payment, and is directed to release it to one or the other party, depending on the results of an engine survey AFTER the sale. Again, by mutual agreement. Perhaps both parties could agree to any authorized shop, for that brand, within 30 days of purchase.

Everything is negotiable.<G>

[GordMay]

Just what is “laser testing”? Is it akin to infrared thermography?

[Alan Wheeler]

Laser temperature testing is a little more fancier in name than what it actually is. But in essence, it takes the temperature of the spot you aim it at, and it gives you an accurate indication of that spot even from a distance. Air temp has no bearing on the measuirment it's self, apart form air cooling the surface you are measuring.
Infrared Thermography, if I am understanding the same word as you Gord, is using a very highly enhanced infrared camera. Not the cheapies that you would use on a helicopter to track a person or hot vehicle, or used to spot heat escaping from a house. Same thing, but more detailed in the heat differences it can show you. "You actually "see" heat flows through metals. Just because a temp tester show's you one cylinder is slightly cooler than another, can't tell you why. It maybe water jacket, exhaust flow, a part fitted that is sinking away heat differently in one area, yada yada.

As for compression and leakdown testing. Compression testing is a rather poor way of diagnosing a fault now. Leakdown testing is more accurate and can tell you a greater story. As Richh, suggested and as I alluded to in m,y earlier post, it still requires eyes and ears and some experiance as to what the "result" the device is givign you means. It basicaly fills a cylinder with a pressure using compressed air. If the cyclinder had absolutley no leaks anywhere, then the pressure would remain stationary at what ever pressure you set. Lets say 100PSI for ease of figures. The test guage is set to "zero" on that supply pressure and if there is any air escaping anywhere, then the guage will drop slightly. If there is a compleate loss of air in the cylinder, the gauge will read max flow. Also as Richh stated, listening will tell you were the air is escaping to. A compression guage requires the engine to be turning over. But is is not as accurate and will only tell you a cylinder pressure and that one or more cyclinders maybe different to another. It dose not show you were the leakage actually is.

Of course the other thing I stated, was using ears and eyes in other means of testing. What smoke do you have if any. What sound is the engine making. Whats coming out of the filler cap. Is the engine sump pressurising and so on and so on. All that comes from experiance and understanding your own engine and looking for an noting changes.

[Charlie]

Thanks Wheels:

How do you get the air into the cylinder? Do you need to remove the injectors? are there different fittings for different engines? If you don't have the experience with listening to a leak test is it worth doing?

Charlie

[hellosailor]

Gord, AFAIK the "laser" in laser testing is only used for sighting. There is an infrared temperature sensor in the gadget "aimed" along the same line as the visible red laser. So, you point the red laser dot at something, and that's the same thing the infrared sensor is "looking" at.

Not as fancy as infrared thermal imaging, but the same basic sensor concept. Except you've just got one relatively "large" sensor instead of a big array of tiny ones.

[never monday]

Charlie,
It requires a presurized air source and a few guages. Normaly the glow plug is removed to do this test. It's lightly intrusive.
Like I said if it starts easily I wouldn't worry too much. The Kubota engines Universal uses are bullet proof unless you run them out of oil.

[Richhh]

Charlie
The air is from an aircompressor, the air flow is typically regulated to 100 psig at the compressor. How you pressurize the cylinders is by using an adapter which either screws into the spark plug hole or fastened to the injector bore. You either drill out the porcelin from an old spark plug and fix a hose to it or drill through an old injector and use the old fuel fitting coupled to the pressure hose of the test rig. You need a 'test rig' with an independent gage as shown in http://www.xs11.com/tips/misc/misc3.shtml The delivered pressure to the cylinder is then monitored and the correlation between the two gage readings is the % leakage: if 99 psig then VERY tight engine, 94 psig is Good for a 'production' engine and 90psig and below means there is a major problem.
When using 100 psig 'charging' air from the compressor --- the 99psig from the above list means a 1% leakage; 94 psig means a 6% leakage; 90 psig means a 10% leakage ... and the engine is virtually 'shot' or needs severe rework. The caveat here is that you need an accurate and closely calibrated gage.

You can also do a 'leak down test' which is more sensitive ... load the cylinder with the piston at TDC, shut off the air supply at the test rig and record the time it takes to get to 50 psig, then 25 psig, then 10psig. Draw a chart of this 'decay' for all the cylinders.

You can 'listen' to the air escaping or simply take a condom and place it over the oil fill pipe to see what volume/per time it takes to fill the condom; same thing with a condom over the air intake or the exhaust outlet. For the cooling circuit - just look for bubbles coming or 'burping' through (or use a stethoscope). Most of the 'problems' will be valve problem so monitoring at the air intake and the exhaust outlet will probably be the best value --- do this with the valve covers removed and tap the rockers/valves with a plastic hammer so that any trapped carbon gets knocked off the valve face and doesnt give a false reading of severe leakage. If the air is principally coming from the oil fill pipe (crankcase), then you have a 'real' problem that usually requires an engine 'bottom' job to correct.

[Charlie]

Thanks Wheels, Pat and Rich:

I guess what I can do is practice on my tractor. It is a New Holland(Ford) but uses a Japanese engine. I have a 2000 F350 diesel, a 1987 Mercedes diesel, a 2000 NH tractor with a 40HP diesel and there is a yanmar on my J105 so learning how to do this is probably a good thing.

Pat As you say the Kubota does make a bullet proof engine. I looked over that site and I figure I have most of the parts to make the tester. The only thing I would need is a bad injector to drill out. I can go down to the local Kubota dealer and see if they have any laying around. Do you know what Kubota engine would be in a 35 hp universal diesel?



Charlie