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Onan: Whistling noise from 7.5JB

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
Well, hot day, and the cooling fins on the engine are badly corroded similar to the image posted by JohnnyC. Before the unit shut down on it's own, RPM dropped from 1800 to about 1600, ran like that for a couple minutes then shut down.
What was your oil pressure at the time of failure? What is it now if you start the set? I assume the oil level is OK, right? and you do have a LOP switch to shut down the set when the pressure drops too low and hopefully it functioned properly.

JohnnyC
New jersey
 

tmhardie

Registered
PM

RPM drop like that indicates something else is wrong. Rusted cooling fins unless blocked with cried will not cause it to overheat in my estimation. If you think it is a partially seized end bell bearing, there should be evidence of over heating in that area. Why not use a yard stick and put one end on the end bell frame adjacent to the bearing, the other end to your ear and listen for way unusual noise. That sound will indicate the condition of the bearing.

What type of fuel are you using? Could be a fuel, metering problem Or even a very late ignition timing problem.

You did not answer my question, Have you checked the cooling air intake path? Was this JB sitting out in a corn field or somewhere mice could have moved in? Tell us more about the history off this JB.
The over heat switch is either an on or off,, it alone would not cause an rpm drop.
Yeah, sorry, I haven't had time to take it apart and check the intake path closely. I also don't know the complete history of the unit. Bought it on Craig's list. The only evidence I've found of damage was a few wasp nests inside the box where the relays live (The type that build them out of mud).

I was thinking the RPM drop could be as the engine is overheating and there is more friction?

The fuel is Natural gas. I adjusted the timing according to the manual for the stopped method of adjustment.

Here's a picture where you can see some of the fins
 

Attachments

tmhardie

Registered
What was your oil pressure at the time of failure? What is it now if you start the set? I assume the oil level is OK, right? and you do have a LOP switch to shut down the set when the pressure drops too low and hopefully it functioned properly.

JohnnyC
New jersey
Correct, I do have a LOP and have tested it trips the breaker correctly when I manually ground it out. When it shut down, I didn't see the oil pressure gauge, but the LOP breaker was not tripped.
 

tmhardie

Registered
PM

RPM drop like that indicates something else is wrong. Rusted cooling fins unless blocked with cried will not cause it to overheat in my estimation. If you think it is a partially seized end bell bearing, there should be evidence of over heating in that area. Why not use a yard stick and put one end on the end bell frame adjacent to the bearing, the other end to your ear and listen for way unusual noise. That sound will indicate the condition of the bearing.

What type of fuel are you using? Could be a fuel, metering problem Or even a very late ignition timing problem.

You did not answer my question, Have you checked the cooling air intake path? Was this JB sitting out in a corn field or somewhere mice could have moved in? Tell us more about the history off this JB.
The over heat switch is either an on or off,, it alone would not cause an rpm drop.
I have an automotive stethoscope coming today, so I will take it apart this weekend and try and find the source of the noise.
 

tmhardie

Registered
What was your oil pressure at the time of failure? What is it now if you start the set? I assume the oil level is OK, right? and you do have a LOP switch to shut down the set when the pressure drops too low and hopefully it functioned properly.

JohnnyC
New jersey
It never gets below freezing here, so I've running 30W oil. I just gave it an oil change and new oil filter. When it's cold (ambient like 60) after starting, OP is a little above 50 PSI. Since the whistling has started, I don't want to let it run for too long since I don't want to cause more damage if it is a damaged bearing.
 

Vanman

Subscriber
Last Subscription Date
06/10/2020
Slowing down then stopping on it’s own due to overheating... Sounds like pistons and rings got HOT and started seizing?? Hope not. :(

In any case, I agree with the others that the whirring sounds like something dragging in the flywheel fan blades. Which could certainly explain the overheating.

Keith
 

Power

Registered
If properly protect other areas, a good power washer (3000+ psi) will remove almost all dirt, crud, rust and corrosion. Narrow strips of plumber's cloth or similar can get last bit. When clean, suggest good paint.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
The rust I see in the picture posted previously is about par with many of the sets that I refurbished. It appears that when the sets were assembled at the factory and painted afterwards, little paint reaches between the cylinder cooling fins and over the decades rust forms. Regardless, the cooling does not seem to be affected by the rust.

When I refurbish my sets, I specifically target the rust between the cooling fins. I use small diameter wire bottle brushes which does an excellent job. I manually push and pull the brushes between the fins and also attach them to my drill and spin the brushes between the cooling fins.

You will never get 100% of the rust removed unless you media blast between the fins and rust will form again just as it did originally unless the bare metal is protected. I usually spray a light coating of professional grade rust converter between the cooling fins, then apply a coating of professional grade paint (NOT big box rattle can crap). This will fully protect against rust and will NOT adversely affect the set's cooling. I've done this to countless motors as many already seen here.

JohnnyC
New Jersey
 

YellowLister

Subscriber
Last Subscription Date
o9/30/2019
I think paint on the cooling tins would not let the heat escape as effectively when not painted.. probably why no air cooled engines cooling fins are painted that are covered by the cooling tins..

But I have no scientific tests to back that theory
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
I think paint on the cooling tins would not let the heat escape as effectively when not painted.. probably why no air cooled engines cooling fins are painted that are covered by the cooling tins..

But I have no scientific tests to back that theory
Actually the cooling fins are painted, BUT only where exposed like on the RV sets. Where the tins cover the cooling fins, there is no paint since poaint could not reach behind the tins.

JohnnyC
New Jersey
 

Leon N.

Registered
Actually the cooling fins are painted, BUT only where exposed like on the RV sets. Where the tins cover the cooling fins, there is no paint since poaint could not reach behind the tins.

JohnnyC
New Jersey
Actually the JB pressurized cooling system is in my experience over designed for most environments. Onan specifies a maximum ambient temperature do 120 degrees with a 140 degree rise over ambient. I’ll bet this user is going to find something restricting the air flow. Since he claims the machine starts and operates, then I would not initially suspect a fuel or timing problem which btw could contribute to over heating. Since he has an functioning LOP then lack of lubrication is not a factor. But, then again who knows the overall condition or what this JB has been through.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
Let me show you what I pulled out of the cooling fins on a 15.0 JC. See the first picture below. It must have got sucked in and over time worked it's way into the cooling fins. What you see kind of looks and feels like something between paper towels and baby wipes.

The second picture shows what happens when mice decide to move into the flywheel tin and make a huge nest above the starter. The third picture is taken from a different view showing the same nest falling down on top of the starter's snout and into the teeth of the flywheel. The last picture shows what it looks like when mice decide to build a nest inside the YD's generator case.

All these pictures are from the same genset. The genset was completely overhauled and looks better than new. See last 2 pictures.

JohnnyC
New Jersey


001.jpg

003.jpg

005.jpg

004.jpg

007.jpg

006.jpg
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
Actually the JB pressurized cooling system is in my experience over designed for most environments....
The easiest way to overheat a JB is to run it for 10 minutes with the cooling air/access door removed.

If the set doesn't have the high temp shutdown, I'm pretty sure that'd be a fatal error...
 

Leon N.

Registered
The easiest way to overheat a JB is to run it for 10 minutes with the cooling air/access door removed.

If the set doesn't have the high temp shutdown, I'm pretty sure that'd be a fatal error...
Jim what’s that got to do with the whistling sound? There are other ways to cause an overheat condition, I would be suspicious of the intake air plenum from the scroll fan being blocked by a foreign object. That is the area just above the scroll fan. There. Is a shelf in that area which is a favorite place for critters to nest.
 

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