Glow plug failures cured with new bearings - why?

[BobBonahoom]

Sorry, I meant is there any way to tell the bearings are failing prior to a plug failure?

 

[gooycheese]

I will just say on my small boats 12 & 21's you can't find the needle or seam to be chasing it, Stop and change your bearings... in my case failure is soon to follow if ya don't. The bigger engines are a little more forgiving for me I guess.

 

[johnsteltzer]

Yeah that's right gooy your needle starts to get where it's all over

the place but the easy way is to pull the head button and you will see

The tiny particles on the squish ban of the button

 

[Brad Christy]

Guys,

Just my thoughts:

When the bearings start to go south, they are no longer "round" or smooth, so they begin to load the engine more. One of the basics signs you are running too big a prop is plug failure. I have always attributed bad bearings taking out plugs for the very same reason.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LC

 

[NeilLickfold]

Sorry, I meant is there any way to tell the bearings are failing prior to a plug failure?

Yes, there will be a slight increase in overall end play of the crankshaft in the engine. Also you will feel that the crank is not totally smooth smooth when rocked at BDC. It will often make a sound that is like a rumble. If the case is rested on an inverted stainless mixing bowl, you will be able to better hear the rumble noise of a starting to fail rear bearing. The initial failure occurs in the outer skin of the ball failing from deformation cyclic fatigue. This is when very small particles of the outer shell of the ball dislodge from the bearings surface. These micro particles also create damage to the inner and more particular, the outer race surface. The micro particles off the ball itself can effect the glow plug wire and it's life expectancy. By the time a ball fractures, or chips of a very significant size separate from a ball,(usually the rear main bearing) it will have been noisy and rumbly for quite some time.

Another cause of plug failure is micro particles of Al from the crankcase or from the con rod or the back plate,migrating through the engine and adhering to the plug element, This will create a local hot spot and then an element will be broken or failed. If particles are adhering to the wire, using a microscope you will see these minute particles attached to the wire and around the inside of the plug body. Hope this helps. Neil

 

[Terry Keeley]

Thanks for adding your expertise Neil, will definitely try your "mixing bowl" check next time I have a motor apart. Can you "see" if the balls are starting to fail if viewed under some level of magnification?

BTW, Neil may not be well known in the model boating community but I have been informed by a very reliable source (thanks Jim) that he knows his chit. He worked closely with Henry Nelson for years and had a good hand in designing and building many of Henry's motors.

 

[Ray Sametz]

Sorry, I meant is there any way to tell the bearings are failing prior to a plug failure?

Yes, there will be a slight increase in overall end play of the crankshaft in the engine. Also you will feel that the crank is not totally smooth smooth when rocked at BDC. It will often make a sound that is like a rumble. If the case is rested on an inverted stainless mixing bowl, you will be able to better hear the rumble noise of a starting to fail rear bearing. The initial failure occurs in the outer skin of the ball failing from deformation cyclic fatigue. This is when very small particles of the outer shell of the ball dislodge from the bearings surface. These micro particles also create damage to the inner and more particular, the outer race surface. The micro particles off the ball itself can effect the glow plug wire and it's life expectancy. By the time a ball fractures, or chips of a very significant size separate from a ball,(usually the rear main bearing) it will have been noisy and rumbly for quite some time.

Another cause of plug failure is micro particles of Al from the crankcase or from the con rod or the back plate,migrating through the engine and adhering to the plug element, This will create a local hot spot and then an element will be broken or failed. If particles are adhering to the wire, using a microscope you will see these minute particles attached to the wire and around the inside of the plug body. Hope this helps. Neil

Radio Shack makes a small microscope, I made a adapter plate with 1/4-32 hole for glow plug. You can see particles attached to wire.

 

[Terry Keeley]

Sorry, I meant is there any way to tell the bearings are failing prior to a plug failure?

Yes, there will be a slight increase in overall end play of the crankshaft in the engine. Also you will feel that the crank is not totally smooth smooth when rocked at BDC. It will often make a sound that is like a rumble. If the case is rested on an inverted stainless mixing bowl, you will be able to better hear the rumble noise of a starting to fail rear bearing. The initial failure occurs in the outer skin of the ball failing from deformation cyclic fatigue. This is when very small particles of the outer shell of the ball dislodge from the bearings surface. These micro particles also create damage to the inner and more particular, the outer race surface. The micro particles off the ball itself can effect the glow plug wire and it's life expectancy. By the time a ball fractures, or chips of a very significant size separate from a ball,(usually the rear main bearing) it will have been noisy and rumbly for quite some time.

Another cause of plug failure is micro particles of Al from the crankcase or from the con rod or the back plate,migrating through the engine and adhering to the plug element, This will create a local hot spot and then an element will be broken or failed. If particles are adhering to the wire, using a microscope you will see these minute particles attached to the wire and around the inside of the plug body. Hope this helps. Neil

Radio Shack makes a small microscope, I made a adapter plate with 1/4-32 hole for glow plug. You can see particles attached to wire.

Hey, I used to have one of those, can't remember ever seeing particles on the plug wire tho...

 

[Ray Sametz]

Sorry, I meant is there any way to tell the bearings are failing prior to a plug failure?

Yes, there will be a slight increase in overall end play of the crankshaft in the engine. Also you will feel that the crank is not totally smooth smooth when rocked at BDC. It will often make a sound that is like a rumble. If the case is rested on an inverted stainless mixing bowl, you will be able to better hear the rumble noise of a starting to fail rear bearing. The initial failure occurs in the outer skin of the ball failing from deformation cyclic fatigue. This is when very small particles of the outer shell of the ball dislodge from the bearings surface. These micro particles also create damage to the inner and more particular, the outer race surface. The micro particles off the ball itself can effect the glow plug wire and it's life expectancy. By the time a ball fractures, or chips of a very significant size separate from a ball,(usually the rear main bearing) it will have been noisy and rumbly for quite some time.

Another cause of plug failure is micro particles of Al from the crankcase or from the con rod or the back plate,migrating through the engine and adhering to the plug element, This will create a local hot spot and then an element will be broken or failed. If particles are adhering to the wire, using a microscope you will see these minute particles attached to the wire and around the inside of the plug body. Hope this helps. Neil

Radio Shack makes a small microscope, I made a adapter plate with 1/4-32 hole for glow plug. You can see particles attached to wire.

Hey, I used to have one of those, can't remember ever seeing particles on the plug wire tho...

Maybe particles is the wrong word. Frosted to see if mix was right. Could definitely see if damaged.

 

[Mike Cathey]

Along similar lines when an engine is being turned over by hand and it gets that double thunk feeling at TDC it is because the needle bearing around the big end of the rod/crankpin are shot. At least when I change them out the double thunk disappears.