[Clem]

Hi,

I have read, on this forum :grin: , that connecting rod failure is attributed to carbon build up on the head and this is understandable. I have also heard that used rods failed when used in a rebuild. Those that failed in a rebuild, was it a rod failure or rod hardware failure? From my experience with engines, the connecting rod will/may fail in an over reved engine or improper hardware torque or used hardware/stretched bolts.


Clem

 

[Hydriv]

It's often pretty difficult to pinpoint what the true failure was. The aftermath rarely leaves a nice clean playing field for observation. When a rod lets go, things that are spinning often collide with things that were going in other directions. I think that most of us see it this way. If the block needs to be bored, then installing brand new rods is chump change to protect the heavy investment that is already going into this engine.

 

[mikebramel]

more such as low oil

 

[boomers_influence]

clem, and club
mike is correct here.
OIL, the lack of it, is the problem in 90% of rod failures.
of those 99.99999% are the # 2 rod.
HE is the last guy in the food chain,
SO, if you only have four oz. of oil in the pan,
by the time it gets to #2 it has all dropped back to the pan. (esp. on an older worn engine)

onan has made at least three rod revisions. ( in the alum. rod)
#1 narrow window
#2 wide window
#3 wide/ no window
when the wide ones break they tend to break near the wrist pin.
they tend to really tear up the inside of the block
.
then the big blocks, (52 and 60 c.i.)
went to the forged steel rod with bearing inserts.
when they break, they break cams and put HOLES in the top of blocks
So, check your oil, and do it often.
thank you. boomer (the used onan engine parts guy)

 

[Bob MacGregor]

Of all the small engines that I have dealt with over the years I have found Onans to be the the most sensitive to low oil levels. I tore down the B48 that was on my 448 after it blew and found the crankshaft seal under the flywheel had a portion of the lip rolled up and leaking oil. This oil mixed with the dirt in the cooling air, plugged the cooling fins on the #2 cylinder to the extent that it looked like there were no cooling fins on the lower portion of the cylinder. The cooling fins were plugged so solidly that I had to use a long drill bit on a drill motor to find the gap. There were marks on the cylinder wall from an expanded piston dragging on it. The rod broke about half way and swung around and busted thru the crankcase making it unrepairable. The cam and tappets are splash lubed in Onans and when the oil level is low the splash gets smaller and #2 rod suffers from lack of oil as boomer has mentioned. From there it all goes down hill quickly. I tore down the P218 that was in my 4018 to find that it had also been worked on when previously owned and the rear main bearing had been severely damaged from improper installation of the bearing plate. The piece of the bearing that was cut out was laying in the bottom of the oil base. The rear cam bearing was so bad that you could hear the cam slap side to side with the engine at idle but at a different frequency than a bad rod bearing would be at.
Mad Mackie in CT :mrgreen: :mowlawn:

 

[akino]

On connecting rods...
I was thinking of boring some out of round connecting rods I have and fitting them with replaceable split bearings. 1.625 is a very common size. Thoughts anyone?
Andy

 

[Clem]

On connecting rods...
I was thinking of boring some out of round connecting rods I have and fitting them with replaceable split bearings. 1.625 is a very common size. Thoughts anyone?
Andy

I would have some concern about doing this since aluminum rods have a tendency to stretch over time. If the big end has been hammered by the crank I would say the aluminum has been stressed and stretched to some degree.

Clem

 

[robynrj]

If your going to modify alum rod for inserts...use a NEW rod.....Brian Miller does it for Kohlers all the time.....you might contact him....think he is a member here. But doing that is not going to help if OIL LEVEL is not maintained......#2 will still starve......Case spec's Onan's have less oil capicty than most Onan's in other brands. Bob M

 

[Clem]

I agree with robynrj. I just got done tearing down the BF-MS in my 446 and #2 rod and crank journal show signs of oil starvation while #1 looks fine. If you do it keep the oil topped off.

Clem

 

[horton20]

People new to the onan engine need to know that you double dip the dip stick to get the accurate reading, first time it shows to be a little high second time gives the true reading. horton20.

 

[Mjoe7]

People new to the onan engine need to know that you double dip the dip stick to get the accurate reading, first time it shows to be a little high second time gives the true reading. horton20.

That is a very good point to mention. :thumbup:

 

[caselover]

i have a 4020 with a failed rod. didn't damage the bore and the crank cleaned up pretty nicely.....has a couple very small marks but is a couple thousands more undersize than it should be now. i think if i use a new rod it'll be ok. i have an nos rod with a window but this engine has solid rods.....can you mix them???

 

[gator_rider2]

No mixing engine be out balance there 3 rod styles that I remember none can be mixed.

 

[Mjoe7]

No mixing engine be out balance there 3 rod styles that I remember none can be mixed.

I second that. :goodpost:

 

[Hydriv]

People new to the onan engine need to know that you double dip the dip stick to get the accurate reading, first time it shows to be a little high second time gives the true reading. horton20.

You mean it's OK to double-dip??? I distinctly remember an Seinfeld episode where this was frowned upon.

:lol:

 

[boomers_influence]

caselover
i sent you an e/mail.
thank you boomer

 

[1031d]

I have a B43M under my bench from my 446, was ran very low on oil numerous times by the previous owners. Both rods completely disintegrated. Broke both piston skirts but block and crank are salvageable.