I thought that sounded like a rod..

The Continental 4 in my '59 MF lost oil pressure a couple years ago. The oil pump drive failed. I caught it pretty quickly, fixed it and have been using it since, however after fixing a noisy exhaust I noticed a knock at mid range rpms. Pulled the rod bearings this morning, sure enough one had spun. Gave the journal a quick sanding, looks pretty good to me, can't catch a fingernail or anything like that. Bearing is worn on both sides. I'm hoping I can just change out the bearings. What do you think? Photo of spun bearing and one from another cylinder. Journal is on your left.

photo

Any time a shell bearing set "spins" it will damage the rod or block too. Rods can sometimes be saved by machining the rod and cap mating surface IF it's not tongue and groove type joint. The heat damage will cause the rod to be out of round when the bolts are torqued. Best tear it down and do some careful measuring and see what the crank and rod look like..

Best to replace the connecting rod, when the rod bearing spins the big end of the rod goes out of round. If you caught it quick the rod can maybe be fixed, but to me its not worth it. The rod journal probably isn't round, and flat across the journal anymore so trying to put it back together without turning the crank you are really taking a chance. You can either do it half-baked, and probably have to take the engine apart a second time, or do it right the first time, and not have to worry about it.

Thanks guys. Sounds like it would be a gamble to try and just change the bearing. OTOH, I don't have the resources to pull the engine, and for $50 and another hour's work it might be worth a try. I could check for a spun main, and maybe put the rod cap back on in situ and mike it and the rod journal (I'm guessing you can't pull the rod and piston out the bottom).

Plastigage it, may give you a better idea if the bearing clearance is excessive,
because of journal or rod end issues. Ben

I would, and I have been where you are...I always use a MICROMETER to check the Diameter of the JOURNAL in Question?

I always use Plastigue to check the clearance of the Bearing and Journal in question:

There is a chance the CONNECTING ROD should be replaced and definitely checked...BIG END may now be elliptical?

As you have done a lot of work thus far.....I would check all the bearing clearances and Journals:


Bob. Retired Power Engineer / Turbine Tech:

(quoted from post at 15:44:22 10/15/17) Thanks guys. Sounds like it would be a gamble to try and just change the bearing. OTOH, I don't have the resources to pull the engine, and for $50 and another hour's work it might be worth a try. I could check for a spun main, and maybe put the rod cap back on in situ and mike it and the rod journal (I'm guessing you can't pull the rod and piston out the bottom).

Click to expand...

You could pull the head, change the rod, and check the rod journal in many places to see if its not worn in some odd way there a bearing won't last. Put a new bearing in the rod, and measure it to see what kind crank/bearing clearance you have. Then see how long it will live, but I won't recommend it.

Many years ago we had an Allis CA cultivating tractor. We had a huge tobacco crop that year and while Dad was cultivating it started knocking. Too much more to cultivate, weeds were coming, so he dropped the pan in the field. My uncle, the mechanic took it to a parts place and they mic'd it, got a new rod bearing, slapped it in there and away he went. He continued plowing with that tractor for many years(>15) and we never had any more problems. When he sold it it was still working fine. I would rather tear yours down and fix it right but sometimes you have to do what you have to do. "Your mileage may vary" applies here. Good luck!

Update: Although the journal on my spun rod bearing still looked smooth, it was worn and out of round a few thousandths. But, with work to get done before winter, for a $30 gamble I relieved a new .010 under bearing until the crank spun easily (didn't take much) and put it back together. I did not measure the rod. Put it back together several weeks ago and have run it 2-3 hours. Oil pressure is in the green on the gauge, at the lower end, with 10-40w. Yesterday I pulled the pan and bearing out, still looks great. I do still detect a slight knock if I rev it up high (which I don't really need to do).

I may check around for someone that has the ability to grind the journal in place, if anyone still does that. Otherwise I'm going to thicken up the oil with an additive and hope for the best.

Pulling the pan is a piece of cake aside from two 3/4" bolts that run horizontally from the front frame back through the pan. I can't find a way to knock them back through the pan, they are up against the diagonal skid plate. I may drill a couple of holes in the plate to use a punch to knock them back. There are two more large bolts on each side on top of these that go into the block. Anyone dealt with this?

The crank will have to come out to be ground on, if you don't want to sit, or you need it back running soon as possible. Ordering a crank kit, with a new or reconditioned rod would be the fastest way to get it back running (have all the replacement parts before tearing it down). If that rod, and or crank should let go it could be really expensive to fix.