550 gas connecting rod nuts

[kenbob]

After having my 550 about a month it lost oil pressure. I tried a different gauge, checked the pressure relief valve and did not find the solution there. SO I dropped the pan. I had suspected there had been recent work done on the engine as the valve train had no sludge at and the oil in the pan was pretty clean. My belief was confirmed when looking at the bottom end. New shiny bolts on the oil pump, and the rod nuts on 3 of the cylinders look to be the locking type with plastic inserts the hardware store sells. The 4th one (no4) i could wiggle the bearing cap. I took it off, and the rod bearing was spun. The ears on the inserts were gone. I am not sure what dumbassary went on, but it would seem that they never had the cap seated correctly. Luckily I don't see any damage to the crank. I guess being loose help that. The question is, are the other rods ok with that type of nut? The rod with the trouble just had normal looking rod nuts and no keepers. They were plenty tight. I retorqued the other 3 with the locking nuts and got about 1/4 turn out of them to get the 50lbs. Gotta mic that journal and order a new bearing, but do I need different nuts? THanks all.

 

[tom upton]

YES

 

[cushman]

The rod with the spun bearing probably needs to be resized or replaced to keep the new bearing from spinning.

 

[kenbob]

The crank looks good but the bearing needs replacing for sure as the ears that hold it in place are gone. I am thinking they put the inserts in wrong so those ears rode high keeping it from being tightened all the way. When they finally spun there was slack. Just guessing tho. Hope to use the micrometer tomorrow. I had only 10 lbs pressure at cold idle before and then nothing after it spun

 

[Gambles]

The rod with the spun bearing probably needs to be resized or replaced to keep the new bearing from spinning.

^This. The rod needs to be resized at the machine shop and if you have the engine spare, do all of them. The bearing tabs help align the bearing during assembly, but the bearing crush is what keeps your bearing from spinning while in operation.
Oh, yea. Since you don’t know the history of the engine or the quality of any of the nuts, replace them all .
Better to cry once about engine machine parts and labor once instead of doing it again later. JMO.

 

[JOCCO]

I am with the others. Since you don't know what was done I would go through all the rods. Replacing the damaged one might be an option verse resize.

 

[cushman]

I also do not see how a spun rod bearing could cause your oil pressure to go to zero,as I do not believe the rod bearings are pressure lubed.

 

[rrlund]

I also do not see how a spun rod bearing could cause your oil pressure to go to zero,as I do not believe the rod bearings are pressure lubed.

I believe you're right about that. I spun a bearing in my 1600 a year ago and they weren't pressure lubed either. There are holes in the top of the rods that line up with the holes in the bearings.

 

[kenbob]

So is there a way to bench test an oil pump? I have never messed with one before.

 

[JOCCO]

So is there a way to bench test an oil pump? I have never messed with one before.

Yes it can be done (not easy) Oil pumps from old engines have been used for other applications. You would need some metrics like pressure and flow similar to hydraulic pumps. Most likely just easer to get rebuild or replace if there is doubt.

 

[rrlund]

I'm a little concerned about the crank. You said it's OK, but the bearing had to be dragging more on the crank than it did inside the rod or it couldn't have spun. On my 1600, we had to clean up the crank with some Emory cloth. It wasn't bad enough to have to be reground, but it was too bad to put a new bearing in the way it was.

 

[Gary Reif]

If it were mine I would remove all four rods and have them checked. The one that spun the bearing will definitely need resized or replaced. You will be very lucky if the crank doesn't need reground. Those nuts on the other rods are only mid steel and not a grade 8 like all rod nuts usually are and will hold up under torque specs. Your mileage may very but I'm speaking from 25 years experience in an automotive machine shop.