Spun Con Rod Bearings

[70spider]

Well my worst fears have come true, Pesto spun 3 con rod bearings. I recently rebuilt the engine and during the break in the stupid carb decided to get stuck wide open when my friend started it and because I was outside the car it hit 8 grand before I could shut it off. I replaced the carb and it ran ok for a day and then I had an electrical problem. In my frustration he sat for a year or so. I figured out the electrical recently and have been trying to dial in the carb. I have been doing short drives and noticed I had almost 0 oil pressure at idle. It took 2 days but I got the oil pan off and sure enough there is major play in the #1 con rod #2 was slight as well as #3.
So, I assume the crank is toast? I guess my only course of action is to rebuild the bottom end? Hmmm that Mazda rotary swap sounds interesting right about now

[18Fiatsandcounting]

As luck would have it, I just finished putting an engine back together for a friend with an '81 spider that had fried the #1 con rod bearing. It didn't spin, but the bearing was mashed into submission and the crank was damaged (an oil starvation issue), which necessitated finding a good used 2L crank.

When you say "major play in the con rod", can you describe this a bit more? There will be some acceptable movement in the same direction as the axis of the crankshaft, but there shouldn't be any side-to-side play (perpendicular to the crank axis). Now that you have the oil pan off, can you remove the con rod caps and see what the bearings look like? And maybe a main bearing cap or two?

Your crank might be OK, but there is no way to really tell without getting in there with a good micrometer and measuring the journal diameters. 0.001" or 0.0015" of wear might be acceptable, but not much more than that. If the crank journals are worn down, you can have it reground, but the issue is that the original cranks were nitrided to harden the surface, and regrinding will take off that hardened layer. That being said, some machinists have told me that a reground crank will be OK unless you are really hard on the engine like in racing. You can have the crank reground, and then heat-treated or "re-nitrided", but now we're talking $$$. A good used crank is likely the better option.

PM me with your phone number if you want to discuss over the phone, as I have many other thoughts that would take too long to type.

-Bryan

[70spider]

"major play in the con rod"

a lot of side to side slop the other two wiggle a bit number 4 is tight.
I will have to pull it out to get a better picture. My hoist is back home with my son so it looks like a road trip. As far as for regrinding the crank I have a 1608 but the crank is worn out and the machinist said the same thing, to get it in good shape they would have to grind it down and re-harden it, $$$$$. If I need, I might be able to source a 1438 crank for a good price.
I'll PM you once I get a better handle on it.
Thanks for the support.

[18Fiatsandcounting]

If I need, I might be able to source a 1438 crank for a good price.

Back when I was traveling down to the Santa Fe area every month or so, I could have tossed a 1438 crank in my checked luggage and given you a good price with no shipping! Try that today with airport security being what it is, and I'm not flying to NM much any more.

A 1438 crank shouldn't be too hard to find, but don't write off your existing crank just yet.

-Bryan

[Nut124]

Sorry to hear about your troubles.

Fiat bottom ends are very good normally. I would try to figure out the root cause. This does not happen. 8000rpm does not wreck the bottom end. Mine runs 8000rpm, just about, every time I drive her.

Likely causes would be assembly error or total loss of oil pressure.

We may need to clarify the terminology for all to be on the same page: I would say side-to-side play is axial and OK, normal.

Is it possible your aux shaft pulley came loose and the aux shaft, oil pump is not turning? This happened to me some 25years ago. The aux shaft pulley bolt came loose. The bolt and the pulley backed out to the point that the aux shaft stopped turning. The timing belt cover kept the pulley from falling off. The pulley was still turning. Zero oil pressure.

[18Fiatsandcounting]

I agree with Nut on this, in that the bottom of the engine is unlikely to be damaged with a momentary excursion to 8000 rpm. He routinely revs his engine that high, and I used to rev my '69 spider (1438 engine) occasionally to 7500 with no problems. These engines are very happy at that speed, assuming they're in good condition.

What does often happen is that the the oil pressure sensors, both the ones for the low oil pressure light and for the gauge itself, go bad over time. On many older engines, it is not uncommon for the low pressure light to flicker when at idle. This is not ideal of course, but it's not as bad as it seems. So, a first step would be to replace both sensors if you haven't already.

But, that doesn't explain the play in the con rod bearings, and since the oil pan is off, you might as well look at things in the bottom end.

Another scenario is that your new carb is running rich and so the oil is being diluted with gas, leading to low pressure and of course the diluted oil is definitely not good for the bearings (or anything else in the engine).

Bottom line for your bottom end: Things might not be as bad as they seem, but I'll be curious to hear more.

-Bryan

[70spider]

When I rebuilt the engine all sensors were replaced new oil pump, new everything if it was available.
The running rich and hard starting did dilute my oil so I changed the oil with no significant change in oil pressure at idle. This is why I suspected a bearing issue.
As for the cause of the bearing issue perhaps my own skills were at fault. It is the first engine I have rebuilt and I just used the plastigauge instead of a micrometer to check the con rod and main tolerances. Unfortunately I do not have easy access to a machinist so I am on my own.
When I put the bottom end together I torqued everything down to specs and waited 2 days then retorqued. My thrust bearing play was well within specs.
Once I get the engine out I'll check it out. Today the weather will be good so I'll pull the cap off the connecting rod and check it out.
Thanks for all the input it is greatly appreciated.

[18Fiatsandcounting]

As for the cause of the bearing issue perhaps my own skills were at fault. It is the first engine I have rebuilt and I just used the plastigauge instead of a micrometer to check the con rod and main tolerances. Unfortunately I do not have easy access to a machinist so I am on my own.

Your skills may be just fine. I did the first rebuild of my 1438 engine back in the late 1970s, in a dark and damp basement with a dirt floor and a wood-burning stove in the corner. I used plastigage at the time, but I have found that you have to keep everything perfectly motionless otherwise the plastigage tends to "smear", making it look wider than it really is, and that translates into a false reading of a tighter clearance than it really is. Hard to keep everything motionless as you torque down the caps.

These days, I use a combination of a bore dial gauge and a micrometer. They don't have to be super high quality, and you can find decent used ones on Ebay for less than $100 each. Basically, you get a micrometer reading on the journal of interest, then set up your bore gauge so that it reads "zero" as measured between the anvils of the micrometer. You then insert the new bearings in the rod and torque down the cap. The "calibrated" bore gauge is then inserted into the bearing shells and you directly read out the clearance. There are YouTube videos on this, for example: https://www.youtube.com/watch?v=Vt0wzLXRlRU

For Fiat rods, I believe the clearance spec is 0.0015" to 0.0025", but I imagine you could get away with 0.003" or slightly higher. 0.004" or 0.005" is too much clearance.

Happy to discuss more when you get to that point.

-Bryan

[70spider]

For Fiat rods, I believe the clearance spec is 0.0015" to 0.0025", but I imagine you could get away with 0.003" or slightly higher. 0.004" or 0.005" is too much clearance.

is that for bearing clearance?
Ok I just checked the side clearance of the rods before doing anything drastic. 0.010" is what I came up with. All four came up with that measurement.
So is the ok ? If not is the issue with the rods or is my crank a bit worn?
The engine only had 53000 miles on it and it was such a chore trying to find a machinist I just assumed the journals were ok, giving the plasticgauge readings.

but I have found that you have to keep everything perfectly motionless otherwise the plastigage tends to "smear", making it look wider than it really is, and that translates into a false reading of a tighter clearance than it really is.

I studied up on using the plastigauge that is why I took two reading from each journal.

[18Fiatsandcounting]

Need to make sure we're talking about the same thing here, as Nut mentioned. The rod ends (with bearings) will slide along their journals in the direction of the crankshaft axis, and that could be around 0.010" and is normal. You can "click" them back and forth towards the front of the engine and then towards the back. However, the rod ends should not move sideways (side to side) towards the sides of the engine. That bearing clearance should be 0.0015" to 0.0025" or so, but if there is oil on the journals, you won't be able to feel any movement. You also shouldn't feel any movement if you attempt to move the rod ends up and down against the journal, but that is harder because it requires the piston to move as well.

Plastigauge will do an acceptable job, so I'm not dissing it. I just keep losing it or mushing it between tools...

I have a short movie (a few seconds) of bad rod bearing movement on my cell phone, so if you PM me your cell phone, I can text it to you.

-Bryan

[70spider]

Sorry I don't have a smart phone, don't laugh to hard. I think I am only one left that doesn't. The only movement I can detect is the 0.010" movement of the con rod along the crankshaft. No up and down movement.
Maybe it is fuel washing past the rings causing the low oil pressure at idle. I had just changed it a couple of weeks ago. The timing and carb are better now, perhaps I will just button him up add new oil and pray.

[18Fiatsandcounting]

Maybe it is fuel washing past the rings causing the low oil pressure at idle. I had just changed it a couple of weeks ago. The timing and carb are better now, perhaps I will just button him up add new oil and pray.

It's worth a try, perhaps using a heavier oil like 10W-40 or 20W-50 if you aren't already.

Did you ever remove any of the con rod caps to take a look at the bearings?

-Bryan

[70spider]

Did you ever remove any of the con rod caps to take a look at the bearings?

No I haven't. I would hate to mess it up, it is a bit cramped under the car and lots of dust and dirt blowing around so I thought it on the safe side not to. If I had a garage I would.

It's worth a try, perhaps using a heavier oil like 10W-40 or 20W-50 if you aren't already.

That is what I was thinking, running 10W30 at the moment, I run 15W40 diesel oil in my '66 Ford and it works well so I might give it a try.
How do I mitigate the fuel getting past the rings, the engine only has about 50 miles on it?

[18Fiatsandcounting]

Do you have a mechanical fuel pump (the one under the intake manifold)? Sometimes the diaphragm inside an old pump develops a leak, and that is a guaranteed way to get gas into the oil. Shouldn't be the issue if you have a new fuel pump, though.

You can also get gas in the oil if the engine is running rich, but it would take a while unless the engine is running way too rich. When you rebuilt the engine, did you put in new piston rings, and were the cylinders honed so the new rings can "seat" properly?

Does the oil smell like gas? If so, there's a problem somewhere.

I have a knowledgeable Fiat buddy who swears by diesel engine oil in all his Fiats. Claim it has extra zinc additives that are good for Fiat engines. I don't recall what weight oil he uses, but 15W-40 sounds reasonable.

-Bryan

[70spider]

You can also get gas in the oil if the engine is running rich, but it would take a while unless the engine is running way too rich. When you rebuilt the engine, did you put in new piston rings, and were the cylinders honed so the new rings can "seat" properly?

New pistons, rings and bored 0.4 mm over. He doesn't smoke but he does run rich. New fuel pump but it has been setting for two years and ethanol fuel eats the diaphragms up. The fuel pump is my next check item, they are a pain to get off with the intake on.
Work in progress, I don't give up easily.