L 20 B Rebuild...a work in progress

[Crashtd420]

Ya that looks pretty nasty.... rods and crank... I'd say you might need a new donor....

[hobbes_the_cat]

Daaaang. Well that explains why it didn't turn. If the crank can't be saved, shoot me a message. I have a buddy that probably has a good one that he'd sell.

[Crashtd420]

That really does look like it melted that bearing.... definitely spun on the crank....

If your lucky what we are seeing is all melted bearing material....

I did that on my atv spindle once.... I though I junked my spindle, turn out to be what was left of the bearing, spindle was perfect underneither ....

One idea I had... and don't get aggressive with it is to See if any of it can easily flake off... carefull not to scratch or gouge what is good.. even use a small file on the journal and see if it comes off or not... might give you an idea if its bearing material melted to the crank or the crank is scored up....

[datzenmike]

The rest of the engine is fairly clean so that dark color of the rod is from the hearing from friction. They will get so hot they turn blue. You can definitely see the darkening on the crank though, on the #3 throw. This occurs at 570F for dark blue and 600F for very dark blue. Crank and rod are literally toasted.

 

L series have 5 large main bearings and huge rod bearings that are capable of supporting incredible loads on them. Breaks my heart to see something like this that is so avoidable.

[KoHeartsGPA]

I'm curious to know what caused that meltdown....Low oil, old oil, bad pump, spun bearing blocking oil passage, how's the cam and rest of bearings?....From this POV I'm going with spun bearing.

[Crashtd420]

So Mike In this scenario is that crank junk now? Is it not even worth regrinding?

[KoHeartsGPA]

You gotta have it measured even if it looks ok, yours looks really bad...

[Crashtd420]

I agree on measuring.. but I'm wondering more about all that heat in that one location... would that cause a weak spot in the crank?....

Or put it out of balance even?

[datzenmike]

The crank is forged so the heat won't be good for it. They are pretty strong and this will still work if turned down but it's no race engine.

 

I'm curious to know what caused that meltdown....Low oil, old oil, bad pump, spun bearing blocking oil passage, how's the cam and rest of bearings?....From this POV I'm going with spun bearing.

 

Started with a knock that was ignored. This could be from normal wear from high mileage or in the short term just abuse or indifference which would include lack of maintenance, tune ups and proper oil changes, can even simply be an oil burner that the owner misjudged how much oil was in it and just kept going. Once there is excessive crank to rod bearing clearance there is no ability for a layer of oil to hydraulically absorb the rod being slammed down by the piston. As the clearance enlarges the rod has room to accelerate even more before slamming into the crank journal which accelerates the wear and clearance in a vicious circle. If going high RPMs and heavy throttle the time from knock to spun bearing can be quite short. If driven carefully weeks and months can pass. I've see bearing shells pounded out between the rod and the crank throw as if like soft clay. I've seen rod bearings ground down to razor thinness. Once the bearing shell slips and begins spinning the oil hole is covered, as if it really matters by now, and the rod will get hot enough to melt. If being driven hard enough the rod welds to the crank but can't stop turning and it snaps off and punches a hole in the block. If lucky the engine slows and just seizes.

 

This is not at all a quiet process and the driver would have been quite aware that something was wrong. If caught early you can get away with a new bearing. But some owners choose to turn the radio up.

 

Cannot imagine a plugged oil gallery. All oil is filtered. Even if the oil filter was plugged the by pass would allow unfiltered oil to pass. Even oil oil is relatively 'clean' there are no lumps in your changed oil.

[Xnke]

The Rod and Crank are both fixable.

 

The crank, even if totally fucked right now, can be welded and reground to stock. Or, if it's not totally ruined, it can be turned undersize.

 

The rod can be resized, but you will need to resize all four rods to keep them the same weight-can't do just one. And it may need to be replaced anyway if the thrust faces are tore up too badly-it's just not worth welding rods up to grind 'em back when L-series rods are so available.

 

Crank welding is not cheap, but it's an option. The shop I have do my race cranks charges 60 bucks per rod journal, unless they're doing the whole crank in which they do the mains too for the same 60 bucks per rod journal. This is in addition to the grinding fee, so probably cheaper to get the rod resized, and try to find a crankshaft kit from a regrinder.

 

Call Crankshaft Rebuilders, they're fairly local and they *will* have what you need, or be able to fix your busted parts. (If you can't find another crank, that is!)

[Suntzuzuki]

The bearings do feel about as thin as rice paper. They crumbled a little bit when pulling them out. And that rod is shot.