3gm30f problems

[westwinds]

Originally Posted by Cheechako

Well, it all doesn't really matter. The fact is, soft or hard , a bad bearing will and does destroy crankshafts. I've seen many.

Yes and eventually the engine will "throw a rod" and the owner will also need another engine.

[jimbunyard]

Originally Posted by westwinds

.... The journals can be reground and undersized bearings used...

It'll be interesting to see how a crankshaft can be (re) ground and use undersized bearings...

Making a slight joke at westwinds expense, others more calm than I have repeatedly, in this thread and many others, stressed the sense of making calculated responses to problems.

So far, the OP's suggested options include; get a new engine as his is toasted, spring for a complete rebuild, complete with micrometers and engine lathes, or inspect and evaluate his engine and proceed accordingly.

Here's a picture stolen off the web, of a spun main bearing and it's mating journal.




If the OP's rod journal looks like the main journal (regarding surface finish) depicted above, he could very conceivably plug the oil holes with a piece of paper towel, polish the journal with a two foot piece of 180-220 grit emery cloth and wd40, slap in a new std bearing and motor away. I wouldn't do it unless I was strapped for time or money; if I was that far into it I'd replace all the consumables while I was there, at the very least I'd pull the main caps and check the main bearings' condition and the crankshaft end play.


If he sees this



a visit to the regrinder is far more likely than not, though I'd have a go at with the emery cloth and some plastigage just for grins.


If he sees this, (though of course he won't since this picture is of a v configured engine, with two rods on a single journal, the point is the amount of wear)




the crank has to be reground, you can actually see that the right journal is smaller than the left. It also looks, from the different metal color, like the surface hardness of the crank journal has been worn through, but that could be an optical illusion.

[model 10]

Here's a picture stolen off the web, of a spun main bearing and it's mating journal.



That is not a "spun bearing". A spun bearing actually spins in the bore. The tabs shear off and the bearing spins with the journal. Damage to the rod or the block is not uncommon.

[Ericson38]

[QUOTE=Guy;1902929]

Originally Posted by jimbunyard

the bearing is sacrificial; i.e. the brg disintegrates before the crank is 'toast'.

That is pretty much poppycock. All bearings are soft. Very soft, but that does not make them sacrifical to save the crank. The best of luck with your crankshaft condition but don't think the bearing gave it up to save your crank.
That ain't no WAG either.

You are 100% correct Guy.

Bearing surfaces are not soft to save the crank, they are soft so that debris can imbed itself in the material and save the crank journal. The lead is the wear surface, the copper is the bonding and heat path agent, and the steel backings are the framework to install it properly in the rod big end.

Clearances are in the .002 to .003 range. Anything much more open than that will throw a bunch more oil up that cylinder, and oil pressure for the whole engine will suffer.

Whoever mentioned on this thread that they took 120 crocus cloth and wiped all the scoring off a crank journal, put in a new std bearing shell and called it good to head out into the surf and get through that passage and a few more ahead of them, is dreaming a little, to the PO's potential demise as far as engine reliability goes.

Maybe on a l splash lubed lawn tractor, or even a low compression straight six from the sixties, but not a 22:1 compression ratio Yanmar rated for 80 % continuous duty.

THe engine is not toast, but the crank journal will have to be ground down concentric and without taper, and an undersized bearing fitted. If Yanmar offers undersized crank bearings.

[jimbunyard]

This is getting ridiculous, I'm quite sure the OP has figured out his plan.

But one last go, just to show where the poppycock really is coming from.


Guy,

This is taken from Hot Rod magazine, complete with their description of the 'spun bearing' pictured. The bearing tangs can be clearly seen in both of the bearings; had the bearings actually spun in their bores, the tangs would have been sheared off. It is common practice to refer to any main or rod bearing failure generically as a 'spun bearing', probably because, as bearings sacrificially and progressively fail, they will eventually spin in their bores.




Right down into the copper: Three rod bearings had spun. Numbers 7 and 8 (shown) were the worst. Self-proclaimed “experts” had told Rob detonation had caused the piston wristpins to seize, in turn resulting in bearing failure. Wrong! Wear all the way around the bearing surface and journals is, as Norm puts it, “A clear indication of an oil-system problem.”

Read more: 481ci Oldsmobile Stroker-Motor Build - Hot Rod to the Rescue
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Ericson38,

From your sentence, 'Bearing surfaces are not soft to save the crank, they are soft so that debris can imbed itself in the material and save the crank journal', it seems that you're agreeing with me (and everyone else who understands the meaning of the word sacrificial) that engine bearing are sacrificial; they are softer so that the more expensive part is not worn out first.

You can find some actual knowledge about bearings, from a manufacturer, here: http://kingbearings.com/files/Engine..._Materials.pdf

This is just a basic text of bearing construction, with descriptions of different types of bearings and materials used, as well as some performance data comparisons.

And I didn't 'mention' that I had, as you say "took 120 crocus cloth and wiped all the scoring off a crank journal, put in a new std bearing shell and called it good to head out into the surf and get through that passage and a few more ahead of them", I flatly stated that I have peeled bearing metal off a crankshaft journal, polished said journal with emery cloth, replaced bearing with a standard bearing, and run the engine as normal for years. I have in fact done this with 2 gas car engines and 1 diesel boat engine. I've also more times than I can count replaced standard bearings with standard bearings, with nothing more than a quick crank polish and cleaning, my 1994 Jeep comes to mind, rebuilt at 186,000 miles, it now has 310,000 miles on it. With standard rod and main bearings. The reason I was able to do this is because the main and rod bearings, being sacrificial, wore out before the crankshaft did. I did have to replace the roller cam and rollers at the first rebuild though, somehow there was enough metal to metal contact to wear grooves in the cam lobes...

The point, as has been repeatedly said by the more reasonable people, is that the OP should evaluate his situation and act accordingly. In his case that could range anywhere from 'change a rod bearing' to 'complete rebuild'.

Anyone who presumes to 'know' what the OP has to do, or what his situation will be, is full of poppycock.

[Ericson38]

. I have in fact done this with 2 gas car engines and 1 diesel boat engine. I've also more times than I can count replaced standard bearings with standard bearings, with nothing more than a quick crank polish and cleaning, my 1994 Jeep comes to mind, rebuilt at 186,000 miles, it now has 310,000 miles on it. With standard rod and main bearings. The reason I was able to do this is because the main and rod bearings, being sacrificial, wore out before the crankshaft did. I did have to replace the roller cam and rollers at the first rebuild though, somehow there was enough metal to metal contact to wear grooves in the cam lobes...


I have done that many times too. That's a refresh of the bottom end, when all was well to start with, basically. PO had a problem bigger than that.

I restore cars and rebuild engines, since 1967. But don't try a hand polish for surface looks only type journal cleanup on a scored journal where the bearing removed was damaged, and replacing the bearing with a new std, unless you are broke, or you are in the movie "the grapes of wrath" by John Stienbeck.

Even with what you did above, at a minimum, plastigage the journal to verify clearance and get a visual of the taper.