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fully grooved main bearings

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Steve_P View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 6:09pm
Grooved crank journals went out in the 1970s- not a good idea to add a huge stress riser to a stressed component.  Cross drilling also went out of style not much later.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jcisworthy Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 6:39pm
LS Block 




Specializing in dyno services, engine building, and cylinder head porting

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 9:20pm
Yeah I was not advocating for grooved cranks, but I’d bet the “stress riser” is not really that. Cross drilling in certain situations could still have merit, or a place, if carefully thought out. 

Worthy makes the point, perhaps unintentionally, but the LS does have a loop oiling system similar to an AMC with the rear galleys bridged. It’s not some “mains priority” oiling. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WARBED Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 1:09am
Wow a lot of information out there. thanks, may try the 3/4 route looks to be the best. I'm not going all out racing and the 390 I'm going back mainly stock other than better pistons. The 360 I am modifying Pistons/Bal/Blu/cam/Heads been waiting and waiting. and should have some respectable numbers. We do or did have a drag strip outside of town but since 2021 it's been hit or miss when it opens. Main reason asking is for longevity and the occasional racing.  ever since I started grooving the cam bearings and making sure the oil passage from mains to lifter gallery is actually drilled out all the way I haven't had concerns with main bearing failures but have all ways ran fully grooved mains. My main concern is the conrod bearings getting the proper oiling.  I know I read that it will be fine but still like full oil flow to the hardest working part of the engine. 
59 American 2dr S/W. 70 390 AMX. 70 232 javelin. Kelvinator fridge ice cold beer storage.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 4:05pm
Originally posted by Jmerican Jmerican wrote:

Yeah I was not advocating for grooved cranks, but I’d bet the “stress riser” is not really that. 

Grooving a crankshaft journal creates a huge stress riser- this is why it went away decades ago for anyone that knows what they're doing. Surface irregularities such as a groove on a crankshaft journal can easily create a 3X stress riser.  It's up there with sharp corners on stressed parts in the realm of stupidity. 

Here is a grooved main cap from a Mitsubishi.  The block is also grooved as shown above in JCs post.  The crankshaft is not grooved.  The lower main bearings are not grooved as you can see.  IIRC the upper main bearing is fully grooved.

Edit- IIRC this bearing has ~150k miles on it.  This is from a 7K RPM redline turbocharged engine, >1.5 HP/cubic inch, that obviously has an excellent oiling system.




Edited by Steve_P - May/15/2022 at 4:09pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 4:59pm
Ok Steve, if I’m hearing you, you are looking to prove that a well machined groove in the middle of a main journal is a “giant” stress riser, and that anyone with current expert thinking would shudder at the idea. Ok. I’ll take the bait. How so? What gives you that expert knowledge? You’ve shared grooved caps and blocks, which to me, says that it gives bearing hole clocking options and timing options. Great. I’m not sure what that proves. You’ve shared a long lived Mitsubishi bearing as an example of? Let’s look at what you’re saying and showing and draw out some learning. I see two feed holes, and perhaps a grooved cap. Ok. 
Now what? 

Seems to me that crankshaft stress is high at the Rod journal fillets or lack of fillets. That’s a stress riser, an unfinished fillet. 
So could drillings be stress risers if not managed properly. Particularly at places of low journal overlap, subject to severe torsional stress. Turning a main journal under 40 thou is probably not a big factor, nor a groove, nicely machined in the middle of a main journal. But like I said earlier, I’m not advocating grooved journals though A journal might be appropriate as an option. I’ll add that it could be an option in certain situations. A poorly designed or manufactured crank modified with a machined change might be a disaster. But a well designed unit with grooves? Seems fine to me, but I’ve not put in the study to declare that fact.

As people of expert knowledge have figured out, well, that they are not always right. Sometimes we sheep and those experts proceed to get it wrong, and profess the wrongs for decades. 

We can look at principle and sound engineering, while trying to reverse engineer what production engineering compromises were made, or deduce a mistake vs current thinking vs availability of solutions vs. on and on. The answer may not be one solution fits all. There is so much more to it then saying “obviously the Mitsubishi has a good oiling system” given your evidence. 

Back to the program. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 7:10pm
Likely there are poorly designed rod drilling’s on fancy cranks for Mitsubishi turbo 4s.

I can look at Porsche 944 engines and find a nice mains bed plate, nice crank driven oil pump, mains look new after 100s of thousands, but suck a little air with modern tires and a long left hand turn and poof there goes the #2 rod. And only that one. 

Solutions just like with AMC V8s (and every darn engine)  are varied in how “good” they are. Often the source of the problem is complex, or Overlooked, and yet.... sometimes solutions have been proven wrong or done wrong because of long standing practice. Like cross drilling. Could a wrong be a right in certain situations? I think so. If it is well understood. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote WARBED Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 11:11pm
Hmmm The LS and Mits are using a totally different bearing and oiling system. Yes a way better system than AMC used.. Didn't mean to start a debate as I said in the first place. Does anyone make a fully grooved main bearing for the AMC V8?????. I guess not from what has been said and my own exploration. So I'll just make them and yes I have the tooling. I'm not a believer of the half grooved set up especially after all the mods I do to help the oiling  process. I've built them and driven them very very hard and have all ways used fully grooved and have not had any concerns with bearing longevity. I'm not about to test the theory of the half grooved bearing on my engine builds or any of my customers unless they insist but that's not happening.

Edited by WARBED - May/15/2022 at 11:17pm
59 American 2dr S/W. 70 390 AMX. 70 232 javelin. Kelvinator fridge ice cold beer storage.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jmerican Quote  Post ReplyReply Direct Link To This Post Posted: May/16/2022 at 11:16am
I think that it is important to look at specific AMC builds to determine your “solution”. Some may not need a solution at all. Reading between the lines, and then reading the lines of skilled engine builders and racers here is key. Some here are not listening well. 

LS is more similar to AMC oil than one might GUESS. 
Way better? By what account? There are reasons, I’ll conceit that. 
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