Is this what crank twist does to the mains? (update)

[Mike T]

Just my preference, but an internal, or neutral, balance rotating assembly is better at higher RPM and increased HP since any harmonics from the crank are also transmitted to the camshaft via the chain, and this can also affect other valve train components?

I agree but at this point the Eagle 4140 external balanced crank seems to be the most cost effective option??

 

[fastblackracing]

Mike,I can certainly appreciate your level of enthusiasm and attenettion to detail, its a good thing and will help you to learn and get better-smarter-stronger. I have seen exactly this and at much worse levels on stock crank and stock block builds with steel caps that made enough power to run bottom 11"s to mid tens. I agree with nick that it is the crank flexing and also add That if there is any way to do the internally balanced crank upgrade you would be better off. I know you have some parts in hand but I would never advise a guy to to spend $ on the external stuff. Since that one bearing is showing some copper it was time to be freshened up anyway so no need to be too bummed about it. The last thing I can offer you is to inspect the area in the block from the main bolt thread pockets up to the main webbs REALLY GOOD and up to the cam bearing bores for cracks. When I was in your position with the stock stuff I lost two blocks due to this , one I found doing a gasket change and the other showed up at the race track, the oil pressure light flickered on and off a couple times, the crack had extended up to the number 3 cam bearing hole and the insert came about half way out letting the oil leak at a massive rate Im sure. One more pass would have been real ugly. keep us posted with your tear down proggress.

 

[BEATAV8]

This was very informative...thank you.

Sure thing man. Here's some better documents with additional failure modes and pictures:
http://kingbearings.com/files/Engine_Bearing_Failures_and_How_to_Avoid_Them.pdf

http://www.wilmink.nl/Clevite/Clevite_lagerschade_tech_info.pdf

 

[Mike T]

Since that one bearing is showing some copper it was time to be freshened up anyway so no need to be too bummed about it.

That's the crazy thing about those bearings...the one on the right looked just like the other (showing what looked like copper) but it went away with one swipe of a scoth pad so I'm a little unsure of what's going on there.

Thank you for the advice and I'll be checking all of those things.

BTW you had commented on a post that I had started about honing without torque plates (this motor was done without torque plates) and my finding were pretty close to what you said I might find.

 

[turbo96max]

Subd

 

[fastblackracing]

That's the crazy thing about those bearings...the one on the right looked just like the other (showing what looked like copper) but it went away with one swipe of a scoth pad so I'm a little unsure of what's going on there.

Thank you for the advice and I'll be checking all of those things.

BTW you had commented on a post that I had started about honing without torque plates (this motor was done without torque plates) and my finding were pretty close to what you said I might find.

do you know why it blew the gasket and what power level do you think your at? did not see it but do you run alky?

 

[Mike T]

The head gasket failure was a long time coming....this was going to be a budget build until the funds allowed me to do my stage II block (isn't that everyone's story). I was just going to re-ring it and put bearings in but I ended up doing what's in my signature.

Now to answer your questions....the reason I say that the head gasket failure was inevitable is that I never ran alcohol (intended to but didn't) or race gas. So after I first got the motor running I started to lean on it a little bit at the time and before I knew it the car was taking over 20 pound from the gtq 70 and my logs only show slight detonation after some long high gear pulls on the road.

I knew the car was pulling hard so I took it to the dyno where the best pull was around 450 on 93 only and 23psi (did a little thread on that). The long and the short of it is that the stock graphite head gaskets were being eroded away a little at the time under these high boost conditions and maybe in combination with a little detonation they gave up.

I've been looking the head gaskets over and trying to learn from them. What I see rather than a darn mess is that it wasn't just 1 cylinder that gave up and as weird as this sounds I was pleased to see that every cylinder was somewhat compromised and in my mind says that a/f was pretty close in all of the cylinders.

The tops of pistons are perfect other than burned oil that must have come since the hg failure ......the plugs always looked good (now black and oily). The #1 piston skirt has a slight scuff that I'll need to look at.

 

[Mike T]

I got this photo from a Camaro forum where they were discussing crank flex and unusual bearing wear patterns. The pattern looks very similar to what I have. There is a machinist/engine builder contributing to the thread that has seen this pattern often and states that crank flex is the cause. There are other explanations but to me his seems to make the most since.

I don't think this pattern would show up on aluminum bearings but the thin tri-coated bearings would show any small deflection of the crank by breaking through the micro layer.

I found the thread interesting and I'm surprised we don't see more of this pattern in our engines. http://www.camaros.net/forums/showthread.php?t=170780

 

[NY Twin Turbo]

I got this photo from a Camaro forum where they were discussing crank flex and unusual bearing wear patterns. The pattern looks very similar to what I have. There is a machinist/engine builder contributing to the thread that has seen this pattern often and states that crank flex is the cause. There are other explanations but to me his seems to make the most since.

I don't think this pattern would show up on aluminum bearings but the thin tri-coated bearings would show any small deflection of the crank by breaking through the micro layer.

I found the thread interesting and I'm surprised we don't see more of this pattern in our engines. http://www.camaros.net/forums/showthread.php?t=170780




View attachment 253533

Perhaps it's a little harder to twist a shorter crank?

 

[Mike T]

Perhaps it's a little harder to twist a shorter crank?

Could be ??

Nicks assessment seems to be dead on in the respect that the crank is moving around. Since finding this I've spoke with 3 different engine guys who know way more than I do and they all agree that the stock crank begins to distort. The funny thing is that they all described the distortion or movement in different ways. It was called "flex" by one, "whip" by another and "twisting up like a barbers pole" by another very sharp Buick guy. When this happens the center caps begin to "walk" causing fretting and eventually block failure.

The more I look at these engines the more it amazes me that some guys can make so much power with a completely stock bottom end. It's been said how tough these engines are but what I see is a weak POS that somehow stays together.

 

[bison]

I've seen that pattern on every stock crank engine I've had in my cars over the years. I've mentioned it in the past. The next thing you see is cracks running from the threads on the mains toward cam bore


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[fastblackracing]

Could be ??

Nicks assessment seems to be dead on in the respect that the crank is moving around. Since finding this I've spoke with 3 different engine guys who know way more than I do and they all agree that the stock crank begins to distort. The funny thing is that they all described the distortion or movement in different ways. It was called "flex" by one, "whip" by another and "twisting up like a barbers pole" by another very sharp Buick guy. When this happens the center caps begin to "walk" causing fretting and eventually block failure.

The more I look at these engines the more it amazes me that some guys can make so much power with a completely stock bottom end. It's been said how tough these engines are but what I see is a weak POS that somehow stays together.

I agree with you on this except for the crank flex causing fretting of the main caps. Any stock short block that has been run hard that I have torn down showed the main bearings to wear on opposite edges like the ones in the pics....... The fretting of the main caps comes from detonation in my opinion, not the crank......... However with that said you will usually see both at the same time since we tend to push our little buicks and run the balls off them........When I pulled apart a stage 2 block and forged crank that blew a head gasket the bearings looked fine and the main caps had fretting on them.

 

[Mike T]

Just my preference, but an internal, or neutral, balance rotating assembly is better at higher RPM and increased HP since any harmonics from the crank are also transmitted to the camshaft via the chain, and this can also affect other valve train components?

I bet swinging the big weights (balancer/flywheel) at each end of the crank plays a role in the flex as well. I may have my numbers wrong but I remember reading that 1/4 of an ounce (out of balance) on a 4 in stroke weighs over 30 pounds @ 6000 rpm.

 

[dank GN]

mine was really bad crack the block and a lot of fretting on the main from crank flex

 

[dank GN]

 

[WPP-Bill]

The fretting of the main caps comes from detonation in my opinion, not the crank.........

Agreed. Cast cranks are brittle and don't like to twist or bend - they often simply crack. If the detonation were to have continued, then a two piece crank or cracked block may have followed.

 

[dank GN]

I was showing no detonation with E85 . That was one of my first tuning mistakes I didn't add timing to at 28+lbs and my egts went through the roof and took my turbo out :-( . I'm feeling like I'm at the hairy edge with the stock bottom end . 510 to the wheel and 600+ ft.lbs

 

[84BuickGNYorkPA]

dank GN your build looks very close to mine, .040 over with forged pistons. To the point, my stock crank broke in half at 520 H/P to the tires.

Chuck

 

[Mike T]

dank GN your build looks very close to mine, .040 over with forged pistons. To the point, my stock crank broke in half at 520 H/P to the tires.

Chuck

Do you have pics of the bearings & crank?

 

[Mike T]

Quick update.....finally getting back to my own projects. Short block with the 4140 Eagle crank installed. Sorry for the blurry phone picture.