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

Mike T

Well-Known Member
#1
I'm doing a teardown because of blown head gaskets and I'm finding a lot of little things that I don't like.

I know the bearings look nasty in the picture but you really can't feel any of what looks like deep scores and scratches. The bearing on the left is as it came out of the motor and the one on the right has been hit with a scotch pad just to see what it would look like.

I see there is a bit of fretting on the top left that I need to deal with but check out the unusual pattern that didn't clean up with the scotch pad.

Is this pattern typical to crank twist?

IMG_1252.JPG
 

BEATAV8

The Engine Whisperer
#2
IMO I don't think so. The pattern at first glance seems a bit lopsided but looking closely you can see the wear is showing across as well and is actually quite uniform. Looks like the wear is just a bit heavy, maybe not a big deal if the motor has been running hard for a while. Fretting looks to me to be quite minor.

even if you know clearances from previous build, check them again. Maybe consider aluminum bearings like King bearings. They have always come out looking good in my motors.
 

Mike T

Well-Known Member
#4
IMO I don't think so. The pattern at first glance seems a bit lopsided but looking closely you can see the wear is showing across as well and is actually quite uniform. Looks like the wear is just a bit heavy, maybe not a big deal if the motor has been running hard for a while. Fretting looks to me to be quite minor.

even if you know clearances from previous build, check them again. Maybe consider aluminum bearings like King bearings. They have always come out looking good in my motors.

Thank you for the input.

The motor only has 10k on it since I built it but it's been run pretty hard the whole time. I spent a lot of time checking everything before I put it together and some things in the motor seemed to have held up excellent and few other things I'm less than pleased with or can't figure out what caused it.

When the head gaskets went it sent debris all through the motor and I expected to see deep scores from debris or maybe some cap alignment issues from having billet mains installed or even signs of detonation damage to the bearings.

The reason I asked about crank twist is because a search on our board returned a few discussions about it but no photos. Something is causing the # 3 main to walk a little and I would suspect that it's either the crank whipping around or I'm getting a little detonation that's not showing up in the logs.

I really do appreciate the input.
 

turbo89

Well-Known Member
#5
I'm doing a teardown because of blown head gaskets and I'm finding a lot of little things that I don't like.

I know the bearings look nasty in the picture but you really can't feel any of what looks like deep scores and scratches. The bearing on the left is as it came out of the motor and the one on the right has been hit with a scotch pad just to see what it would look like.

I see there is a bit of fretting on the top left that I need to deal with but check out the unusual pattern that didn't clean up with the scotch pad.

Is this pattern typical to crank twist?

View attachment 250753

you are correct in your question ... that is typical wear of crank twist and uneven loading

I would also look at the hone on the caps
 
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Mike T

Well-Known Member
#6
I think both of you guys (BEATAV8 and turbo89) are seeing what I'm seeing......my thoughts are that like BEATAV8 said the wear appears to be even when the crank is not being pushed really hard but as you see when it's under heavy boost is when this odd wear pattern is taking place.

I'm learning a little every day and hoping to understand more about our motors so that I can build better motors.

Thanks again.
 

turbo89

Well-Known Member
#7
I think both of you guys (BEATAV8 and turbo89) are seeing what I'm seeing......my thoughts are that like BEATAV8 said the wear appears to be even when the crank is not being pushed really hard but as you see when it's under heavy boost is when this odd wear pattern is taking place.

I'm learning a little every day and hoping to understand more about our motors so that I can build better motors.

Thanks again.

whats the backside of the bearing look like ? and chance of any debris on the backside ?
 

Mike T

Well-Known Member
#8
whats the backside of the bearing look like ? and chance of any debris on the backside ?

I'm treating this thing like a crime scene:) .... so I haven't even pulled the bearings out of the caps yet. I was very careful during assembly so I really doubt that any debris would have been trapped.
 

turbo89

Well-Known Member
#9
I'm treating this thing like a crime scene:) .... so I haven't even pulled the bearings out of the caps yet. I was very careful during assembly so I really doubt that any debris would have been trapped.

That's Great !!! Finally a thread without the standard "SHIP IT" mentality .... KUDO's !
 

Mike T

Well-Known Member
#10
I will say it is a little depressing to see how much debris went through the motor after taking so much time to keep it clean during the build. Check out the HG material on the pickup screen.


IMG_1218.JPG
 

turbo89

Well-Known Member
#11
I will say it is a little depressing to see how much debris went through the motor after taking so much time to keep it clean during the build. Check out the HG material on the pickup screen.


View attachment 250802

I agree depressing and some work for sure ... but in the end it will be RIGHT and will continue to give you the performance you would expect ...

Most guys would have just tossed new head gaskets ( some may even have only replaced the blown side ) and "SHIPPED IT " .. only to have something let go 500 miles down the road.

Bright side .. now you know what you have and you have the chance to correct it ... I applaud your attention to detail ! Kinda refreshing to see
 

Mike T

Well-Known Member
#13
I agree depressing and some work for sure ... but in the end it will be RIGHT and will continue to give you the performance you would expect ...

Most guys would have just tossed new head gaskets ( some may even have only replaced the blown side ) and "SHIPPED IT " .. only to have something let go 500 miles down the road.

Bright side .. now you know what you have and you have the chance to correct it ... I applaud your attention to detail ! Kinda refreshing to see

You may think this is dumb... but if you notice the motor is still upright like it was in the car and the reason for this is that I'm trying (maybe in vain) to keep as much of that garbage from around the rings until I can flush it out.
 

turbo89

Well-Known Member
#14
You may think this is dumb... but if you notice the motor is still upright like it was in the car and the reason for this is that I'm trying (maybe in vain) to keep as much of that garbage from around the rings until I can flush it out.

I don't think its vain at all.. but that's me.. I'm about as pedantic as they come and at the point your at .. I would invest the extra 3-4 hours and pull it down to a component level and inspect everything and re-assemble just for peace of mind.. but again that's me ...

I think that sometimes being meticulous is what contributes to why you see "AVERAGE" results and "UNBELIEVABLE" results :)
 

Nick Micale

Tech Advisor
Staff member
#18
From my experience that looks like crank flex, not twist?

Years ago when we first ventured into the 10's with a 109 block w/2 steel center caps, and a stock cast crank, this is the same pattern we found on the main bearings.

Even before we experienced this on the V-6, the big-block Buick V-8 crank had shown us this issue as well, and that crank being cast and longer, it was even more pronounced there.

At that time we had some connection to Buick engineers that helped in determining what was happening, and the big-block girdle was found to be required at 500 HP to solve this issue since no forged cranks were available for the V-8 Buick.

The crank is subjected to harmonic forces that look like a snake moving along the ground, and when they are pronounced like your's, the solution is to use a good forged crank at least.

After we installed the first Eagle forged crank, this issue was not seen again.
 

Mike T

Well-Known Member
#19
The crank is subjected to harmonic forces that look like a snake moving along the ground, and when they are pronounced like your's, the solution is to use a good forged crank at least.

That's kind of what I was thinking. What sucks is that I bought a JW flywheel and a BHJ balancer for my stock crank and had it all balanced to 36.6 in an effort to give the stock crank a chance. Now I will need to stick with an external balanced crank to fit the components that I've already bought.
 

Nick Micale

Tech Advisor
Staff member
#20
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?