Main Bearings Good Bad Or Ugly?

[RiverJeff]

Alright guys interesting think tank session.

Im tearing down my 572 BBC with the intention to increase compression from 9.8:1 flat top pistons to 11.25 or 11.5:1 domes. This also gives me the opportunity to check out the health of the motor I built in 2019.

Question for the group. The rod bearings look brand new (see pics). But the main bearings look to me like they have accelerated wear. It’s consistent across the mains, no major debris, no side load, but worn past the babbet.

What do you think? First is it a problem? If it is what caused it? I’ll check clearances next. The confusion for me is the rods (priority main block) look brand new!


Max (dog), my garage intern didn’t do the bearing check so don’t blame him…

 

[obnoxious001]

Rear main is destroyed, which of course sends material through the rest of the engine. Photos of the rod bearings are not clear enough for me to say for sure.

Please shoot photos of the thrust surfaces on the rear main bearings. Pair them together and show me both sides.

 

[Romans9]

You‘re gonna need a crank.

 

[Instigator]

The mains are toast.

 

[RiverJeff]

You guys are quick! Got me diggin more which is great.

Here’s pics of the thrust bearing, mains, and rods.

Not to create a spoiler alert but this got me deeper into the build.

History: this motor had an oil issue and spun main & rod bearings. It was communicated the journals for mains and rods were ground 20 under. The bearings in there now are 0.020” oversized main and rod.

I just threw a caliper on the journals and I’m getting .010 under rod journals and .005 under mains.

With .020 bearings could we be looking at “self clearanced” mains?

 

[obnoxious001]

No such thing as a .005 under main, unless it's been ground away by grit in the engine, are you sure you are reading the mic correctly? Or, are you measuring a damaged journal? .020" bearings would not let a .010" crank spin, it would lock up when the main bolts were torqued. What number are you getting for the mains? Are the rod bearings .010"? I didn't see a photo of the back of them?

Crank thrust appears to be damaged. That could have started the problem assuming clearances were anywhere close to being correct. How much crank thrust did you measure when you put it together? It's been a long weekend, not trusting myself looking at these photos since one click of the enlarge button makes them huge, no in between, and I am looking on a 50" screen.

Where are you located? No one out here by me grinding cranks, but there are some places in So Cal.

 

[obnoxious001]

You guys are quick! Got me diggin more which is great.

Here’s pics of the thrust bearing, mains, and rods.

Not to create a spoiler alert but this got me deeper into the build.

History: this motor had an oil issue and spun main & rod bearings. It was communicated the journals for mains and rods were ground 20 under. The bearings in there now are 0.020” oversized main and rod.

I just threw a caliper on the journals and I’m getting .010 under rod journals and .005 under mains.

With .020 bearings could we be looking at “self clearanced” mains?

Calipers are only valid for a rough measurement on the crank. Your mains are chewed up so you can only get a rough measurement anyway. By the way, the rod bearings are definitely not looking "brand new", debris has run through them as well.

Who did the measuring and assembly?

 

[RiverJeff]

Agreed on the calipers verity in measurement. I’ll get the Mic’s on them next.

I’m in So Cal.

Good point on the 0.020” (or .015” small) wouldn’t let the crank spin once torqued. I’ll get a better measurement to confirm.

In there now are 0.020” oversized bearings both rod and main.

The question is where are the journals relative to the bore size (main & rod). Rods didn’t have excess wear (yes some gouges but I’m also not building in a clean room so maybe that lost piece of sand I was looking for).

Mains obviously had a problem. Sounds like we’re in agreement that it’s a set up problem not oil pressure. I’ll confirm all the measurements next. Pfaff Bacca Marine helped with the set up, I’ll give them a call too, to see if they can help.

 

[RiverJeff]

Okay internet you guys were right. I pulled out the mic’s and the journals are .020” under so correct bearings.

Where would you look next? If it was an oil pressure issue wouldn’t rod bearings look this bad too?

 

[HST4ME]

When the crank was ground the radius on the journal probably wasn't held correctly and/or the thrust surface was opened up.

 

[Bajastu]

By tearing it down now, you just saved yourself from a catastrophic failure. I too say your end play was way off and it roasted the thrust. The material made its way through the rest of the engine and started the downward spiral on the rest of the bearings and components. My vote would be improper crank grind.

At .020 on the crank, I’d say it’s time to replace it.

 

[Malibuvride07]

For what it’s worth our almost 17:1 alcohol motor in my modified would use up mains way sooner than rods. For us the biggest issue had to deal with methanol wash down creating lower pressure before the motor made heat and burned the alcohol out. Dad used to trip out cause as a driver I could tell him when mains were needed before it tore up the motor. Saved all but two motors throughout 9 years of racing that way .
Now not likely your cause at that low a compression but just a statistic as to how mains can wear fast than rods. But the real motor guys on here already gave some clues as to look for and appears you’ll be looking for a new crank. Good luck with your build.

 

[obnoxious001]

Where would you look next? View attachment 1346397

I suggest you go back up and read a couple of my posts where I asked who did the measuring, and how much crank thrust there was at assembly. Then look and see if something was jammed up in the driveline. It takes very little pressure to push the crank against the thrust bearing and cut off oil to that side of the thrust surface, which will end up destroying the bearing. I have a couple of bearings I saved that both had known thrust issues.

 

[Bajastu]

One question; what’s the drive propulsion, JET, V-drive, or I/O ? Just curious if it’s a V-drive with a trans or a velvet drive.

 

[obnoxious001]

One question; what’s the drive propulsion, JET, V-drive, or I/O ? Just curious if it’s a V-drive with a trans or a velvet drive.

I think any of them might take out a thrust bearing under the right circumstances, that's what I was sort of leaning towards. Other thing is, was the correct .005-.007" thrust set up during assembly, no answer on that yet.

 

[RiverJeff]

I think any of them might take out a thrust bearing under the right circumstances, that's what I was sort of leaning towards. Other thing is, was the correct .005-.007" thrust set up during assembly, no answer on that yet.

Appreciate the good feedback guys. This is in a jet 21' Daytona.

I set up the mains back in 2019. The thrust would have been set to spec, actually I think that's why the front thrust bearing surface is ground down a bit to set up correctly.

I went on a deep dive into my records for more history on this motor set up. I was having an oil pressure issue early on from a Milodon pan that allowed the oil to get whipped up and aerate. I switched to a Dan Olson pan which solved the issue but not until I had a season on the other pan.

Im wondering now if the aerated low oil pressure coupled with a season of run time could have wiped out the mains, then new pan solved the oil pressure, but damage done on the bearings.

 

[poncho]

Appreciate the good feedback guys. This is in a jet 21' Daytona.

I set up the mains back in 2019. The thrust would have been set to spec, actually I think that's why the front thrust bearing surface is ground down a bit to set up correctly.

I went on a deep dive into my records for more history on this motor set up. I was having an oil pressure issue early on from a Milodon pan that allowed the oil to get whipped up and aerate. I switched to a Dan Olson pan which solved the issue but not until I had a season on the other pan.

Im wondering now if the aerated low oil pressure coupled with a season of run time could have wiped out the mains, then new pan solved the oil pressure, but damage done on the bearings.

The guy's here know way more than me but this subject came up this morning on FB. I have the Milodon pan and when I built my stroker motor I didn't realize I needed to take a quart of oil out for the longer crank throw. Luckily it was one run down a lake and I dropped to idle and saw my oil pressure drop to 10 pounds.
I was thinking heat related so I drifted 10-15 minutes before I restarted it, oil pressure was back.
For some reason that pan is called 10 quarts and really should be filled with 9 quarts and 8 with a stroker.

 

[RiverJeff]

The guy's here know way more than me but this subject came up this morning on FB. I have the Milodon pan and when I built my stroker motor I didn't realize I needed to take a quart of oil out for the longer crank throw. Luckily it was one run down a lake and I dropped to idle and saw my oil pressure drop to 10 pounds.
I was thinking heat related so I drifted 10-15 minutes before I restarted it, oil pressure was back.
For some reason that pan is called 10 quarts and really should be filled with 9 quarts and 8 with a stroker.

Oh trust me I about got committed to an insane asylum over this. More oil, less oil, different weights .... I could never get this pan to work with my set up. that 4.500" stroke was just too much. It's now living happily in a different 496 build and has never had issues in that with 4.250" stroke.

 

[obnoxious001]

Appreciate the good feedback guys. This is in a jet 21' Daytona.

I set up the mains back in 2019. The thrust would have been set to spec, actually I think that's why the front thrust bearing surface is ground down a bit to set up correctly.

I went on a deep dive into my records for more history on this motor set up. I was having an oil pressure issue early on from a Milodon pan that allowed the oil to get whipped up and aerate. I switched to a Dan Olson pan which solved the issue but not until I had a season on the other pan.

Im wondering now if the aerated low oil pressure coupled with a season of run time could have wiped out the mains, then new pan solved the oil pressure, but damage done on the bearings.

Is there a windage tray under the oil in the pan in that photo? Level needs to be set so oil does not sit on top of the tray.

Some of the Milodon pickups use a perforated metal instead of actual screen. I don't like that type pickup and would usually use something else that allows more flow.

 

[lbhsbz]

2 things...

1: Do you have sufficient slip yoke clearance on your driveline? I set mine up pretty tight one time (about .030") and with hull flex, the pump was leaning on the back on the back of the crank and wiped out the thrust surface and bearings

2: While not really visable in the bearing wear, I'd bolt the main caps back on with no bearings and bore gauge them towards the rear and the front of each main bore. I've had one that was line honed, and the shop failed to properly clean things before torquing the caps down, which resulted in the rear main cap being sitting at an angle when it was honed, consequently I had about 0.007" of clearance at the rear of the rear main bearing and about 0.002" at the front....but about 0.004" right in the middle where I originally checked it, which I was happy with.

I'd also throw the crank on some V-blocks (you can make some out of scrap plywood with a jigsaw) and measure radial runout on the 3 center main journals....see if it's bent.

 

[RiverJeff]

I’m back and with some answers!

Took the motor down to the block and brought the rotating assembly to my machine shop for some detective work. After reviewing the current set up and build history I think we found the culprit… damn owner messing things up!

In 2016 I spun a main, apparently these need proper oil flow, ‘don’t cross the streams’ ie oil cooler lines. The machine shop then ground the crank .020 under on mains .010 on rods also main line bore/hone .005. They set up the main bearings in 2016 with half shells for proper clearance (foreshadowing).

Engine ran but I had a consistent oil pressure issue at high RPM. In 2019 I solved this to be the Milodon oil pan not having enough windage protection. In 2019 changed to Dan Olsen (great ever since). But at that time had excessive main bearing wear caused by the low pressure with RPM. So when the pan was swapped so too were the main bearings. Still 0.020 undersized but I was unaware of the half shells.

Fast forward to 2024. I’m rebuilding this 572 to increase power and find the mains are shot! Turns out not enough clearance due to “standard” 0.020 undersized main bearing install back in 2019.

So Sherlock, we’ve solved the mystery! (Hopefully)

Now for the fun.

Crank was re-polished, machine shop set up mains and rod clearances (I verified with mics), cylinders honed, ready for new stuff.

Build list:
AFR 385cc CNC heads
RaceTech custom 11.4cc dome
Final compression 10.38:1
Bill Mitchell Racing intake
Quickfuel 1150 dominator carb
Isky Solid cam 668/671 lift
A/B impeller

Build started this week… stay tuned hope to get a few runs in this year!

 

[mattyc]

I’m back and with some answers!

Took the motor down to the block and brought the rotating assembly to my machine shop for some detective work. After reviewing the current set up and build history I think we found the culprit… damn owner messing things up!

In 2016 I spun a main, apparently these need proper oil flow, ‘don’t cross the streams’ ie oil cooler lines. The machine shop then ground the crank .020 under on mains .010 on rods also main line bore/hone .005. They set up the main bearings in 2016 with half shells for proper clearance (foreshadowing).

Engine ran but I had a consistent oil pressure issue at high RPM. In 2019 I solved this to be the Milodon oil pan not having enough windage protection. In 2019 changed to Dan Olsen (great ever since). But at that time had excessive main bearing wear caused by the low pressure with RPM. So when the pan was swapped so too were the main bearings. Still 0.020 undersized but I was unaware of the half shells.

Fast forward to 2024. I’m rebuilding this 572 to increase power and find the mains are shot! Turns out not enough clearance due to “standard” 0.020 undersized main bearing install back in 2019.

So Sherlock, we’ve solved the mystery! (Hopefully)

Now for the fun.

Crank was re-polished, machine shop set up mains and rod clearances (I verified with mics), cylinders honed, ready for new stuff.

Build list:
AFR 385cc CNC heads
RaceTech custom 11.4cc dome
Final compression 10.38:1
Bill Mitchell Racing intake
Quickfuel 1150 dominator carb
Isky Solid cam 668/671 lift
A/B impeller

Build started this week… stay tuned hope to get a few runs in this year!


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Looking good! Nice job getting to the bottom of your main bearing problem, good documentation goes a long way

 

[RiverJeff]

With the motor going back together I’ll turn this a bit more into a build thread.

Cam timing question for you guys. Isky solid roller card attached. This is a custom grind from them set up for a 21’ Daytona with an A/B impeller max rpm 6,500.

That was made for the last build, flat top lower 9.0:1 compression and iron heads. Hoping for a bit more power with new heads and dome pistons 10.38:1 compression.

I’ve degreed the cam straight up (dot to dot) and it matches the cam card.

The question is do I advance, retard, or leave it from here?

If we’re going to make more power but same limit on the A/B impeller does it make sense to advance the cam to shift the power curve down a couple hundred rpm? I have no experience with this and am leaning toward listening to ISKY with their initial advice to set straight up. Anyone play with this?

 

[mattyc]

With the motor going back together I’ll turn this a bit more into a build thread.

Cam timing question for you guys. Isky solid roller card attached. This is a custom grind from them set up for a 21’ Daytona with an A/B impeller max rpm 6,500.

That was made for the last build, flat top lower 9.0:1 compression and iron heads. Hoping for a bit more power with new heads and dome pistons 10.38:1 compression.

I’ve degreed the cam straight up (dot to dot) and it matches the cam card.

The question is do I advance, retard, or leave it from here?

If we’re going to make more power but same limit on the A/B impeller does it make sense to advance the cam to shift the power curve down a couple hundred rpm? I have no experience with this and am leaning toward listening to ISKY with their initial advice to set straight up. Anyone play with this?

I'm no expert here, but advancing the cam is going to increase cylinder pressures. You're increasing cylinder pressure already with the increase in static compression. Are you planning on running pump gas? I would think leaving it straight up would be the better option. Hopefully someone can confirm or deny this.

 

[obnoxious001]

With the motor going back together I’ll turn this a bit more into a build thread.

Cam timing question for you guys. Isky solid roller card attached. This is a custom grind from them set up for a 21’ Daytona with an A/B impeller max rpm 6,500.

That was made for the last build, flat top lower 9.0:1 compression and iron heads. Hoping for a bit more power with new heads and dome pistons 10.38:1 compression.

I’ve degreed the cam straight up (dot to dot) and it matches the cam card.

The question is do I advance, retard, or leave it from here?

If we’re going to make more power but same limit on the A/B impeller does it make sense to advance the cam to shift the power curve down a couple hundred rpm? I have no experience with this and am leaning toward listening to ISKY with their initial advice to set straight up. Anyone play with this?

I've dealt with Iskenderian quite a bit, ranging from a long time ago and starting up again the past couple of years when my small shop cam grinder friend was not able to buy roller blanks. That being said, I would probably follow their advice, but unfortunately this year we lost Ron Iskenderian whose personal cell phone number I had when I wanted to check something.

Normally speaking with most camshafts I will advance the cam at least two degrees to allow for timing chain stretch. Advancing the cam does move the power band down.

 

[RiverJeff]

Well decided to trust the pros at Isky and set up dot to dot. May mess with impeller size and cam combo down the road depending on performance.

Here’s some of the shots going together.

Now, who knows a good place So Cal adjacent to run on a dyno without breaking the bank?

 

[the deep]

Are those AFR 315's? Lookin' good!

 

[RiverJeff]

Are those AFR 315's? Lookin' good!

Thanks!! AFR 385cc went for the big dogs!

Definitely not maxed out with the current cam. Spoke with ISKY on that and the limiter is the A/B impeller. Bench racing the idea of swapping the impeller in the future and increasing the cam size to maximize the head flow. For now see how much power we have with the current cam...

 

[28Eliminator]

Thanks!! AFR 385cc went for the big dogs!

Definitely not maxed out with the current cam. Spoke with ISKY on that and the limiter is the A/B impeller. Bench racing the idea of swapping the impeller in the future and increasing the cam size to maximize the head flow. For now see how much power we have with the current cam...

That seems like an awful big Port for a 6500rpm N/A engine? have you tried this combo before?

 

[Rennsport]

With respect to dyno services consider Randy Aase at Aasco in Anaheim. Super guy!