what happened to these main bearings?

[ryan319]

this motor has 1500 miles on it. it started to have a knock last week so i pulled the motor. basically all of the mains are TRASHED. What would cause this? even the thrust bearing is wearing. the bearing in #3 seems like it doesn't even fit right in the cap. when the motor was rebuilt i put in a NOS standard crank and had the rods resized.

all the rod bearings have a little wear but #1 was pretty beat up compared to the rest.

until last week the car always had 75 psi cold oil pressure, 25 hot idle and 50+ while cruising. it has a high volume pump and the main bearing holes were drilled. i've changed the oil at least 3 times.

i had the car at the track last week for the this time and thought that it was getting a little knock (detonation) but now i think it was the bottom end knocking. i was only running 16-17 psi of boost with 60lb injectors, hot wire, and a walbro. i've never had detonation issues. my 02's were always around 800 at WOT and i have a caspers knock gauge. i haven't checked the fuel pressure climb lately but i did when i first put a bigger turbo on about 1000 miles ago and it was fine. and if the fuel pump would crapping i would have picked up knock before.

what happened?

 

[m233roller]

Looks like they were starved for oil or way to tight of clearance. All the fretting I see on the mating surfaces of the main caps, you've had LOTS of detonation. Those caps have moved around alot.

 

[ryan319]

Looks like they were starved for oil or way to tight of clearance. All the fretting I see on the mating surfaces of the main caps, you've had LOTS of detonation. Those caps have moved around alot.

what makes you think that it was detonating? i know there were detonation scars from the previous owner, before the motor was rebuilt. i've seen very little, if any knock since the motor has been back together. and my oil pressure was always good. so, could the motor have been too tight?

 

[m233roller]

Oh I see. I would have never put them back in with that much fretting on those 2 middle ones. Yup. Do you know what the main bearing clearances were set up at? Who did the new crank and rods.?

 

[ryan319]

Yup. Do you know what the main bearing clearances were set up at? Who did the new crank and rods.?

i don't remember exactly what the clearances were but i know that we tried several sets of bearings and even had the last set coated a little at swain tech to bring them into spec, somewhere in the high teens or .002. i looked at my build sheet and it's not listed and i didn't check them when i got it back from the shop, they were supposed to be right. i bought the crank from a board member and my machine shop did the rods and assembled the short block.

 

[m233roller]

my machine shop did the rods and assembled the short block. I think there's your problem?? Also Hi - volume oil pumps aren't the best way to go. The higher the pressure the less volume you get.

 

[ryan319]

my machine shop did the rods and assembled the short block. I think there's your problem?? Also Hi - volume oil pumps aren't the best way to go. The higher the pressure the less volume you get.

so you think it was too tight? my oil pressure always seemed good but not excessive. it was a little less than 25 at hot idle. that's about right isn't it? was running 10w30.

 

[m233roller]

Yes, I think your oil pressure is just fine but any shop that wouldn't bring those fretted caps to your attention. Who knows what they did??

 

[ryan319]

Yes, I think your oil pressure is just fine but any shop that wouldn't bring those fretted caps to your attention. Who knows what they did??

they did tell me about the signs of previous detonation but i don't recall them telling me that i should change the caps. if they had told to change them i probably would have because i was trying to build a solid motor, hence the NOS crank, coated bearings and pistons, cometics, arp studs/boltsm decked the heads/block, etc etc.

 

[pmoore4321]

What brand bearings?

 

[ryan319]

federal mogul and coated at swain tech.

 

[ryan319]

federal mogul and coated at swain tech.

actually they are sealed power. the same rods and mains that weber sells.

 

[jawort0]

Check the runout on the mains of the NOS crank you installed. It appears the crank might have been bent slightly in its lifetime before being installed in your engine.

A high volume oil pump makes higher pressure by shoving in a higher volume of oil through the engine.

If the caps have fretted, the original machining marks will be gone. I cant tell from the pics.

Joe

 

[pmoore4321]

I am running FMs as well and have about a 1K on the engine. I know it was mentioned on here that Clevites had a problem. My garage build will probably let loose at 1500 miles also.

 

[pmoore4321]

Check the runout on the mains of the NOS crank you installed. It appears the crank might have been bent slightly in its lifetime before being installed in your engine.

Joe

If the crank was bent, would you be able to turn the shortblock over by hand after assembly?

 

[ryan319]

if the crank was bent wouldn't they have figured that out when the rotating assembly was balanced?

 

[m233roller]

Iv'e seen some pretty badly fretted caps that still have the original machine marks on them. Why would they be gone? Fretting is caused by nothing but the crank moving, mainly from detonation.

 

[m233roller]

True Ryan,
The shop should of?? checked that all out. Doesn't look like a bent crank to me, more like BAD clearances.

 

[TurboDave]

If the clearences were in fact .002ish as the owner thinks, wouldn't that be far too much clearance, and not too tight as was speculated?

 

[Chuck Leeper]

My $.02...
Too tite. A couple "what if" scenarios are coming to mind............
1. Clearances were checked B4 the coatings were applied. [Statement indicates coating used to "adjust" clearances.] Machine shop assembled the engine w/o re-checking the clearances, thus the "too tite" problem.
2. The crush/parting line clearances appear to have been wiped out, indicating the main bores could have been knocked out of round by the previous encounters with detonation.[Obviously the block was not line bored, or else the fretting would have been milled off the caps]. Once the parting line clearance is gone, the edges of the brg shells become "oil scrapers", and remove the film off the crank. It's "down hill" from there....
If in fact, it was line bored, the owner statement of "no detonation" is in error, & Mike's assessment is dead on....
One can look at the underside of the pistons, ring groove clearances, rod bearings, plugs, and pretty well tell if detonation is the culprit. What do they look like?

Time to have a "prayer meeting" w/ the machine shop gooru....