This is sort of a second thread so apologize for that. The first thread was sharing a knock that developed in my freshly built 355 and all the sad I was feeling. This thread for the repair, looking for some advice and don’t think my other thread is titled right to get it.

I pull the pan, found #7 rod bearing took a beating but it did NOT spin the bearing. The crank journal looks OK, but has some bearing material deposited on it. That needs cleaning/polishing. To make things harder, I’m trying to save myself from pulling the engine. I’ve got the crank oriented for the 7/8 journal to hang low, rod caps off and pistons/rods pushed up the bore so I have room to work.

the questions are…

1) how to clean the journal. I’ve seen the videos of sand/emery paper with the shoe string. Seems feasible. What grits? Any way to keep the debris out of the oil galley?

2) do I need to mic this journal or should I be able to use a same size bearing? The crank was professionally machined (prior to this) and I verified clearances with plastigauge. I had 2 thou on all 8 rods. Is 2 thou still a reasonable clearance for this rod? Is plastigauge a good enough measure?

3) any reason to not use the same Clevite bearings? Is there something better or more forgiving to run on a maybe not perfect journal?


The banged up bearing and corresponding cap.

Looks worse in pic. Cannot feel with fingernail.

 

Although I had the convenience of doing it on an engine stand, I used 400 grit sandpaper with a shoestring. Checked clearances with plastigage and never looked back. Did you have detonation issues??? I ran mine with way too much timing and have backed it down since.

 

Thanks for input. It was a little lean in the top end which I sorted out, but never saw any detonation in the datalogs. I’m perplex why it happened and don’t think I’ll find a smoking gun. It did see just shy of 6400 rpm, but the bottom end is balanced with forged Scat rods, would’ve have thought ok.

What do you run for rod clearance? I was at 2 though, wondering if a little more would be better?

 

If the first bearing did not work I would be worried about using the same bearing again and hoping for a different outcome. I would sure make sure the oil is flowing to that bearing. Dan

 

It poured oil all over me through the galley when I removed the bearing shell. When you say different bearing, do you mean brand or size? I’ll definitely circle back around for input on bearings once I get the journal cleaned up. I was thinking of getting 1 new rod bearing to pop in and plastigauge just to see what my clearances are.

The bearings are Clevite CB-663P-30. The -30 indicate for a 30 undersize which is what the machine shop took off after the spun bearing that necessitated the rebuild.

 

This is just a stretch but there is a channel on Youtube where a machine shop was having issues with clearances. When they looked closer, the bearing in the box did not match the labeling on the box. It had been mispacked. Maybe check the numbers on the bearing if you haven't already.

 

Wait...so if there was oil trapped in the galley does that not imply that the oil was not flowing through the bearing?

 

Well I can’t say for certain, but I think once no longer under pressure between the shell covering the galley and surface tension, some oil stays in. This wasn’t the only journal that poured some oil when I removed the cap. About a teaspoon, right onto my sweatshirt.

 

I am not qualified to advise you what bearing to use. I would for sure shoot some high pressure air in that oil hole that shows in your photo. You are correct in using plastigauge to check the new bearing maybe in a couple three spots. Maybe the crank grinder got it a little oblong. Maybe try to mike it in a few spots. Also mike the rod in a few spots. Dan

 

Was this rod bearing the one that spun that required the rebuild or a different one? Dan

 

if it was me i replace all rod bearing and main bearings make sure oil pickup is tight run it for a couple hours and change oil and filter.

 

I got a new ZZ4 shortblock a few years ago, 880 block, forged crank, LT1 pistons/rods, 4 bolt mains. I contemplated pulling it apart and checking everything, but I didn't, should have. i did check the torque on the rods and on the mains, found a couple of them well under torqued (that would have been my first sign, second sign would have been the unacceptable manufacturing tolerances even as stated in the FSM).

Anyway, fast forward to 2023 and although the engine ran strong (340RWHP range on the Mustang Dyno) I pulled the pin on a fresh new engine project.

Pulled the engine, tore it down to the assembled short block, and the cylinders, pistons, all looked great. Sold the short block (cheap) and told the new owner that I recommend teardown/refresh just to inspect everything. He did that fortunately. Found lots of issues. #7 rod bearing was very tight and crank showed some heat distress on the rod journal, but it still had a smooth polished finish. The crank journal measurement however had a slight bit of taper, was slightly oversize, and a new rod bearing showed as very tight also, even with extra clearance bearing... the crank had to be re-ground for correct dimension, and all of the rods were freshened up (resized by a machine shop), new bolts. So the moral of the story is don't assume it was ever assembled correctly by GM in the first place, even with a perfectly running engine. Also found a broken piston ring that seemed like it was broken during installation! Didn't score up the cylinder though. Engine was torque plate honed, properly assembled, with optimal clearances, and it runs great again/still today.

For the crank, it needs to be measured and finished to a high polish at the minimum, and recommend all of the rod bearings changed, crank dimensionally inspected, and the offending connecting rod inspected for roundness and dimensionally otherwise (likely it was hammered larger than original spec). The reason for the more invasive crank inspection and rod bearing replacement, is the possibility of a similar condition with the other rods, and also the abrasive contamination caused by the failed bearing. Dimensionally, I'm not talking about plastigage, but 2-3" mic accurate to 0.0001" and recording taper, out of round, and checking against the spec. Leave that up to a professional if you're not proficient. Best advice is also to remove the engine, it's not much work compared to trying to do one bearing half *** under the car.

 

This is a different rod from the one that spun and necessitated the rebuild. I know pulling it out of the car is the preferred approach. However, I simply do not have that kind of time to invest in it. If the crank cleans up, I’m really looking to throw a new set of rod bearings in it. I hear what you are saying and know that my approach might not be what is considered “right”. I am contemplating getting the same bearing set and also a set that is -1 thousand so I can mix/match and open the clearance a bit.

 

I will let the experts chime in but if you were at 2 thousands before I sure would not open it up any. Dan

 

Just saying….I have previously installed new rod bearings on my c3 beater/drag car every year for a couple years because I didn’t want to commit the $$ to fixing it up right. Saw 125 wet shots too.
I knew my clearances were borderline too tight but I assembled it anyways….oil pressure was >80# cold start.

don’t know what kinda of use the car sees, rod bearings and oil pan gaskets are cheap and pretty easy to change. Double check clearances, .002-.0025 is good, if needed get an one thou extra bearing and consider thicker oil

 

Street car, does see a few spirited rips through the rev range on most drives. The failure happened while pushing very hard during tuning WOT and I think the 6400ish rpm it saw was the issue.

it has a std vol/pressure pump but it is the SharkTooth design and supposedly those output a little more because the angled tooth is longer and therefore moves more oil. Oil pressure was high, seemingly very high but I didn’t think much of it because the analog gauge in the dash isn’t all that accurate. Hot idle was around 1/2-3/4 and anything above idle was nearly pegged. Maybe this was the rods too tight? The old motor did register lower. 5w30 Mobil 1. I don’t intend on pulling the mains as that is getting trickier while the engine is still in car.

If the 1thousand rule per inch or journal applies, I need 21 thou clearance for ideal. The rod journals are cut 30 under, my thought was to use 1 each, a 30 under and 20 under shell, to see if I can get 24 or 25. Too much? I’ve read up to 30 can work but beyond that it’s a problem.

my concern is that though something went very wrong on #7, the other bearing shells do look a bit prematurely worn for such a young engine. Perhaps too tight.

 

That amount of damage in such a short amount of time is concerning. 5/7 are the last rod journal to oil on a SBC so if there is a problem it usually shows up there first.

Something is very, very wrong with the bearing clearance or oiling system. Just a little detonation or miss on the tuneup won't transfer bearing material to the journal like that. 0.002ish (or more) should have been fine on bearing clearance in your application... I run way more than that on my SBC race engines... While to 0.001 of clearance per inch of journal general rule applies.... There's an old adage about clearances in race engine building "If it's loose only you'll know, if it's too tight everyone will know.".... within reason of course. The more power you make, the heavier the parts, the more RPM and load... the more this stuff flexes and the more clearance you need.

What happened there is a break down of the oil wedge.... from lack of clearance or lack of oil supply is impossible for me to determine from here..... I can for 100% sure say that with that much damage to the bearing, there has been a ton of metal in the oil, even if the others were good - they will have debris damage.... as will the main and cam bearings. For this reason I would not polish that journal and roll new bearings in it... Piston skirts and pump gears/housing need to be inspected as well. Block should have the oil galley plugs removed and cleaned before installing new cam bearings and reassembly.

That crank very well may be saveable with just a polish but you'll have to measure it with a Micrometer to see where it is. If I remember correctly, this engine spun a rod before.... There may be underlying problem with that crank and replacing it entirely may be your best option... That one is already 0.030 on the rods and LTx compatible cranks are quite easy and inexpensive to source... not to mention with undersize bearings there is no way to adjust clearance sufficiently other than crank sizing.... With standard cranks sizes you have 0.001 and X STD bearings if you need to less/more clearance and you can safely half shell those to be dead perfect... You cannot half shell a 0.020 and 0.030 (thats 5 thou man, way too much).
Will

 

I hear what you’re saying. The time needed to go any further than cleaning it up and a new bearing just does not exist. I have a young family and the car has been a time vampire from them, let alone expense. I know it isn’t ideal, right, and is a risk. The bypass in the filter has a pipe plug so all of the oil is filtered, gives me some hope that the most damaging bits were captured.

the most I can assume is that I threw more revs at it then it could handle. It did have an oil pickup tube incident as well - about 6 months ago I dented the oil pan. It seemed minor, over the winter I pulled the pan and found it was enough to shift the pickup tube up. It did have some run time on it in this condition. The pickup should’ve still been well submerged and it was driven mild during this time. Never dipped pressure on the gauge. It received a new pan, pickup, and oil pump. Several months later (few weeks ago now) during hard WOT tuning is when the failure happened. Related, maybe. No way to know.

 

Why would you plug the bypass? That seems to be playing with fire. Dan

 

I liked the idea of 100% filtration. I didn’t think it was that uncommon to do. I will say, both the spun rod bearing that necessitated the rebuild and this last dinged bearing were with the oil filter bypass in the adapter plugged. I do run a good filter and I do let it come fully up to oil temp before it sees revs. Could this be my fail point? Looks like there is just 1 filter adapter on that auction site for a pretty dumb price.