The International CBX Owners Association

Hello everyone,

Last time I was on here I was wrapping up a top end rebuild on my 79 engine and chasing an oil leak. After I fixed that oil leak I changed the oil and found an alarming amount of glitter in the oil and material in the pan. Oddly, it looked like an assortment of material. Some of it was magnetic, most of it wasn't. It didn't really make sense to me so I cleaned the pan, put new oil in, ran it for probably a total of 30 minutes, and took the pan off to find pretty much the same thing.
I now have it torn down to bare cases and I haven't really found anything that would explain this. The engine has 19k miles and looks clean on the inside like it had regular oil changes. The cases had never been split before. It didn't have any issues or make any unusual noises. Nothing is broken or missing. The oil pump looks and measures great, it has a couple small scores but it made good oil pressure when it was running. The crank looks good and measures great, most journals are at 35.992mm. A few journals have some grooves, one seems pretty bad. Main journal 7 has a groove that I can catch my finger nail on.
The only other thing I found is some unusual wear on the con rod big ends. The wear on the bearings looked normal for 19k miles, but behind the bearings on the con rods themselves there's some wear or staining maybe. I can't feel any of it so I'm not sure if it's of any concern. On the cylinder 1 con rod there's a wear mark I can feel and it has a corresponding wear mark on the backside of the bearing and a corresponding dark spot on the bearing surface like maybe it was starting to overheat. I'm curious what're your thoughts on all this?

Did you check that rod for trueness, not bent, not twisted?

I haven't yet, it looked straight but of course that doesn't mean much. I'll have to figure out some way to measure it. Maybe line it up with the others. I know these are notorious for bending the number 1 rod and an impact like that makes sense for what might've caused that mark. This engine did eat a screw or something at some point, but that was cylinder 2.

If you did a top end only, you still get all the grit from the stud holes in the head and the studs themselves dropping into the crankcase, unless you take the utmost precautions. That's what the debris looks like to me. There has been some debris go through some of the bearings, probably not fatal though. Plastigauge all the bearings first. If the crank is out, verify all the oil passages are open.

I'd not be too concerned about the look of the bare rod journal - the bearing surface looks fine, pending clearance checking. The bearing clearly has not spun.

Overall, it is extremely hard to rebuild an engine and not be left with some debris that gets to the sump. This is why a couple of oil changes/sump cleanings are absolutely necessary in the first couple of hundred miles, or however many it takes to come up with a clean sump. Your amount of debris was somewhat more than I'd expect - it was hiding in there somewhere.

Dave

Mileage?

That was what I had originally thought and was planning to just keep changing the oil till it came out clean. I probably could have got away with that, but I wanted the extra security of a full rebuild.

I measured all the journals and used the Super Sport Shed bearing spreadsheet to figure out the bearings I need. When I get the new bearings, I'll plastigauge them.

Mileage is 19k.

Have you been able to take a good look at the debris in the pan and determine what it consists of?

I wouldn't just order all new bearings until I Plastigauged the ones you have. If they measure well within spec, there's no reason to change them. BTW - you do have the oil filter, spring and washer assembled in the right order?

Dave

Jeff Bennetts wrote: ↑

Thu Jan 02, 2025 3:20 pm

Have you been able to take a good look at the debris in the pan and determine what it consists of?

To the best of ability, yeah. I'd say Dave is right on, most of what was in the pan was a non metallic grit that probably fell off the studs. Pretty sure all the small debris and glitter in the oil was aluminum, it wasn't magnetic.

daves79x wrote: ↑

Thu Jan 02, 2025 3:26 pm

I wouldn't just order all new bearings until I Plastigauged the ones you have. If they measure well within spec, there's no reason to change them. BTW - you do have the oil filter, spring and washer assembled in the right order?

Dave

Good call, I'll do that. The oil filter is installed correctly.