The International CBX Owners Association

I've got my 79 CBX all put together finally after a top end rebuild and it started right up with only one issue. Oil is running down one of the studs at an alarming rate. I'm fairly confident it's leaking past one of the copper washers (I didn't replace or anneal them ). Lesson learned, but thankfully it's just the one. I'm thinking I could get away with taking off the upper motor mounts, unbolting the valve cover and propping it up, and just sneak a socket in there and replace that one washer. It's one of the front 8mm studs near the cam chain. Is there no harm in that or is there something I'm not considering?

Leaky studs are usually a slow leak/dripping.
Gushing indicates oil pressure.
Check to make certain that the oil line on the back of the head isn't your problem.

That makes sense, the issue is it's at the front of the engine so it's not that oil line. I have no clue where it could be coming from if it's not leaking past that copper washer. You're absolutely right though, it shouldn't be leaking that bad if it is.

Oh, my bad. I see what you're saying, it 100% is the oil line at the back. I forgot the cylinders are open to the back of motor. Nice, that shouldn't be too difficult to fix. Thank you for the input.

I ran it some more and now I'm not so sure. I watched the oil line while it was running and didn't see anything and it appears dry. I wrapped a paper towel around the bolt and that came up dry as well. The oil started coming around in-between the head and cylinders on the left side of the bike now as well. I think this might rule out any of the studs leaking. I'm thinking maybe the oil line itself developed a leak. That oil on the ground was from running it for 2-3 minutes so it's a pretty serious leak.

I used a bore scope and I found the leak, it is from the head gasket at the back of the cam chain gallery. I saw oil gushing out of from there while the engine was running. I can't really wrap my head around how that's possible. Hopefully when I tear it back apart it will be evident what happened.

Bummer!! Good luck.

If you are positive that's where the oil is coming from, then proceed, but that's pretty rare. Honda issued a bulletin in '79 (thanks Terry!) about resealing all the rear cylinder studs due to porous castings. I had one recently that took forever to find. It was the right rear center stud. The bottom of the 'blind' stud hole had a void straight through to a main bearing journal. Pressurized oil was being forced up the stud threads. So check out everything before you tear the engine down. Spray the area clean and dry with ether, then watch carefully. You can sprinkle baby powder around the area and see where the oil first appears also. Alternately, there is dye you can put in the oil, then use a black light flashlight to illuminate the oil. Good luck!

Dave

Just an observation, If you look closely at the last picture just left of the 1047 stamp on the cylinder head and just above the lower portion of the cylinder head, it appears the the cylinder head stud is broken?? Check this out closer.
Mike

I would agree, Mike. Good eyes.

Side comment: With respect to Dave's post above regarding porosity, that's why you don't want to eceed torque specs with these engines -- porosity!!! Believe me, doing a timesert or helicoil is not a fun thing. If it went together at Honda it was with DRY, CLEAN threads at nominal torque. Those numbers didn't come off a dart board.

I started tearing the bike apart and I learned some more about what was happening. I didn't realize the inner rear studs aren't fully
enclosed in the head so now I'm certain the oil is running up the inner right rear 8mm stud, the same one you mentioned. Only that stud and the one in front of it are wet and they aren't wet all the way up which rules out oil leaking down. Good news though, I was thinking I was going to be pulling the head off tomorrow. When I installed the head, all of the head nuts torqued down just fine so I don't think the stud is pulling out and that other stud doesn't appear to be broken. I torqued them to the lower number in the specified torque range. I'll have to try and pull the stud tomorrow, clean it and apply some thread sealant.

I had the exact problem and merely thread sealant did not fix it. As I mentioned above, the bottom of the blind stud hole had a void that extended the whole way to a main bearing journal. Pressurized oil was being forced up the stud threads. I had to JB weld the bottom of the stud hole. then seal the threads. It worked, but it took removing the top end 5 times to find it. You are probably going to be stuck removing the whole top end down to the case to fix it.

Dave

I followed the instructions outlined by Ross in the "Crank case to cylinder block oil leak" thread and after a couple days of letting the thread sealant cure, I went out and started the bike. The leak didn't go away, though it did get better. It took longer for the leak to start and it leaked about half as fast. I got my bore scope out and I noticed that the bottom of that rear stud is dry now, but it is still wet where the stud meets the bottom of the head. I could see oil actively pooling on the stud there as well. I couldn't get an angle on the stud above the head gasket so I'm not 100% sure where it is leaking. I think the only possibilities are at the head gasket or at the copper washer, but I'm leaning toward the copper washer. When I took the stud out I tried to anneal the copper washer with my stovetop, but it didn't get it nearly hot enough. I'll have to get a torch and try again or get new ones.

I coat both sides of the copper washer with Hondabond, just to be sure. (Belt and suspenders).

I had it all apart again and decided to replace the washers on the oil line to the head. This ended up fixing my oil leak. In the end, it makes the most sense that this was the cause of the leak, but somehow I was never able to catch it in the act. Thanks everyone!