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Cracks on lower case

Andy

CB750 Addict
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Found this when I was cleaning and pressure washing this morning. I'm trying to decide whether or not to use it. I have another, but a quite a bit of work to replace. What do you guys think? Would the expansion and contraction cause this to open up enough to leak? It's on the front side of the oil pan below the starter.
oil pan.jpg
 
It will more than likely "weep" oil from it. I would replace it if you dont want to have an oily underside and drips on the floor.
 
Is that the CB450 engine? I don't recognize it. Can you tell that it is actually cracked and not just lines from the casting process where the aluminum comes together?
 
It is from the 450. There are two marks running out in a V shape from the top of the picture. I wondered if they were casting marks also, but I don't see them on my other engine. They are definitely hairline if they are cracks. I'm just worried they could open up as the engine warms up.

Sorry for the 450 stuff. This and the 650 site seem to have the most knowledgeable people I've come across.
 
No problem with the 450 stuff. All lot of tech stuff related to motorcycles is relevant to many different bikes... especially of the same vintage and brand. I tagged this thread "non-cb750".

I would inspect the area of the "crack" near that mounting tab (is that what that is?) and try to find the start of it. Maybe pry on the that tab a little bit to see if you can tell if it's really a crack or not. :shrug:
 
The biggest problem is it is the oil pan. It will always be in contact with oil or oil vapors so it will bleed oil over time. If you can put up with a little oil film and a couple of drips it would last for a long time I would think. Just my thoughts. I would replace it if it was mine because oil leaks are a pet peeve of mine.
 
Thanks guys. I'm going to mess with it some more tomorrow. Bottom line is I have another one, and the engine is already off. If it is a crack, now is the time to replace it. Probably just the cost of a gasket and some time. The problem I've been running into on these is the steel bolts tend to seize in the aluminum and twist off. I was hoping to not have to take the lower end apart. I guess it won't hurt to take it apart and inspect the crank. The motor only has 6000 miles so I'm hoping it's in good shape inside. And I hate oil leaks too.

I couldn't remember the "mounting tab" connecting to anything. It's right on the front of the bike. I found a pic of it in my Honda service manual and it doesn't connect to anything. It's got a reamed hole facing down. Maybe for location on a machining fixture. Another mystery.

I have my frame back from the powdercoaters, the new races installed and the new swingarm bearings installed. I'm anxious to get the motor back together and mounted in the frame. But it can wait another week or two.
 
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