Topic: I found the oil leak....CRAP!

[Hotwheelbill]

Last project purchase a few months ago. 1975 CB750 that I thought I picked up cheap with a transmission problem. I had a little extra time today and pulled the chain guard cover. I think I found my problem to both the oil leak and transmission problem.

[calj737]

Some see a problem, some see an opportunity. 

[Hotwheelbill]

Thank you for that. But I have my other 1976 CB 750 GSXR conversion that I have been working on. I was going to let this once it until I can get to it but I don't think this is something I want to conquer. So it will be on the for sale and/or Parts section sometime in the very near future.

[754]

 It can be done in a few days,if you get another set of cases and gaskets.
 Those can probably be fixed... I can cut out pieces if you are missing them..

[ekpent]

For others looking at a purchase in the future its a good idea to check that area out. Two screws and an impact can save some heartache down the road.

[markreimer]

My 74 750K had a hole in the same place. A thin patch was welded over. That was before I bought it, and about 25,000 miles ago at least. Fairly common injury I think. 


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[PeWe]

First area to inspect when buing a CB750, bike or engine only. If the bike has been driven like that, check for sand inside. Pull engine and clean it.

I have read about guys patching it with JB weld. A good alu weld is a better start, though. Or find a new set of cases. Check the letters at front and you'll might find same letters so you can have same crank/bearings if good. I got an extra K2 cases with same as my K6, BBBBB.

[754]

Once you weld up and fix your first set of cases, you can truly run wide open without worrying...well maybe not Biily B..but most of us..

[lrutt]

looks like a job for a thin sheet of metal and JB unless the rest of the motor needs a refresh.

[Don R]

 A trans problem requires engine removal most of the time anyway, There is surely a cheap case or engine somewhere near you.

[Duanob]

I think I'd just look for a decent used motor. With hole like that who knows if the engine was run without enough oil, there will be other problems like worn bearings, cam journals, etc. It will probably need an entire rebuild with bad cases. But that's just me.

[markreimer]

Here's a photo of my 'discovered' repair. My chain was eating into the patch from the looks of it, I think when the tension wasn't set properly. Thankfully I discovered this shortly after I bought the bike (I could hear the chain hitting the case), which taught me to make sure the chain tension was right all the time. Never had a problem since then. I don't know if this case was split to do the repair as I've never been inside the bottom end, but it sure doesn't look like it was.

[754]

The best motor to do your firsr rebuild on, is one where you got nothing to lose.
Even buying a parts motor, and reassembling everything, with a bit of freshening up, is a tremendous learning experience .

[markreimer]

The best motor to do your firsr rebuild on, is one where you got nothing to lose.
Even buying a parts motor, and reassembling everything, with a bit of freshening up, is a tremendous learning experience .

This!! I second that entirely. I know SO much more about my 750 after doing a top-end build. And now I've got a complete parts engine that I'm going to use for a 'trail' bottom end job.

[Hotwheelbill]

When I bought it, it would not go past 3rd gear, it would just to into neutral after third. From what I have read, it will need a tear down. As you can see, the bike has not been maintained very well, but it does run OK. The air shocks out back are odd, but I kind of like them. But the bike is complete and titled.
I may drop the pan and take a look. Not above JB Weld! It has saved my ass many times before.

[Stev-o]

I think I'd just look for a decent used motor. With hole like that who knows if the engine was run without enough oil, there will be other problems like worn bearings, cam journals, etc. It will probably need an entire rebuild with bad cases. But that's just me.

Not just you, Duanob.  A spare motor could be swapped out in a few hours...

[Hotwheelbill]

I don't see me or anyone else patching or rebuilding this engine case. Take a look behind the sprocket.

[markreimer]

I wouldn't write the case off so quickly personally. You can see my case pictured above had an equal size hole punched clean through the case, transmission exposed just like yours. Can be done.

..Of course, it might be easier to find a donor engine to drop in. That's what I did this summer when I cracked my main oil galley on the case and didn't want the hassle of splitting the cases to weld it back together. 

[Hotwheelbill]

I wouldn't write the case off so quickly personally. You can see my case pictured above had an equal size hole punched clean through the case, transmission exposed just like yours. Can be done.

..Of course, it might be easier to find a donor engine to drop in. That's what I did this summer when I cracked my main oil galley on the case and didn't want the hassle of splitting the cases to weld it back together. 

But what is behind the sprocket is a crack in the lower engine case as well. I suspect it goes down to the sprocket shaft but I will not know until I pull that off. So this involves the upper and lower cases.

[markreimer]

Oh! I didn't notice that, ah...not so simple then. Bummer dude.

[calj737]

Upper and lower cases are matched, so ditch one and you buy a whole set. I think that area behind the sprocket will buff out 

Bill Benton in Alpharetta, GA probably has cases or a spare motor if you're seeking.

[754]

Often its both cases, if only one that a bonus, much easier cheaper, and easier to get it flat.
Easier if you have the chunks.... If not , I have one i could cut.

Often they are fixed for sentimental reasons or to keep correct cases in the bike.
To some it matter, others not. If you live in a registered by motor state, big incentive to fix.