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Help needed with cracked engine case

Bohnzye

CB750 Enthusiast
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Location
Lorain Ohio
Hey fellas, I dont want to bore you with details but this bike was pretty much dropped on my lap...The same bike I have posted about in this forum.. I have a bigger problem then orange peel. My buddy evidently didn't comb over this engine?bike before he bought it and today I discovered a "chunk" of the engine casing broken off/missing from the top side over the timing cover area and its part of the block not the cover..Subsequently some deviant took RTV silicone and filled that space and then greased it/dirtied it up good enough that an untrained eye wouldn't detect it. Well I'm no mechanic and certainly would have picked up on this as it's blatenly obvious. So the question looms, Do I have to start scouting for an engine case or just ride this bike on dry days because I'm pretty sure something is gonna fry if it gets into the timing compartment? 20120809_120505.jpg20120809_120509.jpg20120809_120502.jpg20120809_120505.jpg20120809_120509.jpg20120809_120502.jpg
 
This is the 78 cb750 correct? If it is just in the area of the points then mechanically it doesn't need to be changed, other then getting water into the points. Looks like it is on the bottom case half mostly? Looks like it was laid down and slid across the ground. If you can seal it up good enough to keep moisture out then you can run it as is assuming it didn't crack into the engine part and starts seeping oil. Remember if you decide to replace the cases you need a matched set (upper and lower half) you can't change just an upper or a lower, they are machined from the factory to go together. At least there are a ton of cases on ebay if you decide to change them.
 
since it is the case and not the cover, i would try cutting a small thin piece of metal to go over it,,stupid glue it on then work the edges with jb weld or maybe even just try working jb over the hole,or a piece of screen then jb. that is me though,, as long as it runs i would not tear it apart until i had to.
 
Thanks so much Digger and travlyr, What are weekends for anyways? Yes indeed, I will try the JB Weld as Paul Harvy never Lies.... My greater concern was being on a bike run and the weather changeing. Yes it is in fact a 78 cb 750 digger. It was my Uncles so I'm the second owner and passionate about its restoration. You fellas rock! :)
 
i hate rain and getting caught in it. if possible i head for shelter till it stops. if you are running points you can always dry them with paper or carry a can of air for keyboards in your bag to help dry them once it stops. i have been rigging and repairing on the road side forever it seems sometimes and there has been a lot things patched with wire,hoseclamps, cut up beer cans and jb weld .
 
Bohnzye, I would think that if you went the JB weld route it should hold up. Pull the point cover and see what it looks like up there. I would use a dremel and bevel the edges of the repair inside and out. Then clean them well so there is no oil around the repair area, feather the JB out in to the case metal, after it's dry you can blend it with one of the abrasive tips in the dremel kit.
 
Forgot to metion.... if you go the JB repair make sure you get all the RTV/Silicone off, or else your repair might fall off or in. get the lil' dremel with a mini wire wheel. if you think it's clean, clean it again!!
 
Happy Sunday Guys, Um, I think its Sunday? I just picked up some jb weld grabbed my dremel tool and will commence first think tomorrow. Thats a great idea Jbird. The wire wheel will give me the optimal contact surfaces and allow me to to get it super clean. I only want to do this once.... So much knowledge under one roof. Thanks loads fellas. Cheers.
 
oops, Sorry.. I was forced to do this repair in layers because of the thickness of the case section thats missing.. So far so good. Will do final layering tomorrow. High humidity where I work is causeing the curetime to go off the charts..:((( Grrrr Pictures to follow...
 
20120813_114709.jpgOk, Wonderweld< jb weld is the bomb... I need to do a little finish sanding but if you compare the original picture I posted to the picture of the fill in area its quite remarkable.. I guess if I was dealing with a hole things would have been much simpler but with a portion of a leading edge missing made it tricky.Anyways it's done and Im happy thanks much fellas..20120816_124733.jpg
 
very cool,i love home made repairs. jb is the bomb. back around 71 or 72 a friends brother had a hon 750 with a hole in the valve cover and he patched it with this new stuff that had just come out called jb weld. i have been a believer ever since.

as a suggestion,since the edge was messed up you may want to put a thin bead of rtv sealant between the outside of cover and the jb in the seam there.
 
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