CB750K question, Can I ask?

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Chang_G_Wing
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CB750K question, Can I ask?

#1

Post by Chang_G_Wing »

Ok so,I got a question about a 1974 CB750. I don’t know if we’re allowed or even if it’s cool to ask about other bikes but here goes. me and my buddy are tearing down a CB750K engine. We were just gonna replace a bunch of gaskets we got from Randakks. BBUUUT, we noticed that where the cam shaft sits on the second rocker assembly has been grounded down to a pulp. A pool of Metal shaving sat near. Wasn’t planning on splitting the case, but that may not be the case now. Do you guys think there shaving all inside the crankcase? And we should split it open now? Anyone with a tiny bit of knowledge would be helpful, thanks everyone.
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5speed
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Re: CB750K question, Can I ask?

#2

Post by 5speed »

never owned a 750 so my advice is worth exactly .02¢
Anytime you have metal shavings in an engine..you need to tear it down to the last bolt to check for more damage and to get it as clean as possible..
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tlbranth
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Re: CB750K question, Can I ask?

#3

Post by tlbranth »

You should pose your question here: http://forums.sohc4.net/
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desertrefugee
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Re: CB750K question, Can I ask?

#4

Post by desertrefugee »

In addition to the shavings, the issue suggests an oiling problem. If it was not a local issue specific to the cam, it could be an oil pressure issue that would mean other unseen areas of concern. I'd tear it down.
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low-side
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Re: CB750K question, Can I ask?

#5

Post by low-side »

A '75 CB750 was my baby for years. I'd tear that puppy down. There are almost certainly metal shavings throughout the case, and due to the likely oiling issue you may have issues with your main and rod bearings. To clarify, is the camshaft worn down or the camshaft holder?
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luludog
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Re: CB750K question, Can I ask?

#6

Post by luludog »

tlbranth wrote:You should pose your question here: http://forums.sohc4.net/
+1, good site with vast knowledge on the SOHC 750’s

Since you’re asking; I’d go through the engine. The camshaft cradles are aluminum with no bearing inserts. It’s likely one or both might need replacement. Search for root cause. Ensure the (2) oil restrictors, just below each cradle, are clean (very small holes). Along with cleaning the case and parts; make sure to disassemble the oil pump. Since it’s a dry sump system; be a good idea to clean the oil tank.

Good luck!
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1977 GL1000 - http://www.ngwclub.com/forum/viewtopic.php?f=30&t=40398
1975 CB750K5 - stock restoration http://www.ngwclub.com/forum/viewtopic.php?f=13&t=40426
1971 CB175K5 - stock restoration http://www.ngwclub.com/forum/viewtopic. ... 95&start=0
1972 CB350 - resto-mod cafe project http://www.ngwclub.com/forum/viewtopic.php?f=30&t=47429


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low-side
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Re: CB750K question, Can I ask?

#7

Post by low-side »

A lot of people preemptively heli-coil the 6mm threads in the block. While you have it apart I would check the cam and primary chain tensioners. If there's any question I'd do the chains as well. I also loctite the cam sprocket bolts. It's a bad day if one of those backs out going down the highway. Like Luludog said, good idea to clean out the oil tank. I'd also clean out the major oil passages and if it has an oil cooler I'd clean it as well.
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Lucien Harpress
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Re: CB750K question, Can I ask?

#8

Post by Lucien Harpress »

Doesn't look like it's been mentioned yet, but if you're going deep into the engine, get yourself a hand impact driver and a properly-sized JIS (yes, experts? JIS, right?) screwdriver bit for it.

I'm pretty sure you're motor is old enough to be one sewn together with 10,000 screws rather than bolts, and an impact driver is almost a must in this situation. It certainly helped on mine.

While you're at it, it's a great idea to replace the rubber pucks under the cam towers. They were known to leak, and while not an engine-killer, it makes the motor look like crap and the pucks are a PITA to replace otherwise.
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