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To Crack Open the Engine Case or Not??

750chick

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Hi All! Newbie to the moto world and first time poster.. I own an '81 cm200t and a '74 cb750K. I want to learn as much as I can and I'm definitely not opposed to jumping in there and getting my hands dirty.

I'm currently working on the 750. Everything has been disassembled, frame has been powder coated and I am starting to reassemble. Now, I'm looking at the engine wondering what to do next. When I bought her, she sounded great, no leaks, and no smoke. I want to repaint the engine and make her look real good.. I'm thinking that since I have the engine out of the frame that I should disassemble further in order to get a much cleaner outcome.

So, while I was getting a new title I learned that I actually don't know the mileage on the engine since the current odometer reading was lower than the recorded mileage on the previous title... and since I'm trying to do such a big rebuild, I figure that I should tear her down, inspect as much as I can, and replace anything that needs replacing. However, let's keep in mind that money doesn't grow on trees and even if I crack her open I won't really know what I'm looking for. Yes, I have a manual and I've done a lot of research (and will continue to do so), but I want to know if I should make more trouble for myself. Any and all advise is GREATLY appreciated. Thanks!!
 
I would say don't do the engine yourself if you have never dealt with engine internals before. There are things you have to watch for when tearing apart and assembling. You will have to have tools to accurately measure and accurately torque the bolts. If you tear apart you will at a minimum need new gaskets seals and new piston rings. If anything in the cylinder head is worn you will have to send it off to a decent machine shop for a rebuild, same goes if the cylinders are worn. Assembly can be troublesome especially without help and if you have no experience with motorcycle engines. Unless you can find someone that has dealt with motorcycle engines I would say you should not tear into yourself. just my honest thoughts.
 
Thanks dirtdigger! I heeded your warning and held off on opening the case... then I called a buddy of mine who has owned and worked on many 750s (in addition to many other bikes). He's able to help/supervise. And sorry, I should have mentioned in my original post that I have a digital caliper, torch wrench and various other tools.

Then, with the help of my friend, we opened up the top-end of the motor and this is what we found... IMG_4873.JPGIMG_4884.JPGIMG_4888.JPG

The jugs weren't too bad; gonna take them to a machine shop to get honed (I didn't get a pic of the jugs though - and I know that the above pics aren't that great... I can post some better ones soon). Gonna clean up the piston heads too. I already have a new gasket kit from cycle exchange and new cylinder studs. Just need to order some new piston rings.
 
You need to check the piston to bore clearance first, if the clearance is out of spec then no point in honing, you would have to bore it to next size. You should check the cylinders for out of round...there is a spec for that also. Check the timing chain tensioner wheels, if they are hard they need replaced, they should be alittle bit pliable not rock hard.
 
Any info on where to get fresh tensioner sliders or whatever they're called? I had a few engines and used the best of what I had on my build but if anyone knows where to get these that's not astronomically priced that would be fantastic.
 
So, maybe this is a silly question... but what if my cam chain, slider, and chain tensioner wheels look pretty good? i.e., the wheels are still in round and not rock hard, etc. Is it recommended that they all be replaced? I know it wouldn't hurt, and if it's best to replace something then I'm game, but I'm trying not to go overboard.

And I measured the piston heads and had the cylinders measured and they are all in spec.
 
If they are not rock hard and feel slightly soft with a finger nail then they would probably be ok, any nicks or grooves in the wheels and they need to be replaced. Engine damage will occur if the wheels come apart. If you are going to split the case then yes replace the wheels as well as the primary and cam chains with upgraded ones, the primary chains stretch fast and the cam chains are a weak link. You can use standard primary chains but a heavy duty chain is a must in my opinion. Replacing them is an absolute must if you have the cases split and want a reliable long life motor.
 
People say otherwise but I would and will never use a cam chain with a master link. To many things can go wrong when installing and if it breaks you just did lots of $$$ in damage.
 
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