help with engine repair

[broncomatt]

Looking for some advise on the disassembly of the engine on my 1975 cb750. I started out just wanting to do the timing chain, tensioner and guide (and gaskets of course). Once I had the engine out and the cams out I unbolted the head. This is where things got complicated, as I lifted off the head the jug started to come up with the head before it seporated. This didnt seam to be a bad thing since thats the only way I see to get the whole tensioner out. But it stoped comming up after about an inch, it seems to be hard to get it off the pistions and its not like I can easly pry on it.
As I have heard some people mention the pistons should be replaced when pulling the jug, are there not piston rings? I have a hone setup for car engines it may work for the bike too. Since I do have it out and this far apart I dont mind going alittle farther on the build but I dont want to tie the bike up all summer with this build.
Another question, am I correct in assuming I have to have the cam chain pin removel tool? If so is there a better brand than any others out there (most of my stuff is snapon), and what about the piston pin removel tool?
Thanks for any advise.

 

[dirtdigger]

The cylinder should slide fairly easily off of the pistons unless there is a large ridge worn in the cylinder or there is a lot of carbon build up. Try rocking it side to side and forward and back a little as you are lifting the cylinder. The pistons dont have to be replaced just because you pull them out of the cylinders but the rings do. If the cylinders measure good and you can reuse the pistons then do a cylinder hone, slap some new rings in and you should be good to go.

I would never use a cam chain that you have to break and install a master link. The OEM and the good aftermarket chains do not have a master link. I know others have done it and they say it works fine but I don't trust it and I wouldn't do it to any of my motors. Not with how small the chain is and how important of a component the chain is. You should split the cases and replace the chain, and use an aftermarket heavy duty chain.

I have never needed a piston pin tool on any of the 750's I have torn down but if there is some build up on the pins you may need one but I doubt it.

 

[broncomatt]

Turns out the jug was only up on one side, there was rust holding the alignment pin. Used a plastic pry tool to get it free. Everything looks ok, now I need to find some cash to order the parts.
So I guess I have to split the lower half to unbolt the conecting rods?
Other wise I would need 4 piston ring tools to put the jug back on. I plan to get all my parts from cb750supply, there not too far from me here in Fla.

 

[dirtdigger]

If you are going to replace the rings anyway you have to pull the cylinder off and won't have to mess with the connecting rods.. You would only need two ring compressors ans you only put two pistons in the cylinders at a time.

 

[jbird7262]

Spark Plug Wires from a new guy

I'm new to this site and to bikes in general, I know my way around a paint gun and bodywork but the mechanicals of the bike is another story. I recently picked up a 1975 750K5, hasn't been run in years, though the PO said he had it started a few months ago. yet when I checked in the tank the old familure varnish smell cam pouring out, it had 2 plug wires disconected from the caps, incorrect tank with the petcock on the right side verses the left, not hooked up to any of the carbs. and no air cleaners on the carbs, and the carbs. were frozen. I lubed up all the linkage and freed up the carbs. and choke linkage. This bike has been setting a long time, and the fork sticker was last inspected in 1989. Kicks over fine, the proper tank came with the bike, as well as another engine and bank of carbs, and small parts. This is my delima, when it comes to coils and plug wires, the NGK caps look good, and the wires might be good, but how do you assemble the wires to the cap? I notice that inside the cap is a copper barb, do you expose some of the wire core then push (twist) the wire down over the barb tight then slide the rubber boots back over cap/wire. The coils have fixed plug wires, I found a nice set of coils and wires for a 97' 750 nighthawk with removable wires, will they fit? I know the points coils are 5 ohms and elc. ignition coils are 3ohms. There is also some NOS Honda sets but they are double $$ the used coils. I read that with heat the plug wires cores will tend to become gummy, the wires on the bike are a bit soft. Any tips for the uneducated? I've got a new battery, plugs and will clean and set the point gap, as well as check the compression. I just want to see if she will come back to life!!

 

[dirtdigger]

Yes the caps just push onto the end of the plug wires. Dont know about the nighthawk coils but the Ohm difference could cause issues. I would look for good used coils on ebay there are usually a lot if you think they need to be replaced. Put the caps on the coils you have and see if it runs, if it fires on all four then no need to replace the coils. With how bad the carbs sound like there were stuck you will need to sync the carbs because they are probably out of sync after working to get them open. I would take the carbs apart and clean all the passages as they will have the same varnish as what stuck the slides. Along with cleaning the points you will also need to reset the ignition timing. Check valve adjustment and cam chain adjustments as well.