Topic: Motor tear down what to change help?

[chadayres10]

Hey guys, im a new builder of a 1974 cb750 cafe bike. I have tore this thing completly down to nothing and have already had the frame sand blasted and torn the motor down as it will need some new parts. I have never built a bike and am am new to it all and have alot of questions. So i started on the motor, took it down to the block without spliting the case. I have cleaned it up and ready for paint. But while im here should i replace the cam chain? I also have cleaned up the head and i think im going to need to get the exhaust ports cleaned and the bottom of the valves are pretty gunked up. Should i do the work to the heads or take it to a machine shop? I think im going to put new stock pistons on it that way i dont have to get a bore job or can i go one step up? Also i have the frame ready to start cutting tabs off, how do i know what to keep and what not to keep, the center kickstand tabs i know are coming off, any others? I would like to have a clean look where the oil tank is , any ideas how to make it look like i dont have it there anymore? Same with the battery.  This is a learning curve for me and i am perfectionist as it comes to detail so any ideas and help i will welcome.

[cmonSTART]

Personally I would replace the cam chain unless it's a really low mileage engine.  They do stretch and change with time.  You're most of the way there, anyway. 

Pictures?

[the technological J]

check out the inspiration gallery in the project thread for ideas... and search engine rebuild your question is really common
i wouldnt replace the cam chain unless you have a reason to....its not a simple task.. maybe replace the rings not the pistons
 how many miles on the bike?

[scottly]

Personally, I would not cut off the center-stand mounting tabs. While I do not ride my bike with the center-stand installed, I do put it back on for maintenance. It only takes a few seconds on my bike.

[the technological J]

Personally, I would not cut off the center-stand mounting tabs. While I do not ride my bike with the center-stand installed, I do put it back on for maintenance. It only takes a few seconds on my bike.

+ 100 i miss mine often... stupid PO

[luap]

if the valves are out I would hit them on a wire wheel to get the carbon off, an lapp them, I would say you still need to hone even with new pistons so Id do whats mentioned above hone an new rings with
I just saw a cool 750 build where he built a oil tank flat in the area where its at now but doesnt look like anything is there an I believe the battery is under the rear cowl

[chadayres10]

Guys thanks for the info so far! How do i lap the valves? Would i need new guides or seats? So you guys dont think i would need to take it to a machine shop? Maybe just hone the walls myself?

[mickey6]

what part of oregon are you in... if you need a hand and you're close I maybe able to help

[cmonSTART]

Lapping valves is easy, but you do have to take the cylinder head apart.  I'm sure there must be a good how-to somewhere here.

[wrenchmuch]

You should assess the condition of what you have before you decide on a course of action . Assessing pistons and bores requires a micrometer and telescoping gauges . These tools will help help you assess the bores for taper , oval , as well as their overall diameter . You can do a quick assessment with the piston from that bore and a set of feeler gauges . If this is the only bike you will build then purchasing these tools is probably more money then having someone do the measuring for you . Certain rubber pieces in the engine harden with age / heat . With the cylinders off the rubber bits for the cam tensioner can be replaced . The primary tensioner can only be replaced by splitting the cases . Hard rubber will fragment in use . Head work is fairly easy as long as guides , seats , and valves are in good shape to begin with . Replacing guides , and grinding seats requires specialized equipment and is best left to a machinist .

[chadayres10]

Ok so i dont have the main engine case split, should i? The engine has about 30 k on it for miles. I know it would be the time to do the bearings on it if i were to do it since im this far but money is an issue. I wish there wwas a you tube video on the whole tear down into the case. Ill post some pics of the build as when i got the bike to where its at now. Its came pretty far since i got it, oh and i picked the bike up for 50$ haha awesome deal.