Topic: my story for some advice

[greenninja85]

So i'm new to this forum tho i've been on it many times to look for answers to my questions.  I've been into motorcycles as long as I can remember and over the past couple years got interested in building my own.  I picked up a 73 cb750 that didn't run and the kid who owned it knew nothing about it or motorcycles in general, but it was obvious to me it was in pretty rough shape so I picked it up to see where I could go with it.  I work two jobs and also volunteer as a fire fighter in my town so I don't have much free time but always find time to be in my garage when I can:).  So my projects may be slow going but never at a hault.  After awhile of messing around with that motor and cleaning the carbs I couldn't get it to run, got a compression test and lets just say the numbers weren't good.  So I was considering rebuilding the motor when one of my buddies offered me his 78 cb750f for only $250, I said yes before thinking about it lol.  This bike still needed work itself but kinda ran so I figured it was a better place to start.  I kept some things off the 73 and sold the rest as a parts bike (which it pretty much was all along).  So I have my 78 running but only on 3 cylinders, the 1st being the one that won't fire.  Did a compression test and that one was only at 90 and the rest being good at around 150.  Maybe I should do compression tests before buying something lol.  But I've always wanted to rebuild a motor so I wasn't upset at all, and doing the top end on this would be a good start.  What i've found the intake valve on that cylinder is leaking which this year is notorious for valve problems so no big surprise there.  But i've found that I can't buy a new intake valve for this year.  Cycle x has after market valves with all new guides and springs, would those fix the problem of them wearing out so quickly?  And with lighter valves do I need a bigger cam?  I also plan on putting new piston rings and honing the cylinders while I'm in there and of course all new gaskets.   

[greenninja85]

I didn't mention i'm going for an old skool bobber look.  But first things first having a strong running motor.  I'll be posting pictures of what I have so far soon

[iron_worker]

The cycle x valves do not require a new cam ... however depending on the condition of what you've got in there you may want a new one ... or if you just want it to have more power. Depending on the cam you select you can have a nice torquey motor or something that wants to rev to the moon ... all depends on what you want and your intended riding style.

Welcome to the forum btw.

IW

[lucky]

Before you hone cylinders you need to measure the bores the right way and make sure you do not need boring  and new pistons.

Measure, Bore, then hone.

[greenninja85]

will do, thanks lucky

[greenninja85]

my riding style for this bike will not need to be fast, so as far as the cam i'll probably leave the stock one in there then as long as it checks out fine..thanks for the responses

[greenninja85]

One thing i'm worried about with taking the top end apart with winter coming is it may be apart for a couple weeks or more in a non heated garage..i'm sure the jugs and head will be brought inside to be worked on but the motor will be opened, i'll have it covered up of course but will these parts rust quickly?  If so how can I prevent it?

[Retro Rocket]

What i've found the intake valve on that cylinder is leaking which this year is notorious for valve problems so no big surprise there.

I'm not too sure who told you that but it was the later 78 750F2-3 that had the valve guide problem. If you are going to change out the worn guide then change the lot for brass ones, cyclex will have them as well...

[greenninja85]

Ya I plan on replacing those. New valves and guides all come together in a kit they have

[754]

BEFORE YOU GO FURTHER, F head may require use of F barrel in order for head oil drains to work, check that before you proceed.

[greenninja85]

Not quite sure what your referring too by f barrel. Are you talking about the guide?  All of the parts I plan on getting are for this specific year and modle 

[seanbarney41]

I think 754 thought you were going to try to use the 78 f head on the 73 cylinder barrels...that don't work too easy

[greenninja85]

Ah ok, nope wasn't planning on doing that.  My main concern befor taking the top end apart is things rusting. I'm planning on leaving the motor in the frame which will be in an unheTed garage. Will that cause things to start to rust in there?  And same for the now exposed parts on the jugs, head and valves? 

[seanbarney41]

just keep stuff oiled, or wd40'ed and you should be ok...except...except, someone should probably tell you now, you can't even get the valve cover off a 750 without removing all motor mounts and tilting the engine, and then you really can't do any quality work anyway and might as well just pull the whole motor...

[greenninja85]

Ok thanks for the heads up..any suggestions on the best way to get the motor out?  I've seen people tilt the bike on the side and shake the hell out of it for the motor to come out..but I'd rather not take that route.

[seanbarney41]

remove right side motor mounts, tilt the bike on to the right side, remove remaining motor mounts, lift frame off of the engine...this may not be the easiest if the bike is not totally disassembled...I'd do a search here, guys have come up with tons of ingenious ways to do it yourself, and there are tons of little tricks that help get that baby elephant outta there

[greenninja85]

Got my motor out today, all went well exept the rear top motor mount on the left side broke off at the end. Can this be jb welded back on?  There's most of it still there so it won't be holding much weight right where the jb weld would go. Or any other suggestions?  Thanks in advanced!

[greenninja85]

Got the valve cover off tonight   The first cylinders intake valve at the very top off the stem was dented in pretty good. Which would explain why it was leaking