Topic: 75' CB750 hardtail

[lucky]

Are you se

Running NO  fender in the rear is very dangerous.
IF you slip off of the seat for any reason you will be seriously injured and if your shirt tail gets wound up in the tire or chain you can be seriously hurt.
You will not care about the grease,dirt or water on the shirt or your bare back.
Also with no rear fender all of the gravel ,dirt,water etc will be thrown forward all over your engine and maybe into the carbs depending on your air intakes.
Messy.

[valt]

Pulled the motor the other day to replace the valve guide seals. They were all pretty hard and ripped apart with ease so I would say they were not any good. I'm going to degrease and powerwash the motor and give it another coat of engine paint. Modifying my fender mounts so I can mount the cb750 front fender on the rear. Someone has obviously been in this motor before, but what they did I'm not sure.



Motor on our new workbench that we built from scrap wood. Also you can see the non standard cam chain sprocket.

[lucky]

That is a very nice work bench!

Now you do not have to work on the floor.
I see so many posts where people are working on the floor but
they live in a nice house and spend lots of money on the bike but have no work bench.

[lucky]

When you say oil out of the overflow what are you talking about?
It does not have an overflow.

Do you mean out of the oil tank overflow?
If so that means the oil level is too high OR the tube from the
overflow on the oil tank to the back of the bottom part of the engine is blocked or kinked.

The small tube coming out of the back of the top of the cylinder head is a breather vent hose.

[lucky]

Well after testing and testing. I found out why my bike wasn't charging, and of course it was the stupidest thing ever!

You are learning how to diagnose problems and you are getting very good at it.
Those skills will last a life time.
Two years of hard work and you got excellent results.

How do you like Austin?

[valt]

Well after testing and testing. I found out why my bike wasn't charging, and of course it was the stupidest thing ever!

You are learning how to diagnose problems and you are getting very good at it.
Those skills will last a life time.
Two years of hard work and you got excellent results.

How do you like Austin?

Yah we built the work bench out of scrap wood. It's so much nicer not working on the floor.

As far as the overflow, I'm talking about a aftermarket tank. There is a breather tube on the back of the transmission which plugs into the oil tank overflow. I didn't realize that for the longest time. When I say overflow, I guess I just mean vent.

Austin is pretty sweet 65 and sunny today! I just wish I could get a better job.

[valt]

Bought some different engine paint. The stuff I had originally painted it with would wipe off with your hands. This is Rustoleum cast aluminum engine paint, I can immediately tell that its more durable. I just need to finish modifying my fender mounts and cut my fender and I can put the motor back in. Hopefully my roommate can figure out what is wrong with his bike so we can both be riding by next month.

[junkyhands]

how did you prep for this paint job?  I want to do this to my engine but the paint is so chippy i don't even know what to do. 
looks real good!

[Cqyqte]

I would want to be there when he's aligning it all together, though.  But beyond that, any welding show/welder with a good reputation can handle welding these frames.  Not a BIG deal with the thick walled tubing, etc.

EDIT:: I'll try and start a build thread for my almost-finished 550 hardtail frame.  I bent/made the ass-end myself, its coming along nicely.

The tubing on a Honda CB750 is only 1/16 thickness. Or .062 thousandths.
Most chopper frames that are rigids are .120 thousandths wall thickness.
Also after market rigid chopper frames are 1-3/8 inch diameter and the Honda frame is only 1 inch diameter.

Check out CycleX's website.  They make hardtail frames as well as offer tubing to do it yourself.  Not sure of the wall thickness but I think the OD is 1 1/8".

[lucky]

Alright so I have finally broken down and decided to make a thread about my hardtail project. Basically I bought a rough running 75' CB750 K5, that had a title. I then went to TC Brothers and got a hard tail and electronics and battery boxes. Had the hard tail welded on by a local welder here in town, threw the motor back in it and got it running. That's where I'm at currently, but here is a little back story.

When I got the bike, it had a really bad head gasket leak. I tore the top end down and found this



So basically a completely ruined head gasket, I then proceeded to replace all the gaskets in the top end. Including the base gasket, and all o rings. Now the issue I'm having is that it is DUMPING oil out of either the 2 or 4 cylinder exhaust. I'm pretty positive that its #4, since there is a fair amount of smoke coming from that exhaust port. Before I took the bike apart it had some mild smoke, but it definitely wasn't dumping oil like it is now.

So my question is what could be going on here? I don't think that the rings are that bad, and we definitely didn't break any putting it back together. I haven't run a compression test yet, but if I find bad compression that could be several things. I'm just confused what could be going on here, since the amount of oil coming out of the pipes is pretty large. I don't know how it actually runs like that.

Alright well if anyone has any ideas what it could be I would appreciate it. Also here is a video of it running, you can see how smokey it is here.

! Video not found

edit for more pictures!

When you take the time and trouble to do a build thread, you not only help many people with their own projects , and entertain them but you get feed back from experts that may be very helpful.

Think of guys in hospitals having the enjoyment of reading about your project.
Military members in far away places etc.,.

Thanks for posting,taking photos etc.,.

[lucky]

Well crap, I pulled the plugs and found 2, 3, and 4 covered in oil. The plug on 4 was just wet with oil and looked like it had been barely firing. The strange thing is that #1 looks really rich but no oil that I could see.

Anyone have any idea what could be going on here? I'm going to tear it down again this weekend and see what I can find, but I'm not really sure what would cause this. It absolutely does not leak on the outside at all though, and to the best of my knowledge it did not blow oil before I took it apart.

Was the engine laying on its side? 

[valt]

Well crap, I pulled the plugs and found 2, 3, and 4 covered in oil. The plug on 4 was just wet with oil and looked like it had been barely firing. The strange thing is that #1 looks really rich but no oil that I could see.

Anyone have any idea what could be going on here? I'm going to tear it down again this weekend and see what I can find, but I'm not really sure what would cause this. It absolutely does not leak on the outside at all though, and to the best of my knowledge it did not blow oil before I took it apart.

Was the engine laying on its side? 

Not sure but that motor is long gone, it needed to be rebuilt quite badly.

In other news, I'm a retard! Finally got everything put back together and was ready to ride! My fender is mounted nice and cleanly, new paint on the motor and we are ready to go!



But whats this I flipped the oil lines and my motor seized oh what joy! So the next day I reduced the bike to a pile of parts again and started taking the motor apart. So far the cam is okay and the jugs look alright but it is still seized up.

[SOHC Digger]

Drop the pan and pull the pump.  See if it turns over then.

That sucks.  I just roasted the cam just after rebuilding my engine from an oriface getting plugged.  Stick with it!  You'll find the problem and hopefully it will not be too expensive!

[valt]

Drop the pan and pull the pump.  See if it turns over then.

That sucks.  I just roasted the cam just after rebuilding my engine from an oriface getting plugged.  Stick with it!  You'll find the problem and hopefully it will not be too expensive!

Went out there today and had at it with a 2x4 and got it unstuck. I think I may have lucked out and not actually hurt anything. I'm taking the jugs off and bringing them to a guy I trust to measure them and make sure they are alright. But after I got it unstuck it turns over with a wrench and feels fine. Hopefully I can get away with just new rings and a hone!

Yah I read that your motor died as well. It's a super bummer when you think you finally have everything figured out only to have something like that happen. I always joke with people that WWII continues in our garage because my roommates harley and my honda refuse to work together.

[SOHC Digger]

Just because you got it unstuck and it turns with a wrench does not mean it's ok.  I got mine unstuck and turned it with a wrench.  Then it seized again first time I fired it up.  Whatever your problem is, it will probably be very evident when you find it.  If your jugs come off easily, then that's probably not the problem.  And of course, when you take your jugs off, check to see how easily it turns.  If it's the same, again, not your problem.

[valt]

Just because you got it unstuck and it turns with a wrench does not mean it's ok.  I got mine unstuck and turned it with a wrench.  Then it seized again first time I fired it up.  Whatever your problem is, it will probably be very evident when you find it.  If your jugs come off easily, then that's probably not the problem.  And of course, when you take your jugs off, check to see how easily it turns.  If it's the same, again, not your problem.

I know what the problem was, I flipped the oil lines and starved the top end of oil so it got hot and seized. I have the jugs off now and on monday I'm going to take them in and measure them and see if they need to be bored or if they can just be honed. The bottom end turns over easily, there was plenty of oil in the bottom end anyways when I took it apart. My pistons look fine as well, but they will be taken off and measured as well.

[SOHC Digger]

Oh ok cool.  I think I misunderstood you.  Drive on!

[Nick_701]

Bought some different engine paint. The stuff I had originally painted it with would wipe off with your hands. This is Rustoleum cast aluminum engine paint, I can immediately tell that its more durable. I just need to finish modifying my fender mounts and cut my fender and I can put the motor back in. Hopefully my roommate can figure out what is wrong with his bike so we can both be riding by next month.

How is that paint holding up?

[Roach Carver]

Thats an early stock cam sprocket. The aftermarket version is adjustable... Good luck with the rebuild

[valt]

Thats an early stock cam sprocket. The aftermarket version is adjustable... Good luck with the rebuild

Huh I guess I always assumed that they were all solid.

The paint seems to be alright, but one of the carbs leaked and it sat there with gas on it and it messed up the paint.

[gnarlycharlie4u]

Thats an early stock cam sprocket. The aftermarket version is adjustable... Good luck with the rebuild

Huh I guess I always assumed that they were all solid.

The paint seems to be alright, but one of the carbs leaked and it sat there with gas on it and it messed up the paint.

The new paint is already buggered? Did you sand off the old paint before applying the new paint?

[valt]

Thats an early stock cam sprocket. The aftermarket version is adjustable... Good luck with the rebuild

Huh I guess I always assumed that they were all solid.

The paint seems to be alright, but one of the carbs leaked and it sat there with gas on it and it messed up the paint.

The new paint is already buggered? Did you sand off the old paint before applying the new paint?

Yah I sanded it but gas just destroys all paint I guess. It doesn't help that it sat there all night with a puddle of gas there.

In other news I may have bought something silly.

[gnarlycharlie4u]

that's not silly, it's awesome. haha

you know you're going to have to do some serious rake changing to make that work right?

[SOHC Digger]

that's not silly, it's awesome. haha

you know you're going to have to do some serious rake changing to make that work right?

Front end is awesome!  Make sure you understand how rake and trail work though.  Don't do this:

[gnarlycharlie4u]

that's not silly, it's awesome. haha

you know you're going to have to do some serious rake changing to make that work right?

Front end is awesome!  Make sure you understand how rake and trail work though.  Don't do this:

lol the 'ol shopping cart steering trick.