80 CB750K First Street Bike Project

[hlewis12]

I'm new here I've been doing a lot of reading on this and various other CB sites.  I find that this site is the easiest on newbs so I wanted to start a new thread to track the progress of my build here.  I found this bike locally on Craigslist.  I picked it up for cheap and it had an additional motor included with the sale.  I was told by the previous owner that the bottom end of the motor in the bike needed a new bearing and that the top end of the motor out of the bike needed a new cam chain tensioner.  I thought for $300 why not give it a chance.  My plans are to get it running and then break it back down and powder the frame, new paint, seat and a few other ideas I have.

Anyway here are a couple of pictures from the day I brought her home.

 







Not to bad in my opinion.

I've had the bike for a couple of months now and didn't really get much done for a while besides for tearing the carbs down and rebuilding them.  I had some time off over the holidays so I was able to tear into the second motor.  I got the cam cover off and the cams removed only to find that there were a couple of shims missing when turning the motor over and I either messed up the cam or it was already done before I got the bike regardless the intake cam lobes are fairly messed up on #1 cylinder.



Here are a couple of some of the additional things that I found wrong with motor #2.

Broken cam chain guide.


Cam chain holder/cap is kind of messed up on cylinder #1

 

 

The cylinders look good on this motor.  I think?  The lines in the cylinder are from the reflection of a storage bin in the background.  Should have taken an additional picture of this.



The valves would need to be cleaned.  But I will more than likely be using the head off of the other motor.  I do not have pictures to share of it with me but I got the cams out of it last night and everything "looks" to be in better condition.



So now my plan is to use the entire top end of the motor in the frame and the bottom end of the motor not in the frame.  I checked the connecting rods for side to side play of the second motor and everything "feels in my limited experience" good to me.  My question now is how/what is the best method to clean out the gunk/gasket material out of the crank case without splitting the cases?  Is this even possible?  Can you do it with kerosene?

Here is what I'm talking about.  Of course in hindsight I probably should have sealed the motor up and pressure washed it before taking it apart but what can you do.



Should I replace the rings and get the cylinders honed even though the cylinders don't look like they need it?  Or should I check gap and let that determine it?  I have no idea if it was burning any oil or not.

I will post some additional pictures soon of the other motors cam tensioner and cams.  Like I previously said they look to be a lot newer than the ones in this motor which are shown here.

Oh and I've got a full gasket kit coming as well as valve seals from Jebbysan on the other cb site.

 

[TOOLS1]

So much fun. I would go on and install new rings along with new cam chains, and guides.
TOOLS

[shinyribs]

Welcome to the forum.

Looks like you are already off to a good start! Good luck with your project, looks like it needs some love.

[hlewis12]

Made some more progress this weekend.  I was able to get the head off of the second motor (the one that was originally in the bike.  I was told by the previous owner that it had a problem and if I IIRC he thought it was a problem with the bottom end because of a noise that it was making.  Like I said I got the head off and it appears to be in better condition that the original on first inspection with the exception of exhaust valve #6 from the left.  The retainer pins were just sitting underneath the bucket and the springs were broken.
 
 

I'm hoping that this was the noise that the previous owner was hearing.  I'm not sure why the valve springs were broken and definitely the valve itself is bent because I'm unable to actually remove the valve and you can see that the valve has hit the #3 piston.  

 

I'm thinking that this might not be that big of a deal.  Now I need to figure out how to remove the bent valve without messing up anything else.  As seen in the pic below this is as far as I can get it to come out.  Any suggestions?

[TOOLS1]

Cut it off with a Dremel tool, and push it through the other way.
TOOLS

[hlewis12]

Also beside the valve hitting the one piston it doesn't seem like this motor was ran hardly at all.  I remember the previous owner mentioning something about he timed it wrong because he was used to work on the SOHC CB's and that is how it was messed up in the first place. Also I finally took the time to compare the VIN number on the frame to that of the motor and the additional motor that was sold to me with a problem with the cam tensioner is only 5 #'s away from that of the frame so I assume that is the original motor.  The odometer if it is correct and original only has 14k miles on it so I again assuming that everything above is correct the original motor is barely broken in, right?  

I've got new valve seals coming and a new gasket kit already so I'm thinking of taking an exhaust valve from the other motor and putting it in this head with all new valve seals and putting everything back together and seeing what happens?  I don't really want to spend the money on new rings unless you guys absolutely recommend it but I want to try and save some money to do some cosmetic work to the bike.  I think that I've read that these bikes rarely need new rings.  Is that correct?  Also is there a way to check the crank to cam chain without splitting the cases?  

It doesn't look like it was really ran all that much based on the carbon buildup on the pistons and the head.

 

Oh and I got some toys over the last few weeks as well.  I'm anxious to use them.



Eastwood Powder gun, got the oven from my aunt and uncle's basement, and the soda blaster from Harbor Freight.  I've blasted a few parts to see how it works and the results were fair.  I think I need a larger compressor.

Anyway here is a pic of a soda blasted valve cover and one blasted fork and one unblasted fork.  I think the results are fair for the minimum amount of time spent on them.

 

 

Also did a little shoe storage project for the wife over the weekend to help ease the pain of spending time in the garage working on the bike.  It's give a little take a little.

 

It was kind of an eye opening moment for me to realize that almost half of those dang shoes up there were mine.

[hlewis12]

TOOLS1 wrote

Cut it off with a Dremel tool, and push it through the other way.
TOOLS

I was thinking that would work but wanted to get some feedback first.

[seestheday]

Great job so far.  Reminds me a lot about my engine.

You are going to replacing that old cam chain tensioner, right?  The risk from it blowing up and destroying your engine is huge.  Now that you're in there, you might as well replace it.  Especially if you think it's original.

Even if it has only 14K miles on it, it's still 34 years old.

[hlewis12]

seestheday wrote

Great job so far.  Reminds me a lot about my engine.

You are going to replacing that old cam chain tensioner, right?  The risk from it blowing up and destroying your engine is huge.  Now that you're in there, you might as well replace it.  Especially if you think it's original.

Even if it has only 14K miles on it, it's still 34 years old.

So maybe I'm missing something but I've yet to find somewhere to buy the cam chain A tensioners online.  

Do these need replacing?

 
 
Also what is the best way to clean the crank case out without splitting the cases.  I keep finding gunk, dirt, gasket material down in there.  Obviously I should have cleaned the outside of the cases before taking the head and cylinders off but too late for that.  

[seestheday]

I got my tensioner from A Honda dealership.

I doubt your guide needs replacing (the straight piece).
As for the tensioners, it's impossible for me to tell from pictures. I'd have to hold it in my hand, sorry. For what it's worth those don't look too bad.

It's really up to you if you think they're going to break. Look for deep cracks.

As for cleaning the crank case without splitting the case, the only way I know is with seafoam while it is together.

[sgtslag]

Sees is right:  mix SeaFoam into the crankcase, as per instructions, and run it through all of the gears.  The SeaFoam will dissolve varnish, carbon, and other sludges, within both the engine, and the transmission.  If there is crud to be removed, your oil will turn black within five minutes of run-time.  After that, change the oil, and the filter (the filter will catch a lot of the crud, so it needs to be replaced, to be safe, even if it was new before you added the SeaFoam).  The crud is most likely from the SF rated oils used back in 1980.  Modern, SN rated oils, leave very little behind, if changed every 3,000 miles.  Cheers!

[hlewis12]

Thanks for the response.  There are very few cracks in the tensioner so I think I will reuse it.  

Also on another note I checked all the ring gaps yesterday because I'm trying to decide on my next step.

All of them seemed to be within spec at .27 mm.  I checked them by inserting them from the bottom of each cylinder and moving them up 15mm.  I figured I would post some pictures showing the process.

 



I could barely see the markings on the rings and I was looking for a "T" as described in the manual but I found an "R" which leads me to believe that these are not the original or honda rings.

Very hard to see in the pics.  Also if you will notice on the top ring the "R" is closer to the gap than it is on the bottom ring.  It took me a while to figure this out because I could not tell the difference in the color of the rings.

 

Should I have the cylinders honed before putting everything back together.  I checked with a local shop to see how much it would be they want $50 just to hone it for me.  that seems kind of high but I'm not positive.

[TOOLS1]

Your cylinders look like they still have a nice cross hatch to them. However if you want to hone them, just go to AdvanceAutoZone, and borrow a hone.
TOOLS

[sgtslag]

I was under the impression that honing was required any time the pistons were removed, to ensure the rings properly seated after re-installation, but maybe only when new rings are installed?  Not sure.

If the engine was never torn down before, the rings must be OEM.  I would try to verify whether they were OEM, or not -- I would not want to remove and tear down the engine a second time.  The old carpenter's addage, "Measure twice, cut once," seems appropriate to your situation.  Cheers!

[hlewis12]

I was under the same impression that I need to hone them but I'm not really sure. I'm pretty sure that they are not the original rings or oem for that matter.

[TOOLS1]

Just because the rings were marked with an "R" and not a "T" does not mean that they are not original. Honda used several different suppliers for parts, and the pictures in the manuals are stock pictures used in several different manuals. Are the pistons marked with an overbore?
TOOLS

[hlewis12]

I'm not sure.  The only markings I saw on them were C 425 6 on one side and HONDA on the other.  Does this mean they are standard size if so out of curiosity what would the markings be for an oversized piston?

[TOOLS1]

Oversized pistons are always marked on the top with the size, such as ".010"
TOOLS

[shinyribs]

TOOLS1 wrote

Oversized pistons are always marked on the top with the size, such as ".010"
TOOLS

Well, this is usually true, but not always. If they are service replacement, or Honda, parts then yes, they'll be marked what degree of oversize they are. But some aftermarket pistons aren't marked at all. The ones I got for my SOHC are oversized at 65mm. No markings on them to denote that they are +4mm from stock.

[hlewis12]

Would it be absolutely dumb to swap cylinder sleeves, pistons and rings out of a known block with good compression but has a hole in the channel that the cam chain goes through because of a bad cam chain tensioner/slide into my block with slightly out of spec pistons (~61.88mm at skirt unless I measured wrong)?  The reason I would do this is because the other motor/block that I have ran great (by previous owner) before the cam chain accident.  I would do this by following this thread

Replacing Cylinder Sleeves in CB Block...Pictures Included 

It looks simple enough.  I don't really want to pay to have the cylinders honed, new pistons, and rings.  I'm running out of money for this project.