Topic: Matt's CB750 K4 Full Blown Restoration - Frame Painted

[matt s]

This is my second bike (my first is a 73 cb350f) and I'm planning on doing a full blown restore back to stock on this.  Picked it up for $500 from a guy who thought I would take care of it - I hope he's right!  The story he told was that "it ran when I put it away a year ago" and "I was going to cafe it put didn't have the time."  The thing had pods on it and the handlebars removed so the evidence at least didn't totally contradict his story.  The kick starter worked so at least it wasn't completely stuck.  I offered $500 and he accepted. 

First thing I wanted to do was just try and get it started.  Checked out the bowls and they were completely clean.  Check the points and to my surprise there was a Dyna S ignition installed!  I could peek under the tank and saw Dyna coils as well.  I've always wanted to try those out so I'm kind of excited about having them.  After a little tinkering and reassembling I finally got it started.  I was really surprised how easy it fired up, too.  Literally two presses on the starter for 2 seconds each and it fired right up.  Couldn't believe it.  It didn't respond well to the throttle and I'm not sure exactly what RPMs were doing because the tach is broke.  I assume the pods had something do with the poor performance (nothing against pods but I'm assuming they didn't have the carbs configured properly).  I rode it around the block and found first and second gear to be very "sloppy" and neutral was tricky to get into - I had to tap it just right.  So between the poor throttle response and sloppy tranny I'm glad I'm tearing it down.  Here's the evidence:


"Before" Pictures


Sweet saddle and pipes!


Leaks oil all over the place of course.




Bent and broken clocks, chrome headlight surround and front fender.  Dollars adding up in my head...




Looking forward to untangling this mess




Both my ponies in the stable


I bought this shelf to put all pieces on.  Hopefully this will hold most of it - the box says it will hold 2500 lbs.


Rusty gunk in the petcock bowl


Petcock looks lovely


Going to need to replace this.  Bent and has a crack running vertically as well.


Surprise, surprise


Hello there


How she's sitting now




Carbs look decent


Mystery wire I found in the light bucket


How the shelf looks

This is going to be a long project I'm afraid but I look forward to it.  I'm going to need some help, too - so THANKS in advance!

[Greggo]

That petcock will work.  All the tubes in those come out at an angle, and the cracked tube won't keep it from working.

[matt s]

Ha - just read the engine and frame numbers and found out it's a K4 not a K3 as advertised.

[matt s]

Got another hour in to do some more teardown.  No big surprises today just a couple missing washers here and there.









I'm trying keep things as organized as possible

[matt s]

Another hour in the garage and the bike is starting to look pretty bare.

[Stev-o]

Nice find. Are you going back stock? Please tell us you will not reuse that seat?!

[matt s]

Stev-o: The plan is to take it back to mostly stock although I'm not planning on being to crazy about getting all the details exactly right..  I want to keep the dyna coils/ignition but other than that I'd like it to look stock.  So, long story short - the seat is yours if you want it!

Got some more time in the garage and it looks like the forks are trashed.  There is severe pitting and I had to use a sledge hammer to get them out of the brackets.  Can anything be salvaged on these?

Left fork pipe


Right fork pipe


Both the fork cases look okay on the outside, just dirty


How it's sitting now

[lucky]

#2 and #3 float bowls are mixed up.

[Stev-o]

Thanks for the offer of the seat, but no thanks.  Had one just like it when I bought my K7, first thing I did was toss it in the trash!

[Shane72]

Thinking of that cracked fuel tube...

My most recent encounter with one of the same items resulted in the following DIY repair:

Slip a piece of see-through (read, thin-walled) fuel line over the cracked piece.  Use a tiny bit of grease to get things positioned without causing further damage.  Trim to fit, making sure that the bottom of the new line does not block the reserve inlet space.

A bit of fine whittling work on the sides may be necessary, such that the outside diameter does not exceed the available space in the tank opening.

So far, so good.  The last one that I relied on (not knowing that it was cracked  ) had me running for less than ten miles on reserve before flame out.  The cracked fuel straw negated my reserve, since enough gas flowed through the side of the tube to "rob" all my reserve fuel in the "on" position.   

Good luck,

Shane

[SOHC4 Cafe Racer Fan]

The fork bottoms are fine.  They just need to be polished.  The rest of the forks are toast, except maybe the caps.

[matt s]

All: thanks for the input about the carbs, forks and petcock.

Got a little more done today.

Progress:


Top bearings were very dry and dirty


How its sitting now


Shelf getting crowded


And here's my hillbilly overhead crane setup.  Really helped out since I don't have a centerstand or a bike jack.


I can't recommend this setup unless you don't mind taking some risks

[Ecosse]

time to get another shelf? 

subscribed.

[harisuluv]

Is it just me or was the progressive filling of the shelving just as interesting as the bike progress?  Looking forward to the finished product!

[Stev-o]

Consider upgrading to tapered bearings for the steering head.

[matt s]

@Stev-o: I do plan on upgrading to tapered bearings when that time comes.

Here's a quick update on where I am.  I finally got the engine off the frame.  I did the lay down on the side method and it worked quite well.  I used the two 4x4's in the pictures to lay it on.  The only thing that surprised me was how light the frame was.  I gave a mighty tug when I tried to pick it up but I should have been more gentle because I did bonk the engine a bit with the frame.  I don't know if it was hard enough to make any marks but I could see how that could happen.

[nancy]

Hi Matt
Doing the same thing to my 750.
The next thing you notice after how heavy the motor is - vs how light the rest of the bike is....IS....just how much furrking oil is left in that motor....it pours out of every place everytime you pull off something.
Mark

[matt s]

Got a bit more done.  The biggest things from this segment of work were:

- Manual impact driver was essential getting the screws out of the cylinder head cover
- Camshaft looked good with no obvious signs of bad wear
- The cylinder base gasket peeled right off!  That's awesome, scraping that gasket off my 350 was a nightmare.
- Cam chain guide roller and looked surprisingly good with little wear.  I'll have to confirm after I clean it up more.

Other than that I didn't see anything that was a deal breaker.  Does anybody see anything that stands out in my pictures?













































That's all for now!

[Tews19]

Subscribed
...

How long did it take you to remove the engine? I am debating if I want to do this to mine this weekend

[matt s]

Once I had everything stripped to just the frame and engine (which took probably 4-5 hours) it was really, surprisingly quick.  Like 10 minutes quick.  Just unscrew all the hanger bolts, tip it over and the thing just falls apart.  Definitely do-able in a weekend.

[Tews19]

Cool, keep the updates coming!

[robdrobd]

How many miles were on this puppy?

[matt s]

How many miles were on this puppy?

I'm afraid that is lost to history.  The clock says around 5k - but I just don't buy it.

Update:  I'm now into uncharted territory for me.  That is, I've never cracked a case.  I'm surprised how long it has taken to get this far since I've taken the engine off the frame.  It seems like it took a lot longer to tear down the engine than it did the rest of the bike which I wasn't expecting.  Oh well, I'm in no rush.  Here are the pictures - they are pretty much self explanatory as far as my progress goes.  It doesn't look like anything is completely trashed from what I see.  A proper inspection of all bits and pieces will tell for sure.

Got the pistons off


Shifting gizmos.  BTW: that counter shaft bearing holder was a beast to remove.  I ended up drilling out the screws to get it off.  My manual impact driver had no joy getting those extracted.


Generator and cover.  I ended up keeping the rotor on because I don't have an extractor.


This is how I turned the engine over to get the bottom screws out.  Notice the pan below catching all the remaining oil - there was quite a bit.






The bottom case came off pretty easy.  I just tapped a chisel (carefully) between the two and it came right apart.  I did have to yank kind of hard though to get them fully separated.


Some detailed shots for reference.
























How it's sitting now


That's all for now - cheers!

[matt s]

I got the crank shaft off and have started to read up on how to replace the crank bearings.  I want to make sure I am doing this right so please provide some input if you have any - I have never done this before.

Here are my upper bearings starting from the generator side:

1


2


3


4


5

And here are the lowers in the same order:

1


2


3


4


5

They are all pretty scored and upper number 4 has some weird scratch mark/pit thing.  So I am planning on replacing all of them.

Here is the best pictures I could manage getting the letters off the crankshaft.  This should give you a pretty good idea of what to expect.  The manual makes it seem like these are going to be nice neat letters punched into the side.  Not so.


Looks like I have straight A's - just like my school days


And the letters on the case are all B's

So, based on this information, I need all green bearings according to my handy dandy manual.


Does this make sense?

[nancy]

Hi Matt
I seem to be level-footing it with you through my rebuild. I have just gone through the mental gymnastics of working out crank shell bearings. I'm new at rebuilds - bikes anyway - so I went through the same puzzlement as you. I'd say now - forget the stuff printed on the crank and case..as they just tell you what size of shell was fitted as it left the factory. What you want to know is what is the wear on the crank etc...which determines what colour shells to fit NOW. So - you actually need the new bearing shells FIRST - so as to fit them and measure to see if the clearance is in spec. I did this by buying black - the thickest - and I bought just one set of mains and one set on conrod shells - measured each journal one-at-a-time, moving the shells over one, refitting the covers, torquing down, undoing and checking. Takes a while. Use plastigage - search for that if you don't know. So mine has panned out OK - as BLACK will be good for all mine..as wear is high.
I also took my crank and cases (torqued together) into a machine shop and had him mike measure the journals etc to verify my choices and check for crank problems - cracks, excesive out of roundness etc. He knows I'll be back for a rebore - so this was a 15 min free check. He just inserts his measuring wand in through the crank opening and measures from there. Have to have dowels fitted and gasket faces CLEAN b4 torquing down to measure. I left out the dowels - in ignorance - and he wasted 45 mins trying to find a fault with the cases - as his measurements were erratic. He spat the dummy at me when he worked out the dowels were not there...I didn't know - but these are critical to getting cases zipped up to measure.

Regards
Mark