Topic: 1975 CB750F Project - Total Rebuild

[70CB750]

Nice progress, Chris!

[Kickstart]

slowly making progress.

Doing a dry fit with the bottom end and starting to get more comfortable with plastigage.

Originally, all of my crank and rod journals had green shells, and my plastigage readings were around 0.0015" (maybe a little more) for the crank and around 0.002" for the rod journals.

I had the crank balanced and the journals polished.  To get plastigage readings I'm happy with I went up to brown shells on the crank and black shells on the rod journals.

The crank journals now measure 0.0015" max, or slightly less
I was able to get the rod journals close to, or at, 0.0015" with the black shells, but that's about it.

Overall, I'm pretty happy with my clearances. 

Some pictures attached. I don't have pictures showing the actual measurement of the crank, but they were all squished at least at the 0.0015" gauge or a little more, but well under the 0.001" gauge.

[Kickstart]

Put the cases back together today... went pretty well except for using the Hondabond.

It tended to bead up on me when I applied it.  It did level-out but I had a heck of a time getting it to "stick" where I wanted at first... especially around the bearing journals. 

Those HD lower end case studs do not help.  Trying to get hondabond between them and the bearing journal was a bear. 

Attached are some picture (without the hondabond... I was moving as fast I as could after putting the hondabond on so I didn't snap a picture of it).

[Kickstart]

Here's a picture of the assembled cases.  Man I hope I didn't mess up with the hondabond.

Oil pump and oil pan are also attached (no picture)... slow and steady baby!

[Kickstart]

Well... I wasn't comfortable with how the case halves went together, so I took them apart and put it back together.

Was a whole day affair cleaning up all the hondabond, making sure all the bearing shells were seating properly, etc.

I got a new tube of hondabond... Big difference!  My old tube must have been bad. The color and consistency was completely different.  Instead of beading/balling up on the mating surfaces, the fresh stuff smeared easily on.

I had a timer, I had the cases closed withing 10 minutes of starting, and had the final bolts tightened withing approximately 20 minutes.  Basically half the time it took me before, which I think was probably too long.

Attached is a picture of a composite woodworking shim I cut and glued a piece of nitrile to the bottom of (from a glove). It allowed me to quickly brush some Hondabond around the bearing stud and right up to (about 1-2mm away from) the journal bearing shell.   

[Kickstart]

Cases back together... held the rods in place to install the rotor I had balanced at a nearby NAPA shop.

[Kickstart]

I decided to put a couple coats of copper gasket spray on the head gasket.  I was originally going to put the gasket on dry, but having recently read posts about the newer OEM gaskets not having factory sealant on them, I figured the spray might be a good idea.

Only problem with using this spray on an OEM gasket is it will cause the gasket to rip apart if you have to take the head back off (with the graphoil like gasket material breaking apart and getting everywhere).  Luckly, I didn't have to open it back up due to an assembly mistake or dropping something in the engine - not yet at least

Not that you can tell... but I decided to use some Viton o-rings around the oil supply passages.  I tad bit harder then Buna but it should hold up to the heat better.

[Kickstart]

Assembling the head.

I decided to use some Hondabond HT to help seal the pucks under the towers and  little around the tower studs.  Man, this stuff was tacky and hard to spread.

The Hondabond HT can withstand up to 600F and is non-hardening, and meant for valve cover gaskets and such... so I figure it's a good choice in this application, but it is silicone based, so hopefully that doesn't give me problems down the road.

[70CB750]

Nice progress, Chris.

To apply sealants I dont like beads either, usually use small knife and apply it like mayo - on water pumps, axle covers and valve covers.

[Kickstart]

Thanks Prokop... I can't believe I'm about to hit the 2 year mark on this rebuild.  I really need to pick up the pace, or stop re-doing every other step

Speaking of which:

I was thinking more about using the Hondabond HT on those pucks, and how I left some around the pucks under the towers, and how I didn't tighten everything down for a long time (I got sidetracked messing with some bad threads on points stud). I was also having second thoughts about the adjustable sprocket I put on and.. well... blah blah blah... I decided to take off the rockers, cam, and towers back off, and redo those pucks.

I'm glad I did.  Oil from lubing up the rockers and rocker shafts made it's way around those pucks and sealant. The stuff was just flaking off where I left some around the tower studs... just rubbed right off and turned into little flakes of silicone sealant... so, I'm glad I went in there and removed it.

Re-installed using the stuff Hondaman recommends in his book.  Should have done that in the first place.

I decided to install the cam towers and cam, bolt everything down, and just let it sit over night.  I figure I'll let the sealant set-up overnight before dripping more oil over everything when I install the rocker and shafts.

Oh, I took advantage of taking the towers back off to re-torque the cylinder stud nuts.  I read about others saying it helps prevent head gaskets leaks... so I figured why not.
 

[70CB750]

Looking great, Chris!  Good call on those towers.


My K0 has bad 2nd gear, I need to finish my F build to fix the K0.

But we are in synch know, I just bolted towers down yesterday, kept me warm with some brandy and now I have doubts about the work quality  but I will go ahead with it.  I went over it so many times, it has to be ok.

[Kickstart]

I installed the rockers and dialed in the cam.  I decided to slot my original F cam sprocket rather than use the APE adjustable sprocket as the stock F one is lighter (not sure how much a difference that makes)... and stock one seemed to fit a little better.

I ended up timing the cam to approximately 1.5 to 3 degrees BTDC.  I say approximately as #1 inlet opens at 1.5 and #2 opens at 2.5 (with the degree wheel set at #2 pistons TDC).  I don't remember this difference when I was playing around with the cam last time, but I triple checked.  Another thing that was odd, is the #1 piston TDC appears to be about .5 degrees after the # 2 piston.  So, if I set my degree wheel to the #1 piston, then my cam timing is really 2 to 3 degrees BTDC. 

Anyway, I'm really happy with my cam timing, as I'm now getting the following minimum clearances:

  #1 Inlet: 0.066" minimum clearance
  #2 Inlet: 0.064" minimum clearance

  #1 Exhaust: 0.084" minimum clearance
  #2 Exhaust: 0.088" minimum clearance

And this is exactly where I want to be.

A while back, I did a mock-up and couldn't get a cam timing that would give me approximately 0.065" inlet and 0.080" exhaust clearances:
http://forums.sohc4.net/index.php?topic=117206.msg1327897#msg1327897
When I did this before, I didn't have a piston stop, so the degree settings might be a little off (I used a dial indicator on the top of the piston prior to putting the head on).

At first I couldn't figure out how I was now able to get these increased clearances, but I remembered that I decided to clean-up the valve reliefs on the pistons with some small hand files. I didn't think I took that much off, but I did widen the relief ever so slightly (where I noticed some of the valves impacted during a mistake I made during my first mock-up)... so that probably ended up helping out a lot.

I don't have a picture of the pistons after I cleaned-up the valve reliefs, but here's a picture of where the valve just kissed one of the pistons during my first mock up:

If you enlarge the image, you can see a small groove on the right corner of the valve relief.  I filed all of these corners down.

... or maybe it was the thick coat of copper gasket spray I put on the head gasket that's giving me the extra clearance... either way I'm pretty happy.

#3 and #4 inlet clearances were similar to #1 and #2, I didn't measure #3 and #4 exhaust clearances as it's really hard to pry-up the exhaust tappets now that I have both springs in there, and I already did thorough measurements during my earlier mock-up.  Knowing #1 and #2 Inlet/Exhaust are good, I know the rest is good. 

I used loctite on the cam sprocket bolts and cranked them down really good.  Man, I hope they don't slip now that it's slotted

[Kickstart]

OK... so all the major engine work should now be behind me.

Time to move on to cleaning-up and painting all the covers, and then onto the suspension, wheels, bodywork, and electrical. 

This took me much longer than I thought, but I'm glad I tackled the engine rebuild (well, I still need the covers, but that should be easy once I clean them up).

I sunk a lot of money into this engine (and a lot of over-thinking things), but it was a good learning experience and I feel I have a really "tight" engine here (if that expression makes sense). 

Here's a recap of what was done:

• Polished the transmission gears using valve lapping compound
• Sent the transmission off to APE for back-cutting of the gear dogs
• "Race" balanced the crank (done by APE)
• All new bearings in the transmission and on the final drive - all SKF except the needle bearings in the primary sprocket (those are another brand)
• All new bearings in the crank and rod journals
• New primary chains and primary chain tensioner
• Had my alternator rotor balanced at a local NAPA shop
• Using F2 rod bolts and nuts
• Rods shot peened and balance at a local engine performance shop
• +1.00mm pistons
• APE bronze valve guides installed (and valve job down by a local experience motorcycle machinist)
• De-shrouded around the valve openings in the head and on the jugs as described in Hondaman's book
• Had both the head and jugs milled
• "Carbon copied" the bores to the head (making sure there were no spots where the bore was wider than the combustion chamber in the head (had to do a little more filing/sanding)
• APE HD bearing studs - not really needed, and if I did it again I would skip these
• APE HD cylinder studs - and torqued the head to 20ft-lbs
• OEM head gasket (JUST fits around the +1.00mm bore)
• Added extra oil holes in the rocker towers as described in Hondaman's book
• APE HD valve springs
• M3 racing slipper cam tensioner
• Added extra oiling holes in the clutch as described in Hondaman's book

I think that's everything.

I say the OEM head gasket "just" fits the +1mm bores, but I could feel just the slightest over hang on one side of some of the cylinders.  I decided to sand them ever so slightly until I was comfortable there was no overhang.  Maybe a little risky, but I didn't want to use the oversized Cometic head gasket I ordered... I haven't heard the best things about them lately and there was approximately 1-2mm of extra space that I didn't want. 

I now call the engine "tight" as I had both the head a jugs milled, and the pistons sit ever so slightly proud of the jugs.  I did a clearance measurement with clay, and I'm around 0.035" clearance.  Which is a little less than what I wanted... but hopefully those F2 rod bolts give me some extra buffer.  With the head gasket just fitting, and the low piston to head clearance it will be interesting to see what my compression is.

Overall, I'm pretty happy with the build as is.  I think I have this thing dialed in for a solid performing engine.

Yes - I should have had the head ported... that was a big miss on my part.  I was originally planning on keeping the cost low when I sent out the head to have the guides installed.  It wasn't until after do that did I start going a little crazy.  If I could do it again, I would have gotten the head ported before doing the valve job.... oh well, next build

Attached is a picture of how the engine sits now - just waiting for the covers.

[thirsty 1]

Nice job with all of the engine work. Degreeing and shaping and timing. I did that once on a Ducati 900. It's a lot of work. Nice job!

[70CB750]

That looks great, did you also leave out those pesky M5 bolts that keep rocker shafts from turning or they were not there?

[Kickstart]

Thanks Thristy 1, Prokop!

Yeah, I left out those 5mm bolts.  I just have the one bolt for each rocker shaft that goes in the center so the shafts are free to rotate.  I also drilled four extra oil holes on each side... so those shafts should be very well lubricated.

My shafts do show some wear marks so it's possible the tappet clearances will loosen/tighten as they rotate, but when I mic'd the shiney spots they hardly showed any wear so I should be fine. (I don't remember the measurements but they're someone above in this thread).

[Kickstart]

Laying out all my stuff I need to clean, polish, and clear coat...

[SOHC4 Cafe Racer Fan]

OK... so all the major engine work should now be behind me.

Time to move on to cleaning-up and painting all the covers, and then onto the suspension, wheels, bodywork, and electrical. 

This took me much longer than I thought, but I'm glad I tackled the engine rebuild (well, I still need the covers, but that should be easy once I clean them up).

I sunk a lot of money into this engine (and a lot of over-thinking things), but it was a good learning experience and I feel I have a really "tight" engine here (if that expression makes sense). 

Here's a recap of what was done:

• Polished the transmission gears using valve lapping compound
• Sent the transmission off to APE for back-cutting of the gear dogs
• "Race" balanced the crank (done by APE)
• All new bearings in the transmission and on the final drive - all SKF except the needle bearings in the primary sprocket (those are another brand)
• All new bearings in the crank and rod journals
• New primary chains and primary chain tensioner
• Had my alternator rotor balanced at a local NAPA shop
• Using F2 rod bolts and nuts
• Rods shot peened and balance at a local engine performance shop
• +1.00mm pistons
• APE bronze valve guides installed (and valve job down by a local experience motorcycle machinist)
• De-shrouded around the valve openings in the head and on the jugs as described in Hondaman's book
• Had both the head and jugs milled
• "Carbon copied" the bores to the head (making sure there were no spots where the bore was wider than the combustion chamber in the head (had to do a little more filing/sanding)
• APE HD bearing studs - not really needed, and if I did it again I would skip these
• APE HD cylinder studs - and torqued the head to 20ft-lbs
• OEM head gasket (JUST fits around the +1.00mm bore)
• Added extra oil holes in the rocker towers as described in Hondaman's book
• APE HD valve springs
• M3 racing slipper cam tensioner
• Added extra oiling holes in the clutch as described in Hondaman's book

I think that's everything.

I say the OEM head gasket "just" fits the +1mm bores, but I could feel just the slightest over hang on one side of some of the cylinders.  I decided to sand them ever so slightly until I was comfortable there was no overhang.  Maybe a little risky, but I didn't want to use the oversized Cometic head gasket I ordered... I haven't heard the best things about them lately and there was approximately 1-2mm of extra space that I didn't want. 

I now call the engine "tight" as I had both the head a jugs milled, and the pistons sit ever so slightly proud of the jugs.  I did a clearance measurement with clay, and I'm around 0.035" clearance.  Which is a little less than what I wanted... but hopefully those F2 rod bolts give me some extra buffer.  With the head gasket just fitting, and the low piston to head clearance it will be interesting to see what my compression is.

Overall, I'm pretty happy with the build as is.  I think I have this thing dialed in for a solid performing engine.

Yes - I should have had the head ported... that was a big miss on my part.  I was originally planning on keeping the cost low when I sent out the head to have the guides installed.  It wasn't until after do that did I start going a little crazy.  If I could do it again, I would have gotten the head ported before doing the valve job.... oh well, next build

Attached is a picture of how the engine sits now - just waiting for the covers.

There's a significant investment in that motor.  It should be nice.  It is a pity about the head not being ported -- not too late to do it and it will really wake it up!

[Kickstart]

Hah! Yeah, I guess I could.  But at this point I really just want to get her running on the road.

And I'm pretty happy with what I got.  This is my first full engine rebuild, and I'm just hoping I didn't make any mistakes. I built a solid transmission and crank so I can always come back later and do some head porting and add a hot cam. 

I also have 3 other bikes waiting their turn to be rebuilt... so I'll do the porting on the next one... if I can save up some money after blowing so much on this one

[Kickstart]

Spent much of the weekend cleaning up the covers and hubs, and started polishing (I got one of those 1/2hp Eastwood buffers for Christmas this year!)

The valve cover came out the best. I need to spend a lot more time with sanding the alt cover and then buff it again.  Same with the shift and sprocket covers - they look OK in the picture but they still have some sanding scratches in them.

I'm pretty happy with how the rear hub came out.  I'm not going for a mirror polish on that... really just trying to get it back to the original look.  I spent a lot of time cleaning and then hitting it with with various dremel sanding bits and was able to get all the nooks and crannies nice and clean.

I didn't get around to the fork lowers yet - I'm still not sure if they were smooth or if they had a brushed finish originally.

[edwardmorris]

Looks like we're about synced up on the polishing end of things, I still need to do the alternator and fork lowers as well. I'm sanding it all at once, will buff all together. Your covers look nice!

[Kickstart]

Yeah.. I just noticed your last post.

You're doing it the right way.  My valve cover turned out the best because I spent the most time sanding it progressively through finer grits.  I was hoping the buffer might let me skip some stages on the other covers but I quickly realized this was not going to be the case... as I could still see the sanding scratches. 

I suspect if I went to a rougher wheel the buffer would knock the sanding marks down, but I think that would likely to create a wavy surface.  Again.. you're definitely doing it the right way.

[Kickstart]

Wow... it's been 10 months since I posted an update.  Worse yet, it's been almost as long since I did any work on this project.

I do have somewhat valid excuses:  getting my wife's new cb360 working, tuning and racing my other bike, and trying to restore a cl77 as well... blah blah blah, no one wants to hear excuses

OK, so admittedly, what was really a punch in the gut (to me and the project) was the realization that I didn't torque the rod bolts properly.  I torqued them to the 69-75 specs, but I used the 77/78F rod bolts which require a higher torque.  I didn't realize this until after all the painstaking top-end assembly / valve timing.

So, I finally sucked it up and built a home made engine stand/mount to allow me to flip the engine over. It actually worked out pretty well, allowing me to reassemble the cases and tighten bolts on both sides of the engine without having to quickly flip the engine back over.

The project's back on!