Topic: 72' CB750K2 Resto-Mod

[rickmoore24]

Fantastic work so far! Funny about the missing powder coat on the neck vin stamp. My powder coater went over the stamp on my first build and the CHP officer who inspected my bike hassled me about it, but not to badly as he gave me a green light. Looking forward to the rest!

[FridgeRaider]

So a big shout out to forum member Calj737! Over the past month or so he has helped me out big time with the work I needed done to the engine. He stopped by one day in December to pick up my cylinders, piston kit, and the bottom half of my crankcase. While we were talking, he inspected the rest of the engine parts and found a couple of small chips in two of my exhaust valve guides. He convinced me to have those replaced by his machinist/mechanic while he was at it boring out my cylinders. Thanks to him, my engine ended up getting the full treatment:

- Bored Cylinders for 836 kit
- Rings gapped
- Milled cylinder surface
- Piston heads coated (ceramic I think?)
- Piston skirts coated (dry film lubricant?)
- Decked head
- New exhaust guides
- Re-cut valves seats, both intake & exhaust
- Valves lapped
- Intakes ported (PO had a questionable go at it himself so it need it)
- New valves springs installed (I sent the Kibble White HD springs that I had bought with Cal)

He was also nice enough to even weld up the screw holes that were letting in daylight on the lower half of my crankcase and ship it back. I know I've told him a thousand times but thanks again!

Here's a couple pics of the repaired threads. I'll post pics of the head and cylinders once I un-box them for install.




I took a break from working on the bike for the most part while the top end was in Virginia (I think?) with Cal. Now that it's all back and just itching to be put back together, I tackled powder coating the crankcase shells this weekend. For the most part they came out really nice, not show quality but none-the-less nice for such a first time endeavor. I even had to upgrade my oven in the garage to fit them in. I played musical chairs (but with ovens) to make that happen. I bought a new one for my kitchen, moved the kitchen one to the garage, and then moved the small garage one to the curb. 





My expertly engineered engine adapter. I had an old junk frame sitting out back behind a shed that I thought would be a perfect sacrificial lamb to hold the engine up for the rebuild.







Obviously when I get the crankcase rebuilt, I can just flip it and have it sit normally in the frame for the top end portion of the rebuild. The crankshaft bolts that came with the engine looked like garbage so I bought APE's HD Main Bearing Studs and installed them per their directions on the website.



I used a Motion Pro M8 Stud Installer to torque them into place and ran into a pet peeve of mine. It's obviously designed to be used on metric studs but the mechanism that allows you to relieve pressure off the stud requires an SAE allen wrench. I took me a couple minutes to realize this when trying to get a metric allen wrench to work. We need to just switch over to all metric as a country already. *insert angry fist waving*   





bottom end sandblasted and powder-coated









I did purchase two new sets of OEM green crankshaft bearings to replace the two sets that look liked they had been squished. I plasti-gauged them all and they ended up being within the upper limit of .08mm.

My father wants to participate in putting the engine back together so I will have to find some time next weekend to invite him over. He has a CB550 project of his own at the moment so it will be a good learning opportunity for him (and me). 

[Johnny340]

I used a Motion Pro M8 Stud Installer to torque them into place and ran into a pet peeve of mine. It's obviously designed to be used on metric studs but the mechanism that allows you to relieve pressure off the stud requires an SAE allen wrench. I took me a couple minutes to realize this when trying to get a metric allen wrench to work. We need to just switch over to all metric as a country already. *insert angry fist waving*   

I agree!  Apparently we switched here in Canada in 1979 but still use 'standard' in machine shops and other surprising places...like the new billet Jetski part I bought that had both metric and standard threads in the same piece!  I digress..

Awesome work so far!!
Subscribed.

[FridgeRaider]

So progress on rebuilding the engine has been tediously slow. Every step forward is met with a new challenge that required me to wait for a missing part before I could proceed. At first it was when I was mocking up the transmission that I found that I was missing a half moon key that holds one of the transmission bearings in place.



I found a member who tossed one in the mail for me (thanks again Mike!) and a couple days later a I was "back on track". The next set back I found myself with was after I cleaned and prepped all the innards for the crankcases. I mocked them up and when I went to grab my Hondabond to seal both halves together, it was nowhere to be found. I seem to have misplaced it during a couple of moves over the past year and a half. So there went another week awaiting a new tube to arrive by mail. 

That brings me back to last night, where I finally had all pieces I needed to mate the two halves together. All new seals, cam chain, and crankshaft bearings that plastiguaged within spec.












Inevitably I have run into another issue that I can't figure out after installing the shifter mechanism. I'm hoping that someone with more experience with these transmissions can help me understand what would cause the following. Hopefully a solution can be found without me tearing the cases apart (doubtful but I can still dream right?). When I go to try to shift through the gears, it only wants to do half shifts. It feels like the gears only mesh up in certain spots once I rotate the final drive shaft (front sprocket) by hand.

This is the sequence of the events happening: shift from 1st to 2nd -> half shift up -> shift back to 2nd -> spin final drive shaft a bit -> shift to 3rd -> shift down to 2nd -> now I can't shift back down to first. Sometimes I have to do this to shift up and down through each gear, sometimes I can shift a couple of gears before it will half shift again.   

Another interesting part is if I try to shift from neutral to 1st it will sometimes half shift. It acts like it is still in neutral until I spin the final drive shaft a couple of rotations and I can actually feel the gear engage the clutch shaft (I dont know the technical term) and then I can actually shift it fully into 1st gear.

Half shift to 1st:


1st (sorry for blurry pic, you get the idea):


I tried loosening the neutral indicator thinking it might be to tight and pinning the shift drum but no change.

[FridgeRaider]

I posted my concerns about the transmission not shifting through all the gears as smoothly as I would like in a help thread and received some good feedback. Most were in agreement that I wouldn't be able to 100% tell if there are any issues until I hook it all up in frame and have adequate oil pressure to the gears and splines. So I pressed forward......slowly.

link to help thread: http://forums.sohc4.net/index.php/topic,163911.msg1890010.html#msg1890010

I seem to always take before pictures but forget to take any during/after pics. I modified my clutch hub per Hondaman's book. I drilled 8 additional holes to allow extra oil to get to the plates. Here's a pic of the hub ready to be drilled in a vice.



clutch buttoned up:


I started adding all the covers, found out that I was missing the shifter cover gasket. Another incident of having to buy one piece and wait for it to arrive in the mail  Good thing the stator cover looks amazing.



Next up: Cruzin_image's 836 pistons that had the ceramic coating on top and the dry film lubricant on the skirts. It's a shame that the cylinders aren't see-through cause this pistons are pretty.







I picked up the Kibble White HD cylinder studs while CycleX had them on sale for ~$90 or so. Here was my procedure to installing them:

- run M8 tap into each thread to clean them up
- blow out with compressed air
- add blue loctite to longer threaded end (instructions say to use only if threads are loose, I chose the better safe than sorry route)
- torque down to 8 ft-lbs with help of Motion-Pro M8 stud installer (this made it quicker/easier than double nut method)





There isn't a big rush to finish the engine right now. I'm still trying to find a source for the early style oil jets for the head. A couple members suggested making my own on a lathe but that is a really daunting task for my current machining skills (which is essentially non-existent).

[FridgeRaider]

If you know the dimensions for the jets, send them to me. I'll cut them this weekend if I get a chance.

I'll do my best to get you some accurate dimensions on these darn things. Are they just restrictors to increase oil pressure to the top end? Whats the purpose of the screen on the backside of the early ones? I cant see them designed as a long term filtering device. (I know 750s aren't your thing Cal, maybe someone else can chime in)

[Stev-o]

Motor is looking good

[BPellerine]

when I had my early jets out,I had to clean them,what came out would have been enough to plug the jet,the screen holes are really too big to keep stuff out,the only way to clean them is through the screen holes,using small wire to dislodge dirt and spray cleaner to drive it out,multiple times.the later jets did not have screens so I think a simple disc with the right size metering hole would be ok,but the centre is raised to keep the small oring in place.sandcast did not have screen as well.bill

[FridgeRaider]

Motor is looking good

Thanks!

If you know the dimensions for the jets, send them to me. I'll cut them this weekend if I get a chance.

So the measurements are 11mm diameter and 6.3mm deep. I don't know what size the metering hole is or how high it's raised as BPellerine mentioned.

[FridgeRaider]

Motor is looking good

Thanks!

If you know the dimensions for the jets, send them to me. I'll cut them this weekend if I get a chance.

So the measurements are 11mm diameter and 6.3mm deep. I don't know what size the metering hole is or how high it's raised as BPellerine mentioned.

I need complete measurements to make it correctly. Have someone diagram them and I'll see about cutting some up

I'll make it happen

[edwardmorris]

This should help, courtesy of Mark Paris aka Hondaman

[edwardmorris]

Also, forum member Prokop was making these for the forum folks a little while back, PM him to see if has any extras he may have made.

[FridgeRaider]

This should help, courtesy of Mark Paris aka Hondaman

Thanks for the help edwardmorris but this is for the later (smaller) style oil jets. I'm not sure why it say K0-K8 on the diagram. It seems up to the early K2 heads had early "puck" style jets. I've attached a pic of what they looked like snagged from a quick Internet search.

[edwardmorris]

Drats! Sorry I should have read further back. The only person I know who could have spares is Bill Benton (if you haven't already tried).

[FridgeRaider]

Drats! Sorry I should have read further back. The only person I know who could have spares is Bill Benton (if you haven't already tried).

No problem! I'm still working on Mr. Bill to source some for me out of his mystical CB750 cave.......or spend $500 on a benchtop lathe and try to make my own.

Here's some pics of my restored gauges. I did the ole paint-can-opener-pry-trick to bend back the backside of the chrome retaining ring. Of which I was able to reuse once it put them back together. The black cover was blasted and powdercoated, new faces from our site sponsor CB750faces.com (excellent product), needle tips painted, and chrome back plates got a quick buff.





I thought this was kind of cool, the old plate faded except where the needle rested above. To me that meant the bike sat outside and weathered the elements for a decade or two.









now to put em on the bike............

[Stev-o]

Nice job on the clocks....

[SOHC4 Cafe Racer Fan]

Very pretty gauges! Nice job.