Topic: Potential 1970 CB750 K0/K1 Hybrid

[Lucien Harpress]

Success!  Thankfully I didn't need a full angle-steel mounting plate to get something to tap on since I've only put like two full heat cycles into the engine since assembling it last.  I got away with a piece of scrap with a hole drilled in it.



(Don't mind the discoloration.  I scored the underside of the bores up pretty bad removing the backed on base gasket, so I hit the new one with some copper-coat.  It may not do much, but it couldn't hurt.)

This morning I also stripped what I could of the side pieces- points, clutch, stator, etc.  I'll do the shift mechanism later- that whole assembly is a nightmare, so I need to be real sure I keep everything in the right order.





Now that everything's off I can spin the crank by hand now, and while there's definitely a spot that tighter than the rest of the rotation, it blows my mind how slight it is.  If you get a bit of moment to the crank it's easy to blow right by it.  You really have to start turning from that position to really tell it's sticky.  Ah well.  I still need to drop the oil pan, then I can split these cases and find out more.

[Lucien Harpress]

Cases are re-split, and the verdict is.... not as clear cut as I would prefer.  (In the interest of not re-posting the same bearing picture five times I'll just post the album link.  All the good stuff's in there.)

https://imgur.com/gallery/omxzH1X

The bad?  Lots of crap in the oil pan.  I figured I would have some kind of nonsense, but this seems excessive to me.



The inconclusive?  While there are quite a few shiny portions of my crank bearings, I'm not sure how much of it is "normal", and this also includes wear from the old engine I took them out of.  Still, obviously something is wrong, but it's not so horribly wrong I can immediately pick out what my problem is.

I'll probably pull the transmission shafts, put the crank back in, and torque everything back together.  This way I can confirm it's my crank that's binding and not something else.

[BenelliSEI]

Did you try turning the crank after you pulled the pistons, but before splitting the cases?

[Lucien Harpress]

I did.  I spun a LOT more freely without the resistance of the pistons in the bores, but there was still a very subtle tight spot in the rotation.  Maybe 20-30 degrees of rotation had a bit of resistance, while the rest spun extremely easily.  Honestly, it was hard to notice unless you stopped the crank in that position, and only because it took more effort to get it spinning again from that position than compared to any other point. 

[BenelliSEI]

I think you are going to find something else.

[Lucien Harpress]

Time for a check-in.  So, to make a long story short, it was my main bearings.  I took my crank and my block to Cycle Xchange in Wisconsin to get looked at and balanced because this motor has always been pretty buzzy, and essentially if I would've run it any more, I probably would've ruined something.  A balanced crank with new rod bearings and yellow crank bearings later (I had in green), I think I'm nearly ready to button this block up for the second time.



My experience with Threebond, while probably okay, wasn't the greatest, so for round number 2 I'm trying some Loctite 518 anaerobic sealer.  In theory, because it only hardens in the lack of oxygen, any excess on the outside of the block can be wiped off, and any on the inside will get washed out by the oil.  Plus I'll have plenty of time to get everything lined up.

I also got a couple of parts for my carburetors that, while not strictly necessary, I've wanted for a long time now.



Of course I had to goober up (rather good) carb sync to get them on, but I should probably re-do that anyway.



Plan is to get the block together in a day or two, then we'll worry about buttoning up the rest.

[BenelliSEI]

Nice work. Those boots finish the job nicely. They are a pain, but I like to see them in place!

[HondaMan]

Can you not find the Hondabond for the cases?

My 2 cents' worth: Plastigage those bearings. Do the rods, too.
Don't let the clearance be larger than 0.0020" if you can help it: I set them to 0.0010" - 0.0012" in rebuilds with brand-new bearings, 0.0016" upper limit. This quickly grows by about 0.0002" - 0.0004" in about 500 miles. If the clearance is more than 0.0022" the oil pressure/flow at idle in a hot engine is getting too low. In the previous pictures of the bearings it appeared they were quite loose and run with light oils. That combination is deadly for these cranks.

[Lucien Harpress]

I may pop a plastigauge on the mains before I torque it down for good, just for curious, but I'm not really concerned about it, for one really good reason:  When I dropped the crank off to get balanced, I dropped off the engine cases as well.  In addition to the crank balance, I also got new rod bearings installed, the cases checked and lapped at the main bearing points (not quite a full line-boring, but same idea), and new main bearings fitted to the cases and crank.  And the shop did all of it.

Basically?  I got it wrong last time, so I paid a professional to do it for me.   

As far as the Hondabond goes- I still have it, but I'm not entirely enthused with my ability to apply it.  I did end up with a minor case leak along the front seam, and I'm not a fan of how much ended up floating around my oil pan.  I hear anaerobic sealers are a bit more user-friendly, and at the very least work AS well as the brand-name Threebonds, so I figured it couldn't hurt to try it.

[Lucien Harpress]

So, random question for the group- which is the correct orientation for the APE cylinder studs?  I had them all sorted when I first put them in, but the engine shop pulled them when they re-did the crank, and now I forget which end goes into the block. 

I DO know that the threads are a bit longer on one end than the other, but I forget which end goes where.

[BenelliSEI]

Measure the depth of the threaded holes in the case. I can’t remember, but I think that will tell you.

[Don R]

Red foam has been out of stock for more than a few months, I missed (cheaped) out on getting one before JT Marks passed away, Now I wish I had gotten two.

Don: have you tried contacting his newer JTMarks77 seller? I think it is his daughter (wife?), as I got a girl's name with thanks on my last order from there.

 I was reading tonight and noticed I hadn't mentioned that I did contact JT's daughter. She didn't have any red seat foams and hasn't ordered from Yamiya yet.

 I liked the gauge conversion pics, that may give me a way to put K0 gauges on my last 70 project. I have a couple of usable sets of K1 gauges that I plan to rebuild as K1 but might do a K0 set also. I just found a new/old set of K1's that had a little garage rash but 1.4 miles showing. They'll go on my 72 titled K1 and another set can go on my 71 titled K0.

[Don R]

 I noticed 4into1 has a 4 bulb console light harness. That may be something that could fit the early gauges if you didn't mind the crazy wiring.

[RAFster122s]

Niche Cycles carries that harness also. I'd rather give money to Niche than buy anything from 4-into-1.

[Lucien Harpress]

Modifying my stock wiring harness was what I ended up doing for the gauge lights.  The only real issue was the size difference of the mounting holes, but a bit of surgical tubing around the rubber light socket thickened it up by exactly the right amount to fit in the larger holes in the gauge plates.

The ONLY issue with converting K2 and later gauges to the earlier ones is that the trip meter or odometer (the number readout on the bottom) is wider internally on the later models than it is on the earlier ones.  It interferes a bit with the light tube and boot for the turn signal light- I had to dent the tube in to clear the odometer assembly, and you can just barely see it behind the amber lens if you look for it.  Not ideal, but you really only see it if you know it's there.

Motor assembly proceeds nicely.  I DO have a question about the crankshaft rotor, though.  How do you know if it's fully seated?  I've got it torqued down to 72 ft/lbs per the manual, but I've got about 1-1.5mm of side-to-side play on my starter clutch gear.  Is this normal?  I know Honda likes to run tolerances pretty tight, and I don't need a rotor chewing up the inside of a sidecover.   

[HondaMan]

Those studs: the longer end of threads goes into the cases, short ones on top at the head. 20 ft-lbs max torque.

[Lucien Harpress]

Awesome.  Thank you sir!

Still plugging away and bottom end assembly.  Left side cases are assembled and on, and the clutch pack is in.  I should be able to start on the top end this week.

Question for the future- when it comes to the cam towers, are they matched to a cam?  Or are they just matched to the cap holders?  There's a bit of crud that got embedded in mine, but I do have a spare complete set.  There shouldn't be any issue swapping my old cam into those, should there?

[Don R]

 The cam should swap onto the different towers OK. The cam bearing caps are matched to each position on the tower but if the numbers match up it should be fine. I prefer to keep the two cam towers as a matched set, but they are commonly mixed and matched without trouble. 

[Lucien Harpress]

That's good.  I was planning on replacing the towers as a pair anyway, and was hoping to keep the same cam.

In any case, bottom end is pretty much done.  Everything's in and buttoned up- clutch, points, etc.  I was hoping to start on the top end, but after doing some maintenance on the pistons (cleaning carbon and whatnot) I realized that most of my wrist pins are less than perfect.  Two had some rough areas in the finish, even though they were small, while the third looked like it had traces of either oil starvation or heat damage.  It was enough for me to order a new set of 4 pins so I don't have to worry about it.

Since I had some time, I figured I'd also take a look at upgrading the workbench.  I got a great deal on it when I bought it, but it came with a garbage MDF top.  Twenty bucks for an edge-glued panel from Lowes later, and I got myself something miles better.

[RAFster122s]

Epoxy that can soak into your bench top would help protect the wood...
Use a good packing tape along the bench edges to keep the epoxy from dripping off the edges. When fully cured you can take a sanding block to relieve the sharp edge.

MDF makes a good top of you replace it every now and then

So, you have heat or oil starvation but are only replacing the piston pins? Wouldn't the wear or damage be there for more than just the pins???
I would worry about eccentric wear in the bore or piston wear or rod wear...

[Lucien Harpress]

The bench top is being treated with tung oil.  I was told it wouldn't crack like a polyurethane would, and soaks into the wood so minor nicks and dings are still protected.  That said, I also realize it's a workbench, and expect it to get well-used and beat up a bit.

As far as my engine goes, replacing just the pins is a combination of what I know combined with the things I don't know being almost impossible to find out.  I'm fairly convinced the machine shop that balanced my crank also replaced the connecting rods, because those look new- at the very least they were cleaned and checked.  I also didn't notice the pin discoloration the first time I took the engine apart, so that had to have happened in the 15 miles of my ill-fated trip post-rebuild.  It looked to be on the part of the pin inside the connecting rod, so if both of those are new, that takes care of that.

The only real open question mark is the pistons, and that's the thing I have no real what if knowing if the heat ruined them.  That said, it was only 15 miles of bad running (as it ran fine before that), and I can't imagine they could get that bad.  In any case, I'm willing to run them and see what happens.

[RAFster122s]

Doubt the pistons were defor.ed without visible signs of same... didn't realize you were fixing stuff after 15 mile trip that went pear shape... didn't read back far enough and not remember the thread well enough.
Disregard my comments...

[newday777]

Motor assembly proceeds nicely.  I DO have a question about the crankshaft rotor, though.  How do you know if it's fully seated?  I've got it torqued down to 72 ft/lbs per the manual, but I've got about 1-1.5mm of side-to-side play on my starter clutch gear.  Is this normal?  I know Honda likes to run tolerances pretty tight, and I don't need a rotor chewing up the inside of a sidecover.   

What did you find out on the starter gear side to side play you mentioned? No one replied back yet on it.
Is that play a wobble in the big starter gear as if the bronze bushing is worn?
I ask as I have a friend who was just asking about that on his 750A that the starter would slip occasionally, he noticed that there was play in the big gear and has some case wearing marks from it.(I haven't seen his wear marks yet)

BTW, on the sealing of your cases, do not get extra into the inside of the cases. That is a sure way to end up getting oil starvation when pieces of the sealant separate off the cases and clog the oil passages.....as that can happen fast like you had in 15 miles.

[HondaMan]

I ask as I have a friend who was just asking about that on his 750A that the starter would slip occasionally, he noticed that there was play in the big gear and has some case wearing marks from it.

If one of the little starter rollers has a slight flat spot, it will act just like you described. When it doesn't have the flat spot toward the inner drum, it works fine: if the roller rotates to the flat spot in can slip until the engine counter-rotates it off that spot when the engine starts and then falters and dies quickly. Then it's hard to find! I just replace all 3 rollers when that happens.

[Lucien Harpress]

While I never got a concrete answer on my starter gear, I decided to push through and not worry about it, for a couple reasons:

-I was able to torque the rotor down properly
-The starter clutch operates perfectly- nice grab when I rotate it the one way, zero dragging or interference when I rotate it the other way
-There doesn't seem to be any interference between the rotor and the stator cover once I put that on.

I'm probably going to re-torque that bolt after I run the engine for a bit, but everything seems fine so far.

No pictures, but I actually managed to fully button up the engine as of yesterday.  I may do some last-minute checks, but there's a good chance I can get the engine back into the frame this Saturday.