Topic: Pin2Hot's 73 CB750

[calj737]

So what becomes of the halo lighting when HI is activated? Powered through AUX, it will always be ON with the key. This will add a minor amount of strain to your charging system, but, with the headlight LO and halo ON, HI and halo will also be ON. You need to verify that the light fixture will tolerate that.

I seem to recall from other halo units that the outside ring is deactivated with HI for this very reason. I also wonder what the effect is from an illumination perspective? Or, is there a State Vehicle inspection where you are that will pass this configuration?

Just wondering.

[Pin2Hot]

Good questions.  I haven't thought about the halo's functionality when the high beam is activated, disabling it through another relay would probably be the best idea like you mentioned.  I'd run the high beam switch similarly to how I wired the signal switch and then run both halves of the halo through the N.C. side of the high beam relay to deactivate both sides when the high beam is active.

These LED strips don't pull much current.  The spec says 7W for the entire strip, of which, I'll be using less than a full strip for both halves of the halo.  The strips come with cut marks so you can chop it up as you see fit.  Hopefully it doesn't put too much strain on the stock charging system.  There are other options if it is.

I'm not entirely sure what the state says about this set up, I'll cross that bridge when I get there.

[Pin2Hot]

Some non-electrical updates: I rebuilt the wheels with new bearings, spokes and powder coated rims.  They've been sitting around collecting dust for quite some time but I should have this thing rolling soon.

[Pin2Hot]

I took the heads to get a valve job on them after learning I should have gotten that done after pressing in new valve guides.  I got them back today and they look great!

After having these parts in bags / bins for literally the past 6 years, it's a very satisfying feeling to put them back into service and throw away the old bags.  I put in some CycleX high flow valves / valve guides and APE heavy duty springs.  I re-used the stock keepers and retainers.  One of the valve seals that I got from the Vesrah gasket kit was missing the top spring that pulls the seal around the valve so I've got new ones on the way.  One thing I didn't realize about that Vesrah kit is that is doesn't have the 6 nickel pucks that seal under the cam towers.  Very frustrating so those are on the way as well. 

The next step will be pistons.  I had the cylinders bored to the 2nd oversize because of rust in cyl 4 that had accumulated in the bike when I originally got it.  I have new oversized pistons but the oil control rings that came with them are the older slotted style one piece ring.  I'm having trouble finding +0.5mm 3-piece oil control rings for these pistons so if anyone out there has some for sale, I'm looking for some.  If I can't find any, I'll just use the one piece rings unless there's a compelling reason not to.

Head:


Close up of a valve/spring:


New seal:

[koendd]

must indeed be nice to unpack everything that's looks as good as your engine!

good luck with the rebuild!

[Pin2Hot]

I found a compelling reason to go to a 3-piece oil ring: by snapping a one piece ring.


I had just finished gapping the rings and seeing that they were all within spec when I stretched this one just a little too much getting it onto the piston.  I bought these pistons/rings from another SOHC4 member years and years ago so I don't even know who makes these pistons.  They're an aftermarket 0.5 oversized set of pistons and rings with no manufacturer name so I have no idea where to look for another set.  Or at least that matches these pistons.  I actually had another set of rings (13031-300-014) but the gap was out of spec for my bores by quite a bit so they won't work.

If anyone has a set of 0.5mm over standard bore piston rings, I'm more than willing to take them off your hands.

*edit: After thinking about this, I believe I've made the wrong assumption about the pistons/rings that I'm using.  I gave them to my machinist and had him bore the cylinders to fit them thinking they were 0.5mm larger than stock.  However, after seeing that the stock Honda 0.5mm piston rings had a gap that was too large, that tells me that the bore is larger.  I'll measure the pistons when I get home to see just how large they truly are.  THEN I'll get a new ring to replace the one I snapped.

[Pin2Hot]

So it looks like I've been wrong the entire time about what pistons I have.  These appear to be 0.75 over standard pistons:


So I have a bit of a dilemma.  When I gave the jugs to the machinist, I gave him the diameter for 2nd oversized pistons, 61.5mm.  However, I also gave him the pistons I'm using so he could make sure they fit.  The pistons do fit in the cylinders although it seems like they get hung up verrrry slightly towards the bottom of the cylinder.  Is this normal?  They could be just getting slightly crooked passing through.  Here are some slight scuffs from test fitting the pistons, should I take the jugs back to the machinist?



Also if anyone can help me identify the brand of piston, that'd be super helpful:

[Pin2Hot]

I took the pistons and cylinders to the machinist and he blessed the bores as being in great shape and within 0.001 of the skirts so I'm in good shape to assemble the top end.  He did notice that at the very edge of one piston skirt, it was dragging through the cylinder so he buffed down the high spot and allowed it to drop through the jug without any resistance. 

However, the final drive seal has finally worked its way out again so I ended up splitting the cases . . . for the 3rd time.  Luckily it wasn't that big of deal as I only had to take off the shifter mechanism but I'm not taking any chances this time letting that seal slip out again.

I ordered a new a factory seal and I scuffed up the mating surfaces where it sits to hopefully provide some bite on the seal to prevent it from sliding out.  I'm thinking I may have used too much liquid gasket on the seal which may have allowed it to squish its way out.  I don't plan on using any liquid gasket on this seal this time because there seems to be a ton of pressure surrounding the seal which, well, seals it up.  Hopefully this decision doesn't come back to bite me.  Famous last words.

Upper Seal Seat


Lower Seal Seat

[754]

If the case has been welded, the fit there can change....any evidence of weld in chain area ?

[Pin2Hot]

If the case has been welded, the fit there can change....any evidence of weld in chain area ?

No evidence of that, thankfully.  I'm putting the case back together tonight so we'll know soon enough!

[Pin2Hot]

The new seal is in and holding strong.  I've been measuring the seal to case depth and it hasn't moved, I think I'm in the clear.

Don't mind the orange clamp, that was insurance when letting the liquid gasket set overnight.


Pistons are on and the cylinders and remaining top-end shenanigans will go on this weekend.

[70CB750]

Following.

[Pin2Hot]

I've been struggling to find a set of ring compressors in a local auto parts store to finally get the cylinders installed.  There's nothing too special about the simple band type compressors that I'm willing to pay $50 bucks for so I printed one on my 3D printer.



I haven't used them for their intended purpose yet because I'm pretty sure the layers of the print may bind up on the rings themselves.  I have a couple options, use acetone to smooth out the layers which might work or find some super thin metal (like a soda can) to line the compressor which should let the rings slide nicely.  You can see that it compresses the rings well (below) but I'm worried that either plastic will scrape off and end up in the crank case or the aluminum can might be too soft as well.  Finding super thin steel to line this thing might be a challenge but it's still worth more than spending money on a tool I can make myself.

[koendd]

just use your fingers and patience.. thats what I did.
Tried all the tricks with soda cans etc nothing really worked well, except my fingers...

[greenjeans]

I think you're on to something with those clamps.   I've always just used std hose clamps.   What if you just sanded the inside of them smooth ?   Is the plastic too soft that grabs ?

[Pin2Hot]

I think you're on to something with those clamps.   I've always just used std hose clamps.   What if you just sanded the inside of them smooth ?   Is the plastic too soft that grabs ?

Thanks, hopefully it works out.  I'm pretty sure the rings would dig into the plastic even if it were sanded smooth.  One method for smoothing 3D printed parts is to suspend the part above a small amount of acetone as it is heated up so the vapors pass across the part.  It's very effective but I still think that even if it were smoothed by that method or by sanding, it'd still be too soft and the rings would grab.

I'm going to cut an aluminum can into a strip that lines the entire inside of the clamp and attach it where its squeezed tight.  I'll work on it after I generate the necessary beer cans watching the election tonight.

[Pin2Hot]

It worked!  I ended up sanding down the inside of the compressors I printed like greenjeans suggested and it worked very well.  I had my wife pinch them while I lowered the cylinders when she looked at me and said "just use rubber bands or something."  I knew I married her for a reason.  So I used zip ties to hold them in place while I worked the cylinders down.



Turns out though, the printed compressors only work for the inside rings as there's no way to remove them from the outside rings once the cylinders are down over the rings.  So I did those by hand, one a time.



HOWEVER, it would seem that I didn't do a good enough job deburring two of the rings, one on cyl 1 and the other on 3.  There's a vertical scratch on the inside of the wall but it seems to be rather superficial.  I can't feel it with my finger nor does it hang up on my fingernail when I drag it across the scratch.  Based on where the scratches are, I think they're on the oil ring gaps which I might be able to address without removing the entire cylinder.  Can I ignore this or should I address it?

[SOHC4 Cafe Racer Fan]

Not that you NEED it, but there is a Honda tool.
http://www.ebay.com/itm/NOS-HONDA-CB750-K0-CB750K1-PISTON-RING-COMPRESSOR-TOOL-954-3000000-/332020001616?hash=item4d4def2b50:g:B7YAAOSwKOJYGLRY&vxp=mtr

[calj737]

Did you use any lubricant on the cylinder walls while installing the rings? If not, do so now and cycle the crank. Marvel Mystery Oil is a good choice as its nice slick. If you can not feel the gouge, it may disappear with some cycles.

[Pin2Hot]

Did you use any lubricant on the cylinder walls while installing the rings? If not, do so now and cycle the crank. Marvel Mystery Oil is a good choice as its nice slick. If you can not feel the gouge, it may disappear with some cycles.

I did, just regular motor oil though.  Here's a pic of the same cylinder before I wiped it clean to get a better photo of the scratch.  Like a fine red wine, legs and all ...

[calj737]

It almost looks like the end gap is too tight from that picture. Its interesting that the oil wasn't wiped with the rings on the downstroke?

[Pin2Hot]

It almost looks like the end gap is too tight from that picture. Its interesting that the oil wasn't wiped with the rings on the downstroke?

I measured the ring gap on all cylinders and didn't find any that were too tight and all were below the max service limit but I'm going to check the oil rings tonight just to be sure.  I had applied oil to the entire cylinder so I think what you're seeing is the residual left up top.

[Pin2Hot]

Wellllllllll, it would see as though the gaps are too tight on the oil rings.  I pretty much took the manual to say that any gap less than 0.028 was good.  The gap on the oil ring is less than 0.004 which is what was causing the scuffing.  I'll run the hone through the cylinders very lightly to clean that up, gap the rings and try again.  In the meantime, I'm printing another little tool to help with assembly.

[Pin2Hot]

I looked around here and on the intert00bs and found a couple clever ways to grind rings and ended up making this little jig:



It worked super well and I was able to gap all of my rings to 0.010 which I've read is a safe number.  I ran the hone through the cylinders very lightly just one more time to remove any surface scratches and when I assembled the cylinders, NO MORE SCUFFING!!

Here's where I am now as I wait for new cylinder stud nuts to arrive.  Of all the things I've kept track of, labeled and stored, I can't find TWO of them so I have to wait to torque the head down.  It's actually just sitting on top of the cylinders here because I just wanted to see what it looked like.  I'll be assembling the top end, timing and setting up the PowerArc ignition.

 

[Phoenix]

To my tired old eyes, it looks like you left the two o rings out between the jugs and the engine case.  Hope it's my eyesight.