Author Topic: Nerdos' 750K3 restoration (Read 19321 times)

seanbarney41 · « **Reply #25 on:** October 30, 2013, 03:25:50 AM »

I would still try running it for some miles before tearing it down. Those numbers very well may improve...

Nerdos · « **Reply #26 on:** October 30, 2013, 03:41:37 AM »

That's encouraging to hear. How does that work then? I mean the potential improvement. What can occur within an engine to make this happen?

seanbarney41 · « **Reply #27 on:** October 30, 2013, 01:39:12 PM »

rings get stuck in grooves, valve faces corrode...sometimes running the bike will unstick the rings and smooth out the corrosion on the valve faces. Understand that there may be rapid wear involved in this process but these engines are quite durable and can withstand a significant amount of abuse. Also, even though engine rebuild parts are generally available, it is still quite an expensive and time consuming endeavor.

Nerdos · « **Reply #28 on:** October 31, 2013, 01:30:42 AM »

Thank you for that explanation. Having done some more reading about the 'correct' was to do a compression test - and there doesn't seem to be a hard consensus - it seems I should have conducted the test with the throttle wide open or indeed with the carbs off. I did open the throttle fully and ran the tests agan, twice.
The results are
1) 170 psi
2) 170psi
3) 155psi
4) 170psi

I think #3 is on the margin but given your advice I will chance it that particular cylinder will improve with use. If I have to take the engine out again some time for rings or valves then so be it. I have the luxury that the 750 will be a play thing that I won't depend upon nor miss if it is out of commission for a few weeks next winter.

All I need now is Hondaman's book (which I believe is hot off a press somewhere near me) and I'll start stripping/tearing it down (though not the engine - just the rest of the bike).

edwardmorris · « **Reply #29 on:** October 31, 2013, 08:27:06 AM »

Quote from: Nerdos on October 31, 2013, 01:30:42 AM

.....All I need now is Hondaman's book (which I believe is hot off a press somewhere near me) and I'll start stripping/tearing it down (though not the engine - just the rest of the bike).

I'd recommend getting a copy of the Honda Factory/Shop manual printed alongside Hondaman's book if you're not going to do an engine teardown. Hondaman's book is about the best there is when it comes to hands on engine work, performance enhancements and the electrical system. I find the Honda Shop manual and a parts fiche (printed and set as wallpaper in my workspace

see my build thread) very helpful as I'm going through disassembling mine.

Nerdos · « **Reply #30 on:** December 07, 2013, 01:22:58 AM »

I've very nearly finished the tear down of the frame (or strip down as we call it over here) and I have a question that I've not been able to find the answer for elsewhere. In the section of frame that supports the back of the seat loop I have a bolt - one each side in fact. They are neither use nor ornament as far as I can make out but can anyone else shed any light on their purpose.

seanbarney41 · « **Reply #31 on:** December 07, 2013, 09:55:56 PM »

looks like some of that good old previous owner hi-jinx

Nerdos · « **Reply #32 on:** December 08, 2013, 02:18:38 PM »

I thought someone might say that. I'm hoping the frame hasn't been unduly weakened. It is slightly pinched at this point. If I had a welder I could fill the hole and grind it down. As it is I expect I'll replace the bolts with nice looking ones and pretend it was always supposed to be that way.

In other developments today I got the engine out of the frame using the Hondaman method. I intend putting it on a car engine stand so instead of shifting the unit sideways onto a 10" platform I shifted it onto my bike lift. Once I've finished cludging the adapter brackets I'm making to allow the stand to take a motorbike engine I hope I will be able to simply pump up the bike lift and attach. Pics attached. As I had to move my 75 CB400 from the front of my garage and this is the SOHC4 forum I've included a pic of that too. I restored that about 10 years ago. Still haven't got around to doing the paint nor getting any mirrors for it. The CB400 will be my regular ride soon as I have found that I will have to sell my Aprilia Caponord to finance the CB750.

Nerdos · « **Reply #33 on:** January 12, 2014, 07:33:26 AM »

I've made some progress since I last posted. Frame and assorted parts have gone off for powder coat. Should have them back in a week looking nice but probably a bit too glossy. Having read so many threads on this forum of peoples restorations I have concluded that what I am undertaking here is actually a rebuild. Not only that but I'll be emulating the look of the European direct sales K1 in planet blue metallic. So, definitely not a restoration.
I had the forks off and once I got the gaiters off I was pleasantly surprised by the condition of the chrome. Seems odd that Honda only applied decent chrome to the sliding portion and not the part under the fork ears but I guess some Honda beancounter calculated a tiny saving in Yen over the production run. Anyway, I did the right leg first, stripped it using the broom handle method to get the damper rod out and then removed the lacquer and corrosion using a red scotchbrite wheel on my drill. Then I polished the slider on a polishing wheel to remove any marks left by the scotchbrite. Following that I wrapped the slider in a scotchbrite pad and twisted that back and forth using red, then green then grey pads to get the finish you see here in the before and after shot (or right and left to be more accurate). Gave the slider a coat of lacquer which makes it look too shiny - maybe some 1500 sandpaper is needed.

So, I moved on to the left fork leg to find a line of pitting the like of which I have never seen before. I make the pit, or trench maybe, to be about 1.5mm in depth. I took some shots showing the damage measured in good, old-fashioned inches too since I am seeking the advice of a feet and inches loving nation. Can this fork leg be saved by hard chroming?

Dream750 · « **Reply #34 on:** January 14, 2014, 06:29:02 AM »

Quote from: Nerdos on January 12, 2014, 07:33:26 AM

Not only that but I'll be emulating the look of the European direct sales K1 in planet blue metallic.

Planet blue metallic was not used on the 750 K1. Perhaps you are thinking of the (darker) K1 Polynesian blue metallic that was used on the Euro and Japanese market bikes? Here's some color examples to compare:

calj737 · « **Reply #35 on:** January 14, 2014, 07:36:39 AM »

Those fork uppers need to be replaced, not re chromed. You can purchase replacements for about the same cost as re chroming.

Nerdos · « **Reply #36 on:** January 14, 2014, 07:41:27 AM »

Those are useful pics and I thank you for them. What I am aspiring to is shown in the pic below. My bike is a K3 so has chromed fork ears, black headlight and a different tail light which bolts on at the end of the fender and closer to the seat. It also has a grabrail which is kind of rusty and so I may dispense with. On the plus side it also has the 750 Four chrome lettering on the side panels as the one in the picture does and has its petcock on the right. My K3 was built in October 1972 so I guess some of the cosmetic details like the different side panel badges were introduced as the production run went on. I'll need to replace the side panel badges I have (orange) with red ones of course.

So, the million dollar question - what model and colour is the (frankly gorgeous) bike in the attached picture?

Nerdos · « **Reply #37 on:** January 14, 2014, 07:45:25 AM »

@CalJ737 Ooops. Too late. The forks got picked up this morning by courier to take them to the fork doctor. If they can't be fixed then the forks will be returned to me. Cost is £165 / $271 but the quality is better than factory in my opinion (I had my CB400F stanchions rechromed by him back in the early 90s). Turnaround is 3 weeks so, assuming they come back mended I'll post some pictures of them.

Dream750 · « **Reply #38 on:** January 14, 2014, 01:12:40 PM »

Quote from: Nerdos on January 14, 2014, 07:41:27 AM

So, the million dollar question - what model and colour is the (frankly gorgeous) bike in the attached picture?

I can’t be 100% sure of the color blue used in your attached pic. $:-\$

But, the bike is definitely a K1 and they were produced in two different colors of blue.

Polynesian blue metallic and Candy blue green

Nerdos · « **Reply #39 on:** January 14, 2014, 01:27:55 PM »

Well, that's thrown me a curve ball. I'd convinced myself that it was Planet Blue. Can you tell me what gives away that it is a K1 rather than a K2? I am new to this and appear to have picked up some duff info along the way. For the record the image comes from CMSNL's website and the caption reads simply Blue Factory pic of CB750. From the pics you have supplied I would say my picture was closer to Polynesian Blue than the candy blue.
Also, for what it's worth, Yamiya has this on eBay right now at the princely sum of $1,200. They list it at K2 Planet Blue metallic but they are not asserting that this was a factory option.
http://www.ebay.com/itm/HONDA-CB750-K2-PAINTED-TANK-BODY-KIT-SET-PLANET-BLUE-METALLIC-NEW-G004PLB-/131077995788?pt=Motorcycles_Parts_Accessories&hash=item1e84db7d0c&vxp=mtr

Dream750 · « **Reply #40 on:** January 14, 2014, 02:23:40 PM »

The Yamiya K2 planet blue pic is an official factory production K2 color, but its just not correct for a K2 USA market bike.

Quote from: Nerdos on January 14, 2014, 01:27:55 PM

Well, that's thrown me a curve ball. I'd convinced myself that it was Planet Blue. Can you tell me what gives away that it is a K1 rather than a K2?

I understand that the variations between the different market models add to the confusion.

Let’s compare some of the (USA) market K1 to K2 differences ...

K1 taillight is smaller, bigger taillight for the K2.

K1 doesn’t have a wrap around passenger grab rail, the K2 does.

K1 side cover jewel emblem is red, changes to orange for the K2.

K1 fork ears and headlight bucket are painted the body color.

K2 fork ears are chrome and the headlight bucket is black.

K1 fork ear reflectors are smaller, bigger reflectors for the K2.

These differences make the blue bike in the pic a K1.

Nerdos · « **Reply #41 on:** January 15, 2014, 12:20:48 PM »

Found this thread where the owner states his bike is a Japanese market K1 in Polynesian blue.
http://forums.sohc4.net/index.php?topic=133223.0
The main uncertainty I have is that the tank stripes in the photo I am working towards is kind of pale compared to the much more yellow gold in the Polynesian blue pictures. I could really do with finding an actual example that I can look at. I guess I have a better chance of achieving this than most since I am on the right side of the Atlantic (insofar as finding these bikes is concerned).

Nerdos · « **Reply #42 on:** January 21, 2014, 05:14:28 AM »

Got my frame and other bits back from the powder coater today. A good job done I think from what I have unwrapped so far. This is the beginning of the good times when new and refurbished parts come together to look lovely. Therefore I couldn't resist knocking the top steering head race into the frame before I had to go to work. This worked fine and by the numbers. The spacer though, for the taper roller kit I bought, looks a little snug on the stem. In the picture this is as far as it goes by hand. I could heat it up and then give it some hammer attention but I wanted to check: should the spacer really be this tight? Any insight appreciated.

calj737 · « **Reply #43 on:** January 21, 2014, 05:19:22 AM »

Some of the kits have 2 spacers, and 1 of those goes above the top bridge, under the steering nut. Do you have a second washer, if so that may fit better. But to directly answer your question; no that seems too small to be a proper fit.

By chance, did your powder coater sand blast the stem? If so, you may need to polish it back down if he has raised the surface and THAT is causing the interference.

Nerdos · « **Reply #44 on:** January 21, 2014, 06:09:17 AM »

Thanks for the reply. The kit only has the two bearings and races and one washer. I was so sure this was going to be easy since it appears identical to the pics in Hondaman's book and the bike in that book is a K3 too so I reckoned I was home and dry there. Good call on the sand blasting though. I'll get the polishing wheel on it when I get home from work and see how that goes. If that doesn't make the difference I'll get the verniers on the OD of the stem and the ID of the spacer and see how the land lies.

Nerdos · « **Reply #45 on:** January 21, 2014, 10:27:29 AM »

I've measured the bottom of the steering stem and it appears that it is not circular. It is wider left to right than it is front to back. Also, when I dressed the bottom of the stem with emery paper it shows a sort of crease or line in the metal which I suspect is not supposed to be there. Is this stem junk or should I just file it a little? The ID of the spacer and bearing is 30.00mm and 29.98mm respectively. Sorry about the metric - I had my brain in euro mode at the time.

stewonepot · « **Reply #46 on:** January 21, 2014, 12:30:55 PM »

maybe it had a slight front ender?
regards stew

Nerdos · « **Reply #47 on:** January 21, 2014, 12:36:33 PM »

I was thinking the same. I'm unsure about whether the stem being in need of minor fettling is cause for concern. If it was a footrest or a grabrail or maybe even handlebars I would just straighten them out but with steering and braking I am inclined to call upon the collective knowledge and advice of forum members.

calj737 · « **Reply #48 on:** January 21, 2014, 12:41:23 PM »

It would be "best" to repair/replace that stem. That is in a perfect world, of course. If you can locate a donor stem, the original can be pressed out and replaced with a new press-in.

Else, you could have turned on a lathe pretty reasonably I'd suspect.

To repair, it's a bit of a "knick and knack". Filing the stem would only serve to weaken it, but by how much? Can you see inside it from the bottom? How bad is the deformation truly? If you do repair it, but are worried about strength, you could fill the tube from below with new rod, have it welded in top and bottom. Should be more than sufficient for a now and then street bike (presuming that is the role of this bike).

stewonepot · « **Reply #49 on:** January 21, 2014, 12:48:15 PM »

hi nerdos
you cant be too careful with steering and stopping, try to check another for size!
ps when in uk i liked nottingham a lot
regards stew

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Author Topic: Nerdos' 750K3 restoration (Read 19321 times)