Author Topic: Nerdos' 750K3 restoration (Read 19742 times)

rtbmrgl · « **Reply #75 on:** April 24, 2014, 05:02:35 PM »

Quote from: CB750 Cafe Racer Fan on April 24, 2014, 09:25:50 AM

Quote from: Nerdos on April 24, 2014, 08:29:48 AM
No sweat. Mrs Nerdos quite likes bikes.

This is us on our wedding day on the way to the reception having just tied the knot.

That girl's got a sense of adventure. High heels, dress and wedding hair be damned.

that's great, I love it!!!!.
When I got married my said she would maybe go on a small day ride, nothing else. That didn't last, I cant tell you how many vacations, weekend trips we have taken double up through the years.

Nerdos · « **Reply #76 on:** May 11, 2014, 02:07:22 AM »

OK. I'm in a bit of a quandary now. I'm wanting to refit the oil pump and close the pan and, according to Hondaman's wisdom I should prime the pump in an oil bath. I'm doing this but from my understanding of the instructions oil should be coming out of the port indicated by my finger when the gear is rolled by hand. The thing is that oil is not being pushed through this port and neither can I see how it could be when that port is held closed by a spring and I am just rolling the gear by hand at very low rpm. Oil is drawn in through and push out through the other two ports dependent on the direction that the gear is rolled. Is this correct? I suspect that the port indicated by my finger will open when the oil pump is driven by the engine rather than by finger.
Input appreciated.

Nerdos · « **Reply #77 on:** May 11, 2014, 04:05:05 AM »

Actually, forget this. I pushed the valve open with a small screwdriver and the oil is flowing nicely. Thanks for reading.

Nerdos · « **Reply #78 on:** May 18, 2014, 01:25:34 PM »

Bit of a landmark day today. It's finally officially spring in England. Nice and warm and sunny. Ideal weather for important business like putting an engine in a frame. Due to the order that I have tacked this rebuld I did not have the option of lowering the bare frame over the engine. As you can see I had a frame with wheels and handlebars so I used a method I picked up from the forum. All I needed was 2 sturdy storage crates, 2 axle stands, a 7' steel tube, 2 ratchet straps, some heavy duty cable ties, some padding, 3 x 3' length of 15mm pipe lagging, some wood sheets, three cups of tea and a helper.

As you will see from the pictures I protected the cam cover with some old padding (car sound insulator as it happens) held on with gaffer tape. Then the bar was laid across the padding and secured with ratchet straps. I was worried about the ratchet straps slipping off at an inopportune moment so secured them to each other with the cable ties. I hope this is apparent in the pictures. I also cable-tied some lagging to the frame tubes.
Remembering the bracket thing on the back of the crankcases (ringed in red in the picture) getting mangled when the engine was removed I decided to remove it before attempting reinstallation. Not sure if this is necessary or not but it is done now.

We carried the engine on the bar to the axle stands on upturned storage crates with some spare wood to spread the load through the axle stand feet. Yes, despite reading this forum for months and knowing full well that the engine must go in from the right I managed to set up the engine on the wrong side of the frame. <facepalm>
Sorted that out, slotted the bar through the frame and then just slid the engine along the bar and into the frame. Simples!
I have a roller. I could not resist dropping the tank and seat onto it and admiring it for 15 minutes. Still aiming to have it running in a month from now.

SOHC4 Cafe Racer Fan · « **Reply #79 on:** May 18, 2014, 04:27:13 PM »

That was quite an elaborate suspension rig. Nice going, getting the motor in unscathed.

rtbmrgl · « **Reply #80 on:** May 19, 2014, 04:33:12 PM »

Bloody genius!

jerry h · « **Reply #81 on:** May 19, 2014, 04:52:03 PM »

Very nice,
Looking good!

Nerdos · « **Reply #82 on:** June 04, 2014, 02:25:25 AM »

Can anyone help me out here? I bought a replacement brake piston from DSS but it is hollow/open at one end. Does the open end face the brake pad or does it face the inside of the caliper body?

Sent from my GT-I9305 using Tapatalk

bytio · « **Reply #83 on:** June 04, 2014, 02:28:08 AM »

Open end faces the brake pad, closed end into calliper, don't forget a new seal for the caliper

Nerdos · « **Reply #84 on:** June 04, 2014, 02:31:52 AM »

Thanks very much. Was that a forum record for a speedy reply?

Sent from my GT-I9305 using Tapatalk

Nerdos · « **Reply #85 on:** June 10, 2014, 12:31:44 AM »

I'm getting closer to the big 'turn it over and see if it works' day. However, I am presently perplexed by my oil pressure switch. I am very mindful of the need to circulate oil around a newly assembled engine as thoroughly as possible before starting it and also I will need to be vigilant about the oil pressure. Therefore I am keen to know why my oil warning light is not coming on along with the neutral light. My understanding (illustrated beautifully in my engineer-quality diagram) is that 12v is applied to the warning light on the yoke/triple tree and that connection is completed by the switch when the oil pressure is low enough to allow the switch to ground itself.
So, in troubleshooting I have:
1) Pulled apart the bullet connector for the blue/red wire in the headlamp shell and connected the wire shown as A to ground. The oil light comes on when I do this proving the supply to the bulb and the bulb itself.
2) Measured the voltage at point B (the connector on top of the oil switch). 12v is present there.
3) Measured the resisitance between point B and ground. It is not open circuit.

By my reckoning the light should be on in this situation. The only possible things I can think of is that either the switch only functions when the oil gallery actually has some oil in it or that the switch itself is not screwed in as far as it should be. I remember it was quite reluctant to go back in any further than it is now. Finallly, the oil light did work when I fired the bike up before dismantling.

Any ideas?
Cheers
Paul

Nerdos · « **Reply #86 on:** June 10, 2014, 03:59:03 AM »

The bulb is good, Calj. If I take the blue/red wire from the bulb and earth it the light comes on. The mystery is how it does not come on when the 12v makes it all the way to the top of the oil switch but not, it would seem, to earth through the oil switch. The resisitance between the electrical connector and and earth is nil which by all logic means that the circuit is complete.

Nerdos · « **Reply #87 on:** June 10, 2014, 06:29:06 AM »

I don't mind being told that my logic seems perfect. Who would? Anyway, I will take a short length of wire and bridge the connection on the top of the oil switch to the crankcase. The light should come on in that case. If the light works like that I can pull the switch...hopefully. I do have 2 spare CB400f engines which share that oil switch so I can swap out if needed. I seem to remember taking it off and putting it on with mole grips. Why does it not just have a hexagonal body so you can use a less brutal tool?

Nerdos · « **Reply #88 on:** June 11, 2014, 12:52:02 AM »

I did the bridge with a piece of wire and the oil light did come on so, with my self-imposed deadline of 1 July looming, I decided to junk the switch and take one off a spare CB400F. Problem solved. Same part number according to CMS but spot the difference. 750 on the left, 400 on the right. Anyway, it fits and it works. How do I know it works? Only that the bloody engine fired up first press of the button. I can't say it's purring like a kitten just yet, rather wheezing like an asthmatic and spitting like a scolded cat. I hope I will get the running refined. One problem is that the carbs don't snap back properly. I have read some advice here about taking them off and slackening off the 8 screws that hold the carbs to the mounting plate to cure a possible skewing of the carbs. Given that it took a full hour and a lot (a very lot) of industrial-grade swearing to get them on I cannot say I am relishing the job. The carb to inlet rubbers are new DSS pattern parts (the originals were as hard as wood) and I must say the jury is out on the DSS parts right now. For a start they have a smaller outside diameter than the oirignals which means that the clamps have to be done up fully just to apply any pressure on the boot at all. I can't say I believe 100% that the clamps are doing anything useful like stopping vacuum leaks. I will test that with some propane at the weekend.
Thanks for all the help so far. I know I will be back for more.

Nerdos · « **Reply #89 on:** June 16, 2014, 03:50:43 AM »

Well, as time marches relentlessly onwards I am finding more problems with the bike. The throttle snap back issue has been solved with a new spring - the photo tells a story there.
The clutch lever was all floppy and the only resistance in the lever at all was from the clutch arm return spring. This had me really baffled until I decided to pull the clutch cover and discover that i am missing the part number 7 from this exploded clutch diagram. This lead to a feeling of disgust at myself at not noticing when I reassembled it followed by annoyance that I couldn't find it in my garage. This was followed by more annoyance at the need to spend yet more money on a new one followed by helplessness at finding the part discontinued and finally elation at discovering that it is the same part as used in the CB400F which I have 2 spare engines for. I will say that the Hondabond stuff is very adhesive. The clutch gasket split down the middle leaving equal layers on both of the mating faces. Looking forward to scraping all that off. At least I didn't have to drain the oil to check the clutch - that was a blessing.

The Boyer-Bransden electronic ignition has finally given up the ghost too. This unit has been on my CB400, then my 550, then my 500 then back to my 400 and now it seems the 750 was one move too many. DSS replacement should be en route soon.

Before the Boyer unit died the engine was running on 3 cylinders and the exhaust leaking on 1 and 4. Hopefully I have sorted the exhaust leaks although having to hit the headers with a rubber mallet to seat them was not something I did before exhausting (no pun intended) other options.

The non-running number 2 cylinder has fuel in the bowl and a spark at the plug. The revs pick up when I spray carb cleaner into the throat of no. 2 carb so this does strongly suggest a blockage. I am really, really hoping to be able to remove the slow jet with the carbs in situ and hopefully find the blockage there. I am very keen to avoid haing to take those bloody things off again.

More later in the week.

Nerdos · « **Reply #90 on:** June 17, 2014, 01:15:48 AM »

Still having clutch problems. I have fitted the missing part (no 7 from the picture in my previous post) but there is still no resistance in the clutch lever. That is to say that the clutch lever on the handlebars moves the clutch actuator arm forwards by an inch or so but there is no feeling of any resistance in that lever other than the force exerted by the clutch arm return spring. I have wound the screw in until I can feel resistance and then backed it off a quarter turn but there is still no resistance. Any ideas, fellas? This has me stumped.

bytio · « **Reply #91 on:** June 19, 2014, 01:10:11 AM »

Have you checked the clutch spring length, I had a similar issue after replacing clutch springs that were new but too short

Nerdos · « **Reply #92 on:** June 19, 2014, 02:00:51 AM »

Small update here. I took the clutch cover off and fumbled about with the lifter mechanism and refitted it. Now there is plenty of resistance in the lever. In fact, I would say way too much resistance. The clutch cable was totally seized and the bike had not run since 1994 when I got it so I don't know how the clutch should feel but as I mentioned in a previous post, I have had 3 other SOHC4s in my time and although the 750 is larger and therefore presumably has a heavier clutch, I still think there is something wrong. I can't check its operation right now as I am waiting to fit the new ignition system (arrived an hour ago but I am trapped at my desk). As part of the rebuild I replaced the clutch cable with a genuine Honda part. I also bought a clutch kit of plates and springs. The springs were genuine Honda and the plates were aftermarket with the diagonal cuts on them. Having absorbed the wisdom of Hondaman on these plates I decided to measure the originals, found that they were within tolerance and reused those. So, in essence, new genuine Honda springs and cable with original, 72 vintage, clutch plates. If anything it feels almost as if when I pull the lever something is bending inside the clutch. It certainly does not give the feeling of something being moved as Soichiro intended.
Very much open to advice. The bike has run for about 15 minutes on the bench so oil should have circulated thoroughly in the clutch and yes, I did oil the parts thoroughly as I reassembled.

Nerdos · « **Reply #93 on:** June 20, 2014, 12:31:57 AM »

DSS electronic ignition works a treat I am pleased to say. Love the LED on the backplate so that you can set the timing initially without a strobe.

Clutch still a problem though. It seems the clutch is disengaged at all times. So, lever at the bars is in the correct position at rest and can be pulled back towards the bars by about an inch or so (but it's very stiff). However, if you put the bike in gear with the engine running the rear wheel does not turn. In fact there is barely any difference detectable if I stop the engine, put the bike in gear on the centrestand and rotate the rear wheel by hand or if I do the same thing in neutral. I know I will have to pull the clutch out to find out what cretinous mistake I have made but if anyone can give me some pointers before I get oily I'd appreciate it.

Nerdos · « **Reply #94 on:** June 20, 2014, 07:32:17 AM »

Actually, this looks promising...
http://forums.sohc4.net/index.php?topic=36525.0

Will have to wait till Sunday to find out but it seems the most likely problem.

Nerdos · « **Reply #95 on:** June 23, 2014, 12:20:21 AM »

As suspected, the clutch inner was 90 degrees out of alignment with the basket. Another easy to make mistake which I should have noticed. Now I have this cracked lifter plate to show for my incompetence and they're not particularly cheap to replace either. D'Oh! The clutch does work now though. Not heavy in the slightest - I just can't go anywhere until I have replaced it.

Nerdos · « **Reply #96 on:** July 01, 2014, 07:09:05 AM »

CMS came to the rescue with a new clutch lifter plate and we're mobile.

The bike has just come back from its MoT test - not sure what your equivalent is called in the US but in essence it's a roadworthiness certificate. Anyway, it passed. First time. Very nice too although I think probably a bit lenient on the part of the tester but I'm certainly not complaining.

The most pressing issues are cylinder 3 not firing and teh transmission. I'm sure I will get the first problem sorted without too much fuss. Number 2 had a blocked slow jet. I cleaned that out and it started firing but number 3 then picked up the baton of faultiness and ran with it. I've had the float bowl off and it's full of fuel and the slow jet is clear so that's just the spark to look at I guess.

The most worrying problem is I only have 1st and 2nd gear. The lever will move up when I am looking for third and I can feel the resistance of the spring which returns the lever to the 'at rest' position but no 3rd gear. Nor 4th nor 5th obviously. I am pretty sure I checked the gears all engaged when I was assembling the engine. It all seems so long ago now.
Anyway, any advice on my gearbox woes would be welcome.
In the meantime here's a picture of the machine just before its MoT (which you will have ascertained, does not include a road test).

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Author Topic: Nerdos' 750K3 restoration (Read 19742 times)