Topic: Keep telling yourself - a restored 750 K2 is an investment

[HondaMan]

All of those GREEN wires you see everywhere are the grounding...uh..earthing wires. They should all culminate in a GREEN wire with a ring terminal on it that connects to the frame underneath the seat, under the seat lock on a K2 frame. If this connection is loose, dirty, rusty or missing, all the rest of the system will lose its "ground reference" of 0 volts, and the regulator will work improperly and the rectifier will run at leass than 100% of its capacity. Specifically, the regulator will never engage low-charge mode, which isn't your specific problem, but this particular GREEN wire is the same electrical circuit as the bolt mount for the rectifier, and can cause "raised ground" syndrome, lowering system voltage. So, check that GREEN ring terminal, and then also check the rectifier's bolt-on mount: make sure it is clean and free of paint where it bolts to the bracket. Also, make sure that the removable carriage that supports the electrical parts we're discussing has the little star washers where it bolts onto the bigger battery box and the frame: the brackets all ground through these star washers, so they must be CLEAN and biting into the metal.

[the-chauffeur]

Yeah - I got the earthing bit.  In fact, putting into practice all the assistance so far, I think I've gotten to the point where the charging system works properly (he says perhaps slightly over-confidently).  Took the bike out for a short run yesterday and came back with a battery reading in excess of 12v, which I'm sure it wasn't doing before. Meantime, I'd forgotten just how poor the front brake was; I reckon I'm gonna have to look out for spares to set up a twin disc system.

As for the headlight/main beam, much switching and swapping of wires has led me to conclude it's a problem in the switch. Guess I'll have that off and will resolder the insides.  And while we're still on the subject of electrics, I stumbled accross another aspect of the bike's design that makes its heritage even more weird - according to the wiring schematics, it would originally have been exported/imported to France - it's got a parking/side light, which doesn't seem to feature on any of the other '72 models/wiring schematics I've found. Confused the hell out of me when I was looking at the US/UK schematics and couldn't see the extra bulb/wires.

Barring disasters with the right hand switchgear, I think we must be pretty much done on the 750 for now - for this spring/summer at least.  It's now at the stage where it's rideable and reasonably presentable, but it's by no means finished, because the frankly diabolical paint finish on the engine is letting the rest of the bike down big time.  Since the 450 is still in bits (awaiting paint and tidying up), I'll spend some time just enjoying riding the 750 until autumn/winter (which at this rate looks like it'll start in June) and then pull the engine again.  This time, I may well get the cases blasted with shells to clean off the crap that's on them, and then get them stove enamelled for a proper tough finish rather than the crappy rattle can textures I've been struggling with.  And no, it won't be going anywhere near the shop - if this whole experience has taught me anything (other than it never hurts to have a decent thread repair kit), it's that with you guys watching over my shoulder, I really can do almost all of this myself, and in much shorter time than a shop.  Thanks all (and HM in particular for sticking this one out), but don't expect this to be the last post here.

Now, where are those little bits I'm missing like the chainguard . . . 

[HondaMan]

Now, THAT's the confidence we like to hear! 

[the-chauffeur]

 



Told you it wouldn't be long.

Quick questions on the sticker kit.  I think I know where most of 'em go:



Helmet holder - self explanatory
Engine oil - on top of oil tank so that it can be read when standing next to the bike
341 Showa - on the shocks (but since mine are Hagon's, I might give them a miss)
Preserve nature - on the tank above the fuel cap
Model information/tyre pressure - across rear mudguard

 . . . but I could do with some help with these kiddies:

Battery breather - should that be on the rear mudguard?
Made in Japan - no clue
Exhaust caution - for some reason I seem to have got the idea that this should be on the chainguard . . . but can't find it on any microfiche

Locations - and pictures if anyone's got any - would be really helpful.

Next - what's the best way of getting the Model Information sticker centred and straight across the mudguard?  I really don't want to let the rest of the bodywork down by putting it on wonky 

Thanks again.

 

[mcpuffett]

exhaust caution sticker goes on the swinging arm on the right handside, & i would mark it out for the model info sticker , if your not going to use the showa stickers do you want to part with them? cheers Mick.

[HondaMan]

Battery tube sticker goes on the side of the battery box, so it can be seen amongst the wiring there (opposite the oil tank, left side). On some, it was applied under the seat, on the frame crossmember, so it could be seen when the seat was up.

I don't ever recall seeing a "Made In Japan" sticker like that on the "K" models. 

[the-chauffeur]

More news on the electrical front.  Rode the bike to a classic show 40+ miles away and back again and found the battery was flat - again . . . ba$tard thing . . .

Turns out that - once again - HM, you were right about the rectifier not earthing.   As I think you mentioned previously, the battery tray mounts aren't attached directly to the battery tray - they clip on to the side.  So despite being clipped together, the powdercoat on both pieces meant that there was no metal-to-metal contact, and hence no complete charging circuit.

As a temporary solution, I fitted a connector from the earth wire in the loom to the top of the rectifier bolt.  Started up, and the charging levels fluctuate with the revs (yay!) - and pulling the loud handle spun the charging voltage up well over 13v (territory it hasn't seen for a long time).  While I was in there, I also swapped the cylindrical fuse holder for a blade type.  Makes replacing them a bloody sight cheaper and easier . . .

More good news - 80+ miles at 70/80mph with no worries.  Cool.  And in excess of 10miles/litre.  Thanks chaps. 

The bike got plenty of admiring looks at the show, but while the folks there were very generous about the effort that's gone into it, I could almost feel the underlying rumble that they felt the finish on the engine really let the whole lot down badly (and it does).  So I gotta start collecting bits for when the engine comes out again in autumn/winter for aqua blasting and stove enamelling (so that it looks as good as the rest of the bike).  List already includes drive chains, cam chain, another(!) full gasket kit, oil seals, gear selector forks . . .

 . . . talking of which, are the selector forks/drum/other bottom end internals from an F1 interchangeable with the K2?



Mick - send me a PM with your address and I'll post the stickers to you.

[mcpuffett]

Hi Neil, are you still after a chain guard? if so this might be what you are looking for

 http://cgi.ebay.co.uk/HONDA-NOS-CB750-CB750K2-K2-K6-CLASSIC-CHAIN-GUARD-ERA_W0QQitemZ130299330574QQcmdZViewItemQQptZUK_Motorcycle_Parts?hash=item130299330574&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318

cneers Mick.

[the-chauffeur]

Thanks Mick - I've got my eye on that (although being NOS, I reckon it'll go for stupid money . . . ). 

Stupid question:  Why is it I can't find an explanation of how the cam chain tensioner is s'posed to work in all the manuals and literature I've seen?  I guess everyone whose written these things thinks it's just common sense, but for idiots like me, that just don't work.

OK, I'm not explaining myself very well.  I always thought that the bolt on the camchain adjuster was put there to hold the adjuster pin in a fixed position - so once it was set, it wouldn't move.  Which is probably why the engine has been a bit more noisy than it should . . . but having nothing to compare it with, I just assumed that they all sounded like that. 

It never occurred to me until earlier today that the adjuster is s'posed to move back and forth - and the adjuster bolt is there to just limit the range of movement (and not prevent movement).  I went ahead and removed and greased the whole assembly before resetting it to make sure I hadn't done the slider any damage by over-tightening the adjuster bolt (I hadn't).  Unsurprisingly, the engine sounds a whole lot better now.

[mcpuffett]

The idea of the tensioner is to sit there spring loaded you undo the bolt and the tensioner pushes out makes contact with the camchain you do up the bolt,  bob's your uncle  ;)best way i can describe it, cheers Mick.

[the-chauffeur]

Yup - agreed.   

As far as I can gather, the bolt is to limit the maximum backwards movement of the adjuster.  It can go in as far as it needs to, but restricting the rear motion means the tension remains sort-of constant (I think).  Which is why the back end of the adjuster has a wedge cut out of it.

My problem is more with learning stuff like that - I don't respond well to 'loosen this bolt and then tighten that nut' when I don't fully understand the reasons for those adjustments. Guess I must've been looking out the window when that bit was covered in Maintenance 101 

[mystic_1]

No, in normal operation the cam chain adjuster is locked in place.  It only moves when you loosen the locking bolt.  When you do, the spring applies the prescribed amount of pressure to the plunger to take up slack in the chain.  You then tighten the locking bolt to, well, lock it in position.  The bolt's locknut keeps the locking bolt from backing out on it's own.



mystic_1

[the-chauffeur]

Well, OK then.

Next up - diagnostic equipment.  Have any of you folks got any experience of using one of these - http://cgi.ebay.co.uk/Gunsons-Gastester-Professional_W0QQitemZ280333498999QQihZ018QQcategoryZ30921QQssPageNameZWDVWQQrdZ1QQcmdZViewItem#ht_500wt_924?

They're no longer available new - probably because the manufacturer's realised they could make more money by selling two tools instead of one (they now do a CO analyser as one bit of kit and sell a multimeter that measures dwell, revs and so on).  But if they're any good, I'm thinking about picking one up secondhand 'cos it looks like it'll be handy to use on all of my bikes (all five are carb'd and none are newer than '92). 

Thoughts/suggestions?

[the-chauffeur]

So I won the diagnostic gizmo in the link above and having read the instructions, it all looks pretty straightforward.

Next question is how do I find out what the CO emissions levels should be on a well set-up 750K?


Oh, and while I'm here, for reasons I still can't get my head round, at least one of the carbs leaked fuel into the airbox, which dripped onto the engine and stripped some of the paint.  Not good.

[HondaMan]

Hmmm...sounds like a little crud is still in that gas tank. Maybe check the little filter screen inside the petcock, make sure it's assembled right (and still there?).

Typical normal air contains 2% CO, and more than 5% indicates a rich mixture. These bikes idle at 12:1 mix ratio, so look for around 3-4% nominal CO, I would estimate. With one of my electronic ignitions, as an example, they can be brought to idle down to about 2.5% because the spark is stronger at idle, and more consistently timed. The stock spark is a bit erratic and somewhat weak below 1500 RPM in the stock points setup.

[mcpuffett]

Neil i had issues with my carbs over flowing while the bike was standing & not being used,  i used to put all my drain tubes into a can or bottle when the bike was in the shed & it would overflow in to there, turned out it was my petrol tap even though it was switched off it was leaking past the 2 screws that hold the tap to the tank, i replaced the sealing washers with some new ones and it has been ok since  , cheers Mick.

[the-chauffeur]

Thanks Mac and HM.

The odd thing about the overflow is that it doesn't involve the drain tubes - somehow the fuel has gotten into the airbox, rather than overflow down the pipes.  Before it happened last time, I pulled the float bowls apart and cleaned out both the drain tubes and the drain tube feeds inside the bowls, so the fuel should've gone out that way.  But it didn't.  That said, since the last little episode over a week ago, the bike's been in fairly regular use and it hasn't done it again.  Whether the run prior to the last leak heated the engine cases up more than those since, I'm not sure, but I was wondering if it might have anything to do with fuel atomisation and condensation (although given that there was a good few cc's of fuel in the bottom of the airbox last time, I kinda doubt that's it).

As far as crud in the tank, I gotta pass on that one.  I'll have to drain it to check that, but I'm a little confused as to why that would cause fuel to get into the airbox - or am I not thinking latterally(?) enough? Could it be that dirt is getting into the carbs and preventing the valve needles from seating properly?

Meantime, I got some more info on the CO measurements from a dyno guy on one of the 'busa forums.  Does this make sense . . . ?

Rich = loads of fuel no air
Lean = loads of air no fuel

Use 1% as lean and 4% as rich it will give you a guide.

Airscrews on top or under the carbs

On tickover
- normally 2.5% is ok for your honda's etc.
- suzuki's like 3% for some reason
- some newer Kawaski's like 1.5%

Needle - higher throttle settings (you may need a long extension lead)

- 5-9% (very rich) can be aceived by doing a burnout on half throttle for at least one minute to allow the readings to stabilise.
(Top tip; mark twistgrip before starting and make sure neighbours are out!)

Main jet (fast cable reel) - Flat out

- 9-10%ish.  This requires a long drive probably done in 2nd gear. Be careful of erronous readings as the plug may pull out of the wall or the pipe may pop out before you reach the end of the drive maybe enlist the help of a friend.  Stop and check plug colour   

Current mot legislation is around 0.5% to 0.75% to give you some idea.

This will give you a rough idea but beware it is only a guide. Do not do it on a windy day with the wind blowing up its jacksy (ass) as the readings will be wrong. Always test it and zero it and fully warm it up if that facility exists before use. Using it up the separate pipes is a good idea then you need an infra red temp
gauge to read the egt's will assist balancing the carbs and checking the co.

Welcome to the world of float levels and seized pilot air screws!

And more news on the engine upgrade front . . . I've got my eye on a pre-re-bored(?) set of barrels, which will come with oversized pistons (using them for the rebuild will be cheaper than getting mine rebored and will mean that I can put the thing back to standard at some later point if I decide to go concours . . . or something). Trouble is, it'll be supplied without piston rings, which I'll need to find from somewhere.  Hold onto your ideas for suppliers - with any luck I'll be back in a few minutes (figuratively) with some more detailed info. 

Neil

[the-chauffeur]

Need some help again folks.  Was gonna put this in the general discussion pile, but since this thread is still open, I thought I'd keep things tidy . . .


Finally got fed up with the case paint flaking and falling apart every time someone breathed on it, so I pulled the engine (again) and have stripped it down.  It's a hell of a lot easier this time.

Anyways, last time I put the top end back together, I broke a couple of piston rings.  I had enough replacements for almost everything, with the exception of one of the thin top rings. After measuring and fiddling, and following a quick discussion with the local Honda boys, I decided to try out a thicker ring in place of the busted thinner one. The general consensus was that if it fits, and can move freely in the seat, chances are it'll be fine.  I know, I know - don't shout at me - in my defence, the thicker ones fit nicely, rotate and seem to work just as well. And I was in a bit of a hurry (OK, so that's never an excuse, but . . . )

When I got the top end off this time, three of the piston heads were quite badly coked . . . considering the bike has only done around 1,000 miles, a furry coating of coke seems quite excessive to me - and normally, I'd put it down to bad fuel mix. But the other piston head - the one with the two thicker rings - was almost completely clean.

Surely that can't be a coincidence?

The bores are all fine - completely clean and just as they were when the engine went back together last time. But I'm wondering whether they might have become very slightly irregular over the last 35+ years and the second thicker ring is creating a far better seal than the thinner ones on the other pistons.  Just to be clear, when it went back together last time, all of the valves were cleaned and reseated, and the whole lot was timed correctly.

Any ideas?  Is my train of thought on the right tracks - or have I got derailed somewhere?  And is the thicker ring likely to do any harm?

Thanks in advance

Neil

[HondaMan]

The thicker rings are leaking. That sweeps the top of the pistons, removing the carbon. In time, this will also cause a burn to start down the side(s) of those pistons, which will ruin them.

The carbon is normal, especially if the engine has not seated the rings yet (1000 miles is barely enough for that process), and if is has not been revved enough to blow out the carbon. Excessive buildup, though, can come from a too-high carb float level (i.e., the fuel needles wore a little, need some adjustment), too rich idle mix (air screws should be at 7/8 to 1 turn out on K2), late spark timing or weak spark (burned points) or with Dyna 'S' ignitions on stock Honda coils and lots of slow riding (i.e., weaker than stock spark comes from using Dyna 'S' triggers: don't know if yours has these?).

I have seen carbon as thick as 1/8" (that's U.S. inches    ) on top of 750 pistons, with no ill effects besides frequent plug fouling, though. And, a long hiway trip usually clears this up. If you have a paper air filter, beings as how you're in foggy Britain, the filter will not flow as well as the mainjet expects there: I often dropped the mainjets a full 10 size in humid climes to improve the carbon issues.

What mainjet size do you have? On a K2, I would expect either a 100, 105, or 110: the early K2 had 110, the "middle" of the production had 105, and just before the K3 appeared, they had 100, along with the short-production 7-chamber exhaust pipes. You can see how many chambers your mufflers have by counting the little spotweld dimples along their length: inside the pipe, there is a baffle at each dimple. The HM341 pipes came in 4, 5, and 7-baffle versions: the set I bought last year (new) has 5, for example. My original ones had 4 baffles, the carbs had 110 mainjets. When I replaced the pipes in late 1972 because of an accident I had, they were the 5-baffle types, and I had to go to a 105 mainjet: Honda had also done this in production about that same time. Today, at altitude, I run with 100 mainjets (6000 feet where I live), and I don't have the carbon issues.

[the-chauffeur]

Sorry to trouble you again, HM.  And thanks for the pointers.

Bit late now, but here's a photo of the head/valves . . . (3rd from left is the top of the cylinder with the two thicker rings)



 . . . and here are the pistons . . . I'm sure you can work this bit out for yourselves . . .

[the-chauffeur]

Welcome back . . .

It's been a while since the last update, and things have moved on again.  As I left the thread, the engine was apart again and following some discussion with my powdercoater, we decided that the best way to paint the engine was VHT silver, cured for an hour and a half in his ovens.  Add in a few other mods during the rebuild (inc. new piston rings, re-honed cylinders, primary chain tensioner mod, half a gallon of gasket sealant and heavy duty cylinder studs) and the rebuild pretty much went without a hitch.  Having done it myself now, I'm really struggling to see why the hell it took the shop so damn long to put together.

Anyways, here it is now . . .



 . . . and I've even rebuilt the switchgear so all the electrics work.  Right now, I'm waiting for a couple of replacement side covers and badges before sending the plastics and tank out for paint. It's going to be the same colour as the 450 (see below).

Although it runs really sweetly, the shakedown has highlighted one or two little problems, the most awkward of which is that there's a small oil leak from somewhere around the front of the rocker cover.  Looking round the cover, the only thing it can be is an uneven seal (or not) across part of the front of the gasket.  I've tried torquing the top down, but the join still seeps.  Question - now, I think I know the answer to this before I ask, but is there any way I can lift the rocker cover and re-seat the gasket (or paint some sealant between the gasket and the cover/engine) without pulling the engine out?  I'm guessing not . . .

In other news, the paint on the 450 took the best part of 2 months (again, don't ask), but it eventually came back and looks pretty darn good . . .



Despite a new wiring loom, I'm disappointed to say it's still not running.  For some reason the compression on the left side is much lower than that on the right (and it's noticeable when turning the engine over).  I stuck in new pistons and rings when I put it back together, so I'm praying it's just something simple like poorly adjusted valves, but I really need to make some time to investigate . . .

Stay tuned.

Neil

[mcpuffett]

your 450 looks bloody lovely  hope you get your little niggles sorted out , cheers Mick.

[HondaMan]

On that 750: according to Patrick in Texas, he has successfully replaced the cam cover gasket with the engine in the frame by removing the engine bolts (and exhaust pipe rear mounts, I'm supposing) and letting the engine drop and tilt a little.

On my own 750, when I switched to synthetic oil and installed a higher-flow oil pump (i.e., only 8k miles on it instead of 138k miles), the cam cover began leaking. I thoroughly cleaned away the site and sprayed some Brake Cleaner along the seam (xylene and trichlorothene, evaporates 100% afterward) to degrease it, then finger-tip-forced the hardening style of Permatex sealant into the groove, let it harden overnight. This has worked so far, about 2 months now, no leaks. This will do, until I do my next teardown to bore the .25mm cylinders to .5mm, my next HP increase project (and new cam). 

[the-chauffeur]

Thanks fellas.

I'll give the tilt 'n' shift option a try first and see how I get on.  Let's face it, I've had the engine out so many times now, one more ain't gonna take long . . .

I've ordered a Honda gasket to make absolutely sure that it works this time, but before I put it in, is there any way I can guarantee (pretty much) that it won't leak again?  I'm thinking about putting a thin layer of blue Hylomar (HT liquid sealant - non-hardening) on either side before installing, but if there's a better way, I'm all ears.

And the new side covers arrived today, so they'll go off with the tank and stickers for paint next week.

Incidentally, went out to Brands Hatch today for British Superbikes and as part of the build up, they've got a classic series going on - all sorts of old stuff out there, including at least one of the 6cyl Honda racebikes, lotsa two strokes, Matchless and BSA racers, a Honda Brittan and so on.  We arrived at the display tent to have a look round just as they were coming in, and my little miss got bumped out of the way by Ago on his MV.  Very cool, and kinda surreal, really.

[HondaMan]

Thanks fellas.

I'll give the tilt 'n' shift option a try first and see how I get on.  Let's face it, I've had the engine out so many times now, one more ain't gonna take long . . .

I've ordered a Honda gasket to make absolutely sure that it works this time, but before I put it in, is there any way I can guarantee (pretty much) that it won't leak again?  I'm thinking about putting a thin layer of blue Hylomar (HT liquid sealant - non-hardening) on either side before installing, but if there's a better way, I'm all ears.

And the new side covers arrived today, so they'll go off with the tank and stickers for paint next week.

Incidentally, went out to Brands Hatch today for British Superbikes and as part of the build up, they've got a classic series going on - all sorts of old stuff out there, including at least one of the 6cyl Honda racebikes, lotsa two strokes, Matchless and BSA racers, a Honda Brittan and so on.  We arrived at the display tent to have a look round just as they were coming in, and my little miss got bumped out of the way by Ago on his MV.  Very cool, and kinda surreal, really.

That should be fun! 

On the cam cover, I like to use the Yamabond 4 (or Hondabond 4, same stuff) latex sealant on that gasket. If previous gasket remover persons nicked the surfaces somewhere, this stuff is excellent at sealing up the damage, and lasts about forever, while not being very hard to disassemble the next time around: nice stuff. It also dries slowly (about 15 minutes), giving lots of fumble time for reassembly (the main difference between "regular" sealants and "professional" sealants seems to be a slower setting time for the pro versions, IMO).