Author Topic: 750 K2 Strip & Rebuild - help please  (Read 8671 times)

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #15 on: February 16, 2022, 06:55:12 AM »
Wildo… thanks Trig.

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #16 on: March 03, 2022, 09:58:45 PM »
There’s been a fair bit of discussion on the forums wrt home plating old nuts and bolts vs commercial plating….
Browsing Yamiya website yesterday, I noted CB750 bolt sets for the body & engine - at a price (and convenience) significantly cheaper than either of the above. (assuming a single bike restoration)

Comments / thoughts pls - on paper it seems the way to go in my case.

Offline Johnny4428

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Re: 750 K2 Strip & Rebuild - help please
« Reply #17 on: March 03, 2022, 10:15:15 PM »
Seems a good idea as long as the kit contains like for like bolts that are correct for your bike and also would save a lot of fiddly cleaning/buffing. I purchased a general bolt kit from CMS and also cleaned and plated any fittings that were correct for bike and not had the “hairy ape” with the ill-fitting spanner treatment. (I had one or two of them)
The kit did contain the ones that I had to replace so was good. It would be very nice to get a bolt kit that contained washers and nuts IMO.



1952 Cymoto on Triumph bicycle.
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Offline Trigger

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Re: 750 K2 Strip & Rebuild - help please
« Reply #18 on: March 04, 2022, 06:49:40 AM »
The frame bolt kit from Yamiya is for CB750K0, not for a K2 and the engine bolt kit only contains the JIS screws. There are many other nuts bolts and washers that all add up to lot of money, always better to replate the original Honda ones to keep the bike original  ;)

Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #19 on: March 04, 2022, 08:24:40 AM »
I agree with Graham plus the Yamiya 750K0 kit is quite expensive (replicates early  67-69 JIS bolt head markings)  and many of the bolts are not true 'large figure 8' parts. Well that's how they were a few years back .. perhaps they have improved .. James will know  :) Also a lot of Genuine Honda bolts and ones sold by Yamiya  are heavily yellow/gold passivated. If you replate the bolts and  clear/blue passivate them,  then they look more like the original silverey finish with decent weather protection. I don't know when it changed but the bolts used to be cyanide process, zinc plated but are now bright zinc acid plated and passivated.
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #20 on: March 26, 2022, 11:59:19 AM »
Have struck gold in finding a very nearby SOHC Engine guru, who’s been building, modifying, racing the ‘750 unit (sidecars) since 1972.

And extremely generous with his time / knowledge; I traipse up-to his workshop with bits in hand, and rattle through things that would otherwise take me days … if I even knew to do them.

Anyways, yesterday, Lindsay cleaned out the four oil galleries within the crankshaft. (I was convinced this was a waste of time as I’d bathed it 48hrs in degreaser, and then pressure washed those galleries with a garden hose….)

First up he TIG welded blobs of steel onto the ball bearing plugs, before tapping them out with a cold chisel. This gave us access to the gallery downstream of the big end ports…. which were truly blocked with **it. (same workings as a centrifugal oil filter I guess). With a 6mm(?) drill bit this was all removed to a depth of about 1”… ie the bit broke through more-or-less at the big-end oil ports. (The crap that came out was a plastercine like sludge)

Then a wash out, blow dry… replace with a new ball bearing using the original punch marks to secure.

(The top photo shows the gallery path depicted with the screwdriver. The con-rods have been reinstalled and so the big-end oil ports not visible in the pics)

May not impress the established engine builders here - but this was all new to me.
« Last Edit: March 26, 2022, 12:13:00 PM by Lobo »

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #21 on: March 26, 2022, 12:30:09 PM »
"which were truly blocked with **it. (same workings as a centrifugal oil filter I guess). With a 6mm(?) drill bit this was all removed to a depth of about 1”… ie the bit broke through more-or-less at the big-end oil ports. (The crap that came out was a plastercine like sludge)"

The fundamental problem is from oils of that original period being susceptible to tarring at high temperatures. Newer versions of "mineral " oil have improved in this aspect.
The real change though comes from "synthetic" oils that in reality don't do this. I've put those two in " " as the names just don't reveal the full story of how they differ, with most commentators demonising the newer without understanding what they hold prejudices against.
I've used synthetic oils in most engines I look after since the 1980's and principally because that sludge and degradation is not present.

For another thread really though.

Cleaning the oil ways though, I'd use steam to go through these with. Make a nozzle from copper brake pipe or similar, fit to household steamer and blow through anything you can't immediately access.

Sounds a very thorough engine guy you've used there Simon.

Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #22 on: March 26, 2022, 12:40:03 PM »
Have struck gold in finding a very nearby SOHC Engine guru, who’s been building, modifying, racing the ‘750 unit (sidecars) since 1972.

And extremely generous with his time / knowledge; I traipse up-to his workshop with bits in hand, and rattle through things that would otherwise take me days … if I even knew to do them.

Anyways, yesterday, Lindsay cleaned out the four oil galleries within the crankshaft. (I was convinced this was a waste of time as I’d bathed it 48hrs in degreaser, and then pressure washed those galleries with a garden hose….)

First up he TIG welded blobs of steel onto the ball bearing plugs, before tapping them out with a cold chisel. This gave us access to the gallery downstream of the big end ports…. which were truly blocked with **it. (same workings as a centrifugal oil filter I guess). With a 6mm(?) drill bit this was all removed to a depth of about 1”… ie the bit broke through more-or-less at the big-end oil ports. (The crap that came out was a plastercine like sludge)

Then a wash out, blow dry… replace with a new ball bearing using the original punch marks to secure.

(The top photo shows the gallery path depicted with the screwdriver. The con-rods have been reinstalled and so the big-end oil ports not visible in the pics)

May not impress the established engine builders here - but this was all new to me.

That's interesting Simon ... probably one of the most interesting posts I have seen on here recently and I wonder what our resident engine Gurus on here think.

It sounds a bit like what mate Graham Curtis does on pressed-together Honda roller bearing cranks. There are inaccessible grooves that clog up with thick highly compacted muck,  that can only be removed by pressing apart the crank and physically removing the compacted debris. He claims that the particles preferentially build up in those internal areas rather than being centrifuged out in the oil filter 'cup' mounted on the end of the crankshaft. Also by removing all of the debris, more oil is flung up into the underside of the piston area (as intended)  and lubricates the small end better.
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline K2-K6

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Re: 750 K2 Strip & Rebuild - help please
« Reply #23 on: March 26, 2022, 02:35:13 PM »
Ash, it's mirrored in any specific site within engines that take the oil above critical temperature limits.  Probably in the range of exceeding 155 / 175 C for localised conditions.  This will often be propogated when the oil becomes stationary after turning the engine off and the heat can no longer be extracted by continuous oil flow.

Ultimately, in these small passages it gives compromise to the desired flow as carbon builds, then making it even more susceptible to over heat.

Generally the oil is targeted to run at 90C continuous,  and would largely be out of range for mineral oils above about 135C.

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #24 on: March 26, 2022, 03:27:15 PM »
Your wrong Simon, that impressed me. Never heard of anyone doing that before, great info and might explain those unexplained "why has my engine seized" questions when there is no rational explanation, a big clump of that stuff coming loose would ruin most engines, who knows what it contains.
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Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #25 on: March 26, 2022, 03:59:50 PM »
Your wrong Simon, that impressed me. Never heard of anyone doing that before, great info and might explain those unexplained "why has my engine seized" questions when there is no rational explanation, a big clump of that stuff coming loose would ruin most engines, who knows what it contains.

Impressed me too .. I had always wondered about those sealing balls but thought removal would be a nightmare and since I never heard of anyone removing them and finding what lies underneath them I kind of (probably wrongly) dismissed the idea. I have a decent TIG welder and a scrap crank so going to try it out sometime ... although my scrap crank is a very early die-cast and I seem to remember that that they may be sealed differently. How easy was it to chisel the balls out Simon, that's assuming you were there when he did it. I wonder what Vic World does or possibly sandcast cranks don't have those balls ?
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline taysidedragon

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Re: 750 K2 Strip & Rebuild - help please
« Reply #26 on: March 26, 2022, 04:39:42 PM »
Yes, very thorough.  He obviously knows his stuff.
Old Triumphs have a designed sludge trap in the crank which has to be cleaned out occasionally, along with the oilways.  It can be difficult to access but not as difficult as removing those ball bearings.
Gareth

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Offline AshimotoK0

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Re: 750 K2 Strip & Rebuild - help please
« Reply #27 on: March 26, 2022, 05:28:59 PM »
I found this post on the USA site regarding the sealing balls

http://forums.sohc4.net/index.php/topic,146287.msg1664725.html#msg1664725
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline Trigger

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Re: 750 K2 Strip & Rebuild - help please
« Reply #28 on: March 26, 2022, 06:31:38 PM »
You should always remove the balls when cleaning a crank. The later 750 crank has grub screws with are easier to remove  ;)

Offline Oddjob

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Re: 750 K2 Strip & Rebuild - help please
« Reply #29 on: March 26, 2022, 09:24:22 PM »
I have 2 scrap cranks I was going to give to the scrapman but I might have a go at getting those ball bearings out for a laugh.
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