Author Topic: Remarkable! An unusual 750K6 rebuild.  (Read 6528 times)

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Offline SOHC4 Cafe Racer Fan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #25 on: October 22, 2015, 08:29:48 AM »
MV - my old home town.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline Woodtone

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #26 on: October 22, 2015, 05:23:04 PM »
Steve-O
Orange County plating Chromed the fender, Wheel Works of Garden Grove, Ca laced the new rimes. I did the polish work. Yamiya supplied the parts. Very pleased with all especially Yamiya. Good service and quality. Prompt delivery.

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #27 on: October 22, 2015, 07:25:24 PM »
The front end treatment for the turn signals was done to apparently allow the clear Slipstreamer windshield to fit with the long front "tails", putting the turn signals below it. Otherwise, the turn signals would have forced the shorter windshield, which doesn't help as much (nor look as nice) as the full-length 'Slipper'.

Mike: I know the source of the battery troubles, will bring that topic up in detail a little later. It's something I "treat" fairly often, like 1-2 times per year on bikes that come by. (Right now I am stuck in AR until Sunday or Monday.) It is rooted in the use for BOTH the 3-ohm Dyna coils and the Dyna S ignition on these bikes, which together draws so much power that the battery cannot "catch up" in charge until 4000 RPM. Over time, this damages, then destroys, the battery chemistry, and then the battery.

In addition: the battery ground was not in the right place, causing some losses there, and I suspect (haven't yet seen, though) that I will find fried alternator connectors, all of which add up to weak electrical performance.

;)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Offline knottedknickers

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #28 on: October 23, 2015, 07:35:45 AM »
Beautiful bike! My '76K front fender has supports at the ends (see pics here: http://forums.sohc4.net/index.php?topic=141388.0). Are you waiting to put those on? Or leaving them off? Looks like a lot of unsupported fender without them...
CB750 K6 http://forums.sohc4.net/index.php?topic=141388.0

The plural of "anecdote" is not "data" (Borgmann 2002:5).

Offline ofreen

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #29 on: October 23, 2015, 07:55:51 AM »
Mike: I know the source of the battery troubles, will bring that topic up in detail a little later. It's something I "treat" fairly often, like 1-2 times per year on bikes that come by. (Right now I am stuck in AR until Sunday or Monday.) It is rooted in the use for BOTH the 3-ohm Dyna coils and the Dyna S ignition on these bikes, which together draws so much power that the battery cannot "catch up" in charge until 4000 RPM. Over time, this damages, then destroys, the battery chemistry, and then the battery.

Not to be argumentative, but I've been running a Dyna S and 3 ohm coils in the 750 since 1990.  I have yet to have a battery last less than 7 years.
Greg
'75 CB750F

"I would rather have questions I cannot answer than answers I cannot question." - Dr. Wei-Hock Soon

Offline andy750

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #30 on: October 23, 2015, 09:26:36 AM »
Mike: I know the source of the battery troubles, will bring that topic up in detail a little later. It's something I "treat" fairly often, like 1-2 times per year on bikes that come by. (Right now I am stuck in AR until Sunday or Monday.) It is rooted in the use for BOTH the 3-ohm Dyna coils and the Dyna S ignition on these bikes, which together draws so much power that the battery cannot "catch up" in charge until 4000 RPM. Over time, this damages, then destroys, the battery chemistry, and then the battery.

Not to be argumentative, but I've been running a Dyna S and 3 ohm coils in the 750 since 1990.  I have yet to have a battery last less than 7 years.

+1 similar story to Greg (Ofreen). Same Dyna S in a CB750K4 since 2001 -2015. Batteries have not died prematurely (AGM batteries).
Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. Yamaha Tenere T700 2022

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

Offline andy750

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #31 on: October 23, 2015, 09:30:08 AM »
The Yamiya clear lenses are very nice and I have them on my K2 now for 6+ years. The only issue I have had with them is the bulbs vibrating loose as the internal socket is not as robust as the original and this will blow your fuse.

Love the new colour very nice!
Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. Yamaha Tenere T700 2022

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

Offline Kustomizer

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #32 on: October 23, 2015, 10:29:54 AM »
Very nice!  Love the paint!

Offline Henning

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #33 on: October 23, 2015, 02:29:16 PM »
Mike: I know the source of the battery troubles, will bring that topic up in detail a little later. It's something I "treat" fairly often, like 1-2 times per year on bikes that come by. (Right now I am stuck in AR until Sunday or Monday.) It is rooted in the use for BOTH the 3-ohm Dyna coils and the Dyna S ignition on these bikes, which together draws so much power that the battery cannot "catch up" in charge until 4000 RPM. Over time, this damages, then destroys, the battery chemistry, and then the battery.

Not to be argumentative, but I've been running a Dyna S and 3 ohm coils in the 750 since 1990.  I have yet to have a battery last less than 7 years.

+1 similar story to Greg (Ofreen). Same Dyna S in a CB750K4 since 2001 -2015. Batteries have not died prematurely (AGM batteries).

+2 Dyna S ignition and 3 Ohm coils - never had a charging problem. The Yuasa lead acid battery is going on for 7 years old. I'm such a slacker that I rarely winter charge it, and have yet to check the regulator output. If it ain't broken, don't fix it.
71 or thereabouts 750 K1 - this one should have been put down

Offline Woodtone

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #34 on: October 23, 2015, 04:38:20 PM »
Knotted
The fender support pieces will go back on. Lots of things like that still need to be completed.

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #35 on: October 23, 2015, 08:57:14 PM »
Mike: I know the source of the battery troubles, will bring that topic up in detail a little later. It's something I "treat" fairly often, like 1-2 times per year on bikes that come by. (Right now I am stuck in AR until Sunday or Monday.) It is rooted in the use for BOTH the 3-ohm Dyna coils and the Dyna S ignition on these bikes, which together draws so much power that the battery cannot "catch up" in charge until 4000 RPM. Over time, this damages, then destroys, the battery chemistry, and then the battery.

Not to be argumentative, but I've been running a Dyna S and 3 ohm coils in the 750 since 1990.  I have yet to have a battery last less than 7 years.

Well, I hope this doesn't get too techie, as it has a lot of 'engineer-speak' in it...but it may help explain why this sometimes appears to be OK:

That performance is much more typical of the Dyna S units built before 2005 (which was when their current version(s) came out) most likely because their older Hall Effect triggers had Darlington transistor output inside, making their "ON" voltage drop about 1.2 volts (leaving the coils with [Battery volts - 1.2 volts] as their charge supply): this lowers the total current used. The early ones seemed to last much longer than the ones we have seen since then, too. The last (post-2005) Dyna S that I tested for this output voltage drop (just before the customer removed it and threw it away) measured a scant 0.40v drop, which means their outputs are likely being switched with a second-stage, single-junction transistor (much like in my units) so as to increase the current available to the coils. The newer ones then show a charge voltage available of: [Battery voltage - 0.40v], a difference of [1.2-0.4=] +0.8 volts. With 3 ohm coils, this becomes a current increase to the alternator of 0.8/3= 0.267 amp extra per coil, or nearly (0.8x[2x.267])= 0.427 amp extra on the whole system (where 0.8 = the 80% dwell time of these units).

So, after all that gobbledeegook...what it comes to is this: if the Dyna S is made with their 'new' parts, it uses even more power (over 0.4 amp extra) than they used to, which was already quite a bit.

The [very] few 750s I have seen that got along with the Dyna combination of 3 ohm coils and Dyna S triggers have always (every one) been hiway-ridden bikes, not city or commuter bikes. This makes perfect sense: if the bike is ridden more at speeds over 4000 RPM most of the time, it will 'keep up' with the Dyna parts' demands (even this K6 made the trip across the USA with little trouble). But, if ridden in typical Eastern (or even Denver, CO) city traffic, they have not, in my experience, ever 'lived' with the combination. They could take either the 3-ohm coils or the Dyna S triggers separately and survive, but the combination always put the battery under heavy current loads and frequent low-charge stints (which slowly damages the plates and chemistry). A perfect example of this showed up on my driveway last August: the beautiful, original Antares Red 750F1 in town (owned by the Denver Museum's Curator) suddenly started having low-battery issues. He brought the bike by after completing one of my favorite rides: west out of Denver on I-70 to Glenwood Springs, south thru Aspen over Independence Pass, back thru Buena Vista to hiway 285, then down into Denver (about 300+ miles). The last 30-ish miles of this becomes 30-40 MPH downhill traffic in the summertime tourist season, the rest is open hiway (and the rider said he 'idled' it down the long hill, in the upper gears, at lower engine RPM). The bike had always sported the 3.0 ohm coils since he bought it (8 years ago, I think) just fine, but he installed a Dyna S himself (because I told him I wouldn't do it with those coils) before he took this trip: the battery would not electric start the bike when he got home from the ride, nor on my driveway. It read 11.8 volts until the key turned on, then just 9.8 volts. It was (is) a top-flight, maintenance-free, Yuasa battery only 1 year old. He came by to get a Resistor Pack in 1.5 ohms, decided to make it 2.0 ohms instead, and installed it that weekend. It fixed things right up for him again. So, he effectively replaced the coils with 5-ohm coils so he could get his battery charged up again: that's very typical of what I see happen over and over. The last bike I 'fixed' like this (2 weeks ago) is the K8 I just finished refurbishing: it had 3.0 ohm coils on it, and was parked some 15 years ago for the owner getting tired of "issues" (it had a battery-charge connector hanging under the left side cover, as testimony to electrical troubles being one of those - and a relay feeding those hungry coils, to make it all worse). After installing normal coils, it has been fine again. For racing, these coils with relay feeds make sense: for street, not so much?
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

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Offline ofreen

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #36 on: October 23, 2015, 11:06:23 PM »
Well, I made it through the techie speak and came out the other side. ;)  I still believe the concerns with charging with the Dyna S and 3 ohm coils are way over-stated for an bike with a healthy charging system and clean connections.  As I mentioned, I have been running that combination in the bike for 25 years.  Over the years, the bike has been used in every combination of commutes.   My current commute consists of stop and go for 15 miles, with plenty of idling at lights.   I started using Westco AGM batteries in 2000.  The current battery has been fine, tho it cranked the bike a little slowly yesterday morning when the thermometer read 36 degrees. It went into service March of 2008, so it is approaching the end of the usual service life I've been getting with these.  (The nice thing about the Westco AGMs is that they all have given warning when they getting to the end, unlike the old wet cells that would crap out without warning when I'd push the starter button.)  The bike is stock, except I run an 18 tooth countersprocket which serves to lower RPM's compared to the stock 17.  There is nothing remarkable about the bike other than like all '75 F0's, it was hand built by Soichiro himself.  Even so, he only used off the shelf parts. ;)  You've mentioned before that the Dyna S/3 ohm coil combination fries ignition and kill switches.  Not on my bike.  I replaced the ignition switch a year or so back, but it wasn't burnt, the plastic crumbled and it fell apart.  The bike had 30,000 miles on it when the Dyna was installed, it is over 153,200 today.  It seems like if it was an issue it would have shown itself by now.  So if the post-2005 Dynas result in .427 more amps of current draw, that is still only about 5.5 watts, about the same as a couple of instrument lights.  Hard to imagine it would make that much difference.

I guess I am being argumentative, ha ha.
Greg
'75 CB750F

"I would rather have questions I cannot answer than answers I cannot question." - Dr. Wei-Hock Soon

Offline MRieck

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #37 on: October 24, 2015, 07:06:28 PM »
Well, I made it through the techie speak and came out the other side. ;)  I still believe the concerns with charging with the Dyna S and 3 ohm coils are way over-stated for an bike with a healthy charging system and clean connections.  As I mentioned, I have been running that combination in the bike for 25 years.  Over the years, the bike has been used in every combination of commutes.   My current commute consists of stop and go for 15 miles, with plenty of idling at lights.   I started using Westco AGM batteries in 2000.  The current battery has been fine, tho it cranked the bike a little slowly yesterday morning when the thermometer read 36 degrees. It went into service March of 2008, so it is approaching the end of the usual service life I've been getting with these.  (The nice thing about the Westco AGMs is that they all have given warning when they getting to the end, unlike the old wet cells that would crap out without warning when I'd push the starter button.)  The bike is stock, except I run an 18 tooth countersprocket which serves to lower RPM's compared to the stock 17. There is nothing remarkable about the bike other than like all '75 F0's, it was hand built by Soichiro himself. Even so, he only used off the shelf parts. ;)  You've mentioned before that the Dyna S/3 ohm coil combination fries ignition and kill switches.  Not on my bike.  I replaced the ignition switch a year or so back, but it wasn't burnt, the plastic crumbled and it fell apart.  The bike had 30,000 miles on it when the Dyna was installed, it is over 153,200 today.  It seems like if it was an issue it would have shown itself by now.  So if the post-2005 Dynas result in .427 more amps of current draw, that is still only about 5.5 watts, about the same as a couple of instrument lights.  Hard to imagine it would make that much difference.

I guess I am being argumentative, ha ha.
Why did you have to reveal the "BIG" secret ofreen. $hit....now everybody knows!!!! I don't know....I run an Dyna III and then an S for about 25 years with Andrews and Dyna 3 ohm coils.....I never had a problem.
 Get the Anders R6 conversion.....you run any accessory in the world X 5
« Last Edit: October 24, 2015, 07:09:02 PM by MRieck »
Owner of the "Million Dollar CB"

Offline ofreen

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #38 on: October 24, 2015, 08:59:51 PM »

 Why did you have to reveal the "BIG" secret ofreen. $hit....now everybody knows!!!!

Sorry Mike, I can't keep myself from bragging sometimes. ;D
Greg
'75 CB750F

"I would rather have questions I cannot answer than answers I cannot question." - Dr. Wei-Hock Soon

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #39 on: October 24, 2015, 09:27:08 PM »
When I get F0 #2 on the road it will also sport a Dyna III and Dyna 3ohm greenies. I had this setup on #1 and was having problems but when I fired it back up with the 3ohms and a 2000 the first thing I did was check voltage. I couldn't believe I saw that elusive sought after 14.5V however all the harnesses were replaced and all the other connectors also plus a new ignition switch. I suspect everything BUT the III and the greenies. For #2 I do not have new harnesses but will install a new ignition switch along with the original vr and rect. That should be a good test. Doesn't the III use the same pick up as the S?
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline scottly

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #40 on: October 24, 2015, 09:29:51 PM »
When are you going to break the Gerex out of the box, Jerry? ::)
Don't fix it if it ain't broke!
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #41 on: October 25, 2015, 11:20:05 AM »
When are you going to break the Gerex out of the box, Jerry? ::)

Good memory Scottly. First things first.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #42 on: October 25, 2015, 07:33:25 PM »
I started using Westco AGM batteries in 2000.

There's part of your secret, Greg!
It's also the way I "fix" some of these bikes in similar situations. They go a long way toward absorbing and releasing larger amounts of wattage to help stabilize these small alternator systems. The Mid Fours REALLY benefit from them.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline ofreen

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #43 on: October 25, 2015, 09:16:11 PM »
I started using Westco AGM batteries in 2000.
There's part of your secret, Greg!

AGM batteries have a lot of advantages.  The biggest for bikes that sit a lot is their slow self-discharge rate.  But really I don't have any secret other than the bike is in good shape.  It has always been stored inside, though it sees its share wet weather since I commute on it.  The charging system remains up to snuff and I clean all the connections every decade or so whether they need them or not. ;)  I think if a 750 is having charging problems with the Dyna S/3 ohm coils, there are probably other issues that need to be addressed.  Some old bikes that need attention are challenged just by putting in higher wattage headlight bulbs.  I know you know all that.

As for the smaller SOHC4's, I don't have any experience with them.
Greg
'75 CB750F

"I would rather have questions I cannot answer than answers I cannot question." - Dr. Wei-Hock Soon

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #44 on: October 31, 2015, 10:36:32 PM »
Got the engine apart today: the alternator wires are baked. At one time, someone replaced one of the bullet connectors, covering the new ones with heatshrink tubing: now the wire for the male bullet of that one is burned in two(!). As soon as I went to pull it apart, the wire fell out of the bullet (pic below). The field coil appears (and measures) as a coil from a 750A, which makes a little more wattage than the standard ones.

The [new] owner reported that the battery died when he started this trip and he installed a new cheapie (from Walmart, I think he said?) along the road trip to home. IMHO, that's likely what saved him and helped it make the trip: the alternator had to me intermittent on this one winding, all the way!

The bottom end oil story: without the oil jets in the top end, there is less oil flow in the bottom end. That's how the engine is designed, and as an example of how Honda altered this design over the years: in the sandcast and earliest K0 engines, the cam towers were mirror-imaged (a left one and a right one) and the oil metering holes were drilled into the passages in those towers. This gave way to having strainers in the large oil jets of the K0-K1 engines, which have a 13-hole strainer plate on the bottom side (in a dome shape) with holes .033" diameter. The oil metering hole in those early jets is 0.035"-0.036". In the K2-K6 and F0/1 engines, the smaller oil jets have 7 strainer holes of .033" size and the metering hole is 0.035"-0.037". In the F2/3 the strainer holes are the same, but some of the oil metering holes I have seen are as small as 0.033"-0.034", while more of them are 0.037" size. It was generally thought that the F2/3 engines needed a bit more oil flow at the rods, so it restricted the top end a little with the .033-.034" holes (i.e., about 10% more flow went to the crankshaft).

Since this engine may have suffered from the lower oil flow at the crankshaft, I will be measuring closely to see how it survived the cross-the-country ride (and who knows how many other miles?), for posterity. ;) The first noticeable thing: the piston pins are very dry, compared to most engines I have disassembled. The #1 and #2 pistons show much more wear in the wristpin holes, on their bottom sides (semi-seized markings), than what I usually see in these engines. This makes some sense: the lower flow will certainly result in less wristpin oiling, as this oil squirts out the sides of the rods. None of the crankshaft bearings appear scored, but they do show more wear marks than usual. Measuring will commence shortly: it's bedtime today. :)
« Last Edit: November 01, 2015, 07:57:37 PM by HondaMan »
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #45 on: November 27, 2015, 05:50:26 PM »
Uh-oh....another glitch!
I got the head back from the machine shop where it was subjected to a bath and cleanup (glass bead-blast) process. I had to have them remove the valve guides for me, as my (puny?) 80-lb air hammer would not budge the oversized Kibblewhite cast-iron guides that someone had put in the head before. I couldn't understand why, until I saw some of the guides after removal: they had cracked during installation, then they damaged (and locked into) several of the valve guide holes.

...and #1 has a crack in the head, from all those forces. This head is history... :'(

A word to the wise: if you decide to install oversized guides for some reason in these heads, MAKE SURE THE HOLE IN THE HEAD will fit the guide. Ream or bore it if necessary: don't just jam in oversized guides because "they fit tighter, so will cool better". I wish I had $1 for every time I've heard that lie, as it would pay for the losses on this one.
 >:(

The press-fitup on these heads for bronze guides is about 0.0004" to 0.0008", and for cast-iron guides is 0.0006" to 0.0010". This one was more than .0025" force-fitted.
« Last Edit: November 27, 2015, 08:22:50 PM by HondaMan »
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline 754

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #46 on: November 27, 2015, 06:39:35 PM »
So how far is the crack? Can you bore it out and sleeve it ?
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Offline kmb69

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #47 on: November 27, 2015, 07:48:51 PM »
.....
The press-fitup on these heads for bronze guides is about 0.0004" to 0.008"
.....
Didn't you mean 0.0004" to 0.0008" ?

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #48 on: November 27, 2015, 08:23:23 PM »
.....
The press-fitup on these heads for bronze guides is about 0.0004" to 0.008"
.....
Didn't you mean 0.0004" to 0.0008" ?


OOPS!
Yep, you're right, Fixed my typo, above. Thanks!
 :-[
« Last Edit: November 27, 2015, 08:28:11 PM by HondaMan »
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: Remarkable! An unusual 750K6 rebuild.
« Reply #49 on: November 27, 2015, 08:27:24 PM »
So how far is the crack? Can you bore it out and sleeve it ?

Not this one. It is halfway up the thickness of the guide toward the head chamber, and all the way through the sidewall at the port end. When this happens, it is not long before it finishes the trip into the chamber, as this will still be spread by the forces of the new guide when it is installed. While it's not apparent in the photos (for lighting reasons), it extends almost 1/4" across the top of the port already.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com