Author Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50  (Read 241103 times)

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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #175 on: December 30, 2013, 06:01:32 PM »
I don't know whether a 550 center stand would fit, but I have 2 from bikes I've just disassembled and you're welcome to either of them. I'll even bead blast them to raw metal for you.

Check around and let me know if it's worth the effort  to ship them out to you .
That would be worth it if they are in fact interchangeable. I doubt they are though, aren't the 550s lighter? I'll let the experts weigh in and PM you. Thank you so much!

Offline seanbarney41

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #176 on: December 30, 2013, 06:29:29 PM »
I don't know whether a 550 center stand would fit, but I have 2 from bikes I've just disassembled and you're welcome to either of them. I'll even bead blast them to raw metal for you.

Check around and let me know if it's worth the effort  to ship them out to you .
they fit!...I use one on my 750 because it is actually longer than my bent stocker
If it works good, it looks good...

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #177 on: December 30, 2013, 08:07:18 PM »
Thanks seanbarney, I just did a search and the 550 stand looks a bit different than the 750 one. I'm going for mostly stock build so it may not work. This is the part number 50500-300-020B for the K2 stand. If the 550 had the same, I'd  grab it from calj737

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #178 on: December 31, 2013, 06:52:55 PM »
I managed to get the exhaust flanges out using impacta (didn't hurt the head, was careful with padding and used a light substitute hammer). All but one screw succumbed, so had to drill that one out. Did a little bit of cleaning of the head to see better. Looks like #4 intake is the only one that wasn't ported and has a high peak that can be ground down. Wonder why they'd leave one alone, the other three clearly look like they were ported. I've gotta figure out what to do with this head.

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #179 on: December 31, 2013, 08:05:55 PM »
It looks like someone has "hemi'd" that head. If you can afford it, maybe consider having it milled a little bit to raise the compression back up. Measure the depth of the edge of the intake valve from the deck surface (with calipers), to see if it is more than 3mm. If so, maybe consider milling some of that off?
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #180 on: December 31, 2013, 08:50:25 PM »
It looks like someone has "hemi'd" that head. If you can afford it, maybe consider having it milled a little bit to raise the compression back up. Measure the depth of the edge of the intake valve from the deck surface (with calipers), to see if it is more than 3mm. If so, maybe consider milling some of that off?
Doesn't look like there is much left, what do you think?

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #181 on: December 31, 2013, 08:52:51 PM »
Exhaust side is worse, maybe it was done to balance the head?

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #182 on: December 31, 2013, 09:24:03 PM »
It's a little hard to tell without the valves (intake) in place. Sometimes they sit down in the seat, sometimes more toward the chamber. Stick 'em in, maybe post another pic? That would tell better. It's possible someone already milled it?
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 edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #183 on: December 31, 2013, 09:42:19 PM »
It's a little hard to tell without the valves (intake) in place. Sometimes they sit down in the seat, sometimes more toward the chamber. Stick 'em in, maybe post another pic? That would tell better. It's possible someone already milled it?
I will clean up the valves, put them back in and post back. Two of them are bent, or the guides are bad, should I just grind the tail a little and push them back in or leave those two out?

Offline Terry in Australia

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #184 on: January 01, 2014, 12:05:01 AM »
Looks good Ed, but I wouldn't take any more metal off it, have you measured the valves? It could be that they're a tad bigger than stock? When you take more pics, shoot one into one of your inlet ports with the valve out, I'd like to see if someones reshaped the ports?

More than likely your valves aren't bent, but the tips have mushroomed slightly and are tight in the guides. If you've got a dremel tool with a sanding drum attachment, run it around the tips of the "bent" valves above the collet recess, just little bits at a time until the valves slide into the guides smoothly.

To test if they are bent, chuck them in an electric drill and spin them, if they're bent, you'll see it straight away. Cheers, Terry. ;D
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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #185 on: January 01, 2014, 11:14:49 AM »
What better way to start the new year than shoveling snow? Was hoping for better lighting outside but these still look crappy. Slightly better views of Gordon's kit

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #186 on: January 01, 2014, 11:20:38 AM »
Back to the head

@Hondaman: Pic 1 is #4 inlet and Pic 2 is #1 inlet. The measured a miserable 1.95mm and 1.82mm respectively from the edge of the valve to the edge of the flat surface.

@Terry: Did the drill test for the valves yesterday and all of them have a little run out, but the two bad ones are beyond saving. Looked closely at the tips, not one has mushroomed. The length is 4" on an inlet valve that I had cleaned. Are they all the same length or should I clean one of the exhaust ones and measure it? Doesn't really matter I suppose, will definitely need new ones.

So the question again now is should I upgrade to bronze/brass guides as well?

Offline BPellerine

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #187 on: January 01, 2014, 02:14:20 PM »
if this engine was running with bent valves I would have to think that the guides are shot .are you sure that it would not be better to start with a better head in your case they must be fairly common?bill
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Offline Terry in Australia

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #188 on: January 01, 2014, 02:30:11 PM »
Bill's got a valid point Ed, if money is tight, new valves alone will burn a hole in your pocket. While I've never seen inlet valve guides worn out, you can buy bronze guides pretty cheaply, so if you're buying new valves as well, then you should replace the guides.

Be careful though, I bought some new bronze guides for the engine I just finished building, and while the clearances were fine on the exhaust valves, they were way too tight on the inlets so I had to knock 'em back out and reinstall the old OEM inlet guides as I didn't have a valve guide reamer on hand when I did them. Cheers, Terry. ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #189 on: January 01, 2014, 05:49:11 PM »
Thanks BPellerine, my concern with a used head is I might run into the same problems all over and I'm inclined towards suggestions made by many helping me out, which is to save up and do it right instead of having it croak when I'm on the road. I'd gladly save up and take it to a shop if a local one agrees, but its the shipping to far away places (granted excellent work) is what is killing me. I want to keep that as a last resort. I've learnt that nothing will happen overnight, so I'll take my time to save up and get new and correct valves, springs, guides and seals and if necessary send it away.

I took the pics of the inlet port with the valve removed for you Terry, hope this is what you needed.

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #190 on: January 01, 2014, 05:55:12 PM »
I started cleaning the jugs today, what a tedious nightmare scraping off the lower gasket is. Brought it down to Pic 2 and quit for now. Used so much elbow grease, feels like I'm getting a tennis elbow. Any tips on getting the last really burnt in bits off without hurting anything?

Pic 1 shows the top side, as I was cleaning I noticed that there is a rim of carbon/soot deposited at the edge. Is this normal? I wan't to work on getting the paint off of this thing too, so is it ok or stupid to try and remove the jugs?

Offline BPellerine

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #191 on: January 01, 2014, 07:23:16 PM »
not trying to steer you away from doing things right but just the amount of thread damage combined with the head being modded by someone unknown would give me pause.I live in Canada so I know all too well the cost of shipping and getting parts.I would have to think that in the states you could get a GOOD used head worth putting the money into I know in Canada this is fairly easy to find but I don't know about your area.just my thoughts bill
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Offline Davez134

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #192 on: January 01, 2014, 08:06:11 PM »
I started cleaning the jugs today, what a tedious nightmare scraping off the lower gasket is. Brought it down to Pic 2 and quit for now. Used so much elbow grease, feels like I'm getting a tennis elbow. Any tips on getting the last really burnt in bits off without hurting anything?

Pic 1 shows the top side, as I was cleaning I noticed that there is a rim of carbon/soot deposited at the edge. Is this normal? I wan't to work on getting the paint off of this thing too, so is it ok or stupid to try and remove the jugs?

To clean mine up, I soaked the surface in a shallow pan of sea foam that I had lying around for most of the day, then i scraped with this hard plastic scraper I had lying around, seemed to come off fairly easy. If you are talking about the ring of carbon at the top of piston travel, I had those on mine as well. I soaked that side as well and used the plastic scraper again to remove the deposits. After honing, the cylinders look new. If you want to remove the paint, I would look into finding a place near you that does media blasting. The shop that did mine was not very expensive, and they could probably get those deposits off too.

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #193 on: January 01, 2014, 08:26:26 PM »
not trying to steer you away from doing things right but just the amount of thread damage combined with the head being modded by someone unknown would give me pause.I live in Canada so I know all too well the cost of shipping and getting parts.I would have to think that in the states you could get a GOOD used head worth putting the money into I know in Canada this is fairly easy to find but I don't know about your area.just my thoughts bill
Turns out its not even a K2 head.

SCREEEAAAAAAAAAAAAMMMMMM

Was going for a correct resto, now gotta decide which way to go.

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #194 on: January 01, 2014, 08:37:54 PM »
I started cleaning the jugs today, what a tedious nightmare scraping off the lower gasket is. Brought it down to Pic 2 and quit for now. Used so much elbow grease, feels like I'm getting a tennis elbow. Any tips on getting the last really burnt in bits off without hurting anything?
It's not unusual for me to 'spend' 2 or 3 razor blades on a well-cooked bottom side like that. I sometimes soak the whole cylinder set in gasoline (until it evaporates away!) with some Marvel Mystery Oil mixed in, that seems to soften the paper up. There are also paint-on gasket softeners at auto parts stores that will help with this part. It can be tedious, especially if the gasket is OEM, now 40 years old, and they were impregnated with an excellent sealant.

I've also used a propane torch: heating up the gasket until it starts to smoke will reactivate the old sealant and make it tacky-er for a minute or so, which helps. When it cools again, it glues tight! That made them very dry: I wish the equivalent gaskets were still around today.

Quote
Pic 1 shows the top side, as I was cleaning I noticed that there is a rim of carbon/soot deposited at the edge. Is this normal? I wan't to work on getting the paint off of this thing too, so is it ok or stupid to try and remove the jugs?

The carbon on the top deck is an outline of the metal ring in the head gasket. Often, the head gaskets are not an exact match to the bores, because the stock gasket has to fit up to +1.0mm oversize pistons, too. Once in a while I've seen where someone goofed and used, say, an 836cc gasket on a stock cylinder bore or an 811/812cc set: this makes a 65mm size carbon ring that can cause preignition (ping), in real bad cases.

The head: it does look like someone has both milled it before, and 'hemi-ed' it before. That was the correct thing to do, at the time. If it has a bent valve, I'd suggest the following steps, as this would be my 'checklist' if I had it here:

1. Take the engine's bottom end apart (this doesn't imply you haven't, it's just my method), and check for the rounded gear dogs (and slots) on the C2-C5 gears. These are the first 2 gears that are by the removable bearing on the left side of the engine: the C2 has to come out before the countershaft can be removed. Reason: if the dogs and slots here are worn, it likely caused a missed 1-2 shift, which may have been the incident that caused the other damage (pretty common). In almost every engine I have received to fix a bent valve, these gears were worn like this, and needed to be fixed up. APE (Big Jay and Company) does a wonderful job of it.

2. Replace the cam chain and tensioner hardware (rollers, etc.) as they received a mighty snap when the engine stopped so suddenly that day. They are very likely damaged from that event.

3. Check the rod bearings under the bent valves. They might have been hammered oval by the event. You can Plastigage them in 2 different places, 90 degrees apart, to "see" the shape - one spot will show larger clearance than the other, usually by about .0004" or so. New bearing shells fix this one back up.

4. Replace the valve guide(s) where the bent valves showed up. They are cracked (or will be soon), bet on it. The cast iron/Stellite in the pre-1974 heads was hard as nails and brittle as glass. In most instances, there will be a chip on the guide at the port side, usually toward the center of the head, from the event. This shows where the crack starts, has to be out of the head to see it all.

5. If you want to just replace the guide(s) where the event(s) happened, this is OK if the others are not worn out. This was the standard Honda shop repair, back in the day. It's more common today to replace all the guides simply because so many of these bikes have a zillion miles on them, and they are worn - and, the bronze guides we can get today put up much better with the ethanol-laced fuels we suffer. I keep some stock Honda iron guides for those situations: Honda still sells them, and they are pre-sized 98% of the time so you can just install them and lap in the new valve. The only caveat: once in a while the hole where the guide fits may have been tweaked a bit out of alignment from the impact event. In this case, a new valve seat must be cut, as the new angle will not allow the valve to seat. I've even seen where someone used too big a hammer to remove the old guide (instead of heat & cold finesse) and this tweaked the angle, too. Don't do that...
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

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #195 on: January 01, 2014, 08:45:50 PM »
not trying to steer you away from doing things right but just the amount of thread damage combined with the head being modded by someone unknown would give me pause.I live in Canada so I know all too well the cost of shipping and getting parts.I would have to think that in the states you could get a GOOD used head worth putting the money into I know in Canada this is fairly easy to find but I don't know about your area.just my thoughts bill
Turns out its not even a K2 head.

SCREEEAAAAAAAAAAAAMMMMMM

Was going for a correct resto, now gotta decide which way to go.

Definitely not: it is a K4-style head. The cylinders are K2 style, though. The K2 head, like the K0-K3 early types, have a curved front top fin, where yours is a trapezoid shape: pic of my K2 head shown below. Note the front top fin shape (bottom side in the picture), that's the outward 'ID' mark.
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 edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #196 on: January 01, 2014, 08:56:00 PM »
Sigh, I guess I will hunt down a new head (already started). Will the rocker arms, cam shaft, etc still work with a proper K2 head?

Offline BPellerine

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #197 on: January 02, 2014, 11:50:51 AM »
Edward you should take the member up on the offer for the free stock cam and springs your cam towers should fit and you will be back to stock when you get another head .start from a stock baseline and then decide if you want the pleasure or pain of perf gear however you look at it.you could set all the perf stuff aside till you get things under control.bill
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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #198 on: January 02, 2014, 12:14:49 PM »
Edward you should take the member up on the offer for the free stock cam and springs your cam towers should fit and you will be back to stock when you get another head .start from a stock baseline and then decide if you want the pleasure or pain of perf gear however you look at it.you could set all the perf stuff aside till you get things under control.bill
Already arranged, have a lead on a better head (minus towers) as well. I hope this is the last thing that is out of place on this bike. Managed to scour pretty much all of the K2 stuff, have a lead on the handlebars as well. Anyone see anything else that is off? I can take as many pix as you need me to. Almost have the baseline now, unless I find something chaotic within the cases.

Offline Kickstart

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #199 on: January 02, 2014, 03:41:20 PM »
You may want to consider just getting a whole engine (if you can find one for not too much).  I'm not sure what the going price is for a solid, k1/k2, engine - but it may be worth posting a WTB for one.

Reading Hondaman's post below, I'm also wondering if there may be more problems lurking in your engine.
Don't mean to bum you out, I'd just hate to see you get the new head and parts only to find out you need you need to replace a bunch of stuff inside the engine.  Of course, getting a replacement engine takes some of the fun out of project and it's less of learning experience... but something to consider.

Did you do the checks Hondaman suggested?
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