Author Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50  (Read 241065 times)

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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #125 on: December 22, 2013, 02:00:36 PM »
Thanks Terry, for the clutch reminder and looking at the cam sprocket. Been on house cleaning duty all day today  :( the missus doesn't want our xmas time guests to smell simple green and mineral spirits all over the house  ;D. Also, thanks for describing in detail how to measure things properly, very useful notes. I will definitely try and get those in the next few hours.

Also, any tips on removing the points plate? I'm still searching how to get it out.
« Last Edit: December 22, 2013, 02:03:11 PM by edwardmorris »

Offline Terry in Australia

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #126 on: December 22, 2013, 02:10:09 PM »
No worries mate, I'm in a similar situation, I've been building a K2 engine in the patio for the last few weeks and I have to move it into my garage and tidy the patio in readiness for our Christmas Eve Barbecue tomorrow night. Cheers, Terry. ;D

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Offline Davez134

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #127 on: December 22, 2013, 04:45:42 PM »
In case I missed it, what's wrong with your points plate? Should be a simple removal of 3 screws and a nut at end of advancer shaft...

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #128 on: December 22, 2013, 06:12:05 PM »
Dave: Nothing wrong with the points plate, I wasn't sure how the large and small nuts hold together and didn't wan't to break anything.

Terry: Sweet looking K2 engine there, been keeping an eye on the daily thread. Can't wait to see the polished covers against that awesome black.

Made just enough time to measure the pistons and cam lobe height.

Pistons are 60.9(6-8)mm (range because of my flimsy hands when measuring)
Cam lobe height is 32.5mm at the highest point.

Once I wiped some of the oil off the cam, found two markings. One says "K6", the other says "web cam 41-A".

Its a K6 cam?
« Last Edit: December 22, 2013, 06:16:27 PM by edwardmorris »

Offline Davez134

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #129 on: December 22, 2013, 07:33:41 PM »
Just remove the smaller one with a socket like normal as you hold larger one still with open end wrench. Be careful not to put much lateral force on it though. Should come off easy.

Offline Terry in Australia

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #130 on: December 23, 2013, 03:41:45 AM »
Terry: Sweet looking K2 engine there, been keeping an eye on the daily thread. Can't wait to see the polished covers against that awesome black.

Made just enough time to measure the pistons and cam lobe height.

Pistons are 60.9(6-8)mm (range because of my flimsy hands when measuring)
Cam lobe height is 32.5mm at the highest point.

Once I wiped some of the oil off the cam, found two markings. One says "K6", the other says "web cam 41-A".

Its a K6 cam?

G'Day Edward, no worries, so you've got a Webcam 41-A. I'm not sure what the "K6" thing is, according to the Webcam 41-A timing card, the 41-A is recommended for the 75-78 "F" engine, but there's not much difference between the early F's (1975/76) and the K6 engine anyway, so no biggie.

http://www.dynoman.net/bikepages/sohc/cams_web2.html

That explains the heavy duty springs etc. Have you checked your head for modified ports yet? The pistons are stockers, so the cam is probably a waste if the head hasn't been ported, in which case you might be better off taking Marks advice and return it to stock with a stock cam and springs. Cheers, Terry. ;D



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Offline calj737

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #131 on: December 23, 2013, 05:52:21 AM »
Or send the head out for porting... Especially given the work needed to repair the stripped helicoils. Why not take advantage of the cam and springs, and have it done up properly?
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Offline Kickstart

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #132 on: December 23, 2013, 06:36:25 AM »
+1 
If you can afford it, and are looking for an improvement, now would be the time to send the head out. 
I believe the consensus is that head porting is the basically the best bang for your buck when it comes to performance improvements... and really the first thing you should consider if you are going to start spending money on performance improvements (vs. just restoring the engine to stock)

That said, you can still use that 41 cam if you decide not to do any porting... MRieck himself told me it would be an improvement even without head porting (long story but I screwed up on my build and rushed into have new valve guides installed and valve seats cut before I realized I should have done the porting work - MRieck suggested I skip the porting but I could still get an improvement with the 41/41A cam).

BTW, you don't need to have performance springs/retainers with the 41 cams - I believe they are drop-in ready.  I suspect the PO decided to opt for a little rev insurance and replaced the springs (which was a good decision by the PO, IMHO).

Wait... did you confirm that your head wasn't already ported?  :)
- Chris
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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #133 on: December 23, 2013, 10:45:38 AM »
Please pardon the noobness, how do I check for head porting? Can you guys tell if I took some real close pix of it?

Offline Kickstart

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #134 on: December 23, 2013, 11:26:20 AM »
Please pardon the noobness, how do I check for head porting? Can you guys tell if I took some real close pix of it?

Yes... we want more pictures!  :)

Seriously, I don't have as much experience but I'm pretty sure I could tell if you shot a couple of clear pictures (focus the camera on the floor of the port when looking in the intake) - and maybe another picture looking through the inlet valve back into the port.

I'm sure the other guys on this thread could easily tell based on a couple pictures.

 
- Chris
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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #135 on: December 23, 2013, 12:49:12 PM »
@Terry, that engine looks a lot like my next winter project  :P

@all, I'd gladly restore to stock, if I can find those springs and a usable K2 cam. No luck there yet. I guess I'll dig deep and see what kinda performance options are based on what the PO has done to it so far, then pick the doable route.

Here are some pix of the head on the inlet side, and a few of the valves after I wiped off whatever I could. If you need me to remove the springs and valves and take more pix, let me know and I'll work on tearing down the head later today.

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #136 on: December 23, 2013, 12:50:58 PM »
Outlet side

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #137 on: December 23, 2013, 12:53:04 PM »
Valves and the last outlet.


Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #138 on: December 23, 2013, 12:56:50 PM »
I got along a bit further, the clutch is out. I made me a poor man's clutch nut removal tool - THANK YOU greenjeans -- that worked like a charm. The plates are half stuck together eventhough everything is pretty soaked in oil. The bell looks alright, anyone see anything crazy, please let me know :)

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #139 on: December 23, 2013, 01:01:11 PM »
Stuck at the damned points plate. I got the nut off like Dave suggested, and marked it for realigning later, but the three screws look to have been overtightened. I didn't even bother with the first one coz it looks stripped, but the other two are also jammed in there and even the JIS tips are slipping on them  :( I don't have an impacta #2, and is that even an option on this fragile thing? Suggestions on getting it off safely? Only thing in the way to get the crankcase open today.....

Offline seanbarney41

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #140 on: December 23, 2013, 01:03:49 PM »
doesn't look to be any porting going on there (at least in the intakes, I didn't examine the exhausts closely)...the factory casting line "grinder swipe", which Hondaman clearly depicts and describes in his book, is still clearly visible in all 4 ports...and it is this feature that is the most obvious obstacle to good port flow that any cylinder head porter would attack first...
If it works good, it looks good...

Offline flybox1

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #141 on: December 23, 2013, 01:12:07 PM »
an impact wrench is a must-have for your tool box.
carefully drill off the screw heads, and then a vise-grip + some heat to turn out the remnants.
PB blaster overnight if needed.
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Offline Kickstart

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #142 on: December 23, 2013, 08:47:30 PM »
doesn't look to be any porting going on there (at least in the intakes, I didn't examine the exhausts closely)...the factory casting line "grinder swipe", which Hondaman clearly depicts and describes in his book, is still clearly visible in all 4 ports...and it is this feature that is the most obvious obstacle to good port flow that any cylinder head porter would attack first...

+1
I don't think any porting work was done.  So, if you're interested in any performance improvements - this is where I would start. You could probably take care of those casting misalignments yourself, if you're up to the challenge... or just send it out to MRieck or APE if you can afford it.
Even if you don't, you can still keep the 41 cam and performance springs - I think these are generally considered better than stock. (although I have no experience with performance cams myself).
- Chris
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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #143 on: December 23, 2013, 09:02:06 PM »
I don't think I can afford to send anything anywhere anymore. Just the packaging for a swingarm cost me $30! just packaging, not shipping (don't ask...ouch). I might brave doing the porting though. I've done it on my car's exhausts and intakes when I was active on the TRD forums (wasn't called porting there though), and Hondaman's book has this covered in excellent detail. I still wanna go back to stock springs though just so nothing snaps mid ride.

Its been hard with xmas almost here, finding very small pockets of time to work on the bike and then I get pulled away. Updates will be slow the next couple days. I managed to get the points plate out by using a mini vice grip (thanks to Hondaman's book that recommended this for stuck cover screws). I went ahead an took the shifter assembly apart as far as I could get, but the next step looks daunting. Extremely hard looking screws that I'm nervous about hammaring out or stripping them. Any tips on getting these out?
« Last Edit: December 23, 2013, 09:04:18 PM by edwardmorris »

Offline Kickstart

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #144 on: December 23, 2013, 09:35:48 PM »
I don't think I can afford to send anything anywhere anymore. Just the packaging for a swingarm cost me $30! just packaging, not shipping (don't ask...ouch). I might brave doing the porting though. I've done it on my car's exhausts and intakes when I was active on the TRD forums (wasn't called porting there though), and Hondaman's book has this covered in excellent detail. I still wanna go back to stock springs though just so nothing snaps mid ride.

Its been hard with xmas almost here, finding very small pockets of time to work on the bike and then I get pulled away. Updates will be slow the next couple days. I managed to get the points plate out by using a mini vice grip (thanks to Hondaman's book that recommended this for stuck cover screws). I went ahead an took the shifter assembly apart as far as I could get, but the next step looks daunting. Extremely hard looking screws that I'm nervous about hammaring out or stripping them. Any tips on getting these out?

I'm very impressed with your progress so far... making me feel lazy.  I need to get into the garage and work on my rebuild, but it's a lot easier to just read about your project :)

No need to remove that screw on the end of the shifter drum.  I wouldn't touch that.
For those four screws holding the bearing retainer/oil supply cover, you'll need to use an impact wrench.  I didn't have a JIS set, so I just used a regular hand impact wrench - but they were in tight, and I actually ended up using a small sledge hammer with the impact wrench.  I was scared to death I would crack something with all that force, but it worked out ok and I managed to get all four out without having to drill any of them out.
- Chris
75' CB750F Orange flake (rider)
75' CB750F Blue (Project)
75' CB750F Painted black (Project)
No Reserve Racing #171 AHRMA

Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #145 on: December 23, 2013, 10:00:41 PM »
Thanks! The 4F weather is hardly encouraging but it will be another year before I can afford some time off, so trying to get the engine cleaned and inspected, hopefully this week if I can manage to skip the xmas stuff :p

So sledge hammer hunh? I'm worried about breaking my impacta too, I like it too much and I've already broken a menard's impact driver. If I make any progress I'll be sure to make some time and post it. Sorry for the flimsy pix, just got the two hands and its a paint to keep taking glove off every
time.

Offline Kickstart

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #146 on: December 23, 2013, 10:29:08 PM »
Good point... if you're trying to stick to your time and money budget, then just focus on doing a solid rebuild.
Maybe grind/file down those casting seams in the inlet ports if you have a dremel tool handy.

I wouldn't use a sledge on the impact driver that came with your JIS set... I'd be worried about breaking that as well.

Just get an inexpensive hand driver at sears or an autoparts store:


That has some more mass (which will help), and can handle a heavy blow from a hammer... even if it does have Phillips bits.

Also try adding some heat if you have a propane torch lying around... try the impact with a regular hammer first.  I did multiple attempts with a normal hammer before I finally used the sledge... be careful if you use the sledge hammer.  It worked for me without damaging anything but I might have just gotten lucky.
- Chris
75' CB750F Orange flake (rider)
75' CB750F Blue (Project)
75' CB750F Painted black (Project)
No Reserve Racing #171 AHRMA

Offline Terry in Australia

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #147 on: December 25, 2013, 04:02:29 PM »
Looking good Edward, I'm going to argue against the opinions of the previous posters and say that those inlets look like they've been "smoothed", as do your combustion chambers. It's a bit hard to tell as you've taken your pics with the head upside down so not much of the ports are visible, but I've got a couple of stock heads here and the casting marks in their ports are a lot more prominent than in your pics, so I wouldn't be surprised if someone's already done some work there.

Do you have an air compressor? If you do, don't fart around with Dremel tools, buy a cheap die grinder (20 bucks) and an Eastwood Company "Porting kit" (under 40 bucks)with the necessary mandrels and abrasive rolls, and you can clean those ports up even better, in only a few minutes each. As you've already seen, the aluminum in the CB750 head is very soft, so the abrasive rolls turning at 20,000 RPM remove a lot of material, very quickly.

As has been said previously, there's no need to remove the screw on the end of the shifter drum and there's no benefit in doing so anyway. Use a hammer and an impact drive to unscrew the other 4 screws though, and that won't be a problem. Use your hammer and an impact driver to re-tighten them as well. Don't go mental, just one whack on each of them after you've done them up hand tight will be sufficient. Merry Christmas! ;D   
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So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #148 on: December 25, 2013, 06:28:43 PM »
For those 4 flathead screws that hold the countershaft bearing cover in: I suggest just drilling them with a 3/16" drill until their heads pop off, then go to Ace Hardware and buy 4 more for $1 + tax (they are 6x20mm on the K2, can use flat head or oval head, either type, in crosspoint or 'Allen head' versions).  You'll usually find the threads turn out with your fingers, once the bearing housing is removed. They corrode and stick to the aluminum under the tapered side of the screw head, much of the time.

About 75% of them won't come out without ruining the JIS crosspoint slots, anyway.
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Offline edwardmorris

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Re: 1972 CB750 Four K2 -- Project "Ice Cream"-- ENGINE TEARDOWN
« Reply #149 on: December 25, 2013, 09:41:25 PM »
Thanks Terry and Hondaman, I guess I'll leave the stopper drum alone if it won't get in the way, and glad that I can find replacements at ACE for the other four. My fear was not finding replacements, but now that I know, I suppose I can make more progress. I do have an air compressor, and Eastwood seems to have a kit that includes a mini die grinder as well, so I will probably make that worthwhile investment soon. If I can make the time, I will clean up and disassemble the head tomorrow and post pix with the right side up :)