Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50

[edwardmorris]

Exhaust

[SOHC4 Cafe Racer Fan]

Puuurdeeee!!  Mike nails it, again!

[jerry h]

Wow!  That is a piece of art.    

[edwardmorris]

Wow!  That is a piece of art.

Indeed! And I didn't even go for the ultimate service!

[edwardmorris]

So I managed to make a bad situation worse. In my haste to get the head and jugs painted, I totally destroyed one of the dowel pin on the jugs. All others came of easy, this is the same one that game me trouble when I was trying to separate the head during teardown. Now, the top half is near complete destroyed and everything below the Aluminum level isn't budging. Heat and penetration oil isn't doing squat. Anything I can try before I take it to a machine shop?

[MCRider]

So I managed to make a bad situation worse. In my haste to get the head and jugs painted, I totally destroyed one of the dowel pin on the jugs. All others came of easy, this is the same one that game me trouble when I was trying to separate the head during teardown. Now, the top half is near complete destroyed and everything below the Aluminum level isn't budging. Heat and penetration oil isn't doing squat. Anything I can try before I take it to a machine shop?

I was able to get a mangled one out with a drill. USe a bit that's just a skosh larger than the ID of the pin. Hold the driill real steady and slow, turn it in till it grabs the knock pin. In my case it spun it right out. But that was before I had all the nice work done on it.

[edwardmorris]

So I managed to make a bad situation worse. In my haste to get the head and jugs painted, I totally destroyed one of the dowel pin on the jugs. All others came of easy, this is the same one that game me trouble when I was trying to separate the head during teardown. Now, the top half is near complete destroyed and everything below the Aluminum level isn't budging. Heat and penetration oil isn't doing squat. Anything I can try before I take it to a machine shop?

I was able to get a mangled one out with a drill. USe a bit that's just a skosh larger than the ID of the pin. Hold the driill real steady and slow, turn it in till it grabs the knock pin. In my case it spun it right out. But that was before I had all the nice work done on it.

Thanks, tried that, its just honing it, not quite biting. Next larger size drill is too big, and I'm a bit paranoid. Its not the head, its the cylinders, one of the two lower one, same one that needed a chisel to separate the head.

[oldhatt45]

Not sure if this is worth a try or not, but, can you get something like an Ice Pick between the knock pin and the hole it sits in and get the pin to fold in on itself and hopefully release the pressure on it?

Don't know if that is even an option, but thought I'd throw it out there, just in case.

Charlie

[MCRider]

So I managed to make a bad situation worse. In my haste to get the head and jugs painted, I totally destroyed one of the dowel pin on the jugs. All others came of easy, this is the same one that game me trouble when I was trying to separate the head during teardown. Now, the top half is near complete destroyed and everything below the Aluminum level isn't budging. Heat and penetration oil isn't doing squat. Anything I can try before I take it to a machine shop?

I was able to get a mangled one out with a drill. USe a bit that's just a skosh larger than the ID of the pin. Hold the driill real steady and slow, turn it in till it grabs the knock pin. In my case it spun it right out. But that was before I had all the nice work done on it.

Thanks, tried that, its just honing it, not quite biting. Next larger size drill is too big, and I'm a bit paranoid. Its not the head, its the cylinders, one of the two lower one, same one that needed a chisel to separate the head.

Maybe you could insert a toothpick sized shim flashing or such to get it to grip.

Don't want to hear this yet i suppose. But I always polish the pin and hole to where I can insert and withdraw the pin by finger pressure.  Never tap one in.

[edwardmorris]

Damn, should have checked back here for the more civilized option 

I've got one or two days tops where I can paint so in my head, I went "The barbarian approach is never the best option, but sometimes its the only option".

Cautiously crappy approach, used a hole punch to get it to bend in a corner just enough to get small flathead behind it and voila, tapped all around and it caved in. The corrosion has somehow melded into the alu, I scraped it a little to see how bad it was. Iz got some cleeenin to do now.

On a brighter note, little pieces are now happily baking 

[MRieck]

Damn, should have checked back here for the more civilized option 

I've got one or two days tops where I can paint so in my head, I went "The barbarian approach is never the best option, but sometimes its the only option".

Cautiously crappy approach, used a hole punch to get it to bend in a corner just enough to get small flathead behind it and voila, tapped all around and it caved in. The corrosion has somehow melded into the alu, I scraped it a little to see how bad it was. Iz got some cleeenin to do now.

On a brighter note, little pieces are now happily baking 

Heat works well with those dowels (MAPP gas). Be sure to clean up that edge (a 90 degree chamfer works great but a grinding stone on a Dremel will work)

[754]

Sometimes you can run a tap in and slide hammer them out.
Or tap a round piece inside near inner hole size, then grab it with vise grips..keeps it from collapsing..  But use heat as well

[edwardmorris]

Thanks for the pointers guys, I'll clean it out once I finish baking them.

Barely hit 60 today so I toasted up the garage with my handy propane thingy. Masked up the head nicely and had at it.

[edwardmorris]

Damn gas ran out too quick so couldn't use it to aid with the drying, will let them sit overnight and dry out before baking them up.

[edwardmorris]

Somewhat better pix, mostly trying to see if the paint got everywhere between the fins.

[edwardmorris]

Can anyone spot a fin repair?

[oldhatt45]

Ed,
At anything above 5 mph, anyone that can spot it is likely to be wearing tread marks shortly and probably won't tell.  ROFL

Nice Work!

Charlie

[edwardmorris]

HA! Good one Charlie.

So the head and cylinders are nicely baked and safely packed away. I took Ron's suggestion and polished out the dowel pin holes nice and smooth to the point where the pin now goes in and out with minimal effort. When packing the head, I noticed that the the four cam tower studs are missing  I'm assuming Mike had to remove those for getting the machine work done, so I emailed him. I'm not half as worried about the fact that they may be lost, as much as I'm now worried that the head will leak. From what I read around here, these things are cursed and once removed, a leak is inevitable 

Branden's top end write up mentions using a high temp thread sealant to avoid the leak, anyone have any luck with that?

Also, now I've gotta go pick up a stud wrench/tool....right??

[754]

Nope. Double-nutting is fine when installing newly cleaned fasteners.
Sometimes i grab my lathe tailstock chuck to hold studs to install.. Quicker..

[edwardmorris]

OK, will try that. Just found out that these are NLA from Honda, so I really hope Mike saved em!

[MCRider]

HA! Good one Charlie.

So the head and cylinders are nicely baked and safely packed away. I took Ron's suggestion and polished out the dowel pin holes nice and smooth to the point where the pin now goes in and out with minimal effort. When packing the head, I noticed that the the four cam tower studs are missing  I'm assuming Mike had to remove those for getting the machine work done, so I emailed him. I'm not half as worried about the fact that they may be lost, as much as I'm now worried that the head will leak. From what I read around here, these things are cursed and once removed, a leak is inevitable 

Branden's top end write up mentions using a high temp thread sealant to avoid the leak, anyone have any luck with that?

Also, now I've gotta go pick up a stud wrench/tool....right??

My first non-Mike top end had the studs removed by a good machinist and reinstalled by same. But he simply didn't know the CB750, working on mostly newer things. It leaked within 20 easy miles. 2nd top end by Mike, I installed the studs with sealer as he recommended. No leakd in 20 hard miles. Not much I know but fingers crossed.

The reason to use studs in an application (I think) is so that you don't crank down on the stud to case threads. Dbl nutting here is fine as you just want a firm handwrench tightness. Like 8ft lbs. The higher torque goes on the other end which will pull both ends appropriately. But even there in this case, 8 ft lbs is enough.

[edwardmorris]

I heard back from Mike, he's going to look for some straight ones and send them to me, so that's good. Permatex high temp thread sealer is what in Branden's thread, will have to try that unless there are better options.

I wondered about just using regular bolts instead, but Ron basically answered the question before I asked

[MCRider]

I heard back from Mike, he's going to look for some straight ones and send them to me, so that's good. Permatex high temp thread sealer is what in Branden's thread, will have to try that unless there are better options.

I wondered about just using regular bolts instead, but Ron basically answered the question before I asked

Yes studs have their place and if Honda wanted them there they should stay. You'll want to goop the stud and the hole with a Q Tip, let it set up for a few minutes till tacky, then thread in. When you're done you'll see your goop dripping out of the holes on the outside of the head. Better goop than oil!    Mike had me use Harveys TFE Paste with TEflon. I'm sure your Permatex is similar.

[edwardmorris]

Pro tip from JMR: If you're storing the freshly worked on head, spray some WD-40 into the ports to keep the seats from rusting.

[edwardmorris]

Little time, so little progress, but progress nonetheless.

Crank drain and oil galley plugs, I showed them the least love when it came to prep work as I didn't wan't them too shiny and guess what, I can't take a pic without them blinding the camera! The levers, I sanded off some deep pits then quick incremental wet sanding rounds, they came out alright.