Topic: Identifying CB750 Cam Towers

[HondaMan]

It doesn't appear to have the kind of metering hole I'm attempting to describe. These tiny holes were drilled in the center of the little dome that is left by the end of the larger drill bit that makes the oil hole. This sort of increases the mystery of the part you have?

[ekpent]

 Looks like they got Ole' Hondaman thinkin' 

[stikman]

It doesn't appear to have the kind of metering hole I'm attempting to describe. These tiny holes were drilled in the center of the little dome that is left by the end of the larger drill bit that makes the oil hole. This sort of increases the mystery of the part you have?

Right.  These look more like a notched sleeve pressed into the cross-drilled passage (with the concaved marking in behind left by the bit used to drill these holes from the bottom), more notched in one hole than the other.  When I get a chance I'll try to check the corresponding cam tower to see if the hole sizes are mirrored, which would indicate a specific right and left tower I'm assuming.

[kmb69]

.....
The early sandcast and K0 engines had no oil metering jets in the head. Instead, the cam towers had one small hole drilled in the inner (toward the cam chain) hole of each one, and they were a "right" and "left" tower, and precious few had a second "exit" hole on the opposite end, thus no O-ring (1.5x3mm) was needed on the far side.
.....

Wow! Not trying to stir the $hit, but absolutely NOT BELIEVING what I'm reading! 

I own CB750E-1000069 and a few 200's - all original, unmolested engines. All of their "HOLDER, camshaft"'s, are more or less as symmetrical as machined Sandcast parts get. I worked at Pasadena Honda when these bikes came out, wrenched on a bunch of them, and never saw anything like what Mark is describing. Never saw a Right and Left holder. If somebody has a pair as Mark describes, please post pictures.

The original "metering jets", per se, were the actual small hole size drilled in the head connecting to the stud oil passage - not in the holder. I have attached the pages from a Honda Parts Manual, dated 69.4, which I think is the first one published and it shows both of the "HOLDER, camshaft"'s to be the same part number starting with CB750E-1000001. I should add that the same Parts Manual only calls out 2 of the O-rings but shows both O-ring cavities machined on each side of the head. Should also add that Honda did some "funny" stuff back in the day. Assuming that Mark saw one like he is describing, it was either an extremely rare bird or somebody had already messed with it IMHO.

[stikman]

The original "metering jets", per se, were the actual small hole size drilled in the head connecting to the stud oil passage - not in the holder. 

...it shows both of the "HOLDER, camshaft"'s to be the same part number...

This has been all I've ever come across before.  Thanks for sharing that manual page, kmb.  Any chance you have pics of your sandcast cam towers (camshaft holders), or thoughts on how mine look?  There's gotta be a solid answer out there, whether these are early replacements, sandcast, or just another version of the common early sets.

[BPellerine]

the inside orings on the heads I have do not fit the outer cavities,on my 900 engine I got some matched up to fit the outer cavities,as I thought they should be there.used a nos Honda gasket set on my buddies ko and there were only two orings in the set?bill

[kmb69]

Checking the "distinctions" list over on the Sandcast Only forum, they list "Sandcast" cam carriers through E338 but nothing I can find about lefts and rights.
Checking MARKB's extraordinary thread restoring CB750E-1000100 on the Sandcast Only forum and this forum, the cam holders appear to be symmetrical on the top side.
I wish I would have ask MARKB to document those bottoms when MarkP mentioned this anomaly in that thread.

http://forums.sohc4.net/index.php/topic,79183.msg1625577.html#msg1625577

Scroll down a little further and MARKB has good pictures of the 4 O-ring counter bores in 100's head as well as the small hole in each pair that "meters" the oil flow.

.....
Any chance you have pics of your sandcast cam towers (camshaft holders), or thoughts on how mine look?  There's gotta be a solid answer out there, whether these are early replacements, sandcast, or just another version of the common early sets.

I am pi$$ poor about taking pictures of my restorations and do not have any of the cam towers. Pretty sure yours would be applicable to Sandcasts and early K0's. Sure hoping somebody can pinpoint the vintage cause I want to know too. That early Parts Manual indicates version -020 so some mods were apparently made even that early.

the inside orings on the heads I have do not fit the outer cavities,on my 900 engine I got some matched up to fit the outer cavities,as I thought they should be there.used a nos Honda gasket set on my buddies ko and there were only two orings in the set?bill

Bill, looks like MARKB's head is symmetrical but Honda has done some strange things like I mentioned before. Hell, there could be multiple differences between E69 and E100. E69 is in VIN 33 so it was probably assembled on the first day or two of production. I don't know if anybody knows if the engines were run tested before final assembly at that time but that difference in numbers, that early, may indicate something. Pure speculation on my part.

Maybe MARKB will chime in here if he has additional info.

[Don R]

 I read at some point one engine of every 100 were dyno tested. Early on I'd assume they tested more then 1%.

[HondaMan]

Looks like they got Ole' Hondaman thinkin' 

Yeah, bank on that!


I am 100% sure of the "right" and "left" cam towers in Jim's sandcast (first 750 sold in Peoria, IL, in 1969), as he took it apart for the rebuild at a little over 80k miles and we talked about it. I think it did have the spot-drilled outer O-ring recesses (in the head) like the later K1 (which I was more familiar with at that time), which uses the small 1.5x3mm O-ring like is used on the heads with the "large" oil jets, which was one of the topics we mused over. What drew his attention to is was: there were no [oil] holes on the outer sides of those cam towers, while there always is on the later heads, requiring the sealing O-rings, so he marked them "L" and "R" to not forget. IIRC, he decided to put the outer O-rings in anyway, to have them if he needed to replace the bearings someday.

I'm not too surprised by these cam bearings (or other interesting things like them): I have reported here before some other oddities that popped up in the Chicago-Great Lakes area back in those days, like the 'street killer' 700cc version of this bike that was sold at Mannheim Honda (no one knew it was any different from any other 750 when it was sold) that lose a valve in a street fight (missed 2nd gear). I was called into the fray by one of the Mannheim wrenches when they discovered the valve was not OEM 750, but bigger: he thought it might have been a 1968-style Superhawk intake (with the bigger valves) and called me to have me bring one of my spares over to see if it would fit (the stem was about 0.5cm too short, the face was correct, though). It was 60mm bore (instead of 61) but otherwise appeared to be all CB750. There are also the [rare] CB750F0 bikes with the drum rear brake and "early" style swingarm, the CB750F1 bikes with the 530 chain and sprockets, the early K3 with the 4-post Starter solenoid that cut off the headlight during Start cycle, and which also had the sidestand switch (like the clutch switch), the K5 bikes with the 2-port fuel petcocks but with one hole not drilled (so they have just one fuel line), and all sorts of little other things!

These are the coolest bikes for this sort of stuff: it was like Honda was building them [with whatever they had that day] to sell, so long as they LOOKED like a 750! And yet, almost all of the parts interchange between them.

[stikman]

I looked closely down the oil holes of both cam towers and they are definitely both the same, no left and right.  They have been cross drilled and the oil holes are drilled down to line up with the main cross drilled hole, that's where the odd shape comes from deep in the oil holes.

[PeWe]

These cam holders are too special to be inside an engine? Better on a shelf on display somewhere?

[BPellerine]

+1 on that pewe,belong in a collection.any camtower would be ok in a modern perf  build.billp

[HondaMan]

the inside orings on the heads I have do not fit the outer cavities,on my 900 engine I got some matched up to fit the outer cavities,as I thought they should be there.used a nos Honda gasket set on my buddies ko and there were only two orings in the set?bill

This is starting to happen in the Vesrah kits, too. And in the "red" kits Made in Japan. There should always be 4 in the kits. The earliest engines used 1/5x3mm, later were 1.9x5.8 (but 2x6 is common and works fine).

[HondaMan]

I looked closely down the oil holes of both cam towers and they are definitely both the same, no left and right.  They have been cross drilled and the oil holes are drilled down to line up with the main cross drilled hole, that's where the odd shape comes from deep in the oil holes.

Yep, that's entirely "normal" construction. Other than the interesting-looking castings!

[markb]

There seems to be more questions here than answers. Here are some observations that might help.

stikman’s original pic is a close match to the towers from those on my engine E1789. I’ll call these the ribbed style.

stikman’s


E1789


I have six sets of sandcast towers. Three are like the ones above with pronounced ribs (one set is E1789 and the other is E748), and the other three look like this. I’ll call these the unribbed style.


Unfortunately I’m not sure what engines the other four came from but I’m 99% sure the other ribbed one is from E1490.

Then you have the third style which looks like stikman’s pic of the ‘74 tower. I looked in my CB750-K2 manual and it shows two styles of towers. The early style looks like the early sandcast ones without the four extra holes as shown on the ’74 towers. According to the book the early style went up to engine number 10337. The rocker arm shafts also changed at 10337.

Also the manual indicates that the right and left towers are the same part number. The so called metering holes on the E1789 towers are both on the right side (from operator’s position) of the towers. The towers are not symmetrical. So they are definitely not right and left hand, they are the same and technically interchangeable. Even so I always put them back on the side they came from to match the camshaft or whatever. Whether there are some towers out there that are right and left hand, I don’t know can can’t say.

Here’s another interesting thing. Back when I was working on E100 I decided not to use the original cylinders. They had been bored to 1mm oversize and had a broken fin. I compared then to E1789 and found them to be identical. The engine wasn’t going to be completely original anyway I decided to use the E1789 cylinders.

Since I was using the E1789 cylinders I decided to use the matching head. It was in better condition than E100 and I found them to be identical too. So here comes the interesting part. While researching towers for my reply I happened to look at the E100 head. Here’s pics.


Can you spot the difference?


It is missing the outside spot faced holes! I can’t believe I didn’t catch that. According to the CB750-K2 parts manual only two of the small o-rings were required up to engine number 563. Makes me wonder if the E100 towers could be right and left hand. Well guess what? I am going to find out. The last thing I want to do is pull E100 out of 97. But as you might know about me I can’t let it go without being correct.

Conclusions:
•   At least some, maybe all, of the early towers had ribs and stikman’s towers are probably early too.
•   Although E100’s towers are slightly different I would called them ribbed.
•   While I have E100 apart I will check the towers for right and left hand.

I hope this helps. I certainly learned something.

[kmb69]

Oh boy! Can't wait to hear your findings on this.

[754]

The ones I dug out had ribs,but they dd not go all the way up to the top.
I posted a. Pic in post #13..

[markb]

I can't tell from the pic, do they have the extra four holes for the rocker arm shafts?

[stikman]

I have a set that look like yours with the mild and partial ribs too, Frank.  Even though they do not have the extra rocker shaft holes of the later style, they are definitely different from this style with the prominent ribs.

Thank you for doing that research and sharing it, Mark.  Very helpful indeed.  That's the first time I've seen another set of towers that look like this set I have.  So I take it they are either the early sandcast style or just a different specific cast used during the sandcast era?  One other question I had while reading your post was what you meant by the rocker shafts changing.  In what way did they change from 10337?

Also, I'm now wondering about the cam that came with this set of ribbed cam towers.  Is there any particular way to tell a sandcast cam apart from later models other than mounting it in a motor and getting the specs with a degree wheel?

[754]

No small bolt holes up top , the xtra hole ones look the pic.

Stikman look for a cast in ring or rings or square raised pad on the cam, between the lobes.

[markb]

Thank you for doing that research and sharing it, Mark.  Very helpful indeed.  That's the first time I've seen another set of towers that look like this set I have.  So I take it they are either the early sandcast style or just a different specific cast used during the sandcast era?  One other question I had while reading your post was what you meant by the rocker shafts changing.  In what way did they change from 10337?

No problem.
I don't know as much about the later diecast engines. I'm assuming there must be extra notches in the shafts for the extra screws in the later towers. I'm sure someone can chime in here.

[stikman]

No problem.
I don't know as much about the later diecast engines. I'm assuming there must be extra notches in the shafts for the extra screws in the later towers. I'm sure someone can chime in here.

Ahh okay, you just mean the basic early shafts with the single center groove before they drilled and tapped holes in them.

Stikman look for a cast in ring or rings or square raised pad on the cam, between the lobes.

Frank, the cam has R6 stamped into it, which I know is pretty meaningless.  I don't see any raised pad or rings but it has an odd stamping that looks like "D G" maybe.

[BPellerine]

3 types of shafts,one is waisted,in the center all the way around,no 5mm holes
next the one that is waisted only on one side,no 5mm holes,the shaft will not rotate
and the later waisted type with 5mm holes.bill

[HondaMan]

3 types of shafts,one is waisted,in the center all the way around,no 5mm holes
next the one that is waisted only on one side,no 5mm holes,the shaft will not rotate
and the later waisted type with 5mm holes.bill

Bill, you have this right: I might add that the "slashed" ones (not cut all the way around the wasp-waist) were only found in replacement parts. They first appeared during the late 1990s and came-and-went in the Honda parts supply until Honda quit making them in 2008, IIRC, with sometimes fully-waisted ones appearing again, gone again. The ones found in the engines always had the wasp-waist cut fully around: a strong encounter with piston-to-valve events could crack the waist on the ones without the extra holes. While the Honda parts fiche declares the 5mm-hole-type to be a K2 part, they did not actually appear in the engines I saw until about halfway thru the K3, in 1973.

[BPellerine]

yes,I think the racers like the insurance of the 5mm bolts so the shaft does not come out in the event of a break and destroy more stuff.bill