Topic: Identifying CB750 Cam Towers

[stikman]

I picked up this set of cam towers, rockers, and shafts off ebay a couple years back, apparently from a 1970 K.  I'm considering using them or another early set I have in the engine I'm currently building.  When I pulled them off the shelf yesterday I noticed the cam towers look different from any I've seen before.  They have distinctive vertical casting marks along the sides, and the overall casting design looks different from any others I've seen.  Anybody have insights?

And a side note:  What's the difference between rockers with the notch cut out of the nose and those without?

This cam tower is from the set in question:


This cam tower for comparison is from a 74:

[BPellerine]

if you pull the shafts on the 70 ones there should only be a waisted centre no bolts holding the shafts,said to be better for hp and wear,the ones in the bottom pic are later with bolts holding the shafts in place.billp rings on the way!

[754]

73 and later is the lower one..
 I will look at some early ones and see if they have the ribs.

[stikman]

Yeah, the bottom picture is of a set from a 74 just for comparison.  The rocker shafts from the set in question are the aftermarket type with just the center slot down one side.

[Don R]

 I'd guess early number sandcast but that's a guess. A 70 could be a low number bike. Mine don't have the rib but I don't know the serial number of the engine they came out of.

[Retro Rocket]

Interested to see what the experts say about using mismatched cam towers, seeings though they were line bored from the factory...? 

[PeWe]

Ask Hondaman. He will like the old set. He has explained all details in a thread somewhere including early secret testbikes....

[Medyo Bastos]

Ask Hondaman. He will like the old set. He has explained all details in a thread somewhere including early secret testbikes....

Agreed


Sent from my iPhone using Tapatalk

[stikman]

Good call.  I sent him a PM, see what he thinks.

[754]

I may be interested in them if they are different for early motors, i have 3 70 motors that do not have all  the correct pieces..

[stikman]

My brother has a really early diecast 69 K that he's currently doing the top end on, so I asked him for pics of his cam towers (assuming they are original to the motor) and they look like any other early K0 and not like this set I have.  Only ideas I can come up with is that they are either sandcast or early replacement ones, since they aren't drilled for the extra rocker shaft bolts.  But I don't know what sandcast cam towers look like either.  Still hoping Mark might have some insights.  Anyone have pics of sandcast cam towers for comparison?

[ekpent]

 PM a picture and a question to this Mark, see he was active today, undoubtedly one of the best experts around who has worked on very early Sandcasts. They possibly look similar to his engine #100 he did . Its an epic thread and even more so on the Sandcast site. Best way to learn is get your hands on them   Eric    http://forums.sohc4.net/index.php?topic=79183.0

[Medyo Bastos]

thc ones with red wire ties are mos-def from an early engine. there are a couple different shafts used for the tappets without the little screw holes

[754]

Here is a pic that came off a 26,*** or lower, but not sure they are original to that head.
Had a XX stamped on top of one holder, note 2 ribs.

I checked another early head, the cam tower had at least two ribs.. Should have taken a pic of it.. It has the cam with the raised rectangle with the markings...XX

[754]

Here us a 73 or later with the extra bolts, note it has a date code.... 49. 10. 28 Not often I recall this on Honda stuff.. I know Z1 have it all over their parts.

[BPellerine]

Here is a pic that came off a 26,*** or lower, but not sure they are original to that head.
Had a XX stamped on top of one holder, note 2 ribs.

I checked another early head, the cam tower had at least two ribs.. Should have taken a pic of it.. It has the cam with the raised rectangle with the markings...XX

my early ones are like that.bill

[754]

I have a 44*** motor, if I run across it should pull the valvecover and have a looksee, not sure if its ever been opened. Its like about the 200 th motor from end of KO.

[stikman]

Here is a pic that came off a 26,*** or lower, but not sure they are original to that head.
Had a XX stamped on top of one holder, note 2 ribs.

I checked another early head, the cam tower had at least two ribs.. Should have taken a pic of it.. It has the cam with the raised rectangle with the markings...XX

Very interesting!... I can definitely see some similarities between yours and mine.

I took a look through Markb's sandcast thread and saved the pics of his cam towers.  Not exactly the same, but mine have lots of similarities.  Here's a few pics I did up to compare mine to his.  Mine are the top and his are the bottom in each picture.

[HondaMan]

Stik:
Check inside the oil-delivery holes on the bottom side of your cam towers: see if there are either 2 holes (one each side, like the later units) or if there is just a very small (metering) hole in the tower, instead. Here's why:
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. This was the oil metering system to the top end, and it frequently failed because a tiny bit of [whatever] would plug the metering hole and toast the cam and towers. Very quietly, without issuing a recall notice that would be embarrassing, Honda sent out the "new" rocker towers, shafts, rockers and cam in a kit called the 'rocker tower kit' (which was how this nomenclature came into common use, instead of "cam bearing", BTW) to shops like ours, stating that if an engine came in that might have "dirty oil problems" (as our rep put it) that we should pull the engine and head and replace the towers, they would pay standard warranty rate for it.

I only know of one instance where this actually happened (Chambo's own sandcast bike, at 80k miles in 1971) and got paid for, but I know of MANY instances where the bearings got toasted and later ones installed, warranty or not.

The first oil jets in the K0 engines are a 7/16" (or so) diameter insert with a 0.0375" metering hole and 13-14 0.033" strainer holes in a dome on the bottom side. The later ones, beginning late in the K2, are 7 strainer holes (0.033" (early) or 0.035" (later)) in a longer, tube-like strainer with a 0.037"-0.039" metering hole. The smaller holes were used in the F1 and later engines, with a 0.035"-0.037" metering hole, the former in the earlier engines.

All this said: last year I pulled down a K6 that had 67k miles on its clock, and a gorgeous set of rocker towers and unscathed cam, but which had NO metering jets at all in the head! The top showed evidence that someone had gone to great trouble to seal the cam cover because it was awash in oil, but the bike had just been ridden from Michigan to California in the weeks before I got it, with no ill effects of any kind visible, anywhere!

[PeWe]

bottom pics needed so we'll know

[754]

Last two pics..dirty one looks diecast or forged..
Clean one looks sandcast...

[stikman]

Underside shows 2 oil holes.

[BPellerine]

well now I know that you need orings on the outside plugs on the ko/sandcast heads many diagrams show only two on the inside by the jets.interesting set of camtowers.bill

[HondaMan]

Underside shows 2 oil holes.

If there a smaller hole drilled up inside the larger oil holes that you can see? The metering holes were about 0.5cm (5mm) up inside the larger hole, just a little lower than the cross-drilled passage that is fed by them.

At the least, those appear to be similar to the replacement types that were sent out in the "kits" I mentioned earlier. They were still a sand-casted mold, made in a hurry at Honda's foundries, to solve the problem. Then they made the nicer-looking ones were are all more familiar with. I have seen a K0 within the last 4 years that had some that looked similar to yours, but they were junk form having been blocked inside, then run dry. I might still have one of them around here, if I didn't turn it in for scrap: I am still toying with the idea of making a jig to cut the bearings clean and lay in some shells of some kind, but to do so requires potentially destroying one: my PTOCD (part-time OCD) makes that hard for me to do!

I also have to find someplace that makes small babbit-style bearing shells in the odd size that Honda chose for these cams. The clearance can be anything from .002" to 0.012" and they work fine. The only time they have trouble (outside of total burn-up) is when they have worn forward far enough to make one cam tower's bearings further forward by about 1mm than the other side: then the engine loses smoothness because the cylinders on the worn side of the cam have less cam lift (intake side) by a significant amount.

[stikman]

Here's the best I could do for pics down those holes.  2 Holes on the same cam tower.  Looks to me like the second hole seems to have a smaller metering hole up inside it.  What do you think?

Hole 1:


Hole 2: