Topic: Couple CB750 head questions

[y2kc0wb0y]

Purchased a "performance" CB750 head from a swap meet years ago. I could tell, at the time, it had some intake porting work and possibly some upgraded spring hardware but otherwise not much known about it. Never really compared my old head with this until this Pandemic lockdown refreshed my interest in my idle projects. I'm seeing some differences that I'm not familiar with and wanted to run it by everyone.

1. These attached pictures it looks like the heads are slightly different in casting? One has reliefs one does not.
How can that be on same engine?
2. Different oiling ports? looks like tiny oil holes on one and much larger on the other near the intake side.
3. The spring seats on "performance" head look much much higher than the other. I guess this is normal to performances springs to raise seat* pressure but it's odd they are almost twice as high as the others?
4. Can I swap cam journals and rocker assemblies safely between the two?

[754]

The head with the green spring collars is like 71 to 72.
 The one below is 73 to 76.  You can tell by front edge of top fin, and looking at the side of the head...at the bar's between the fins.
 One oil jet for cam bearings is missing on the one head, they can be pull out, some even come out blowing off the head with air.
 Cam holders will swap between those heads.

[ekpent]

Yep both oil jets are missing on picture #2.

[y2kc0wb0y]

Thanks guys. Are the oil jets different from year to year? Can they be sourced if I cannot get them out?
Any thoughts on the springs?

[fxef79]

The head with the green spring collars is like 71 to 72.
 The one below is 73 to 76.  You can tell by front edge of top fin, and looking at the side of the head...at the bar's between the fins.
 One oil jet for cam bearings is missing on the one head, they can be pull out, some even come out blowing off the head with air.
 Cam holders will swap between those heads.

754, This is good info, as I think my own engine is a bit of a frankenstein, and not sure I can trust the serial number.  But I'm trying to make sense of what you said about how to tell the year on the head.

You said "you can tell by front edge of top fin"... by that I assume you mean that the fin has the numbers cast into it:  "300" in a circle, and "6".  That's the one you say is a 73 to 76.
I found this other post that references the casting numbers:
http://forums.sohc4.net/index.php/topic,126477.25.html

In that it notes the numbers "300, 341, 392, 405, 410, etc"
And it references HondaChopper page for engine timeline differences:
http://www.hondachopper.com/engine/engine_timeline/timeline.html

But when I look at that timeline it seems to imply (the "prod code" column) that "300" would indicate a 69-71 year head?

I also hunted to find more description of the "the side of the head...at the bar's between the fins", but haven't found a good explanation of how to visually tell the difference.  Is there more you can share on that?  I'm continuing to try to search the forum different ways, in case I just don't have my search formed properly.

[bryanj]

There are 3 variations
1 VERY eary--not seperate from head

2 Pepperpot, small piece visible, big hole, teastrainer underneath

3 Current--medium hole, straight top, circular "pin" underneath with holes in.

Looks to me like green spring picture is 2 whilst lower head need 3.

As i do more 500 i'm willing to be corrected there!

Available from Yamiya but sit down before you look at price

[754]

Front fin 73 to 76 is flat in the middle, slight angle on the sides.
 Earlier , flat in the middle,  then across going to straight on the sides.
 But I can tell from25 feet away by the struts in the fins, looking at side of the head.

Won't hurt to pull a few springs to test, some early Hipo springs were overly strong and cause undue wear of parts.

[PeWe]

The later oil orifices available on eBay
Here a set of 2
https://www.ebay.de/itm/401454357261

Here one by one
https://www.ebay.de/itm/292357104521

Shipping is horrible for a few grams!!

I ordered used set from CB parts seller from Netherlands a few years ago, OK shipping.

Both the sellers here sale lots of other parts to purchase at the same time.
 
Off topic but if you will order shocks from these :
CCC sell a very good version of chromed Ikon shocks with progressive springs that works better than the non progressive spring version that Motorradteile sell.

I have both. My K6 has the progressive version that work better and is more comfortable at the same time. (2)

My K2 has the other version more stock like, comfortable soft ride (2) or harder with better high speed handling on bumpy roads, not that comfortable (3).

It's just about damping 2 or harder 3, same spring height (2)

[y2kc0wb0y]

PeWe - thanks for the german link. I found the US eBay ad for those parts and @$50 US shipped. I'll consider that a win.

Does anyone know if the spring purchases below the black retainers look correct?

[PeWe]

You saw that one seller sale in set of 2 pcs, the other 1 pcs?

[Trav-i]

I'm about to send a head and cylinder set out for vatting, is there a way to safely remove the oil jets without damaging them?

[y2kc0wb0y]

You saw that one seller sale in set of 2 pcs, the other 1 pcs?

Check it out.
https://www.ebay.com/itm/Honda-CB-750-Four-K1-K2-K6-K7-K8-A-F1-F2-G-orifice-oil-control-cylinder-head-new/292357104521?_trksid=p2485497.m4902.l9144

MREICK chimed in offline and sent David Silver's Spares link.
https://www.davidsilverspares.com/CB750F-SUPER-SPORT-1976-USA/part_322071/

This is all very good information.

[PeWe]

Like I did 1 year ago

http://forums.sohc4.net/index.php?topic=175940.msg2051709.msg#2051709

Mikes link the best alternative of the oil orifices

[754]

 I can check if my display motor has jets in it I can pull out. 72 head., might be a bit cheaper..

[y2kc0wb0y]

Looks like I just got refunded on those german reprods I purchased.

Got this in reply..

Hello Scott, unfortunately all letters to America or Australia are sent back to me. This means that distribution in the states is not working at the moment and no programs are accepted by the countries in this regard. Small packages with DHL are still being delivered, but unfortunately the shipping costs 35 euros.

Mit freundlichen Grüßen,

Best regards,
Met vriendelijke groet, Yoroshiku onegaishimasu,
meilleures salutations,
saludos cordiales

Andy

[754]

I have a damaged head with the steel jets in it, I can try to pull them out, Pm me if you need them.

[y2kc0wb0y]

I have a damaged head with the steel jets in it, I can try to pull them out, Pm me if you need them.

Thank you Frank. Turns out this head is junk as the PO drilled out the Oil Jet housing for some unknown reason

[bryanj]

Not total junk, could be reamed to a size the sleeve made

[y2kc0wb0y]

Not total junk, could be reamed to a size the sleeve made

Not following exactly


Sent from my iPhone using Tapatalk

[bryanj]

Make the hole slightly bigger but perfectly round with a machine reamer then make a sleeve outside diameter same as hole, inside same as outside of oil jet, bit like a small dowel. May cost a few $ depends if rest of head is worth it, everything is getting scarcer

[754]

It can be sleeved or machine a new jet to fit.