Head Bolt Seals

[Joe K]

Hello,

Does anyone know what the head bolt seals are for? I have gotten them in CB750 engine gasket sets before and am not sure what they are for?

Thank you,
Joe K

[hondasan]

"Head bolt" seals would appear to be a variation of the Honda parts list description for these items, which is "packing, cylinder stud bolt", part number 12115-300-000. They were fitted from engine number 2352923 on wards (K3 or K4 ish?), and fit at the cylinder barrel / head joint at the 8 studs which act as oil drains from the top end. The idea seems to be to reduce the chance of oil leaks at the head gasket (not a problem anyway in my experience on any CB750 if later Honda gaskets / seals are used).
The cylinder barrels on these engines have opened out stud holes into which these "packings" fit, around steel "knock pins" (hollow dowels), and a corresponding late type head gasket is used.

They are not required, and cannot be used on sandcast motors unless also fitted with incorrect post 2352923 barrels and corresponding later type head gaskets with large oil drain holes at these eight stud locations.

Being rubber oil seals, I would suggest NEVER risking fitting old / hardened used ones either. Far too much work involved in tearing down one of these motors to risk the use of "used" seals and gaskets   

Cheers - Chris R.

[imabass]

Joe,

Here is an O-ring post that I had on a different site. it has pics of the KO setup vs the later K's. Basically If i recall correctly, there is only a few small orings that you will need on the KO setup. There are some that are about 1/2 inch diameter on the main oil feed holes going up. These are the ones nearest the cam chain on the intake side of the engine. Then there are some small ones just under the cam tower where the jets are. As far as I know the only seals were on the oil feed side (feed side is pressurized from the pump). The remaining holes are drain holes back to the crank case. See post here

http://sohc750.yuku.com/topic/2000

[Joe K]

Chris and Imabass,

Thank you for letting me know what they are for. I have rebuilt two 1970 CB750 engines now and knew about the o-ring placements on the K0 setup, but couldn't figure out the bolt seals. Now I know why because they are for later model engines. I wish the engine gasket companies would include instructions with the kits.

Joe K

[imabass]

Joe... i agree. When i got my gasket set i had a handfull of seals left over.. since my engine was disassembled in boxes, i didnt have a clue where all that stuff went. When i had a handfull of seals left, i figured that it was going to leak, but it never did... I didnt realize it untill i took apart my 75.

[ashimotok0]

I have a head gasket in my gasket kit which is of the later type with the larger holes. Can I still use this on a '69K0 head? I am pretty sure the one which was fitted already, was the same. it is an NP gasket set. I also plan to use some low mileage barrels off a 750 K1 if I can, if that makes any difference (I am aware that these will have a 'spare' 6mm threaded hole, which will not be used)

I also found this Service Bulletin

http://data.sohc4.net/SB750/750_42.pdf

cheers Ash D

[hondasan]

Yes, you can use the later "large hole" gasket on the early engines, but be aware that you are actually creating a small cavity that oil can sit in at the head / barrel joint around the 8 drain studs. On the odd occasion that I have used these later gaskets on early engines, I have fitted 8 "o" rings of an appropriate size from an engineering supplier to effect a seal.
Any later K series barrels will go onto a '69 motor, but as you say, you just have that "spare 6mm threaded hole (which can't really be seen anyway once built up sandcast). It is only obvious that later barrels are fitted if they are the late K1 and onwards die cast type which have a different fin profile at the ends.

Still working on that K0 then Ash?

Cheers - Chris R.

[ashimotok0]

Yes Chris - got the bug- and now getting obsessed!!

Managed to get a K7 for 25GBP !!!!!!!! from my mate who is a bike dealer in York which had a decent crank.

I modified the above post with link to the service bulletin

http://data.sohc4.net/SB750/750_42.pdf

Ii think the 'K1' barrels I have may not even be K1 (but they were sold to me as K1) as they have the knock pins in them. I suppose the only other option would be to swap the liners over or just use them as is!!

Cheers Ash