Topic: what are 12115-300-00 and 12116-300-000 good for?

[caller]

In the part list for Honda CB 750 k3, K4, K5,  section E5 cylinder/piston there are two items that particularly interest me;

12115-300-000, packing, cylinder stud bolt  and

12116-300-000, pin special knock 12mm. Eight of each number. 

The fit Honda CB 750 -K4 from engine number 2352923 and higher. My Honda is an early K4 with engine serial number 2346499 and consequently don't need these.

My question is what are they good for?

Caller 

[Jerry Rxman Griffin aka MuthaF'er]

Possibly prevent oil leakages from those areas.

[DH]

Possibly prevent oil leakages from those areas.

+1............noticed mine were going bad when I changed cam tower pucks that were also bad on my k5.

[Garage_guy_chris]

its recomended if the holes in the headgasket will allow, on earlier "non dowel" engines to use o-rings to help seal. Hondaman recommends this on the forums all the time. If you look around you will find other threads talking about it.

Headgasket - Pre K4 oil sealing - 2mm X   12mm - (HG 1.6mm thick holes 16.8mm dia)

I got mine here:

http://www.mcmaster.com/#9262k176/=1057kg2

[caller]

If I am not mistaken, the oil goes from the oil-pump to the cylinder head thru two passages, the two inner dowel pins. Why should the packing, cylinder stud bolt  and pin special knock prevent this, attached to the other dowel pins? 

[madmtnmotors]

If I am not mistaken, the oil goes from the oil-pump to the cylinder head thru two passages, the two inner dowel pins. Why should the packing, cylinder stud bolt  and pin special knock prevent this, attached to the other dowel pins? 

 


Because those "other" cylinder stud locations are the oil return passages. The manual has a very good illustration of the oil pathways through the engine.

[PeWe]

My CB750K6 has the wider holes for specal 12mm pins. Very important to measure the depth in head and cylinder and compare with the special pin that cannot be too long. If head is decked, pins might need to be grinded shorter.

- Anyone that have widened an old cylinder block 8 oil holes so these pins will fit?  I have one additional cylinder.

I did not use the 8 special knock pins at last rebuild when the head gasket was of the old model. (Cometic CFM20)
I'll use the 8 pins with o-ring at the winter job. Yamiya and cruzinimage 65mm head gaskets have both the wider holes.
I have an oil leak. Will check all holes for valve cover too. I know that 2 of them are drilled and threaded thru the head with longer bolts when threads gave up. Thread inserts and thread sealer.

[Ellz10]

I'm having a hard time believing that I have the correct ones as well. My bike is a '77 K7 (836cc 65mm over, HD Cylinder Studs). Now I know I don't have the knock pins installed (because I figured they'd come in my dowel kit, but I was wrong, probably cuz they're not "dowels", so they're on their way here), but as you can see, there is alot of extra room from the edge to that stud bolt gasket. This can't be correct, can it?

[madmtnmotors]

there is alot of extra room from the edge to that stud bolt gasket. This can't be correct, can it?

They will be fine. These are passive, gravity oil returns from the top end back down to the crankcase below and are not under any real pressure. These seals and "knock pins" were used in later models to prevent oil weeping/leaks. Cheap insurance.

[HondaMan]

Yeah, what MadMtn said: they often look like that.
The steel dowels are shorter than the rubber and the rubber dowels seal up lightly against the bottom of the head gasket to contain oil drainage to the cases. It's a little debatable WHY honda did this, as I don't ever remember the pre-K3 engines weeping oil from those holes: usually oil weeps on the front of the engine came from Honda occasionally installing under-thick O-rings at the 2 oil feed passages at the back of the cylinders. Their spec of 2.5mm thick there in the K0 sandcast engines became 2.4-2.5 thick in the K0 diecast, and the machining tolerance depth of those oil passages are +/-0.01mm (based on measuring a ton of them, empirical data here) at 2.3mm deep FROM THE TOP OF THE UNCOMPRESSED HEAD GASKET. This is why, when asbestos was 'abated' from head gasket in the 1990s and they all got thicker by 0.2mm on average, the leaks became a big-time issue that made this bike fairly unpopular to rebuild. All that is needed to stop it is to use 2.6mm thick O-rings in those 2 holes back there, and the rest of it works as originally planned.

[PeWe]

Service bulletin explaining the later gasket.

[Ellz10]

there is alot of extra room from the edge to that stud bolt gasket. This can't be correct, can it?

They will be fine. These are passive, gravity oil returns from the top end back down to the crankcase below and are not under any real pressure. These seals and "knock pins" were used in later models to prevent oil weeping/leaks. Cheap insurance.

Yeah, what MadMtn said: they often look like that.
The steel dowels are shorter than the rubber and the rubber dowels seal up lightly against the bottom of the head gasket to contain oil drainage to the cases. It's a little debatable WHY honda did this, as I don't ever remember the pre-K3 engines weeping oil from those holes: usually oil weeps on the front of the engine came from Honda occasionally installing under-thick O-rings at the 2 oil feed passages at the back of the cylinders. Their spec of 2.5mm thick there in the K0 sandcast engines became 2.4-2.5 thick in the K0 diecast, and the machining tolerance depth of those oil passages are +/-0.01mm (based on measuring a ton of them, empirical data here) at 2.3mm deep FROM THE TOP OF THE UNCOMPRESSED HEAD GASKET. This is why, when asbestos was 'abated' from head gasket in the 1990s and they all got thicker by 0.2mm on average, the leaks became a big-time issue that made this bike fairly unpopular to rebuild. All that is needed to stop it is to use 2.6mm thick O-rings in those 2 holes back there, and the rest of it works as originally planned.

So Honda did all that and went thru the trouble when all they really had to do was increase the size of the oring for those 2 oil passages to 2.6? Sounds like a headache. 

Now that I've already ordered them and they're on their way, am I still okay to install them or should I just forgo installing them?

[PeWe]

Important to verify the cylinderblock is not milled, making the grooves for those 2 o-rings more shallow.

Too thick o-rings can cause problems like collapsing inwards blocking the oil flow.
It has been discussed in other posts.
CycleX mention it too on their website.

It would be easiest to measure the total depth, gasket thickness + groove in block and add a height for proper o-ring compression.

[Ellz10]

Important to verify the cylinderblock is not milled, making the grooves for those 2 o-rings more shallow.

Too thick o-rings can cause problems like collapsing inwards blocking the oil flow.
It has been discussed in other posts.
CycleX mention it too on their website.

It would be easiest to measure the total depth, gasket thickness + groove in block and add a height for proper o-ring compression.

I hadn't thought about that, until you said something, but then remembered talking to Ken about it briefly when he did all the work. This was the first time this motor had been apart, ergo the first time it had been decked so Ken said it wasn't a problem!

[HondaMan]

I install the 2.6mm thick ones even when the cylinders have been decked, up to 0.015" depth. They will not seal off the oil flow and will help prevent weeps on really hot days in city traffic on freeways. This is a common scenario in these engines, the worst being in the K3-4 era. On those the oil weeps out and makes its way down to the front between cylinders 2-3 (and out the back at the cam chain tensioner) and make a thin oil weep appear. It washes off at the high-pressure carwash, but it is often there.

[PeWe]

Interesting o-ring compression recommendations.
https://www.marcorubber.com/o-ring-groove-design-considerations.htm

Some examples I made up:
I measured 3 cylinders, the o-ring groove were 0.9 or 1.0 mm deep.
An old used compressed fiber head gasket (836) was 1.0mm thick (probably Cometic 65mm)
Total depth: 1.9 or 2.0mm
O-ring thickness 2.5mm vs  2.62mm
(11x2.5 vs 10.78x2.62mm)

Compression: 24% or 20% vs 27% or 23,6%
All these combinations within the recommended face seal compression of 20-30% if I have understood everything right.
- The 2.62mm thick o-ring might be the better one here

Same Cometic fiber gasket and cylinder is decked 0.25mm
Gasket:1.0mm thick, groove in cylinder 0.75vs 0.65mm= 1.75 vs 1.65mm
O-ring 2.5mm
Compression: (2.5-1.75)/2.5=0.3 (30%)   (2.5-1.65)/2.5=0.34 (34%)
-Stock o-ring thickness of 2.5mm is absolute max


If head gasket is 0.75mm thick + groove in cylinder 0.9. Gland depth=1.65mm. O-ring 2.5mm
Compression:
2.5-1.65=0.85mm  ---> 0.85/2.5=0.34mm -->34% (30% if cylinder groove is 1mm)

0.8mm gasket when compressed and 1.0mm groove in cylinder make 28% compression if o-ring is 2.5mm thick
(32% if cylinder groove is 0.9mm)

******Abnormal numbers *********
Head gasket 1.2mm and cylinder groove 1.0mm, total gland depth of 2.2mm.
(That thick gasket when compressed might not exist)
Compression:
2.5-2.2=0.3  ---> 0.3/2.5=0.12 ---->12%
2.62-2.2=0.42 ----> 0.42/2.62=0.16 --->16%

2.8mm o-ring is needed for that depth or head gasket thickness when compressed.
2.8-2.2=0.6 -----> 06/2.2=0.27 --- 27%
******************************
EDIT: Thicker o-ring will make ID smaller. 
Very thick headgasket need cylinder to be shaved to maintain compression and correct o-ring compression.


OD is max 16.0 mm as stock.

[PeWe]

Another o-ring size that has stressed me lately is the o-ring under cam holders.

Here how it looked like when I removed cam holders. Later oil orifice.
O-rings were 6x2mm viton.
Close to cause cam/rocker issue if blocking the small oil holes



I used the slightly thinner NBR o-rings  provided in a gasket kit when I assembled it.
Should be 5.8x1.9mm
Honda 91305-323-000

The outer o-rings were not that bad.
Probably wider groove to compress in. The orifice is a limitation.

[Tracksnblades1]

PeWe,

I’ve seen that before when the wrong thickness oring is used in a split flange hydraulic application.
With the pressures in a hydraulic system it will fail in minutes..Seems like it crushes all the resilience
out of the oring. Changing it into more of a gasket instead of a reactive seal…

I think you may find orings used as seals under 100psig are considered static seals..
Face oring seals use the pressure of the fluid to assist sealing. And the orings are usually oriented to the ID or OD of the space they occupy depending whether they are sealing fluid in or trying to keep it out…  in either instance the oring will not occupy any more than 75% of that space… I think you’ll find the same specifications for static oring seals.

Static oring seals compression is a range between 18-25% depending on temperature, material, surface finish etc…