Topic: CB750 oil feed dia in head vs HD studs.

[PeWe]

I was lucky to find a problem in time for the ongoing head swap.
Oil feed diameter of the 2 holes in head were only 8.5mm!

Not good combination with Heavy duty studs that are 8.0mm thick. Not much for oil to flow there.

The oil restrictors at top have only +1mm hole, but only for max 20mm followed by the narrow holes in cam holders lubing cam and squirting oil over rocker pads etc.

Stock studs are slimmer, 6mm no problem with 8.5mm holes then.

I checked another head I have that was tight enough with 9.0mm.
I massaged all stud holes with 9.0mm drill after another head had married stud threads when alu collapsed a little.

I saw the ported head has meat enough for 9.5mm drill to ensure oil flow outside the thicker 8.0mm stud.

I think at least a 9mm drill is a good idea when going with HD studs.

Oil flow now closer to stock, the thinner 6.0mm studs vs the small 8.5mm holes.
8.0mm vs 9.5mm
This feels better.

I have not tested the flow, closer to stock oil channel is enough for me.

Lack of oil at top-end might not only be clogged oil restrictors or  holes in cam holders.

My CX-cam had damaged ex lobes I noticed after I have changed to another cam.
Only the highest point, no scuff marks on head nor cam holder. I could never explain that.

Later cam got better oil and might have helped. Mostly synthetic Red Line.

CX-7 got low quality Castrol 10-40 mineral for break in. 20/50 later. Bad flow might have caused it?

HD studs and tight holes in head. See photo of which.



Understandble why RC made studs with thinner diameter on these 2 in head area.

[craz1]

Whats important is the actual areas of the metering orifice compared to the area between the 8mm studs and the cylinder wall. If you do the math I would assume the area of the stud to wall is greater than the area of the metering orifice. As long as the area is greater you should have plenty of oil to the orifice. Your only going to flow so much oil through the orifice no matter how much room you have between the stud and wall. Im pretty sure APE has taken that into account. You could also look at it another way. Since the area to fill is less with the 8mm stud compared to the stock 6mm stud oil should reach the orifice sooner. Hmm. Just a thought

[PeWe]

Yes, oil flows thru there. But there is only 0.25mm around the stud. Stock stud gives 1mm.
Risk for blocked flow too.
That's more like an oil leak up to top-end than a reliable flow

I think my long after seen cam failure can have been caused by not enough oil flow.
Higher lifting cam, harder springs more oil dependent than stock configuration.

My oppinion now is drilling those 2 holes to at least 9.0mm if smaller whith the 8.0mm cyl studs.

Drilling shaves off a little. Important to make sure the passages to oil orifices are not blocked by burrs. I used a steel wire I guided in thru the orifice hole, down the stud hole, fished up with a thin nosed plier and massaged the edges with the wire.
My K6 has KPMI studs, my K2 APE. They look very similar.

[Old Scrambler]

I was advised to relieve the HD studs between the threaded ends by 0.5mm to get a 7mm shaft for improved hot/cold stretch/shrink and maintain sufficient oil-flow..........came from a contracted Suzuki performance tuner. I have yet to use HD studs, but file this type of info for potential use

[PeWe]

Thanks for the input that gave me some thoughts!

The tightening torque must be very vital in respect to
hot/cold stretch/shrink....

The entire package of cyl block and head will swell when hot.
- If the stud does not expand as the package it holds, the tightening torque will increase.
(Or if studs expands more, leak..)

Using metal gaskets has no "dampening effect". Torque might become too high for the head when hot, the head's aluminium under nuts compress and nuts sinks into the head.

Metal deform when pressed too much, head will be a pain to remove when head is formed around the stud threads.

This will make torque to be too low and leak might occur.

- If this scenario can occur, this can be what happened my old head. Nuts on the exhaust side sunk into the head. I got a base gasket leak I could not explain.



Bike ran too lean for a while in a specific throttle area which might have been involved too.

Nuts tightened by 28Nm (20.65 ft-lb) which can be too much.
I hope 25Nm (18.44 ft-lb) can make a difference and properly jetted carbs.

Metal gaskets will not compress as fiber gaskets after several heat cycles.
 So no need to overtighten for later gasket compression.
Stock studs could most likely flex more. I remember how they felt and sounded when I tightened by 28Nm.

I plan to assemble a head today on that engine. The new package is ment to increase the compression....

[Old Scrambler]

I have OEM studs in my C.B.R. at 19 ft-lbs with a copper head-gasket and metal base-gasket..........21 ft-lbs on my K3 with fiber gaskets.........all measured at approximately 80-degees F.

[PeWe]

Thanks for that verification Dennis!

I used stock studs in the 80's with 836cc. Tightened 28Nm which flexed a little. The fiber gasket compressed some later so the final torque must have been much lower.

I tightened 25Nm today (18.44ft-lb)
I oiled the nuts underside and thread with 20W-60 synth before to ensure the torque.

** About these oil feed holes. **
I remember that my old K2 head had 9.0mm holes since I punched out the oil orifices (restrictors) with a 9.0mm drill.

http://forums.sohc4.net/index.php/topic,175940.msg2051709.html#msg2051709

[disco]

Hi PeWe,

I had blue smoke issues on a recent 836 build. I used a K1 head with no valve stem seals. I noticed that on start up (when the oil was thick) that the valves were being submerged in oil. The oil was not returning to the sump quickly enough. I had also used the Ape HD studs and noticed there was now less clearance. (The original Honda studs being “waisted”) I had my machinist open those holes up a bit more, and the problem resolved itself.

[seanbarney41]

I have OEM studs in my C.B.R. at 19 ft-lbs with a copper head-gasket and metal base-gasket..........21 ft-lbs on my K3 with fiber gaskets.........all measured at approximately 80-degees F.

Dennis, I am curious what your reasons for not using hd studs are, especially on the race bike.  It seems like everyone just automatically assumes they are required for any kind of performance build.  I have not yet had a necessity to use hd studs myself, and the stock studs have performed perfectly, torqued to 20 ft. lb.  with an oem Honda gasket.  I just torqued down the head on a new built K1 836 and plan to do the same except this time I used oem style gasket from Yamiya, as there is no Honda oem gasket to fit 65mm bore.  Am I gonna be plagued by leaks and problems for being too cheap and lazy to change to hd studs?  Hopefully your experience says no.

[PeWe]

If the 836 (65mm) gasket is the later type with larger oil return holes, earlier cylinder with smaller holes.
8x o-rings (12.5x2.0) will help to seal. There is a Honda Service bulletine about it.

The head gasket must be flat against cylinder to be sure that no o-ring will move under the gasket when assemble the head.

[Old Scrambler]

Sean...........I've been hanging around the pits at Road America for many years. Sooner or later a few 'tips' are learned from the mechanics.....especially early in the AMs   Also advice from Dave Murre, my guru, and my observations about other builder's gripes about breaking a HD stud. Dave and the pros use OEM studs up to 12:1 compression because their 'waisted' design is meant to both stretch and contract. I believe the larger diameter thread area is the primary factor for using HD studs in a hyper-built motor. Dave also taught me that if you feel any tread-resistance before the final 'tug'.......to remove the nut, clean the threads, re-apply oil, and 'do it right'

[seanbarney41]

Thanks Dennis...good to hear that stuff from you, as I suspected as much, but had no real experience or expert advice.

[PeWe]

Good info that has been written here.
Hopefully more experiences to come!

I doubt stock rods should cope with 1000cc.
836 was OK.
12:1 pistons were 62mm?