Topic: TAO --- The South Seattle Cafe Project

[Jerry Rxman Griffin aka MuthaF'er]

"Pump screen was clean. Oil pressure was good until the event happened then it dropped to 0-5 on my gauge. Started smoking and making the spun bearing sound. Luckily I was 1/4 mile from home so just coasted to the garage. Top end is good and had plenty of oil".

I could have written that about mine! Started acting/running funny 1/2 mile from home, smoking out the breather and that nasty bottom end knock. Top end good too. Not sure what a spun bearing sounds like though.

Clogged oil filter? Non-working filter bypass? Cooler?

[iron_worker]

Do you have an actual pressure gauge or just the idiot light? What were the pressures?

Seems like maybe the main bearing clearances were too tight.

Or, maybe the pump was just weak? Did you open it up and inspect the gears for damage?

IW

[70CB750]

Pressure with a cold engine was over 60psi but once everything warmed up at idle it was about 20psi. Riding around with rpm's up it was about 50-60psi. No idiot lights just the guage on the side oil gallery. Pump has been rebuilt but no I haven't opened it up since this happened. Turns freely.

Thats what I get on the K0, great pressure numbers.

[chewbacca5000]

Would it be easier to get a good working crank and rods and drop it in?

I am liking this idea. I found a crank and rods on eBay from a CB750 F3 "with less than 12000 miles". But who knows what your really getting.

These things can go for 100,000+.  No real need to mess with crank / rod assembly unless getting HD Rods like cycle x superrods, and they I would pay the extra $200 and have them put them on.

I would do what Jerry is suggesting and put a little Kero in there see if you get an idea for flow.   I would then blow out with compressed air.

Have you done the better shifting oil pressure mod on this engine where you replace the counter-shaft oil ring and drill extra holes in the clutch hub?  I have done this and I am able to get 60 PSI at idle on a hot engine.  It is not hard and works great!

[brandEn]

I have drilled my clutch hub. I have never heard of the counter shaft oil ring mod. Any more info on that?

[flybox1]

.

[brandEn]

That sums things up well!

[flybox1]

I though so. 
I hope you get it all remedied and keep it in the stable.

[Tews19]

Is the K0 an option to use for the crank? I thought I read the gears or crank are better then any other model for speed. If so Branden PM me. If you are interested.

[flybox1]

After rebuilding the engine once again I think I don't have a choice but to keep it!

right there with you.
PITA my (lack of) 5th gear is, but i'll figure it out

[chewbacca5000]

I have drilled my clutch hub. I have never heard of the counter shaft oil ring mod. Any more info on that?

Same mod, but does not work unless you replace the O-ring to the counter shaft olier.  It has 3 screws.  They get flat and loose pressure.  You will need nice impact driver like the ones Gordon sells.

http://forums.sohc4.net/index.php?topic=78643.0

[brandEn]

Happy 4 year birthday to this thread
 

[SOHC4 Cafe Racer Fan]

Why replace the head?

[timbo750]

I am little confused here.  I was always under the impression that the F rop end was better than the K. But I will also admit to still being a bit nieve about the comparison between the models.

[BPellerine]

the f top ends offer more perf but are kind of finicky to work with.bill

[brandEn]

the f top ends offer more perf but are kind of finicky to work with.bill

This

[MidnightLamp]

The F's eat through guides, have a habit of dropping valves due to retainer design, were generally bagged on (thanks to the nice "higher" redline), and generally have rather expensive/limited after-market support due to the different combustion chamber shape and different cylinder machining (the oil ports at the bottom).

[seanbarney41]

Branden, pming about the cylinder head...

[MidnightLamp]

Got some pics:

K cylinders:
http://imgur.com/4hBIuI8

F2 cylinders:
http://imgur.com/gD2EJpA

F/K Cases:
http://imgur.com/fAl0AAF

F2 Head drainage:
http://imgur.com/zaBUFOX

K head drainage:
http://imgur.com/KSRVGYn

Long story short, the K uses all 8 drain holes, the F2 only uses the outer two. If you put a K head on there, the inner two valve pockets will fill with oil and have to overflow before they drain out of the outer two head drain holes, as the F cylinders will only drain from the outer two drain studs.

It's been a while since I dug into this, but I remember coming to the same conclusion a while ago. Someone please correct me if I'm wrong, but as I remember, you can use either top end with either bottom end, but the cylinders are matched to the head via drainage. You can also (if I'm not mistaken) use a K cylinder for both, but can't use the F cylinder for the K head. Looks like it's workable if you modify the K head (by bridging the valve oil pockets and plugging one of the drain holes), or by die grinding or machining the oil pocket at the bottom of the F2 cylinder to match the K cylinder to make it work.

[Jerry Rxman Griffin aka MuthaF'er]

I have been assuming that I can just bolt a K cylinder and head onto my F3 case. Is this possible or am I screwed? Its been brought to my attention it may not be possible. I thought the only differences was with the oil drainage on the cylinders.

Yes, replace BOTH pieces as a matching set.

[brandEn]

The K matched set of head and cylinders will bolt onto my F3 case without modification or oil draining issues?

[Jerry Rxman Griffin aka MuthaF'er]

Lets get another to chime in here also! Who has ACTUALLY done this and/or who has both sets of cases to compare?

The 77/78F has a -410 part number and it does not cross reference to other years/models. Could that be only because it is black?!

Send MRieck a PM and see if he has actually done it or has knowledge. I know it gets done but do NOT know the details.

[brandEn]

I sent Mike a PM. Hopefully he will chime in.
 
Here is post #6 in the engine FAQ
Dr Rieck says the following:

...once and for all.

First, the 77/78F2/3 heads shared a common head drain back hole which early K,F and late K heads did not.
This eliminated the middle drain back holes in the F2/3 heads.
The 4 studs next to the eliminated drain back holes require cap nuts and copper sealing washers on the F2/3 head only.

The late F2/3, 77/78 cylinders CAN accomodate the knock pins(or dowels) and the rubber gaskets which allows you to run these early/late K and earlyF/F1(75/76) heads.

The later F2/3 castings are good as they are more stout but this does add weight.

Trying to run a Wiseco 836 kit with an F2/3 head will result in low compression secondary to the increased volume of the F2/3 chamber.

Bottom line....early/late K and early F1(75/76) heads will work on late (F2/F3) cylinders and early/late K and F1 upper cases with mild opening (joining) of the F2/F3 two inner drain back holes at the base of the cylinder.

[timbo750]

I am not expert on this and maybe someone said this before but it looks like there has been a foreign material in there to cause that sort of gouge. Where any of ghd rings broken? Might want to check the sump for metal parts.

[Blackfin5]

brandEn - ditto...no expert but "guess" you caught the edge of an oil ring which broke off.  Are the rings on that piston in tact?