Topic: 750k barrels with F2 head?

[hndlbrs]

Howdy all,

I recently picked up a 78 cb750f2 basket case. It came with a wiseco 836 kit for an F2 and the barrels had been bored all nice and such. Seems ive run into a head gasket mounting problem.

It seems I may have K model barrels, as there are wider (oil passages?) stud holes at the 8 points (4 each between cyls 1/2 and 3/4)

The disassembled top end came with 4 pin collars for these oil passages, and the gasket kit had 8 rubbers, so I assumed maybe 4 collar pins had been misplaced, so I ordered 4 more.

From reading other posts, I now understand that on the F2, those oil passages are not used, and looking at the underside of the F2 head, this seems to be the case. With the pin collars and rubbers inserted into the top of the barrels, the pin sits about 1 mm proud of the deck surface, but the stud hbottom of the head

The head gasket that came with the Wiseco 836 kit (for F2) has smaller stud holes at these points

So my questions are:

Can I use an F2 head with K barrels?

If so, can I simply disregard the pin collars (not use them)
And mount

[hndlbrs]

Oops

Please disregard the above, I seem to have posted before my message was complete
Please read below.


 hndlbrs
Full Member

Join Date: Jun 2010
Posts: 19
 

750k barrels with F2 head?
« on: Today at 05:52:46 pm »
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Howdy all,

I recently picked up a 78 cb750f2 basket case. It came with a wiseco 836 kit for an F2 and the barrels had been bored all nice and such. Seems ive run into a head gasket mounting problem.

It seems I may have K model barrels, as there are wider (oil passages?) stud holes at the 8 points (4 each between cyls 1/2 and 3/4)

The disassembled top end came with 4 pin collars for these oil passages, and the gasket kit had 8 rubbers, so I assumed maybe 4 collar pins had been misplaced, so I ordered 4 more.

From reading other posts, I now understand that on the F2, those oil passages are not used, and looking at the underside of the F2 head, this seems to be the case. With the pin collars and rubbers inserted into the top of the barrels, the pin sits about 1 mm proud of the deck surface, but the stud holes at the bottom of the F2 head are not wide enough to accept the pins. I did not try forcing the pin deeper into the barrel deck, as I thought I'd check here first.
The head gasket that came with the Wiseco 836 kit (for F2) has smaller stud holes at these points

So my questions are:

Can I use an F2 head with K barrels?

If so, can I simply disregard the pin collars and rubbers (not use them) and mount the supplied F2 head gasket that has the smaller stud holes?

Anyone out there used an F2 head on a K that can chime in here?

Want to get it right
Thanks in advance.
Jacob

Should I try

[mick7504]

This is from the FAQ section and it is gospel. 

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.

[hndlbrs]

Okay
Thanks
So it seems I probably have an F2 cylinder after all, since all of the 8 holes between the 2 pairs of cylinders are recessed for knock pins, even though on the F2 they are not all draining oil...?

So if the inner holes are not carrying oil on the F2, then I do not need to use knock pins and rubbers on those?

As well, is there anything I need to have on the "eliminated drain hole" studs below the barrels?  O- rings perhaps to seal them off?

I have 5 tiny O-rings that came with the gasket set, and am not sure where they go. 5 seemed like an odd number (no pun) to me.

Thanks
J

[mick7504]

This should help.
These are the Honda microfische exploded views of the cylinder block and the head for the F2.
The part numbers and the descriptions are a good guide to working it out.
See how you go with this and we can help you sort it out if you are still unsure.

This is the block.
http://www.cmsnl.com/honda-cb750f2-supersport-australia_model14693/partslist/E03.html
http://images.cmsnl.com/img/partslists/cylinder-cb750f2-supersport-australia_bigma000087e03_ea5c.gif

This is the head.
http://www.cmsnl.com/honda-cb750f2-supersport-australia_model14693/partslist/E02.html
http://images.cmsnl.com/img/partslists/cylinder-head-cb750f2-supersport-australia_bigma000087e02_145d.gif

[hndlbrs]

Ok thanks.

So today I explored more around this forum and spent a good amount of time in the shop scratching my head and freezing.

To solve my initial confusion, Im pretty sure now I don't have a K cylinder block, but in fact the original F2. Because it had 8 recessed spots for knock pins and rubbers to go, i had assumed it meant it was a K. (never assume anything!!! Argh!!!!) Now I get that the F2 cylinders had 8, (which allowed them to be used with earlier heads), but the head only connected with 4 of them

So this would mean I just omit the knock pins and rubbers on those 4 unused recesses in the F2 cylinder (?) or do I still have to use them.

Also for the 4 inner studs that were eliminated as drains, do I need to have any o rings on the crankcase deck? Or any other seal anywhere up the length of those studs?


And as for the F2 head....

I now see that the small O rings go under the cam towers next to the sleeve pins, 2 in conjunction with the injectors, and 2 in the recess opposite the injector on the intake side.

I'm confused by why I would have 5 of them. An extra with the kit perhaps? Or is there another spot that takes a small o-ring in the head somewhere I don't know of?

There are also the 6 rubber pucks, which must be sealed, even if new, sitting under the cam tower brackets.

I see that the cam bearing bolt holes on the exhaust side of the head actually go thru the top of the head to the opening right above the spark plugs, therefore these bolts need a thread sealer, so oil won't weep from there.

As for the 4 outer stud holes that do get used as oil drains, I see that they are sealed at the top with copper sealing washers and cap nuts. Do these copper washers and cap nuts do the trick, or should I thread seal those too?



Also, on the above block fiche, there is a part #5 (rubber inserts)
The fiche diagram shows 5 of them in a stack.
The head fiche shows rubber inserts as well, but calls them part #3. They are the same (not available) part number (12195410000) on the list as for the block.
What are these?

Anyhow, it's starting to make sense.

Anything I'm forgetting?
Thanks much
J

[Terry in Australia]

Hmmnnn. Not wanting to start an argument with Mick, but contrary to his previous posts, even with domed nuts and copper gaskets I still wouldn't recommend using a K series cylinder block with an F2/3 head without some additional machining work and sleeving as CycleX does. If there's a burr under the copper washer or the head gasket compresses slightly you may still get an oil leak. I wouldn't risk using it if it is indeed a K block, get the correct F2 block and if you need to, swap your 836cc cylinder liners into the correct F2 block.

The easiest way of identifying the 2 blocks is to flip them upside down, and check out the oilways, they're markedly different. I can probably pull a couple out to take a pic if you'd like?

Also, for awhile Wiseco did manufacture a special 836cc kit for the F2, which is discontinued now, but if you have that kit, you definitely won't have a reduction in compression ratio, I had the "rare" Wiseco 836cc F2 big bore kit in my gold K2, (fitted with an F2 engine) and it went very well, indeed. CycleX and (I think) Dynobike sell special F2/3 836cc kits now as well. Cheers, Terry.

[mick7504]

The other way around mate.
Early/late K & early F head on an F2/3 block.
Is that a bottle Wild Turkey for Xmas. 

[Terry in Australia]

The other way around mate.
Early/late K & early F head on an F2/3 block.
Is that a bottle Wild Turkey for Xmas. 

I must be drunk Mick, because I assume that this guy has an F2 head and thinks he has a K cylinder block? From first hand experience, I know that this is not a good combination. Cheers, Terry.

[mick7504]

It's a bit confusing mate - That's for sure.
Some photos would be good to see what he does have there.

I've sunk a couple of WT's myself already after mowing till 9:30 tonight.
It's bloody murder through the day with this heat up here at the moment.
The good thing about the John Deere Ride On is that it's got a provision for a stubby holder on the mudguard.
That was the selling point for me when I bought it.
The old Cox Ride On didn't have that and I always finished up with more beer spilled on the tockleys than down my neck trying to hold a beer between my legs. 

Hope ya havin'a good one mate.

[Terry in Australia]

G'Day Mick, well it's only gonna be 20 tomorrow, so very nice for working on my K1. I had a Cox mower until a couple of years ago, fantastic old beast, it had been sitting in a paddock for years before I rescued it, the owner said it flooded all the time and he was right, the float was full of holes because the silly prick had left the aircleaner off it for years!

I got it running Ok, then eventually gave it to a mate for a bottle of JD when I bought a newer Bolens "Golf Cart" mower with a 5 speed gearbox. I have a ball on it chasing the dog, the cats and the wife, I really don't need a ride on, but I never had a decent gokart when i was a kid, ha ha! Cheers, Terry.

[mick7504]

Mate I'm hoping to be able to put a bit more time into the 836 tomorrow or at least over the weekend sometime.

The pistons are clayed up and ready to check the o/s intake valves for clearance.
I think that it'll all be ok but it worth spending that extra time to know for sure.
There's no second prizes if they punch the pistons on fire up and I don't think that Santa will be bringing a spare set of slugs this year. 

Sorry for hijackin' your post hndlbrs but we like yippity yappin' after a coupla coldies on a hot day. 
Let us know how you go with yours mate.
 

[hndlbrs]

Yeah, I like beer and chatting too. No prob.

I had thought they were K barrels, because they had 8 knock pin recesses, but F2 also had 8, right? Kinda makes sense to me that they wouldn't change the barrels if they didn't need to.

The wiseco kit I have is for the F2, says so on the box!

If anyone has a pic of the oil passages under the bottom of F2 barrels that would be great.

J

PS once again,  so do I only need 4 knock pins and rubbers?

J

[liPPy]

If anyone has a pic of the oil passages under the bottom of F2 barrels that would be great.

Also interested! I have a mystery cylinder block that was thrown in by the seller of my project that I'd like to properly identify.

[Terry in Australia]

Okey Dokey, I'll snap a pic of some F2 and K barrels side by side so you can see the differences. Cheers, Terry.

[Terry in Australia]

Here you go mate, here's a comparison between a K2 and F2 cylinder block, as seen from underneath. Oh and yes, you should have 8 of the metal sleeves and rubbers. Cheers, Terry.

[liPPy]

Nice one Tel!

Great picture - they really are quite different aren't they? Thank you!

[Terry in Australia]

No worries mate.

[hndlbrs]

Ok
Thanks for the photo!!!

I'm still a little cloudy on a few things, still not clear as to exactly where it all goes.  

What I understand is (and please please correct me if any of this is wrong...)

My understanding is that there are 8 studs that are located (4 to each side) between Cyls 1/2 and 3/4. 

These would act as drain holes, but in F2/3 motors, the 4 inner ones (2 each beside cyls 2 and 3) are not used as drains. 

For an F2 motor, the cylinders are recessed for all 8 knock pins and rubbers, even though only the outer 4 (2 each near cyls 1 and 4) are used as drain holes. The F2 motor needs all 8 knock pins and rubbers installed, even though only 4 are used for drains (?)

The inner 4 of these studs (unused drains) most have tiny O-rings installed at the bottom of the studs to keep oil from traveling up and also from the elements getting in. (?)

Is it the actual drain hole studs (outer 4 of the  or the unused ones (inner 4) that get the copper washers and cap nuts? (I'm sorry, maybe it's just me but I seem to have read seemingly contradicting, or perhaps confusingly worded, posts relating to this matter)

Thanks again for the pics
Much help
J

[hndlbrs]

Oops!

I meant "(outer 4 of the 8 )", not "(outer 4 of the  "
Smileys...