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f2 750 head and barrell identification

f2dazzler

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hi every 1, im a new member to your site after finding and reading your forum last night and finding some intresting items on here and some of you have lots of experiance with these sohc's. im hopeing some1 may be able to help please im in the uk and the 1978 model cb750 f2 sohc is a very rare bike ive owned mine for about 8 yrs now and did a full bike restoration and got it back on the road about 5yrs ago, the engine had had a fair bit of work done previously chains and shells ect after insp it just got new rings and barrels honed valves lapped and had pressure test usual all went together new gaskets, seals ect all ran lovely first yr nxt yr had a oil leak from head so redid head been ok since. now tho having problem with oiling up 1 and 4 plugs anyhow ive got engine out again and taken head off all the piston tops are oily as you can wipe them with a rag theres now compression loss bellow pistons so gona get everything measured and looks like my exhaust valve seats are stepped so cud be new valves and guides are slightly worn so will be looking into that but im needing help with identifying my barrels as the f2 is only meant to have the 4 rubbers and collars between the head and barrels but my barrels have 8 holes to take the rubbers and collars over the studs I rebuilt it with 8 but as im having oil probs again cud some1 tell me if I have an early barrels my head is deff f2 with the correct size valves ect I will put on some pics if any1 has any info that would be great. ive also realised now I really need to change the cylinder studs but advice on the head gasket wud be good altho I carnt get a Honda 1 where ive looked. many thanks daz
 

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The only difference between F and K cylinders is underneath. The picture below is taken from underneath. Understand that the cylinder sleeves have been removed from the cylinder blocks pictured below:

BarrelsX2.jpg
 

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hi thanks for your time showing that looks like I do have the right barrels as you show the inner 4 studs blocked off have a recess do u know if they should have an o ring that fits between the barrel and crankcase over the 4 studs and also would u know as I fit 8 of the rubbers and collars over the studs between the head and barrels when I rebuilt it would it create any problem. thanks again
 
hi thanks for your time showing that looks like I do have the right barrels as you show the inner 4 studs blocked off have a recess do u know if they should have an o ring that fits between the barrel and crankcase over the 4 studs and also would u know as I fit 8 of the rubbers and collars over the studs between the head and barrels when I rebuilt it would it create any problem. thanks again


Yes, there should be a fat little o-ring over these four studs between the base of the cylinders and the crankcase at the four "closed off" locations. They are no longer distributed by Honda for the CB750, but they are still produced by Honda for other Honda engines. The original CB750 part number is: 91301-410-000 and is item #6 on this parts fiche:

http://www.servicehondapsn.com/fich...=Motorcycles&make=Honda&year=1978&fveh=131108

The identical 5.5x3mm o-ring from http://www.boats.net/ is: 11-91353-921-310

The 8 seals between the cylinders and the head are optional. Early engines did not use them at all. I use them all the time, at all eight locations, on both F and K engines.
 
I mistakenly referred to the cylinders in my earlier post as heads (now corrected), but I think it was clear we were discussing cylinders in the earlier post. The differences in the heads can be visually observed by the absence of four oil return holes:

The K heads have four pairs (for a total of 8):

K%2BHead3X2.jpg



While the F heads only have four single oil returns:

F%2BHead1X2.jpg



You can even see how much different the F casting is with the material removed to permit oil to flow to the individual oil returns.
 
thanks for your help again that's great and looking at the k head there miles apart yes id got the head/barrel switch sussed cheers, you have obviously built up some f2 motors im hopeing to have these niggly oil leaks sorted this time pian in arse takeing engine out to get top end off ive been trying for last 5 yrs to find someone who knows about them there arnt many over here. just to use on the road wat would u say uve had best results from as regarding head gaskets as the Honda 1 wasn't avalible and the after market ones david silver supplies seem ok at first but then start weeping after a winter lay up any info would be much appreciated, cheers, daz
 
Was the head machined at all? If the head was machined something like .020" then the 8 dowel/tubes could need a little taken off in height. I also have the head and barrel surface cleaned with mentholated spirits before assembly.
I also put a tiny bit of loctite 515 gasket eliminator between my thumb and pointy and rub each seal with it before fitting the seal. The loctite 515 disperses with oil and won't block oil galleries, never use any silicon.
 
Hi all,

I realise this is an old thread but I would appreciate if you could tell me how different the head gaskets are between K and F2.

Can I modify the K gasket to fit the F2?

Thanks
Vini
 
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