Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: mick on January 20, 2012, 10:51:06 PM
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Evening all, i've had this engine under the bench since 2005 and have robbed some parts off it over the years, so i thought i would drag it out and start pulling it
apart & see what i had :-\, so over the last 3 nights ive been in the shed for an hour or so ;)
it appears to be a F1 bottom end CB750E 2544770 with F2 Barrels and Head (marked 410 on the back of the head).
Rocker cover & cylinder head came off very easily, camshaft & towers have already been robbed, head gasket just lifted off not stuck to either surface ?
Barrells came off ok to, thats when i got a nice surprise its fitted with a Yoshi 812 kit 8) bores look very good and pistons look fairly new, the top lip of the
sleeves feel sharp to the touch ? maybe been recently rebored or honed?,
so far i've stripped everything off it and split the cases no major issues so far everythings come apart very easily,
my plan is to strip all the internals clean the cases and paint them and start rebuilding the engine,
can anyone see any problems with the F1 bottom end and the F2 top end and 812 kit?,
i'm sure i'll have plenty of questions as i get into this so watch out ;) in the meantime heres some photos i've taken so far ;), cheers Mick.
(http://i234.photobucket.com/albums/ee75/mcpuffett/11.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/1.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/2.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/3.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/4.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/5.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/6.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/7.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/9.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/12.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/14.jpg)(http://i234.photobucket.com/albums/ee75/mcpuffett/15.jpg)
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Hey Mick,
Sorry for that Yosh kit, will take it of your hands and get rid of it for you. LOL
Sometimes life still has some small surprises for us.
Good luck with your engine.
Cheers, Rob
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You might find it will go even better with an F1 head, unless they are F2 specific pistons, if they are yoshi pistons for normal sohc engines, the F2 head with its larger combustion chambers will effectively lower the compression ratio. I'm not sure what markings on the pistons identify F2 ones, but if you look at some of the U.S. big bore manufacturers sites you will see one set for K0-7 and F1, and a different set for F2, the F2 ones having a higher crown to raise the compression ratio
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You are right hairygit,
But do not think the cr is actually lower than oem, but lower than it would be in a K-series head. The dome on the Yoshi piston seems higher than the F2's. Tho maybe the deep pockets will 'even' it out.
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I think you missed my point there, if they ARE F2 yoshi pistons, then all will be fine, if they are K0-7/F1 yoshi pistons, using an F1 head will unleash the full advantage of the Yoshi kit, and it would be a shame not to get the full benefit of a Yoshi big bore ;D
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I dont think Yoshimura produced specific F2 pistons, if my memory serves me right.
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Cheers HairyGit & Rob, the only markings on the crown of the pistons are A & E, i'll look into it further and see if i can find any more info, cheers Mick.
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I am pretty sure they did a yoshi kit for the f2 , your probably in luck and have it,
i have to say you will have all sorts of problems, so save yourself the agro and sell it all to me LOL!
Check out the US site, there was a post on using a f2 top end on a k or f1 engine, i seem to remeber that the oil galleries at the bottom of the f2 barrels might have to be slightly machined to match, i found this post and it shows you the difference at the base of the barrels http://forums.sohc4.net/index.php?topic=99165, if you search a bit more honda man has a post on the subject, and a guy called yoshi on this forum had a yoshi kit on his f2 some years back, search the user name yoshi on hear and take a look through his posts
pete
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Yoshi823 (also named Pete) hasn't been around for a while. He's in SE London. I think I have his number somewhere if you can't contact him via the PM system.
Steve
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Thanks for all the suggestions and help ;), after a bit more detective work on the US site it would appear that i have either K series barrels or F1 not sure which yet?,
i found a photo from Terry in Oz which shows a f2 & k2 barrels side by side,
first pic Terrys
(http://i234.photobucket.com/albums/ee75/mcpuffett/DSCN0574.jpg)
my barrels
(http://i234.photobucket.com/albums/ee75/mcpuffett/22.jpg)
my barrels look the same as the k2 barrels but i'l have to try and find a photo of some f1 barrels to compare :-\, cheers Mick.
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I believe there is a difference with the top of the barrels. The later (K7 on I think) had deeper recesses for the oil seals.
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Top view of a set of K2 barrels.
(http://i140.photobucket.com/albums/r31/Gearbox_photos/Johns%20CB750/nogasket.jpg)
Sorry about the picture, bit taking it apart. Note round oil seals on top of barrel.
Hope this helps. If I have a better picture, I will post later
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Cheers Seamus i'l get a photo of the top of these barrels to compare ;), cheers Mick.
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I have a set of early barrels (K1/K2) as well as a set from a later bike. The later barrels look the same underneath as your barrels, but different on top. I will photograph this afternoon for comparison
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Hi Seamus heres a photo of my barrells top and bottom i'll post on the US site aswell might get to the bottomof this one ;), cheers Mick.
(http://i234.photobucket.com/albums/ee75/mcpuffett/23.jpg)
(http://i234.photobucket.com/albums/ee75/mcpuffett/22.jpg)
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Mick, they have the "K" shape oil drain holes at the bottom and the 8 extra rubber sleeves(should have the hollow dowels as well) which means it cannot be a up to K4 according to my very early parts book.
From aged memory, here in UK, the first to have the extra rubbers was the F1 so my best guess is and F1 with the Yoshi kit
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Hi Bryan it does have the extra rubber sleeves and the metal dowels , it would be handy if the Barrells were F1 as the bottom end is , just need to get a F1 head then i'd have a decent motor 8), cheers Mick.
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Hi Mick, this may be handy, my F1 barrels as they left the factory (first strip) and rebuild photos, can't find any pics of the bottom though.
Cheers
Den
(http://i192.photobucket.com/albums/z244/DennisMcc/CB750F1BARRELSTOP3.jpg)
(http://i192.photobucket.com/albums/z244/DennisMcc/CB750F1BARRELSTOP.jpg)
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Hi Den thanks for the photos, i think i have got it sorted now, it looks like i have F1 bottom end barrels & pistons ,
so at some point i just need to find a F1 head , to make a complete engine, i haven't touched it lately it been to cold in the shed ,
my next plan is to empty the crankcases and clean them maybe get them vapour blasted? the engine is only going to sitting around again so i don't know if its
worth painting until i need it?, how you doing with your bikes have you done anything to the F2 yet?, cheers Mick.
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Hi Mick, the F2 is on hold at the moment as it's too damp and cold out in the "man cave", I did start refurbishing some of the parts and the top end is off, I rebuilt it many years ago with new valves, springs, pistons, rings etc, and it has not run since but I wanted to check it out before running it. Hopefully when the weather gets better I will restart working on it, I already have lots of parts for it, and it will not be as meticulous a build as the F1 so should not take too long.
Cheers
Den
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The F1 and F2 heads had the extra oil seal recesses in the top face as has already been suggested (there is also a cut-away in the liners for this recess)............HOWEVER, the later K engines also used this design, but I do not know when this was introduced? Bryanj suggests up to K4 were a different design to the later ones, and I would say he's probably on the money?