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Honda CB750/900/1100F SuperSport Website: SuperSport Forums |
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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 Posted:
Thu Oct 10, 2013 8:38 pm |
 
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Ok this is gonna be a headache to explain but here goes.
I got this bike from a trade I did.
Bike is a 82 CB900f which had a 750 motor in it.I received the bike with its motor out,the motor divided into 4 boxes.with the crank being damaged on two big end journals and two damaged conrods.The motor had its bored out to take 900 pistons with a ring gap of +/- 0.2mm,still pretty fresh.
The damage worked out to be in the range of about 4500 ZAR(South African),cranks are pretty expensive here.I got a lead on a 900 engine for 3000 ZAR minus head.I also got a lead on a 900 head with cams for 400 ZAR.Great I thought,Id be saving 1100.Got home with the parts and started stripping the engine.
Lying fucking bastard!!!He told me the motor only need a head but was otherwise perfect.The crankcase was completely scrap.Somewhere someone had spun no 3 bearing and wore the bearing holder so bad that it formed a "V".Surprisingly,the crank suffered no damage.In fact it measured perfect all round.
The cylinder block and sleeves were also fucked.The PO had used epoxy putty to patch up a hole in the cam chain tunnel and the ring gaps measured over 0.5mm.
I phone the prick and all he says is "well that's a chance you take".I tell him what Ill do if I ever find him.Fat chance,we meet at a half way location so I don't have a effing clue where he lives.
So,Im sitting there with a bored out 750 with a stuffed crank and two conrods and a 900 that's completely stuffed apart from the crank and conrods.
So I did what any backyard South African would do and modded the bored out 750 cylinder block to accommodate the extra stroke of the 900 crank.
I had a spacer cut out in the form of a base gasket out of aluminium.The difference as I measured between the 750 and 900 cylinder blocks was at 6.4mm.I had the spacer cut to 6mm and used a 0.8mm gasket to make up the 0.4.The extra 0.4 was to compensate for gasket compression.
Here you can see the spacer between the crank case and cylinder block.The maroon crap around the edge is the shellac I used to seal the deal.Sofar no leaks.
Ive heard this mod has been done before but I cant find any reference.
Ive started the engine and yes it runs.
Right now Im dealing with the usual crap,2 and 3 not firing,cleaning carbs,leaky shifter seal ect ect.Will update as I go along. |
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genesound
Red CB1100F
Joined: Feb 20, 2006
Posts: 11919
Location: Studio City, California
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Thu Oct 10, 2013 9:26 pm |
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Yep, I answered you at the other site. It should work, with the caveats I mentioned. |
_________________
We do not see things as they are,
we see things as we are.
What might have happened if that which did happen had not happened,
I cannot undertake to say.
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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Thu Oct 10, 2013 10:08 pm |
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| genesound wrote: |
| Yep, I answered you at the other site. It should work, with the caveats I mentioned. |
Thanks for the replys.
Well,I did manage to start it so I think it will be ok. |
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Shawn_Mc
CB1100F
Joined: Jul 30, 2012
Posts: 2788
Location: Anaheim Hills, Ca.
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Thu Oct 10, 2013 10:31 pm |
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Lemons...lemonade?
Hey, it runs right? At least you can ride it while your looking for parts for what you really want... |
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Use your head and be respectful, stupid aint cool. |
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damage
Twinstar
Joined: Sep 02, 2009
Posts: 238
Location: Bunbury,Western Australia
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Fri Oct 11, 2013 12:35 am |
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G'day all,
If my memory serves me correctly,this is what Honda US did when only the CB750F was being imported into the US and the rules stated that the original cylinder barrels had to be used.You could use the CB900F crank but you had to use the 750 barrels.I remember seeing an article in one of the US bike magazines back in the day,possibly Cycle World.
Chris. |
_________________
1999 Triumph Sprint St 955
1979 CB900f
1992 Suzuki GSX1100G sidecar
1996 Suzuki 1200 Bandit
1970 Honda CB350 P4 race bike
1985 Kawasaki GPZ900 P6 race bike
2012 MV Brutale 1090RR
If you're not living on the edge,you're taking up too much space |
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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Fri Oct 11, 2013 5:12 am |
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| damage wrote: |
G'day all,
If my memory serves me correctly,this is what Honda US did when only the CB750F was being imported into the US and the rules stated that the original cylinder barrels had to be used.You could use the CB900F crank but you had to use the 750 barrels.I remember seeing an article in one of the US bike magazines back in the day,possibly Cycle World.
Chris. |
I would really like to read that article,if anything,inspiration that it has been done before without hiccups would really help me along. |
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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Fri Oct 11, 2013 5:16 am |
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| Shawn_Mc wrote: |
Lemons...lemonade?
Hey, it runs right? At least you can ride it while your looking for parts for what you really want... |
Abject poverty lead me down this path,haha.Do what you must to ride right?
Well sofar it runs,so hopefully if someone lands up in the same situation this could help along. |
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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Fri Oct 11, 2013 7:49 am |
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Ok carbs done and aircutoff mod done.Just reassemble.
Got this ticking sound coming from the head so I either have a loose valve,loose chain or bent valve.Shit. |
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Hansy
MB-5
Joined: Nov 23, 2011
Posts: 14
Location: Netherlands
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Fri Oct 11, 2013 1:21 pm |
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| stompie wrote: |
| damage wrote: |
G'day all,
If my memory serves me correctly,this is what Honda US did when only the CB750F was being imported into the US and the rules stated that the original cylinder barrels had to be used.You could use the CB900F crank but you had to use the 750 barrels.I remember seeing an article in one of the US bike magazines back in the day,possibly Cycle World.
Chris. |
I would really like to read that article,if anything,inspiration that it has been done before without hiccups would really help me along. |
Good memory !! 
The article was in an issue of Cycle World, november 1979.
It is about Kazuo Yoshima. He had been working at Honda's engine R&D department and moved to the US. At that time (1979) he was working for Ontario Motor Tech Corp.
He reveals what he did to make his CB750F 130 bhp at 10,000 rpm.
The spacer is a part of what he did and here is a quote:
"Since AMA Superbike Production rules mandate the use of standard cilinder castings, Yoshima coud'nt bolt on a CB900 cylinder. Instead, he machined a half-inch thick aluminium plate to fit between the crankcase and the cylinder base. Yoshima countersunk the head an equal amount around the cylinder stud holes so that the standard cylinder studs and nuts could be used".
That was all about the spacer.
If you want to read more about it, there's a copy available on Ebay: http://www.ebay.com/itm/CYCLEWORLD-NOV-1979-CB-750F-80cc-MXER-SHOOT-OUT-ke-250-xr-80-SEARS-POINT-RR-/180960419915 |
_________________
1980 Honda CB900FA (Red)
1981 Honda CB900F2B (Gray) |
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Hansy
MB-5
Joined: Nov 23, 2011
Posts: 14
Location: Netherlands
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Fri Oct 11, 2013 4:50 pm |
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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Fri Oct 11, 2013 8:12 pm |
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Thank you so much Hansy!!!You made my day!
I'm so glad to see that he also used aluminium.In fact my spacer looks exactly like the one on page five.
Its to bad his shim/bucket idea didn't work at first but perhaps the heat treatment would have worked?It would stretch the life of a head so much further.
Again thanks! |
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stompie
Twinstar
Joined: Jul 24, 2013
Posts: 69
Location: South Africa
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Sun Oct 13, 2013 5:22 pm |
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It fires on all 4 cylinders!!!!!!
Ok it misses abit but screw it.It runs,runs!!!! |
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