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Help with b31 big screw up!
#797219 02/01/20 5:16 pm
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I think I really screwed up, long story short I have a beautiful rebuilt head part number 65-1705, was under the impression it was for a b31 but I think its a b33 head, CRAP!
I am tired of kicking myself, I really don't want to throw in the towel.
Any constructive advice besides giving up?

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Re: Help with b31 big screw up!
dean toensing #797224 02/01/20 6:15 pm
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The B31 and B33 heads are quite different size wise. The bores are 71mm and 85mm respectively so if you add a bit for going over any protruding cylinder spigot you should be able to tell exactly what you have for a head.

Is this the same head that you had issues with valve clearance?

If you do have a B33 head and rest of the engine is B31 then the easiest solution would be to sell that head and source a B31 head. Could your original head be repaired?

Can you post photos?

Good luck

Gordo


The roadside repairs make for the best post ride stories.
Re: Help with b31 big screw up!
dean toensing #797227 02/01/20 6:44 pm
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Yep, head with pushrod adjustment issue. Old head is cracked badly. Really discouraged.

Re: Help with b31 big screw up!
dean toensing #797229 02/01/20 7:00 pm
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You could also try to find a B33 barrel and enjoy the extra power


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"
Re: Help with b31 big screw up!
dean toensing #797236 02/01/20 7:58 pm
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So just a barrel and piston? Would the b31 rod work?

Re: Help with b31 big screw up!
dean toensing #797242 02/01/20 8:43 pm
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The 1949 parts book shows the B31 and B33 with the same conrod but they do show different flywheels. 65-1125 and 65-1123 for the B31 and 65-1235 and 65-1233 for the B33.

Are you aware of what flywheels you have?

Gordo


The roadside repairs make for the best post ride stories.
Re: Help with b31 big screw up!
Gordo in Comox #797243 02/01/20 8:54 pm
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The stroke is the same for both engines, Differences in crankshaft will be related to balance and weight so of little consequence.


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"
Re: Help with b31 big screw up!
dean toensing #797245 02/01/20 9:24 pm
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I can't confirm whats in the bottom end.

Re: Help with b31 big screw up!
Andy Higham #797262 02/01/20 11:59 pm
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Could he bore & sleeve his cylinder??

Re: Help with b31 big screw up!
dean toensing #797311 02/02/20 5:12 pm
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Would the larger cylinder option require any machining to the crankcases? I sure appreciate your collective knowledge.

Re: Help with b31 big screw up!
dean toensing #797313 02/02/20 5:51 pm
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Dean: The mouth on the cases should be all the same size so no machining. The B33 piston would be heavier from a balance point of view so high revs might be interesting. For example a BB32 mid compression piston no pin weighs 311 grams, low compression BB34 piston no pin weighs 430 grams and a higher compression BB34 GS piston no pin weighs 493 grams. The experts can tell you what issues the weight increase might be. Of course you may well have a B33 bottom end.

Gordo


The roadside repairs make for the best post ride stories.
Re: Help with b31 big screw up!
dean toensing #797327 02/02/20 7:22 pm
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The additional power sounds appealing and I'm not concerned with originality but I sure don't want to jeopardize the engine or have a bad vibration problem. Since I've never ridden a b series, you that have, does this seem to be a worthwhile way to go or risky?

Re: Help with b31 big screw up!
dean toensing #797335 02/02/20 8:23 pm
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Originally Posted by dean toensing
I can't confirm whats in the bottom end.

It does not really matter what is in the bottom end. The rods are the same, the crank stroke is the same. The B33 is essentially a "big bore" B33


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"
Re: Help with b31 big screw up!
dean toensing #797336 02/02/20 8:26 pm
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This has absolutely standard B31 cases
[Linked Image from live.staticflickr.com]20180609_152238 by Sigma Projects, on Flickr


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"
Re: Help with b31 big screw up!
dean toensing #797359 02/02/20 10:18 pm
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Hi Dean
PM sent

John

Re: Help with b31 big screw up!
dean toensing #797374 02/03/20 12:01 am
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Side note, the carb that came with this basket case is a AMAL monoblock 376/17.

Re: Help with b31 big screw up!
dean toensing #797458 02/03/20 7:10 pm
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As bodine031 asked, could the b31 cylinder be bored to b33 size?

Re: Help with b31 big screw up!
dean toensing #797460 02/03/20 8:00 pm
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Originally Posted by dean toensing
could the b31 cylinder be bored to b33 size?
No. The bore of a B33 is over 1/2" larger, which means over 1/4" would have to be removed from the walls and there isn't nearly enough material to allow that.

Re: Help with b31 big screw up!
dean toensing #797462 02/03/20 8:20 pm
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Thank you Magnetoman.

Re: Help with b31 big screw up!
dean toensing #798598 02/18/20 1:01 am
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There is a small fin B31 head on fleaBay in the US right now


Never underestimate the human ability to elevate stupid to a whole new level!.
Re: Help with b31 big screw up!
dean toensing #798806 02/20/20 1:39 pm
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They all seem to have a broken fin or two. Been told thats not a easy or cheap fix.

Re: Help with b31 big screw up!
dean toensing #798811 02/20/20 2:20 pm
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Cast iron welding or brazing needs skill and knowledge, the finding of the person who can do it is the hard bit, the actual fixing is not costly.


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