Topic: CB550 cylinders on a CB500 case?

[Scott S]

 Will CB550 cylinders fit on a CB500 engine case without machine work? Are the skirts/spigots or whatever the're called at the bottom of the 550 cylinders larger than the holes in the 500 engine case?

 If they'll drop right in, do 550 pistons, wrist pins, etc., work with 500 rods?

[Greggo]

Yes, yes, and yes.  I've heard in some cases that the case may need a little finessing, but they do interchange.  Only thing that changed was the bore of the cylinders, besides the transmission.

[Scott S]

 Sweeet. Thanks. I guess you can see where this is headed, huh?

[Greggo]

Yeah, but most guys go the other way when swapping top/bottom ends with these bikes - for racing.  You get the 500cc class standing, and the stronger gearbox from the 550's. 

I've thought of doing this myself though...buying a +3mm big bore kit, and having a set of 550 cylinders honed.  It'd save on machining costs, which I have to pay for, and I don't have a spare, solid 550 motor to build up.

[Scott S]

 Well, I swapped a 550 motor into my CB500. I now have a good running but leaky 500 engine. I found a title CB550 frame of Craigslist for $175.
 My plan is to put fresh gaskets on the CB500 engine and drop it into the 550 frame using leftover parts from my other bikes. I think I can get a running, titled bike out of it for less than a grand.
 If the cylinders are coming off the 500 anyway for gaskets.....maybe I can score a good deal on used 550 pistons/cylinders somewhere and make a STF (sweep the floor) franken bike out of it.

[Danno]

there was a european model 500 that had the 500 heads and barrels mated to a 550 bottom can't remember which country it was sold in but it was done that way because there was some sort of tax on bikes over 500 cc in that country many of the owners of that bike put the 550 jugs on

[bryanj]

Depends on the age of the 500 cases, later cases ahd bigger holes so the 550 liners NORMALY fit BUT you need to fit carefully to make sure the outer dowels with the oil restrictors are OK

[Matte Black]

Sorry to rectify such an old post, but this thread is the reason I bought CB550 jugs, and have some questions referring to the comments, hope y'all are still around.

Depends on the age of the 500 cases, later cases ahd bigger holes so the 550 liners NORMALY fit BUT you need to fit carefully to make sure the outer dowels with the oil restrictors are OK

I read the liners are snug into the upper case but damn, when I tested the figment it barely sits and will require some heavy hitting! I have a '73 CB500 case with '74 550 jugs. Do I need to machine the case or the liners a tad?

Sweeet. Thanks. I guess you can see where this is headed, huh?

I saw in your signature your 500 is described as CB500/550, so I'm assuming this all went well. Was it a super tight seating like I mention above? Did you do any adjustments? How'd it go with the pistons? Havnt bought em yet.

Thanks!

[Scott S]

 I never did this particular swap. I ended up sealing the 500 and using it.
 The current bike is a 500 with a complete 550 engine.

[Matte Black]

I never did this particular swap. I ended up sealing the 500 and using it.
 The current bike is a 500 with a complete 550 engine.

Ahhh I see, engine swap sounds better.

Any ideas? Is it safe to pound the cylinders in the case or would it be a good idea to to machine down the outer liners?

[bryanj]

NEVER pound the cylinders on something will break expensively, you will have to open out the crankcase holes slightly so the liners fit in. Must be earlier 500 cases, later ones had slightly bigger holes. The European 500 was the K3 and was same as 550 K3 but with smaller pistons and different jets in the horrible PD carbs

[TwoTired]

The European 500 was the K3 and was same as 550 K3 but with smaller pistons and different jets in the horrible PD carbs

What made you decide the PD carbs were horrible?

They are "different", I grant you.  But, mostly do the same job as prior carbs with the ability for more precise adjustments.  Too "fidly, perhaps"?

Cheers,

[Matte Black]

Machine the case openings, don't thin the sleeves to fit.

Cool, aluminum is softer anyways.

[Matte Black]

NEVER pound the cylinders on something will break expensively, you will have to open out the crankcase holes slightly so the liners fit in. Must be earlier 500 cases, later ones had slightly bigger holes. The European 500 was the K3 and was same as 550 K3 but with smaller pistons and different jets in the horrible PD carbs

Hmm, let me step back a sec. What was appealing for this swap was to easily increase the bore up 46cc without having to machine anything. It's looking like I have to bore up the case to bore up the cylinders. In order to open up the case bigger I'll need to split the case which wasn't originally part of the plan. I have to decide if all this is worth the extra bore or not. I'm only $20 into the 550 jugs. Will I even notice a power difference? Will I really gain a horse or two? If the difference would be noticeable maybe I'll split the case, but I at a crossroads. What's your opinion? Thanks for your help

[strynboen]

i like the later carbs..specily the full adjustabel cabel choker..is very nice..i hate to run my 400 four..vith its on/off choker..

[Matte Black]

Machine the case openings, don't thin the sleeves to fit.

Wait a sec, when we machine out a larger cylinder bore, aren't we thinning the sleeves all the same? The amount of material would be very little. My neighborhood machine shop could handle that I'm sure, grabb'n for straws I guess

[Matte Black]

Machine the case openings, don't thin the sleeves to fit.

Wait a sec, when we machine out a larger cylinder bore, aren't we thinning the sleeves all the same? The amount of material would be very little. My neighborhood machine shop could handle that I'm sure, grabb'n for straws I guess

Boring the interior of a sleeve is a horse of a different color than machining the exterior down. There's a gentle taper at the bottom of the sleeve that if you overbore too far, or turn down the exterior, you'll make too thin and it will likely crack. Conversely, if you open the case aperture, there's no ill effect.

As to your question about HP gains, with a stock 500 vs 550 bore, you'll see virtually nothing from the swap. You will see/feel a difference if the motor is now healthy, has solid/strong compression, and is in a good state of tune. But you can achieve that with your stock 500 too.

So, split the cases and make the 550 jugs fit, or button up the 500 with new, fresh pistons (you can overbore the stock 500 sleeves to 59mm safely anyway) and get the same result with no case splitting. Make sense?

Makes sense thanks. I have to decide to either up bore the jugs or the case. Unfortunately one of the deciding factors that lead me to get 550 jugs was that my 500 jugs has broken fins and I decided to replace it. This is a tough decision :/



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[Scott S]

 See this in the classifieds? Maybe he can get the 500 pistons and cylinders set up for you and you'll be ready to go.

http://forums.sohc4.net/index.php/topic,167067.0.html

[Matte Black]

have you tried popping your 500 sleeves in the 550 block? I never have pursued this, but wonder if its an option

I havt tried that, that could be my third option of using what I have. I'd keep the 500 bore and won't have chipped fins. Good thinking, I'll weigh it. Now how easy is it to swap a sleeve?

[Matte Black]

See this in the classifieds? Maybe he can get the 500 pistons and cylinders set up for you and you'll be ready to go.

http://forums.sohc4.net/index.php/topic,167067.0.html

Now that's an easy option! +1 500 pistons with jugs, not a bad deal at all! What cc does +1 piston bore out to I wonder. Thanks Scott

[DaveBarbier]

'79-'82 CB650 motors drop into the 500 frame. Just saying.


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[Matte Black]

Removing the sleeves is pretty easy- just head the block up gently, set the block inverted in some blocks and the sleeves will slide out. Reinstall in the other block.

+1 oversized pistons are 56mm (2.20)+ 0.25 x stroke. Stock CC is 498 (IIRC) so you would be up a little bit. But again, it's not going to suddenly turn your bike into a fire breathing dragon.

Wow you def know the math, so the cc would stay at 498? I think I may just grab the rack/pistons. If I had the newer 500 case I'd continue with the 550 rack but I have got so much still to do to bike I should keep it simple. It's a complete rebuild.

'79-'82 CB650 motors drop into the 500 frame. Just saying.


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Totally, I have an '81 650! Good motor, carbs always causing me grief but pulls strong.

[bryanj]

Std is (56 squared x3.14)/4 times 50.6 times 4 divide by 1000 to get cc (498.26)
+1mm is same altering 56 to 57 and comes out at 516.21cc or just over 3% extra

[Matte Black]

Std is (56 squared x3.14)/4 times 50.6 times 4 divide by 1000 to get cc (498.26)
+1mm is same altering 56 to 57 and comes out at 516.21cc or just over 3% extra

Man y'all really know the math. Thanks!