Topic: How to make a cb550 engine to a 500 ?

[DresdaHonda]

Hello Racers
I have this dresda framd honda racer i bought in nederland years back.
I did some race in sweden and it was very fast (for me anyway)
It burnt a exhaust valve, mayby because of leak o-rings (no casket) or bad cab setting.
(junk setup with 2 cabels to 4 cabels)
I took it apart and stop there. and workd on another bike (BSA B50 for fast street use)
OK now I BACK to the Honda.
I have a roling chassi and 3 std. cb550 engines.
My idea is that the engine is not really legal in the 500 classic race class.
It´s a cb550 bottom with a cyl. with 61mm piston ??
Mayby the head is cb550 with cb650 cam ??-don´t know to see the difference
the gearbox is a mix of cb550 and cb650 spockets- I think.
Cab is 29mm from cb750.
So my questions is:
How to make a cb550 fast and legal in 500 class ?
Peter
 

[turboguzzi]

hei dresda, welcome to the club

you need to read your rulebook well first

i race in the 500 class in italy and many people are racing here 500's with 550 bottom part of the engine (better gearbox) and 500 cylinder block bored to 57mm (maximum allowed). It's quite an easy thing to do, no special modifications are needed.

but best is if you simply talk with the organization that is runnning the races and get an ok for what you want to do.

TG

[Bill/BentON Racing]

Read TG's posts and Paulage's etc.Plenty of great info on here.Welcome. As TG stated use your 550 BE if legal(probably is) as it will work better.TE many options. Good Luck,Bill

[DresdaHonda]

OK, its legal to use the bottom of a CB550, but it has to be a 500cc.
It is a RC181 lookalike and look very classic, the rulebook says bike/parts up to 1972.

 ::)what is TE ??
Regards Peter

[turboguzzi]

bottom end, top end...

[DresdaHonda]

offcause
So a set up with CB550 BE
CB500 cylinder (57mm pistons)-oversize CB500 Pistons ?
CB550 Head with cobber casket
CB650 cam
CB750 cab
4-4 Exhaust
Flowing the head and bigger valves (size??) (springs ??)
Is that the budget racer engine set up ?

[Howell]

offcause
So a set up with CB550 BE
CB500 cylinder (57mm pistons)-oversize CB500 Pistons ?
CB550 Head with cobber casket
CB650 cam
CB750 cab
4-4 Exhaust
Flowing the head and bigger valves (size??) (springs ??)
Is that the budget racer engine set up ?

Welcome to this forum.
I understand you have a Dresda chassis for the cb550/500 ?
I only know Dresda made them for the CB750.
Will you show some pictures of it ?
We race a CB500 with 57mm pistons , flowed 500 head and bigger inlet valves.
See for the details my thread :http://forums.sohc4.net/index.php?topic=63228.0

Regards René

[CPHjimm]

Welcome Peter to the forum....  or velkommen til denne tidsrøver af et forum....

See you soon at the workshop!!

/Jimmy

[turboguzzi]

offcause
So a set up with CB550 BE
CB500 cylinder (57mm pistons)-oversize CB500 Pistons ?
CB550 Head with cobber casket
CB650 cam
CB750 cab
4-4 Exhaust
Flowing the head and bigger valves (size??) (springs ??)
Is that the budget racer engine set up ?

basically yes, but...
- i am not aware of any difference between 500 and 550 heads
- if the 500 class in your place is really competitive, i dont think that a 650 cam will be enough, megacycle/webcam make race oriented ones. you will want stronger springs in that case.
- some fast bikes here running 28mm 750 carbs
- flowed head yes, dotn forget higher compression, electronic ignition, stornger clutch springs

hard to put it all into one post

[DresdaHonda]

To Howell
Yes they did make frames for CB500 and CB750
I'm not sure what type i have, there is no number in the frame.
here a pic. of the rolling chassis

[DresdaHonda]

Hello Jimmy, I really like to copy your 4-4 exhaust.
See you at the workshop.

Thanks TG
I know its not easy to put the complit set up in one post.
I just like to know that I have to look for (std. parts)
and after that I know I have to bye the really racer parts.
-I read allot old post about CB500 racers
Still need info about the 57mm pistons you use !

Regards
Peter

[turboguzzi]

57mm pistons with 15mm pin are quite common, used in many big bore kits for honda "monkey" bikes, etc.

Modified Honda XL125S are a good option too if you dont want to change too many things.

My 57mm pistons are very low so required to lower the cyl block by quite a few mm, causing new problems with the cam chain tension.

I think that the pistons howell uses need less work to fit.

regretfully there are no off the shelf high compression pistons for the CB500 that are not big bore so any solution will require work.

TG

[Sam Green Racing]

Peter do the rules in your country let you go over the 500cc limit with a manufacturers maximum rebore limit of 1mm. The 57mm piston that Yoseph (TG) is talking about takes you to 516.5cc.
There are high comp pistons made for the CB250 (56mm) but off hand, I don't know the pin size.

Sam.

[Howell]

Peter,

The pistons we use are for the Honda Dax minibikes such as ST50, ST70.
But the piston pin diameter is 13mm instead of 15mm , so you have to make bushings to fit them.
Also you have to do some work on the valve pockets.
The brand of these pistons is Shark.
See here:
http://forums.sohc4.net/index.php?topic=63228.msg829031#msg829031
http://forums.sohc4.net/index.php?topic=63228.msg829112#msg829112
 

[turboguzzi]

Peter,

The pistons we use are for the Honda Dax minibikes such as ST50, ST70.
But the piston pin diameter is 13mm instead of 15mm , so you have to make bushings to fit them.
Also you have to do some work on the valve pockets.
The brand of these pistons is Shark.
See here:
http://forums.sohc4.net/index.php?topic=63228.msg829031#msg829031
http://forums.sohc4.net/index.php?topic=63228.msg829112#msg829112
 

rene, i forgot about your 13mm pin.....

see dresda? no easy solutions for high performance 500 pistons.

like sam says, our federation allows up to +3.5% over the limit displacement , so 57mm are still ok, so check your rules before

TG

TG

[Sam Green Racing]

I've been looking around and there are 12 to 1 forged pistons available for the CB250 that are 56mm same as the 500 four.
http://www.haleshonda.co.uk/pricelist.htm

Sam.

[turboguzzi]

I've been looking around and there are 12 to 1 forged pistons available for the CB250 that are 56mm same as the 500 four.
http://www.haleshonda.co.uk/pricelist.htm

Sam.

where exactly? seen only 66's.

Sam have you been drinking early today?



TG

[mlinder]

Yeah, he been drinking.

That said, it looks like the xl 125 pistons from wiseco could be made into pretty nice cb500 pistons. About 140 bucks per piston, after machining shoulder and valve pockets as needed, is my guess.

[Sam Green Racing]

No, he hadn't been drinking, he just posted the wrong link.

http://www.d-mengineering.co.uk/store52/agora.cgi?cart_id=3900891.26961&next=8&exact_match=on&product=CB250K%2fCB350K

Perhaps he'll not bother trying to help, afterall, he hasn't got a 500 that needs decent pistons.

Sam.

[turboguzzi]

No, he hadn't been drinking, he just posted the wrong link.

http://www.d-mengineering.co.uk/store52/agora.cgi?cart_id=3900891.26961&next=8&exact_match=on&product=CB250K%2fCB350K

Perhaps he'll not bother trying to help, afterall, he hasn't got a 500 that needs decent pistons.

Sam.

interesting... the 250 pistons look like having too much dome for a 500/4. makes sense, the twins have much deeper combustion chambers than the small sohc4's.

on the other hand, on the cb500/4 page, the pistons on offer look like high comp, not flat like stock. though these could easily be reworked XL125's....

http://www.d-mengineering.co.uk/store52/agora.cgi?cart_id=3461625.9339&product=CB500/4&xm=on

Will check with him. What's the name of the guy running the show there?

Mlinder, does wiseco have 57mm pistons for XL's? I know they usually make only bigbore kits.

TG

[Sam Green Racing]

I don't know his name, I didn't look for CB500F race pistons, I got the impression nobody did them due to the fact that you all seem to be modifying odd ball pistons from other models.
I knew that there were race pistons made for the CB250Ks that were the same bore but didn't know the pin size.

Sam.

[DresdaHonda]

Thanks TG
They look very OK, with some dome. -OK price and less work
I like to hear what the compresion is, and if there are over sizes.
About dome, look at the work here, is it a god idea with o-rings ??
Peter

[mlinder]

I still don't see the 250 racing pistons.. 

[Rod]

Will check with him. What's the name of the guy running the show there?

TG

Dave is the guy you need to speak to - an ace bloke, very helpful and knows some #$%*.

[turboguzzi]

Thanks TG
They look very OK, with some dome. -OK price and less work
I like to hear what the compresion is, and if there are over sizes.
About dome, look at the work here, is it a god idea with o-rings ??
Peter

never did cyl o-rings so have no idea how they should look. cant see why you would need them in a 500 unless you are turbo-ing.

the rings should be gas filled, have no idea where you'd get them in such small size. 

Some people race with the stock gasket without problems, i use copper one for better heat transfer.

would use it only if its already ported.

TG