Topic: High CR 500-550 pistons anybody?

[Sporkfly]

I'm intrigued and interested, but I can't guarantee I could put down the cash for this...

I think stock (550) bore or the 62mm pistons would be good were I capable of coming up with funds.

[Soos]

XL175 pistons are 64mm and XL185 are 63mm. These look interesting, I wonder if they are still available from Honda? Also heard to look at KZ650. Anyone know the max botre for CB650 sleeves?

Here's and interesting site listing many bore sizes http://www.imoto.co.za/pistons.htm

About 63mm without re-sleeving would be the MAX you can run.
62mm safely




l8r

[vintroadracer]

I can get you EXTRA NICE NEW pistons up to 13-1
They are not cheap about 700 with out rings. They might have pins for that I have to check.

[moham]

For what it's worth, I just got back my 550 head and cylinders back from the shop that I had bored to take 60mm pistons from a '85 Kawasaki Ninja  ZX600 A1. The results of the cc measurements of the pistons and chamber showed a CR identical to stock at 9.00-1. I know that's not as high as some would like here but makes them a viable option (if everything else fits properly) for people looking for 550 overbore possibilities.

It will probably take me a couple months to get the whole project complete but I am quite hopeful at this point that they are going to work.


 

[turboguzzi]

XL175/185 are always an option and OK for street use. thing is that these pistons are pretty low tech, full skirt, long pin, thick piston rings, not much potential to get nice squish band.

My initial idea was to make slipper type, high CR, short pin, maybe two ring, lighter pieces.

Vint, waht are you racing? What diameter would these be? would be great to see pics. I see you are new, hope you know how to post pics 

Cheers
TG

[bwaller]

Here's a pic of three pistons, left a 750F-61mm, (410) middle an XL175, right a 500 just to show difference in bore and dome.

The XL175 is 64mm, same size bore as a CB350, so that gives a nice bump for a 750 (to 810) but like the 350 piston will need to be heavily modified to work in the 750.

As TG mentioned that XL175 piston is a big heavy chunk, wider rings than the 500/550's, plus with a full width pin would be adding a lot of weight. The dome would really need to be reworked, as well as the skirts. Not to mention the need for bigger sleeves.

It could be done, but I feel it isn't a good choice. We need lighter more modern pistons. I have been in touch with a manufacturer re 60mm pistons with a 25mm compression height and a 15mm pin. Discussions are stalled until I get cam related info organized, but will report back if it works out.

I also welcome more info from vintroadracer on his piston selection.

[turboguzzi]

indeed, these pistons are all very old school.

it's pretty amazing how much piston technology has advanced lately, got the chance to hold in my hands a Ducati SBK piston (106mm bore!!!) and it's so advanced, like from another planet, see pic.

From what i see, there are plenty of options if you want to do a street going hot rod that doesn’t have to live all the time at 9-12K rpm. That end of the scale (which I guess is what most people need) is covered by the various XL, 750, ninja , etc pistons.

What I’d like to make (because it simply does not exist) is a full racing unit i.e. minimal skirt, 0.8mm piston rings, and with the right deck, squish and top surf for 13:1 CR.  Trouble is that the 56 to 57.5 range I need is useful only to the handful of guys racing in a 500 capacity limit, very few and seemingly, only in europe.

The 60mm bwaller wants might be a bit more popular, catering for 550cc racers in the US.

A few other options that might be worth checking:

Yamaha SR 125 pistons (specially for you bwaller)

Yamaha TTR 125 big bore kits

Honda CRF 150 kits

If anybody’s got access to these, make yourself heard!

Cheers

TG

[MRieck]

 Brent and turbo are certainly right on concerning "old school" pistons. Big, heavy clunky things that belong in the past. Look at new 4 stroke bike pistons.....almost no skirt, short tapered wrist pins, skeleton backsides and very thin rings. If Jay gets those 1000cc piston kits they should be lighter (or certainly no heavier) than the OEM piston/ring/pin assembly they replace.

[turboguzzi]

hei mrieck

welcome to the hot topic!

thought i'd never see you here

;-)

TG

[MRieck]

hei mrieck

welcome to the hot topic!

thought i'd never see you here

;-)

TG

No problem turbo.....I've voiced my opinion about that old crap before. Some people hang on to that stuff like treasure. Old dentures are worth as much. A well designed large piston do great things for these engines (550, 750 etc).

[bwaller]

TG,  looks like the SR125 is 57mm, TTR is 54, CRF150 is 66mm.

Thanks anyway, I'll keep looking for newer dentures. 

[turboguzzi]

ahem, mixed up a bit.....

I've seen 58mm's kits for the TTR made by a certain BBR but now i recall you need 60mm.... sounds like you are in deeper piston trouble than me..... Unless you find oversizes for those kits and go for 58.5 or 59. The pistons look finger licking good. Check the pin dia before ordering though!

Think I am going to stay with the 56.5 CG125 I run this year after all, they held well and were a good 20 grams lighter than stock cb500/xl125, 1.2 mm rings and "almost" slipper type.

Good luck with your 60's!

TG

[Soos]

Here's a pic of three pistons, left a 750F-61mm, (410) middle an XL175, right a 500 just to show difference in bore and dome.

The XL175 is 64mm, same size bore as a CB350, so that gives a nice bump for a 750 (to 810) but like the 350 piston will need to be heavily modified to work in the 750.

That XL175 piston dome looks suspiciously like a cb650's piston dome, got any measurements on that piston?
As far as deck height, and dome height...

Looks like it would be a good overbore piston for the 650 mabey...
   Yeah I know you guys are looking for piston for the 550....



L8r

[speedracer741]

I have also been looking for a 56mm piston to make a race legal CB500. Here are some pics of a stock Suzuki GS550 piston. It is 56mm but like other 56mm options it has a really high dome. Both the piston and/or chamber could be machined to work but I have not put that much thought into it, just figured I would share the pics. It also has a 16mm wrist pin so that is another obstacle. Oh well, had them laying around

[FunJimmy]

I guess nothing came of this eh!

I'm still looking to find some 550 slugs if anyone has a suggestion.

Cheers
FJ

[Flying J]

Im in the market too. I think im going to go with the modified 750 pistons if Soos ever gets around to making more.

[turboguzzi]

gee guys, this was two - three years ago.....

I was back then in the market for 57mm max pistons with high compression, as it turns out, this is solvable with some mini bike big bore pistons, me and howell went that way. Back at the time there werent many racing 500's, this has changed a bit but I am moving on to the open class.

if you are not limited by displacement/bore or dont need CR higher than 10:1, there is quite a lot of mix and match that can be done with various XL/XR pistons.

TG
 

[bwaller]

Agreed there isn't much choice out there for 550 larger bore. I had pistons made but haven't talked about them much since I haven't even run the engine yet. Ross Pistons will make whatever you want and there is no minimum. These are however forged, full skirt and are heavier than stock. For racing I don't mind, but being forged the clearances have to be larger so keep this in mind for a street engine.

Rings are a huge consideration in light of the disasters with those cheap big bore kits. I decided to use thinner VF500F rings for my 60mm pistons, bought a few sets and now these are discontinued.    I just told Ross I wanted to use these rings you make them fit....done. Modern Japanese engines use nice thin rings so it might be possible to find some in a size for whatever bore one chooses.

Perhaps not an easy option, but an option none the less.






 

[FunJimmy]

Brent

Those are beautiful slugs.
Forged on the street doesn't bother me and I love the fact that the piston can be taylored to the specific application.

Thanks

[Flying J]

I think im just going to go the 750 piston route. If i can get soos to do it. You can get a set of .25 over pistons for $199 +$50 for soos to machine them. i think id be happy with a big bore kit like that for $250.

[crazypj]

one thing no one seems to mention about thin ring, 'skirtless' pistons in modern race engines, the design life is EXTREMELY SHORT
 Most MX bikes need a new top end at around 30 hrs race use, longer if not abused
The lack of skirt allows piston to tilt as it wears causing pretty severe blowby and, in at least one case I know of, the 'plating' on thrust side of cylinder was damaged pretty bad and needed a new cyl (about 4 months running with only oil/filter changes)

[turboguzzi]

Guess there is short and there is shorter. been running a pretty modern design, short skirt, slipper type for two seasons  and they hold extremely well. Modern sport bikes have all this kind of design and you can easily get 60K miles or more out of a set of pistons. Agree that current mx motors are on the extreme side, but have a look at supersport bike pistons and these hold extremely well, reduced height, "no skirt", thing rings and all. Conrods and big ends love lighter pistons...

TG



 

[bwaller]

That's why I mentioned I didn't mind that they were full skirt...it may out live me!

This after I recently saw a piston change in a CRF450 without many hours as crazypj mentions. They are extreme indeed though.

[crazypj]

Yep, CRF450 has just enough material to support the rings and close up the hole 

[DeppJones]

one thing no one seems to mention about thin ring, 'skirtless' pistons in modern race engines, the design life is EXTREMELY SHORT
 Most MX bikes need a new top end at around 30 hrs race use, longer if not abused
The lack of skirt allows piston to tilt as it wears causing pretty severe blowby and, in at least one case I know of, the 'plating' on thrust side of cylinder was damaged pretty bad and needed a new cyl (about 4 months running with only oil/filter changes)

But here you´re talking about 1 cylinder bikes. These pistons wear much faster than the pistons in a 4 cylinder. Becfause of my job I´ve seen lots of pistons (often like the one that TG was talking about...Ducati) and none had any wear that wasn´t okay for the kilometres the bike ran. I wouldn´t make myself mad!

Regards
Achim