Topic: more 500 racer developement

[turboguzzi]

Some of you might be familiar with my CB500 racer build.

Bike's been doing OK, rider too but with me now being third in the championship (and bike starting to smoke heavily) I thought it was time for an upgrade/rebuild.

Here is the progression in pistons,

first year I modified the stock to get 12:1 and good squish (on the right) it lasted ecceptionally well
in the middle there's the last piston by TKRJ that didnt do so well. it not only smeared itself but the gudgeon pins wore really badly. Was not impressed
on the left there is the new 57 pisotn I am fititng after an overboe. very modern design, thin rings, low friction coating

last picture shows it compared to the stock CB500.

[turboguzzi]

As you can see, the new piston is lower by a good 3mm, 1/8", compared to stock

Have milled the block and head to keep the 1mm/040" squish area but at this point the stock cam tensioner run out of range.

Even before this last step, I had started to see light signs of valve to piston contact which led me to believe that the thin tensioner blade was not able to cope anymore.

A fellow racer gave me the tip of scrapping the stock tensioner altogether and fit the one from an early CBR600 / CBF599.

As you can see it's way more robust and by creating a manual tensioner, it can keep the chain tight even after a lot of lowering of the head to raise compression.

first pic is the stock setup, the rest the new one

[turboguzzi]

to position the tensioner I used the top hole in the head enalrged to 8mm while on the bottom, I enalrged the 6mm tnesioner adjuster hole to 10 mm and pushed it back to the center line. the stock adjuster bolt is 2mm offset to the left

the tensioner sits close to the timing wheel and it's position is cotrolled by the top turned spacer in the last pic.

the other one with the bolt in it is the threaded mamber that takes the tensioning force.

quite a lot of work to sort out but if you are running into camchain tesnion problems its certainly a solution. Who knows? something similar could work also on the 750's? from what I hear they often have problems with the tensioner.

[turboguzzi]

last upgrade is going to be fitting the #bay CR 29's

they came with way to large spigots meant for an FZ600.

not wanting to spend more money on new original keihin spigots (50$ a pop i think) I turned them down to 35mm to fit aftermarket rubbers and even did a small groove to hold on the bump inside the rubbers

Just 2mm more than my VM26's measured actually 27mm) they look like a big step up.

Still have to finish turning the manifold tubes between rubbers and head and then weld the ears for the bolts.

Hope that tuning them will not be too much pain....

Cheers
TG

[FunJimmy]

Nice info there.
Any chance of finding those pistons in a 59mm bore?

If your piston crown is 3mm lower than the 500 piston, could you use a 650 crank (55.8mm stroke vs 50.6mm) and shim the cylinder the additional 1.8mm? Then you would have a stroker kit.

Just a thought.

Jimmy

[FunJimmy]

TG

The FZ600 carb spacing looks pretty close to the CB500 spacing.
How close is it?

Thanks
FJ

[turboguzzi]

nice idea funjimmy, only problem is that I am racing in the 500cc category

that means stock stroke and +3.5% max allowance for capacity in case of service overbore, with 57mm I am already on the limit, next rebore I should install new stock sleeves, (in theory at least   )  

I think bwaller will know a lot more about that size of pistons as he is working on a CB550 racer.

The CR's have adjustable spacing  you can make them match the ports exactly

Tg

[FunJimmy]

nice idea funjimmy, only problem is that I am racing in the 500cc category

I sorta thought that.

The CR's have adjustable spacing  you can make them match the ports exactly

Good to know.

Thanks
FJ

[bwaller]

Your a good guy to share TG, nice work.

So the bottom of the tensioner isn't located at all? It is a more substantial looking piece especially with that 10mil bolt. Don't tighten that baby with a pipe extension!

Your piston looks good too man. It appears that 15 degree squish ring was completely removed from the chamber?

[MRieck]

 What ring pack are you running TG....XA or XG? XC maybe?

[bikebitzofvt]

Are there any manual cam chain tensioners out there for these engines?  I replaced the one in my CBR600F2 track bike (it was oil pressure fed) to a manual one, just can't recall who made it.

Really nice of you to share your findings, thanks!

[turboguzzi]

What ring pack are you running TG....XA or XG? XC maybe?

not so sure what you mean by that, both of the non stock pistons i used have three piece oil ones

Are there any manual cam chain tensioners out there for these engines?  I replaced the one in my CBR600F2 track bike (it was oil pressure fed) to a manual one, just can't recall who made it.

Really nice of you to share your findings, thanks!

the stock set up is semi manual, you have to release and tighten a nut every now and then. The system is quite unique to the 500 and to be totally honest, works very well even with tuned engines. I went that way only because of the pistons I wanted to use. If I knew where to get yoshi made pistons in 57mm size, It would never be an issue.

I know APE makes manual tensioners for newer stuff

[turboguzzi]

Hei brent, kind of jumped your post....

Your a good guy to share TG, nice work.

So the bottom of the tensioner isn't located at all? It is a more substantial looking piece especially with that 10mil bolt. Don't tighten that baby with a pipe extension!

Yes the bottom isnt pocated at all but this is also the situation in the CBR600 engine it's coming from, the face of the slipper blade has a deep recess that the chain fits into, so if the tension is right, the tensioner stays aligned.

Your piston looks good too man. It appears that 15 degree squish ring was completely removed from the chamber?

Yep, the pistons are very low and with flat outer edge so to maintain the squish I had to machine the whole head flat.

Hope it pays off....

[Bill/BentON Racing]

Hey guys,anyone know where I can get rings for Yosh 590 pistons? 61mm I think,Thanks Bill

[turboguzzi]

Honda has a model called GL 145 who's got a 61mm bore

[bwaller]

Hey guys,anyone know where I can get rings for Yosh 590 pistons? 61mm I think,Thanks Bill

I suppose the rings you need would be thinner than standard CB750K items? Latter F rings are narrower, but damn sure tougher to find. I have a set of standard K rings if you want to send me groove widths.

Turbo, I hate to ask, but are you planning to run the bike on a dyno before your next outing?

[B.O.X.N.I.F.E.]

Any chance of adapting a primary tensioner on the 500/550 motor?

[turboguzzi]

Bwaller, yes sure do, specially since I fixed the dyno's PC by myself for this guy..... he is still running the software on Windows 98 and the Dynojet program was installed in 2000! The PC could "not see" the Dynojet card that connects the PC tot the dyno, but I somehow made it work. When I called the dynojet guys to ask if they had the drivers thye just laughed at me.

The engine just needs assembly now but I want to try at the dyno also the CR 29's, so need to finish the manifolds first.

Will sure publish the results!

Boxnife,
that could be cool indeed, even if the stock chain has no problems coping with even 50% more power from what I've seen. I guess it's more of an issue for people who do high milleage on the street. But nowadays, who exactly puts 10K miles a year on a 500/550?

So, nice to have, not sure it's worth the trouble, surely an intersting mechanical design challenge. 

[HB-1fan]

Hey TG, when I go tommorrow to take pics I will see what the pistons are that came with the kit. They were smaller than advertised if I remember right. I think he just through them in to make it complete. I got the larger set from a friend later and bored the cylinders for them. They are 59mm. The ones in the auction pic are the ones that I'm not using and might be 57mm. He did blast them to make them look good. Hope that doesn't affect ring fit!!!!

Bill, I have some spare and odd POPS ring sets. Don't know if I have what you need but I will look tommorrow. I know there was a couple Kaw and suzuki sets in there that might be big enough. Sets as in per piston, not all 4.

HB

[Bill/BentON Racing]

All of ya'll Thanks,Bill.I get some rings we are coming apart,bike sits as it did after winning 2 nationals @ Roebling Road.Reading where you guys are,I have alot of catching up to do.But let me know,we will all meet at Daytona one day!,Bill

[turboguzzi]

Hei HB, so here's the list of close ups I'd liek to see:

1. side view of the manifolds attached to head

2. view of both ports fron inside and outside, maybe without the manifold?

3. piston crown shape.

4. a shot of the valves.

thanks in advance

TG

[MRieck]

What ring pack are you running TG....XA or XG? XC maybe?

not so sure what you mean by that, both of the non stock pistons i used have three piece oil ones

Are there any manual cam chain tensioners out there for these engines?  I replaced the one in my CBR600F2 track bike (it was oil pressure fed) to a manual one, just can't recall who made it.

Really nice of you to share your findings, thanks!

the stock set up is semi manual, you have to release and tighten a nut every now and then. The system is quite unique to the 500 and to be totally honest, works very well even with tuned engines. I went that way only because of the pistons I wanted to use. If I knew where to get yoshi made pistons in 57mm size, It would never be an issue.

I know APE makes manual tensioners for newer stuff

XC, XA and XG are pretty standard ring packs for aftermarket pistons. XC rings are 1mm top, 1.2mm second and 2.8mm total thickness oil ring pack. Both the XA and XG are 1mm, 1mm and 2 mm. The difference between the XA and XG is the type of scraper (2nd) ring. There is also the XN ring pack but you don't see that with Japanese based aftermarket pistons.

[turboguzzi]

hei mike

the rings are 1mm, 1mm, not that sure about the last one....  maybe 2mm, will check in the evening

for whatever it' s worth, the 2nd ring has a step,

tried to google XA, XC, but couldnt find any referenceo to those rings std's, any links?

Cheers

Tg

[Sam Green Racing]

As you can see, the new piston is lower by a good 3mm, 1/8", compared to stock

Have milled the block and head to keep the 1mm/040" squish area but at this point the stock cam tensioner run out of range.

Even before this last step, I had started to see light signs of valve to piston contact which led me to believe that the thin tensioner blade was not able to cope anymore.

TG, I hope I am not seen as trying to teach you to suck eggs but the slight valve to piston contact may not have anything to do with the tensioner.
When removing as much as you have done from the block and head to retain your 1mm/040" squish area, you have brought your cam to crank centers much closer together.
If the old tensioner is maxing out before becoming fully tensioned, your cam timing will be way out.
This could be the reason for the valve to piston contact and can be corrected with a variable cam sprocket, check where your cam timing marks have moved to and how much your lobe centres are out.

Sam.

[turboguzzi]

Hei Sam,

not really into egg sucking, but in any case...

Valve timing was sure checked (got adjustable sprocket, dial indicator, timing wheel)

left a good 1.5mm at closest of valve to piston clerance with light spring mounted, you name it....

So I do tend to believe that  ihave been running out of cam chain tension, we'll see.

If anything, the new twensioner is so much more sturdy, the stock slider steel strap is  like 1mm thick, the new one is 2.5mm

TG