Topic: StrongPerf CB550 bike, CB650 Engine, KZ650 62mm pistons. Planning thread.

[StrongPerf]

Hi All,

I'm planning to put a CB650 Motor in my CB550 but want to bump it up a knotch. I'm considering 62mm pistons from a KZ650 instead of the 59.8mm stockers. This would be .087" (2.2mm) overbore. Do you guys think this would be ok boring the stock liners or would I need to put bigger liners in it?

Also wondering if the deck heights on the piston would be simiar enough. I'd like to bump up the compression but don't want to spend mega bucks on expensive pistons... 

Any input?

[paulages]

can't answer you on the deck height, but i can measure some 650 liners today and give you some specs.

[StrongPerf]

That would be great kind sir!

I'm also wondering if the wrist pins are the same diameter. The pistons I can get are cheap so I'm considering buying them just to try it out. I could possibly re-sell them if they don't work.

62mm would put me around 673cc's.

[cafe75-550]

StrongPerf- You're right on with the math, I figured at 672 cc's actually. And the wrist pins are the same diameter, so that's not a problem.

The CB650 sleeves will take the bore, I've measured since I've considered doing the same myself.That would be the max bore possible, you'd need to resleeve if you wanted to rebuild. I can't remember exactly, but it gives about the same sleeve wall thickness as an 836 bore on a 750.

I have heard of these pistons being used in a CB550/650 hybrid before (a 550 case and block with a 650 head), but not without modification. You'd need to turn the tops down to lower the compression ratio, and possibly increase the size of the valve pockets. Given the price of the pistons, plus that machining, it may be worthwhile to go custom...

I've got a set of used KZ650 pistons, just based on rough measurements with a caliper the pin to dome height is 4.5 mm taller than the stock CB650 pistons, and the pin to shoulder height is 1.5 mm taller... You can see the differences in the pistons below, I joined them with a wrist pin to put them side by side. The KZ650 is on the left, CB650 on the right, with a spacer to take up the shorter skirt on the KZ650 piston so they'd sit level.

[StrongPerf]

Answers! Man you guys are great.

I can get a set of the pistons very cheap and I can get machine work even cheeper. Unfortunatly I can see photobucket pics at work. Can you e-mail that to marcus.strong@navy.mil. Thanks.

I like the bigger domes because taking off is easier than adding and I want to raise the compression. Do you think there is enough meat to take off the 1.5mm on the shoulders?

Is there a cam chain adjuster on the CB650 motor?

Thanks guys!

[cafe75-550]

There's a cam chain tensioner adjustment, but I don't think that's what you're looking for...

As for the 1.5 mm, I'm not positive. As I mentioned, I do know of a case where KZ650 pistons were used with a CB650 head, but they weren't stock pistons (wiseco's instead) so I don't know if the shoulder was taken down that much. You also might be able to get away with not taking that much off, depending on the deck clearance, but you'd have to put it together to get an accurate measure on that.

Sent the picture to your address. What kind of tooling do you have access to?

[paulages]

1.5 mm is fairly significant, but isn't that much taller than the 750 pistons i had to work with. if you end up using them, i can give you fairly accurate measurements of how much you'll have to take off, and at what angle the edge of the dome should be cut to. for my 64mm pistons, it was roughly .020" in, and .050" down (if i remember right) and cut at a 47deg angle, before dialing in the CR. i got my piston to head clearance to about .050.

unfortunately, you won't be able to even check for piston to valve clearances until you get the piston to fit in the head.

[StrongPerf]

Thanks guys.

I have access to any tooling. I've built many car race motors too. Unfortunatly my very good friend and machinist moved to Arizona but there's always shipping and I'll be there in a couple of weeks to visit him. I have a lathe and drill press in my garage. I have another friend that works at HAAS automation (CNC tooling) who has it all. Really the machine work isn't the hard or expensive part for me.

Also some of this 1.5mm can also be worked out some in the rods. I wonder what are the measurements on the rod specs for the KZ650 vs the CB. Anyone know if the journal diameters are the same? Lengths close?

Maybe I am barking up the wrong tree with the cam chain tensioner. Just thought it might be possible to shim the barrels out a little to make up some of the 1.5mm and use a slightly longer chain if needed.

Paul - I'm sure I will need much help and input from you once the project starts. I appreciate you offer for specs. Thanks. I think I have enough info to pull the trigger and buy the pistons.

Do you guys see any "I don't think so's that I might be over looking"? 

[cb650]

What year KZ 650 or did I miss it somewhere?




                       Terry

[StrongPerf]

77

Thanks

[cb650]

What kinda HP increase you expect?   5-10 maybe?





                            Terry

[StrongPerf]

Well a 672cc 650 based motor with ported heads, 650 carbs, higher compression, bigger cam and a custom header vs a stock 550. What do you think?

[cb650]

I dont know really.   On a 650 i would think just the piston change without the others would be 5-10HP.  You never know though.



                     Terry

[StrongPerf]

I'm guessing from around 50hp for the stock 550 to 70hp for the modded 650. Anybody agree or want to educate me?

[cafe75-550]

Unfortunately I don't know anything at all about KZ650's other than the piston stuff, that's really all I looked into and I only have the pistons.

You may be able to get away with spacing the head out a little and running a longer cam chain, but you'd have to come up with one. After that the tensioner should be able to keep things in check. Keep in mind though that the cam chain is one of the weak links in these engines...

As for horsepower, stock 550's were about 45, though the early 650's were rated at 63BHP with the improved heads and larger displacements. A 672 with the mods you're talking about should land you on the + side of 70, conservatively, when tuned. More depending on compression ratio's and your cam. You can also run CB750 carbs on the early 650 heads, '79 for sure, and early '80 also I'm pretty sure, as they had the same spacing.

[paulages]

cb650 liner specs:

O.D.: 66mm
I.D. : 59.8

[Soos]

Thanks guys.

I have access to any tooling. I've built many car race motors too. Unfortunatly my very good friend and machinist moved to Arizona but there's always shipping and I'll be there in a couple of weeks to visit him. I have a lathe and drill press in my garage. I have another friend that works at HAAS automation (CNC tooling) who has it all. Really the machine work isn't the hard or expensive part for me.

Also some of this 1.5mm can also be worked out some in the rods. I wonder what are the measurements on the rod specs for the KZ650 vs the CB. Anyone know if the journal diameters are the same? Lengths close?

Do you guys see any "I don't think so's that I might be over looking"? 

Well i've been looking into a set of rods that are 1.5(min)mm to 2.5mm shorter as well for my '79 cb650....
Heck, i'd even go for 3mm shorter. Could omit the base gasket if i had to.
If you find anything that will work, PLEASE post it!!!

In about a month or so, i'll be getting a conn. rod from a cb550 to check against a cb650's rod..
Hoping that the big end is the same as the 650's, and shorter in center to center length..



Those KZ650 pistons look WAY more promising than the pistons I have.
But I am limited to 1 set of 65mm high comp. cb750 pistons, and a set of 750 DOHC (62mm) pistons.
Either set will need 1.5mm(min) shorter rods....and machining on the DOHC's(if they will accept that big of a valve releif)


Has anyone attempted to re-cut the big end on a set of connecting rods to shorten them?
mill off say 0.045 off the rods mating surfaces, re-bore close to size and hone out the last little bit?
I have toyed with the idea lately...
Having no access to a good hone for that job, I may pay to have it done if I cannot swap in shorter rods from another motor.


l8r

[StrongPerf]

Cafe 75 - That's good info. I didn't really know what year model 650 to buy. I believe I like the look of the 750 carbs better and I'm guessing they are easier to find. I'll do the homework later to figure out all the details of what will work best in that dept. For now I just need to decide to pull the trigger or not on the pistons.

Paul - So that would leave me 4mm of meat in the liners. I'm guessing that's enough. Anybody disagree?

Soos - The pistons I'm gonna buy come with rods so I'll just buy them and figure it all out. You can shorten rods by re-sizing. I've done it on a Chevy 327. Don't look for 1.5mm though. I believe that would weaken your big end too much. I'm guessing some from resizing the rod, some from shimming the base gasket thicker (not thinner) and some from machining the piston could easily take up the 1.5mm we need. I would approach the piston first...

I will let you all know how it turns out and just what it took to make it work or why it didn't.

Thanks for all your help!

[turboguzzi]

Soos, why dont you simply put a distance plate between block and cases? This was often done in all the GSXR750/883 conversions.

TG

[754]

45 thou off the rod wouild be 1 1/8 mm.

It may work, use the wrist pin hole to fixture it and use a boring head in a mill to cut them.

If you made a spacer plate out of .040 alum and used a second base gasket you would be close to 1.5mm. or just remachine the pistons..

[MRieck]

Soos, why dont you simply put a distance plate between block and cases? This was often done in all the GSXR750/883 conversions.

TG

Certainly would be the easiest solution but who makes a spacer plate? Cometic can make a copper base gasket up to .040 if it were a 750. Maybe they could make one for the 650?

[crazypj]

You will get a massive torque increase but probably not the power output you expect as the CB650 valves are smaller than KZ650 valves (from memory)
 As machining isn't a problem, I found it better to fly cut the cylinder head to a 7~10 degree angle out to the new bore size, it gets close to intake valve seat, but, if done correctly, unshrouds it very well and increases flow on short side of intake (forget which angle, and the special cutter I made is 4,500 miles away)
PJ

[754]

Spacer plate.. hold a base gasket on the piece of aluminum with layout dye or paint on it, then scribe around perimeter and holes.

Then cut and remove eveything that does not look like the gasket..deburr.. done.

[paulages]

Soos, why dont you simply put a distance plate between block and cases? This was often done in all the GSXR750/883 conversions.

TG

Certainly would be the easiest solution but who makes a spacer plate? Cometic can make a copper base gasket up to .040 if it were a 750. Maybe they could make one for the 650?

yes, they can.

[StrongPerf]

All great ideas and all along the lines of what I was thinking. I'm a make it happen kind of guy and I believe the 1.5mm will be very workable.

I like spacing the jug out but need to work within the limits of the timing chain/adjustment, etc.
It's easy to resize the rod to get a little room there but not much. I could also offset bore the small end and re-bush it. I'll probably look at this possibility. What ever I do I don't want to weaken the rod.
Milling the piston shoulders is a snap (within limit).
Cutting the head chamber is a little time consuming but can make some power from flow.

I will take these all into account to improve flow, get the clearance I need and manage compression. And I'll keep you guys informed all the way. Thanks guys keep it coming!!