Topic: My piston project(s).

[Soos]

Well, not sure if this is the right forum..... but here goes.

I have FINALLY gotten a area in my garage to be heated(WHOHOO!), I've been able to get ready to modify my assortment of pistons for cheap overbores.
(claying pistons is near impossible at 10 F. I have found)

Gotta get some pics here soon.
Heck mabey this morning before my wife wakes I'll try to take pics.



I have my "mock up" cb650 motor and cylinders set up to be able to clay 59.8mm(stock), 61mm, and 66mm pistons.
To do this, I bored 1 sleeve 61+mm(61.05mm), left one stock, removed 2 sleeves.
One of the removed sleeve holes I bored to 66.05mm as well.

The fire that got me going lately is Pinheads piston mods I need to get done soon.



So to list the pistons I have to modify for 650's, in order largest to smallest.
66mm Kz750 pistons
65mm high comp. pistons out of a cb750
62mm KZ650 pistons
61mm cb750 Auto pistons (best 650 overbore option I have found so far!!!)
61mm cb750 '78 pistons (high dome)(next best, but better than above if wanting a higher CR)


I also have a set of '73 61mm cb750 pistons I'm tempted to mod for a 550 overbore.
But not having a 550... i'll wait until someone asks for those to fiddle with them.



So far I have found this....
stocker 650 pistons have 2.5mm protruding past the head gasket.
'78 cb750 pistons (yours pinhead) protrude 6.0mm past the head gasket
cb750 Auto pistons protrude 2.5mm



l8r

[Soos]

here come the pics!
first pic is the pistons I have to modify for the cb650.

far laft and to the front Pinheads '78 cb750 pistons.
On the back lineup, from left to right:
my 750 auto pistons, kz650 pistons, cb750 65mm pistons, and far right the KZ750 66mm pistons.

next pic:
the '73 cb750 stock low dome pistons next to the 550 pistons I got from paulages.

next pic:
my heater, and the cb650 "mock up" motor I am using for this

and the last picture is of the dome protruding past the head gasket for the 66mm pistons

[Soos]

Last pic for now.
Pistons listed left to right:
Pinheads piston, 65mm cb750 overbore piston, stock 650 piston, and the 66mm KZ750 piston.



l8r

[Soos]

I know that the stock, and the 750 auto pistons are the only 2 sets that as is will turn over.
the 750 auto pistons kiss the head a tad though on the outter edges however.....


All the others interfere with the head in one fashion or another.
Have yet to clay anything in the heated part of my garage.
That will probably happen today or tomorrow.
Gotta spend at least 1 day a week with the family. The OT at work kills most of my free time....





l8r

[Soos]

Oh yeah....
Got a few measurements so far.

I measured the protrusion of the piston domes past the head gasket.
Well all except the '73 pistons and the kz650 pistons.

'78 pistons : 6.0mm
auto pistons : 2.5mm
65mm pistons 6.5mm
kz750 pistons 5.5mm

stock pistons 2.5mm










l8r

[traveler]

Okay, so....

What mods would be necessary to run a KZ750 (66mm) piston then?  Do the shoulders need to be milled down?  valve pockets deepened?

And..when using Kawi pistons...what about rings?

I like the idea of 66mm pistons, but it requries alot of machinist work, as You have to fit 900 liners in the cylinders, and bore the case out to fit (in my case a 550 block).

And then you have to decide if a few extra mm's on a piston size is gonna get you any farther ahead?

How far can you bore a stock 650 liner safely?

763 cc's sounds killer, but is an extra 20-30cc's worth the cost?

I'd like to put the money in the head (MReick~Stage 3, and a HOT cam!)

~Joe

[kslrr]

Neat research Soos.  I like seeing "thinking outside the box".  Once I get settled into my new job in Las Vegas and get my shop into shape I'm going to research meathods of off-the-bike carb balancing and alternator output boosting.

Slight hijack over.

[Soos]

Okay, so....

What mods would be necessary to run a KZ750 (66mm) piston then?  Do the shoulders need to be milled down?  valve pockets deepened?

And..when using Kawi pistons...what about rings?


And then you have to decide if a few extra mm's on a piston size is gonna get you any farther ahead?

How far can you bore a stock 650 liner safely?


763 cc's sounds killer, but is an extra 20-30cc's worth the cost?

I'd like to put the money in the head (MReick~Stage 3, and a HOT cam!)

~Joe

It is possible to bore stock cb650 liners to 62mm with no problems.



Uhhh...... 763cc's is 136cc above stock. remember this is on a 650 I plan on running these. Or were you comparing these to paulages 64mm pistons?
(his needed bigger sleeves as well)

Yes the shoulder(deck height) needs turned down(or optionally could be cut down on a CNC circle interpolating it, or on a manual using a rotary table. Heck you got the time, patience, and skill you could hand grind them if need be... But not even I pretend to have any of those 3 abilities to manually do that feat)
The valve pockets will DEFINITELY need deepened.

Nothing major IMO. Basically what I ended up doing to my 61mm pistons in my '79 cb650 right now, just bigger pistons.
But again I am a machinist and do all my own machining work.


Rings are a NIGHTMARE to find compared to cb750 pistons.
I paid a small fortune for my set of rings.(about $100 on E-bay, but to my budget it's a small fortune)


Being a machinist allows me to at least get the machine time for free, even though I have to spend time not money.



And the extra few mm's... it's exactly what I want to run at the salt flats.
Every ounce shaved off, and every cc gained will help.

Neat research Soos.  I like seeing "thinking outside the box".  Once I get settled into my new job in Las Vegas and get my shop into shape I'm going to research methods of off-the-bike carb balancing and alternator output boosting.

Slight hijack over.

Thnx! I like seeing (and doing) outside the box thinking as well.
The 66mm KZ650 pistons however wasn't my original though.
I read a article about a earle 70's cb750 bike using mod'ed KZ750 pistons.
And knowing that cb750 pistons work for a cb650 overbore... the conclusion was logical that the 66mm's would work for a 650 with even less machining needed from what I have seen in the differences of cb650 to the diff. cb750 pistons I have seen.








And on a side note....
Anyone wanting a turbo cb650:
stock low dome cb750 ('69-'76) pistons protrude 1mm above the head gasket.
In comparison, thats 1.5mm LOWER that the stock cb650 pistons sit.
Although the valve pockets will probably need machined deeper to accomodate the cb650 cam.




I plan on doing up some prints(sketches really) and notes on the mods needed, where and how much to cut on these pistons to get them to work.
Especially on Pinheads pistons, as he is going for high CR.



l8r

[Pinhead]

Now I'm starting to get excited. I just need to get to finishing my cylinder head so I can have it all ready when I get the pistons back.

What would you guess the CR to be in my finished engine?

[traveler]

Okay, so....

What mods would be necessary to run a KZ750 (66mm) piston then?  Do the shoulders need to be milled down?  valve pockets deepened?

And..when using Kawi pistons...what about rings?


And then you have to decide if a few extra mm's on a piston size is gonna get you any farther ahead?

How far can you bore a stock 650 liner safely?


763 cc's sounds killer, but is an extra 20-30cc's worth the cost?

I'd like to put the money in the head (MReick~Stage 3, and a HOT cam!)

~Joe

It is possible to bore stock cb650 liners to 62mm with no problems.



Uhhh...... 763cc's is 136cc above stock. remember this is on a 650 I plan on running these. Or were you comparing these to paulages 64mm pistons?
(his needed bigger sleeves as well)

Yes the shoulder(deck height) needs turned down(or optionally could be cut down on a CNC circle interpolating it, or on a manual using a rotary table. Heck you got the time, patience, and skill you could hand grind them if need be... But not even I pretend to have any of those 3 abilities to manually do that feat)
The valve pockets will DEFINITELY need deepened.

Nothing major IMO. Basically what I ended up doing to my 61mm pistons in my '79 cb650 right now, just bigger pistons.
But again I am a machinist and do all my own machining work.


Rings are a NIGHTMARE to find compared to cb750 pistons.
I paid a small fortune for my set of rings.(about $100 on E-bay, but to my budget it's a small fortune)


Being a machinist allows me to at least get the machine time for free, even though I have to spend time not money.



And the extra few mm's... it's exactly what I want to run at the salt flats.
Every ounce shaved off, and every cc gained will help.

Neat research Soos.  I like seeing "thinking outside the box".  Once I get settled into my new job in Las Vegas and get my shop into shape I'm going to research methods of off-the-bike carb balancing and alternator output boosting.

Slight hijack over.

Thnx! I like seeing (and doing) outside the box thinking as well.
The 66mm KZ650 pistons however wasn't my original though.
I read a article about a earle 70's cb750 bike using mod'ed KZ750 pistons.
And knowing that cb750 pistons work for a cb650 overbore... the conclusion was logical that the 66mm's would work for a 650 with even less machining needed from what I have seen in the differences of cb650 to the diff. cb750 pistons I have seen.








And on a side note....
Anyone wanting a turbo cb650:
stock low dome cb750 ('69-'76) pistons protrude 1mm above the head gasket.
In comparison, thats 1.5mm LOWER that the stock cb650 pistons sit.
Although the valve pockets will probably need machined deeper to accomodate the cb650 cam.




I plan on doing up some prints(sketches really) and notes on the mods needed, where and how much to cut on these pistons to get them to work.
Especially on Pinheads pistons, as he is going for high CR.



l8r

Yeah, you read my mind....I'm sorry.  I was talking in comparison to what Paul has in his 718 motor.

At some point, it comes down to AIRFLOW...which means headwork.


~Joe

[Soos]

Now I'm starting to get excited. I just need to get to finishing my cylinder head so I can have it all ready when I get the pistons back.

What would you guess the CR to be in my finished engine?

I'm working on a way to determine that with some degree of accuracy.
I have clayed the stock piston and am wishing I had a large accurately graduated cylinder right now.


From what I can tell at 156.5cc/cyl, and at 9:1 (stock CR) there SHOULD be approx 17.3cc's of clay I have here.
So with 61mm(your pistons) at 163cc/cly, to get to 9:1 there SHOULD be about 18.1cc's of clay. Being your pistons are 3.5mm taller than stock, I'm thinking I can get quite a bit higher compression.

Assuming(I hate that word...) I can get any CR you would like, what would be the ideal CR you would like to achieve?

I have read that about 10.5:1 is about what a 750 can handle with the stock starter on a cb750.
I would like to think the 650 can handle roughly the same range without starter/starter clutch damage.
At 10.5:1 (with your pistons pinhead) I would need to end up with about 15.5cc's when I clay the motor.

To even clay your pistons I still have to do some basic shaping of the piston to get to be able to turn over the motor without the piston hitting the head.
It hits out at the edges, so after I cut the deck height I will be able to clay it at least to get the basic form, then I get to work on valve clearances.




Glad you are excited.
'Tis a bit of work, but it is (IMO) well worth it, if for nothing more than being able to "blueprint" the work needed for that particular type of piston.




And Traveler, From what little I have seen of the 750 head... the 650 is already a breathing demon... STOCK.
Although I do have thoughts forming on what I may do to my head already.....
Boring bar here we come.....

l8r

[Soos]

last post edited for lack of mathematical ability to divide by 4 today.....










l8r

[Pinhead]

Hmm... Never thought about worrying about the starter with a high CR... I was thinking 12:1 would be my upper limit but now I'm thinking 11:1 would be better.

[Kemp]

Soos,
     Was thinking of using the KZ650 pistons in my CB550/650 conversion. The KZ650 piston appears to have quite a nice dome and might give good compression with the 650 head. I'd be really interested on what your development yields in this regard.

[Soos]

I will have to make a new fixture to do 62mm pistons.
'Tis possible, but it will probably be the last set of pistons to be mod'ed.
However, YES they do seem to be very good high compression pistons for the cb650.
Not bad for not having to sleeve it out.
670 something cc's. about 50cc bigger than stock.



Sorry no pics, soon(too much OT... yes, too MUCH.)

But I have started on Pinheads pistons, set the deck height, and evened the dome heights out.
NOt off by much, but why not, the entire piston dome will get touched in one way or another before I am done.
I will be able to clay pinheads friday, or on the weekend, tomorrow is shot for anything.
Just remembered though......

I have exactly 1 cb650 cam.
and it's in my 650.
'eh what the hell, I'll put that cb550 one in it for now.
been meaning to have that 550 cam hard welded, but am awaiting funds to accumulate first....

Anyways, definitely this weekend I'll swap them.
(I have 2  550 cams anyway)

I also cut my cb750 auto pistons.
I like them, a very nice perfect height(within 0.010) of stock cb650 pistons.
The dome I end up with will be nice.


But the BIGGIE surprise was the 65mm cb750 overbore pistons I modified as well(or started at least) today!!!
I will have to take off about 0.040 off the faces of the valve pockets is all!
Ok, besides a minor deck height adjustment.



I am documenting the measurements, and on request will give out measurements to fellow machinists.
However, you are on your own for the fixturing.
A mans gotta keep some things private.
All I will say is it is nice and easy, but I need one for each different diameter of piston.
Got :
59.8(cb650)
61mm
65mm

Still got to finish the 66mm and the 62mm ones.
Come to think of that.. I think I need to get some material for the 62mm ones.
In the end I want a 63 and 64mm one as well.




Would anyone be interested in a set of cb750 pistons modified for a cb550 application?










gotta go,


l8r

[Soos]

I think I have a line on a graduated cylinder with accurate cc measurements, so at least I will be able to figure out the CR the pistons.
Whohoo!



l8r

[Pinhead]

Woohoo x2!

[traveler]

.....Would anyone be interested in a set of cb750 pistons modified for a cb550 application?

l8r

YES.
PM sent.

~Joe

[Soos]

Well, I gots #'s!!!
(I er un Ingleesh Mejur.)

These #'s are APPROX.
Some pistons still need valve pockets (among other things) added.
the auto pistons are not done, nor pinheads.
I did get a graduated cylinder today, nit the most accurate but it gets me in the ballpark.

750 auto pistons 7.4:1 (I will probably sell these)
pinheads '78 pistons 10.7:1(looking good!)
My 65mm (836 kit) pistons 10.7:1 Thats AFTER machining the valve pockets though!





I have been re-thinking my high domed 66mm pistons now, especially after checking out these 65mm high domed buggers.
Those 62mm KZ650 pistons are looking WAY better as well in my eyes.
I was really let down by the cb750 auto pistons. I was hoping for at least 8.5:1 to 9:1
same dome height, but with the added diameter...
the cb650's dome is flat quite a ways, then rounds off sharply, the autos humps in the middle then drops off about halfway to the OD of the piston from the center.



Still waiting on the material to make my 62 and 66mm fixtures.
THOSE are going to be nice.


I will get some pics when I have a few sets done.
I'm thinking of offering piston mods to members here for a fair price.
If anyone has pistons they would like machined, or want to buy a set I have going, PM me.


l8r

[Pinhead]

So after valve pockets and machining is done, I can expect ~10.5:1? Not too shabby... Could you do a measurement on your testbed on what the CR would be without the base gasket?

[Soos]

So after valve pockets and machining is done, I can expect ~10.5:1? Not too shabby... Could you do a measurement on your testbed on what the CR would be without the base gasket?

 
 



hehehehhe... sure why not.
I had been meaning to ask you if you might do that, so I know whether or not to deepen the valve pockets accordingly.
Be interesting to see the CR when all is done.
(REALLY curious how the "surface turbulence" thing goes for you!)



speaking of omitting the base gasket....
I wonder what those auto pistons would end up like as well!
Mabey the auto pistons might be good go with no base gasket.




Ahhhh, cheap overbores galore!


l8r

[Pinhead]

Yeah, people are probably calling me crazy right now. But as I see it, worst case scenario: it pings like mad and I tear the motor back down and reinstall the gasket.

[Soos]

Well without the base gasket I am getting about 11.4:1.
With the valve pockets then the surface turbulence grooves....
I'm guessing no base gasket CR to be 11:1.
And about 10:1 or so with the base gasket.
I would stick with a base gasket though. 10.5:1 CR is what the 750 riders keep reporting as about the limit for their starters.
(although starters aren't that hard to replace when needed. )


Mabey you might make a base gasket yourself out of thinner material?
You can buy gasket material in rolls.
I have heard of cereal cardboard base gaskets being made in a pinch.


l8r

[bwaller]

I just got some 0.010" viton coated steel base gaskets from Cometic for $20 odd.

[traveler]

Work that head.....the power you are getting from this will go up 10-12% I estimate.

~Joe