Topic: High compression 73mm piston question.

[dragracer]

I changed rods to the longer CB900C units to push the crowns deeper into the F2 head. Did a little machining to the edges of the chamber to avoid detonation............







For big-bore ideas..............take a look at the Dynoman site...........Two crown profiles

That's an interesting idea since the rods are supposed to be 1.5mm longer. So you started with positive deck height I see.

[Old Scrambler]

We measured the rods at 1mm longer by differential between piston heights ..........some have measured 1.3mm...........and some at 1.5mm

The early CB900C rods are very standard but use the improved cap-bolts. Later production and the CB1000 units have 'squirters' for more oil under the piston. We bushed the small ends for the 15 to 17mm pin differential, and shot-peened & polished the rods. I have plans to build a 915 or larger motor and use the squirter rods and similar head setup, but stay at or below 1000cc's.

The current 762cc build revs past 11xxx

[MCRider]

Hmm.  I didn't recall that.  I'm glad your were suitably amused...    

Perhaps it's worth have a few kickstart shafts shot peened and heat treated to have on hand.

George

When I built Phaedrus (889cc) I had 3 shafts shotpeened locally. (Indy) That was the easy part, about $10 each iirc. But finding a heat treater was not possible. One needs to know to what level you want treatment, and have several to do to spread the charge, est $!00 each.

Instead I had them cryogenically treated for about $8 each. I have since sold my 2 spares.

I was able to KS my first 889cc engine, (1980-1995)  w 10.5:1 CR. But I was younger then than now.      

[MRieck]

Heat treated is science and you really should the the material. I wonder what this Japanese steel was made of (old Chevys). You cannot go wrong with cryo but heat treat.....I had 2 bad experiences involving brittleness.

[Big Jay]

What kind of studs are those?

[Old Scrambler]

The studs in the above pics are STOCK from a very low mileage K4.  Big-bore motor is planned to have HD units

[dragracer]

I was digging around in the closet looking for a cam when i found several boxes of pistons that i had forgotten. They range from an old set of 70mm pistons with what appears to be a 12.5-1 K dome, a set of 71mm k pistons with a 10.5-1 dome and a new set of 73mm Arias piston that the literature adverstised as 12.5-1, again for a K model chamber. Since I'll be using an F2 head on this proposed build, I know i'll be loosing compression no matter what set of these pistons i use.

Hopefully some member out there has a used set of F2 model, 72 or 73mm high compression pistons they'd like to part with for a reasonable price to help me put this motor together the right way. This is an economy build but i'd like to halfway do it right based on my tight budget.

[seanbarney41]

does not APE have high comp pistons for F2/3?

[dragracer]

Both Dynoman an Cycleex sell 70mm F2 domed pistons. In reality, the smaller bore 70mm bore, high compression pistons would produce more power than the k model high compression pistons in a larger, 73mm bore that don't fill the F2 combustion chamber completely.  I've got 73mm, 12.5-1 k pistons on hand with a block capable of reboring to 73mm. The alternative is to buy new 70mm , high comp F2 dome pistons and sleeves for $800. Then get someone to bore another block to press the sleeves back in and o-ring it for another $200. Hmmmm, I think nitrous oxide can fill the void in the F chamber left by the K pistons.

[dragracer]

In looking the pictures of Old Scramblers pistons, it started me to thinking about this build using the longer 900 rods with 17mm small end. Since my choices of high compression F2 chambered pistons are limited 970cc(70mm), i decided to look at a KZ900/1000 piston in 72 or 73mm at 12.5-13.5:1 compression domes. The KZ pistons have 17mm wrist pins like the 900 rods and deep valve relief pockets. I'm unsure of the exact valve angle of the F2 head versus the KZ head but i'm going to do some research during the off season to see if these pistons will work under the F2 head. If need be, The pockets can be cut to match the valves angles and positions and the crown could be massaged to fill up the chamber for a tight fit. Deck height could be the achielles heal but varying base gasket and head gasket thickness should help to remedy clearance issues.

Oh well, another potential option to ponder. I'm on a mission for next season!!!!!!!!!!!!

[cbr954]

Not sure what it would cost but I talked with Buzz at Dynoman and they will build custom pistons...any crown shape any compression any bore size...you make a combustion chamber mold and send it to them and the build the pistons.  I'm sure its not cheap.

[kmb69]

.....
The early CB900C rods are very standard but use the improved cap-bolts. Later production and the CB1000 units have 'squirters' for more oil under the piston. We bushed the small ends for the 15 to 17mm pin differential, and shot-peened & polished the rods. I have plans to build a 915 or larger motor and use the squirter rods and similar head setup, but stay at or below 1000cc's.
.....

In looking the pictures of Old Scramblers pistons, it started me to thinking about this build using the longer 900 rods with 17mm small end.
.....

Pretty sure all CB900's, C,F,& K use -438- rods with a 15mm wristpin.
The 1000's and 1100's use -MA3- rods with a 17mm wristpin.

[dragracer]

Yes, custom pistons are another option, although pricey. Si9nce this is a budget build, I'm thinking more of looking at an off the shelf item I can get my hands on readily. I already have the 900 rods and a machinist that helps me out who can cut the pistons/head as needed. Hoping I can probably find a set of used KZ pistons from some of my local racing buddies who may have upgraded to big blocks. 72mm in a KZ is a 1075cc and 73mm is 1105cc. Again, I'm just exploring options and will pursue this possible route until it hits a dead end. Piston pin height, rod length and deck height will play a big part in this as I feel the pistons can be massaged to fit the combustion chamber.

Not sure what it would cost but I talked with Buzz at Dynoman and they will build custom pistons...any crown shape any compression any bore size...you make a combustion chamber mold and send it to them and the build the pistons.  I'm sure its not cheap.

[dragracer]

.....
The early CB900C rods are very standard but use the improved cap-bolts. Later production and the CB1000 units have 'squirters' for more oil under the piston. We bushed the small ends for the 15 to 17mm pin differential, and shot-peened & polished the rods. I have plans to build a 915 or larger motor and use the squirter rods and similar head setup, but stay at or below 1000cc's.
.....

In looking the pictures of Old Scramblers pistons, it started me to thinking about this build using the longer 900 rods with 17mm small end.
.....

Pretty sure all CB900's, C,F,& K use -438- rods with a 15mm wristpin.
The 1000's and 1100's use -MA3- rods with a 17mm wristpin.

Ahhhh, you are correct. I remember having this discussion on the use of the 900 crank in the SOHC cases.

[Old Scrambler]

I can be temporarily confused..........  

Just went to measure my spare set of rods.............must be from a CB1000.........they have 16.75mm pins..........just like the one I used in the 762 build.  I bought them from an ebay seller last year. I put them in a box thinking it was good to have spares for my 762-build.  So now I will begin to search for appropriate pistons to stay under 1000cc with another F2 head. 

This board is WONDERFUL

[dragracer]

I can be temporarily confused..........  

Just went to measure my spare set of rods.............must be from a CB1000.........they have 16.75mm pins..........

This board is WONDERFUL

Wonderful in deed.

Your comment about the 16.75mm pin in the MA3 rod makes sense now. I thought i read the diameter was 17mm. This explains my concern about the rods i recently purchased being compromised because the 17mm KZ piston pin was very loose when i put the pin through. Now i have a new dilema- to tighten the hole will require a bushing. This will entail boring the small end of the rod to get the proper 17mm ID bushing inside. I'm now concern about compromising the rod once its bored to a bigger size to accommodate the bushing. Hmm, i'll have to measure the amount of material on the small end of the rod to see if this is doable.

Crap, I didn't see that coming!!! At least i've got a back up plan in mind.

[Bill/BentON Racing]

Oh yeh, like the song says " One thing leads to another! ! Hehe, Bill Clinton

[BPellerine]

the rc steels had a bushed end,never saw ma3s though.bill

[Old Scrambler]

Frank..........my measurements are not the LAST WORD   The OEM used pistons on the MA3 rods do not 'feel' loose when moving up or down..........but they rock to the sides a small amount. Dave Murre tells me he likes to have pin to piston 'tight' to the point he heats the piston to install the pin. As the piston warms up.........the clearance increases. I don't know how that effects the small end of the rod, but I would think alloy rods need to be 'tighter' than steel...........even with bushes. Dave tells me, and confirmed with NASCAR & Cup-motor data, clearance at running temps is GOOD for oil-cooling.

[dragracer]

Alright, time to get this party started. Chips have to fly to get this dome to fit inside the F chamber. The MA3 rods will need some massaging on the small end to fit inside the KZ piston.  I got lucky and found two more sets of MA3 rods. One set is on its way, the other set is being removed from the engine some time this week. Found a 3rd set but need to get some pictures so i know exactly what i'm getting this time- that first set i bought off Ebay taught me a lesson about being patient. I can still use those but they'll need bushings so i'll box them up for later use.

And so it begins. Hopefully by the end of the month, we'll have the pistons matched to the chamber so the valve and port work can proceed. Odds are the valves will have to be sunk back some but thats to be expected when bumping up the compression with a large dome. I'm shooting for as much compression as i can get so its got to be really tight inside the chamber. I'm looking to make power with compression, not by maximizing the bore or by increasing stroke. OF course the head will have to be done right  to flow enough air to make it all come together. If these 13.5:1 high compression pistons don't work, i'll fall back to the 72mm, 10.25:1 KZ pistons or bump up to 73mm.  This engine will have to be push button start at 24volts- i can't imagine trying to kick it over. I catch enough hell with my 1030. F head, K piston engine.

Stay tuned. The show just opened for viewing. Not only do i have to build a brand new engine, i've got to build a bike from the ground up. This one may not be ready for the first Cup race but should be on deck by Memphis in the street ET class with a novice rider onboard .

[POPS 911]

FRANK in the 10's: NOW You are going SUPER GAS RACING 9.90 on motor and leaving the SUPER STREET 10.90 class to the other SOHC riders,  I will check on that 72" BUSA that has the garage lien on the title for the shop bill the owner did not pay = TOP GAS ?? no bar.

[dragracer]

Well Pops, Bill is building a big stroked motor, adding a light weight front end, shaving weight with lighter wheels and finally putting shocks back on the bike with a long arm. He's shooting for the 8's. So I'm the one getting left in the 9's. Lol.


Heck,  all I'm trying to do is take a bunch of off the shelf, cheap, used  parts that anyone can afford, do some basic machine work, and build a dependable, consistent 10 second high compression engine using an F model head with stock size valves..

[madmtnmotors]

should be on deck by Memphis in the street ET class with a novice rider onboard .

Novice?     

You're no novice! 

[dragracer]

should be on deck by Memphis in the street ET class with a novice rider onboard .

Novice?     

You're no novice! 

Uhhh, I'm not going to be the primary rider on this one. Trying to get my older brother to come out and play with us some this season. He's only participated in a drag race one time. I can only hope he does as well as you. You did very well for your first attempt at racing.

[madmtnmotors]

should be on deck by Memphis in the street ET class with a novice rider onboard .

Novice?     

You're no novice! 

Uhhh, I'm not going to be the primary rider on this one. Trying to get my older brother to come out and play with us some this season. He's only participated in a drag race one time. I can only hope he does as well as you. You did very well for your first attempt at racing.

The more the merrier!