Topic: High compression 73mm piston question.

[Old Scrambler]

Frank..........See pic to get your own degree measurement. We all hold the compass a little differently than shown in the 'book'.............2nd pic shows the clamps we made to hold the pistons in the mill for fly-cutting.  We measured the valve lengths to be 1mm shorter in the F2 head than the K-head.

[dragracer]

Thanks for the information on the angles George. I did make it down to the machine shop today. We did a check fit of the high compression, 13.5-1 KZ pistons into the F model chamber. Looks like we can make it fit after some minor cutting. It'll be tight for sure and that's what I'm after. Once the chamber is opened up, we'll begin the process of changing the valve angle and moving the exhaust pocket over. Going to see if we can install oversized intake valves using Evo valves as blanks. The stem is much longer than the Honda valves. If we have to sink the valves back, we can then cut the keeper grove where its needed to get proper seat pressure. Playing with a cheap Evo valve to begin with.

One more step forward.

[dragracer]

Old Scrambler, I appreciate the pictures and information on measuring the true valve angle. I like the big too. Any finished pictures of the chamber work on your head to get the high compression pistons up in there. I want to be absolutely certain we don't take out anymore material than necessary. Of course my piston design is a little different and the bore larger but I'd just like an idea of what you did to yours. Just hoping once we get the pistons to fit, the valve angles right, oversized intake valves installed, that I can find a decent cam to make it all come together. Any RC454 cams available anyone?

[Bill/BentON Racing]

One sold a month or so ago.  Don't recall who on here got it.

[Old Scrambler]

Frank..........take a look at the last pic on Page #1 of this thread.

You will likely need to remove more material on the edge of the chambers depending on how thick your base-gasket is. You may end up with blended and polished chambers to match Billy Bling You can dry-fit and measure pocket clearances with a helping hand. Ours were very good with a .408-lift cam and old-school J&E racing pistons.

Thinner valve stems may require lash-caps........especially if you re-angle the valves and/or use a high-lift cam. We have 5.47mm stems, lash-caps, bee-hive springs, ti-retainers, and 35/31 flat valve faces. Your big-bore may allow a 35.5 or 36 intake. We used exhaust-guides (shorter) on the intakes to be sure of seal clearance. 

[754]

JeffT sold a 454 cam.. Around end sept.....I think to someone on here..NOS I. Think it was..

[bear]

Old Scrambler, I appreciate the pictures and information on measuring the true valve angle. I like the big too. Any finished pictures of the chamber work on your head to get the high compression pistons up in there. I want to be absolutely certain we don't take out anymore material than necessary. Of course my piston design is a little different and the bore larger but I'd just like an idea of what you did to yours. Just hoping once we get the pistons to fit, the valve angles right, oversized intake valves installed, that I can find a decent cam to make it all come together. Any RC454 cams available anyone?

We attacked it a little differently Frank.

Because we, like you strive for maximum cylinder pressure and  tend to use different pistons from time to time we usually modify the  piston rather than the head.
If the piston's construction would allow it ie there was enough gap between top of ring and piston shoulder and enough piston crown depth.

Sometimes pistons with the biggest lump in the middle are not the best option for maximum cylinder pressure.

After sorting out the best piston crown to combustion chamber contour match we can achive useing a contour gauge. We start by setting up the piston to top of headgasket first using baseplate thickness ( something you may have to consider if you are using MA3 rods). Then we will machine the shoulder and crown of the piston to finish.

As for valve pockets,  our solution looks a little agricultural but it's effective.

Cheers,
Brian

[Bill/BentON Racing]

Hehe, I recognize dem boxes! 

[dragracer]

Bear,

I was wondering when you would pop in with some wisdom on the use of the F head and high compression pistons. I remember you saying before that you prefer not  to cut up the head but to modify the pistons as they are more expendable than the head. I believe you were going to give me a Honda piston part number at one point but i can't recall if i ever recieved it from you. I guess i started going down the path of the KZ piston since i felt availability for a used part was easier for me in my circle of friends or on Ebay. Cutting up a cheap used piston versus destroying new pistons doing R&D just seems more logical. You guys have paid your dues with experimentation- i'm just getting into trying to come up with an inexpensive alternative. Odds are i may end up following your path- sometimes it doesn't make sense to reinvent the wheel when someone else is successfully rolling on it already .

Old Scrambler, I appreciate the pictures and information on measuring the true valve angle. I like the big too. Any finished pictures of the chamber work on your head to get the high compression pistons up in there. I want to be absolutely certain we don't take out anymore material than necessary. Of course my piston design is a little different and the bore larger but I'd just like an idea of what you did to yours. Just hoping once we get the pistons to fit, the valve angles right, oversized intake valves installed, that I can find a decent cam to make it all come together. Any RC454 cams available anyone?

We attacked it a little differently Frank.

Because we, like you strive for maximum cylinder pressure and  tend to use different pistons from time to time we usually modify the  piston rather than the head.
If the piston's construction would allow it ie there was enough gap between top of ring and piston shoulder and enough piston crown depth.

Sometimes pistons with the biggest lump in the middle are not the best option for maximum cylinder pressure.

After sorting out the best piston crown to combustion chamber contour match we can achive useing a contour gauge. We start by setting up the piston to top of headgasket first using baseplate thickness ( something you may have to consider if you are using MA3 rods). Then we will machine the shoulder and crown of the piston to finish.

As for valve pockets,  our solution looks a little agricultural but it's effective.

Cheers,
Brian

[Bill/BentON Racing]

Frank, Bear shared with me a couple years ago now. 17mm pin, 73.00- 74.00, mine are 73.25mm. Mid 80's XR250R.slightly domed also! K, thanks Bear!!

[dragracer]

Got another set of CB1100F rods in the mail today. I think that about wraps it up for my acquisition of MA3 rods. Only 4 can go in an engine and I now have 3 sets. Oh yeah, and this set cost only cost me the price of shipping. Got a free CB1100F starter to boot. Not going to attempt to kick start this one.

Going to the machine shop tomorrow to check on the progress of matching the F head to those 72mm, KZ high compression pistons. Hoping i'll get my green light on the chamber matching so I can order some oversized valves for the next phase.

This motor bench racing is killing me. I need to get to the dragstrip tomorrow to smell some race and gas and burning rubber.

[Medyo Bastos]

sorry to hijack, but i am looking for your monoshock build thread.  i cant find it???

[dragracer]

sorry to hijack, but i am looking for your monoshock build thread.  i cant find it???

The thread is still active. I've just been focused on building this high compression engine for it right now. No issues with anyone hijacking a thread of mine.