Topic: CB750 AHRMA Sportsman 750 Racer

[slikwilli420]

I approached Kenny about some custom pistons, noting that the only off-the-shelf solution was Dynoman and they were a traditional (heavy) design. I wanted many of the features available today but lacking in those pistons. These will have asymmetrical skirts, inboard pin bosses, modern coatings and be substantially lighter than other available options. I realize some of these things will decrease longevity, but in an effort to build a competitive bike, I have chosen this route. These will take full advantage of the head Mike did for me and the balanced rotating assembly Kenny built, which is back there now to have the alternator stub cut off and the hole plugged. No sense in it hanging out there in the breeze when its no longer needed, besides, its extra weight I don't need.

So it's you who tipped them! This post was on their FB page, announcing the introduction of such pistons:
https://us2.campaign-archive.com/?u=99d88788f6a9b29a346b6d5a5&id=b5683e91ab

It was me. I surely won't get credit for pushing it, but I do get the first set!! Kenny really came through and worked his magic on these. His contacts in the piston industry were what made it possible. Talking to Kenny about these on the phone and you can hear how excited he is about offering these up.

[bwaller]

It likely isn't a huge market opportunity, so good on Kenny.

[livefast_dieold]

I wrote them asking if it would be possible to have them with 63mm diameter, lower CR, and improved squish...

:-)

[slikwilli420]

I wrote them asking if it would be possible to have them with 63mm diameter, lower CR, and improved squish...

:-)

I certainly don't speak fit Kenny or his business but that's probably never going to happen. 63mm is an odd size and didn't fit into displacement restrictions for racing in the US where the primary sales will be. Additionally these pistons are already far superior to the Dynoman ones on every way so squish won't be an issue. And for what they will cost there is zero sense in offering them in 62mm and 63mm.

[gschuld]

It’s hard to tell.  I don’t deal with pistons, but in general a great advantage with CNC milling from billet is the ability to modify the CNC program to stretch and pull dimensions a bit.  Whether it’s cost effective for the supplier to go through the effort is another question.  Usually it’s easier to justify if there are several buyers interested in the same set of alterations of the basic design so the programming time is spread out through a few sets of pistons/sales.

George

[turboguzzi]

Ric, i agree with our american friends. if the ahrma doesnt allow 63mm like our federation, how many people are going to ask for a set? it's not a big bore size either that people would want to buy as an uprgrade.... and dont forget that it's not just the pistons, kenny would also need to source a 63mm ring set.

if it's any help, while reading an old classic bike number (june 2010) i came across this article about a guy in UK who secretly makes pistons sets for many race teams, doesnt even have an internet site. he seems to make custom pistons with no minimum order:

Cegway Ltd - Ph+44 0121 552 4195 pncutler@btopenworld.com

   

[MRieck]

I approached Kenny about some custom pistons, noting that the only off-the-shelf solution was Dynoman and they were a traditional (heavy) design. I wanted many of the features available today but lacking in those pistons. These will have asymmetrical skirts, inboard pin bosses, modern coatings and be substantially lighter than other available options. I realize some of these things will decrease longevity, but in an effort to build a competitive bike, I have chosen this route. These will take full advantage of the head Mike did for me and the balanced rotating assembly Kenny built, which is back there now to have the alternator stub cut off and the hole plugged. No sense in it hanging out there in the breeze when its no longer needed, besides, its extra weight I don't need.

So it's you who tipped them! This post was on their FB page, announcing the introduction of such pistons:
https://us2.campaign-archive.com/?u=99d88788f6a9b29a346b6d5a5&id=b5683e91ab

It was me. I surely won't get credit for pushing it, but I do get the first set!! Kenny really came through and worked his magic on these. His contacts in the piston industry were what made it possible. Talking to Kenny about these on the phone and you can hear how excited he is about offering these up.

I spoke with Kenny at length about these pistons. Finally a modern design. Just wish the pin OD was larger....could get a really light pin in there.

[slikwilli420]

I approached Kenny about some custom pistons, noting that the only off-the-shelf solution was Dynoman and they were a traditional (heavy) design. I wanted many of the features available today but lacking in those pistons. These will have asymmetrical skirts, inboard pin bosses, modern coatings and be substantially lighter than other available options. I realize some of these things will decrease longevity, but in an effort to build a competitive bike, I have chosen this route. These will take full advantage of the head Mike did for me and the balanced rotating assembly Kenny built, which is back there now to have the alternator stub cut off and the hole plugged. No sense in it hanging out there in the breeze when its no longer needed, besides, its extra weight I don't need.

So it's you who tipped them! This post was on their FB page, announcing the introduction of such pistons:
https://us2.campaign-archive.com/?u=99d88788f6a9b29a346b6d5a5&id=b5683e91ab

It was me. I surely won't get credit for pushing it, but I do get the first set!! Kenny really came through and worked his magic on these. His contacts in the piston industry were what made it possible. Talking to Kenny about these on the phone and you can hear how excited he is about offering these up.

I spoke with Kenny at length about these pistons. Finally a modern design. Just wish the pin OD was larger....could get a really light pin in there.

Mike I know you talked with Kenny extensively about this and my race engine build and it's VERY appreciated. Based on your discussions I'm going weigh the cx10 cam and these pistons are becoming a reality. With this bore size are bigger pins necessary? They will be shorter but could we do a tapered pin as well?

[livefast_dieold]

Understood! I asked as at dynoman they realize the pistons in whichever size you want...

[gschuld]

Mike’s involvement only adds to my interest .  I’d love to see a piston top view so I can start to wrap my head around squish clearance depending on the shape of the particular ported chamber.  That’s a big piece of the puzzle for those trying to get as much x clearance squish as possible.

Plus the 12.5:1 compression ratio is based on what final chamber cc?

Do we have an expected price on these beauties yet?

George

[slikwilli420]

George, those are stock photos and not the actual pistons. They don't quite exist yet except on paper. I'm not sure about compression based on which chamber size. As to pricing which I have discussed with Kenny but wouldn't divulge here without his say so, they won't be cheap by any wild stretch but are very cutting edge which is why I am all in. As soon as I have my hot little hands on them I will post up for the world to see. The expectation is to be able to set squish with gaskets as you would any other piston.

[MRieck]

George's pics are the right idea. The larger OD pin allows for a greater ID but the pin strength is not compromised. Like modern bike axles and swingarm bolts...large OD/ID hollow pieces that are light and strong. I'll give Kenny the credit....we talked a bunch about piston design but he got it done.
 Throw some Ti rods (or Carrillo A beams which are lighter than H beams but plenty strong) and you have a nice reciprocating package for sure.

[slikwilli420]

George's pics are the right idea. The larger OD pin allows for a greater ID but the pin strength is not compromised. Like modern bike axles and swingarm bolts...large OD/ID hollow pieces that are light and strong. I'll give Kenny the credit....we talked a bunch about piston design but he got it done.
 Throw some Ti rods (or Carrillo A beams which are lighter than H beams but plenty strong) and you have a nice reciprocating package for sure.

Ti rods would be awesome. Hoping to "get it done" with cycle x rods for now.

[slikwilli420]

Got a bunch of things punched off the list this weekend. AHRMA rules are pretty specific on having brake components safety wired and the way my rotor is setup, it would be a pain to wire the bolts and nuts. I realize that if bolts are wired in series, if one loses the nut it still wont come out but I thought this up and like the results:



The hub is going to Buchanan's today with the spokes for some adjustments. Things didn't fit quite right when I laced them up so they are going to fix it up for me. I also found that the rotor was slightly out so it's going to Tom at TrueDisk to take a whisker off each side and get it night and flat. I only have one brake up front and it needs to be totally on point to be effective.

I also finished up my new rearset bracket design. It looks much less "home made" than the other ones, despite still being totally home made, but is also a half pound lighted for the pair.



I was also able to rough in my breather box for the 4 places the engine will breathe, starter hole, rear of cases, valve cover and clutch cover. I got a nifty little vise bender for Christmas that has worked very nicely for little odd jobs like this.



My titanium pivot bolt is also all set using grade 5 Ti for the shaft and 160,000psi nuts on each end with thick washers. I don't have a comparison to the stock unit but this puppy only weighs 257g!



And finally good progress on the oil tank. This thing is really shaping up and will get more welding soon. I needed to find a way to get the sight glass incorporated into the side panel near the fill cap. I was going to try and form the aluminum but that proved a bit unpredictable for me and I needed a way to hold the nut on the back of the sight glass. I machined a bung from 5/8" aluminum so the sight glass would be mostly recessed and machined the back to hold the hex nut. I will pin the nut on the back so I only need to access the front and then I can add the sight glass after the tank is finished.

[calj737]

I wonder if that etched logo makes it go faster? 

[slikwilli420]

I wonder if that etched logo makes it go faster? 

We'll see. I really cant complain since they worked with me and got me exactly what I needed with no hassle or anything. I have only a few vendors I have ever worked with that have been flawless transactions, and GPS racing is one of them.

[bwaller]

North American Hard Chrome
2230 Speers Road,
Oakville, Otario
L6L2X8

Contact: Gerry Groen  905 847-5200

A fellow racer sent me the info. He had a pair of tubes done in 2011 ($150 CDN for the pair then)....and claimed it was a high quality job.

He mentioned telling Gerry that you're a vintage racer.

[slikwilli420]

North American Hard Chrome
2230 Speers Road,
Oakville, Otario
L6L2X8

Contact: Gerry Groen  905 847-5200

A fellow racer sent me the info. He had a pair of tubes done in 2011 ($150 CDN for the pair then)....and claimed it was a high quality job.

He mentioned telling Gerry that you're a vintage racer.

I'll keep that in mind for when the time comes. My concerns are that 2011 was a long time ago and shipping to Canada and back might kill it. Nonetheless I will look into it.

[turboguzzi]

not that we'll tell anybody but does AHRMA allow Ti for this age bracket? here in italy Ti is not allowed quite across the board, even for much younger machines than yours.

[slikwilli420]

not that we'll tell anybody but does AHRMA allow Ti for this age bracket? here in italy Ti is not allowed quite across the board, even for much younger machines than yours.

Nothing in AHRMA rules about such things at all. Carbon fiber is another thing that isn't disallowed in any age range. Rules are really more concerned about the right brakes and the correct engine mods by class. What's the idea of not allowing it?

[gschuld]

Well in theory, not allowing carbon or titanium and things of that nature are generally intended to be a means to keep the classes budget friendly(anti arms race theory).

George

[slikwilli420]

Well in theory, not allowing carbon or titanium and things of that nature are generally intended to be a means to keep the classes budget friendly(anti arms race theory).

George

That never made sense to me. I have  $10 grand in my motor, all with legal parts per AHRMA. A few bucks in Ti won't make the difference between winning and losing. I like my things to be different and unique to me, so while it does save weight, its different from the guy who chooses SS bolts. Besides, it helps me just a little bit on my quest for the lightest racing CB750. I would wager that it is the lightest CB750 in AHRMA currently.

[slikwilli420]

Kenny at Cycle X is chugging away on a bunch of fun stuff for me to get my engine project further down the road. I sent my crank back to have the alternator stub cut off and just got word that is complete. I could have done it on my own, but feared getting metal shavings into the oiling passages and had no real idea of how to plug the hole at the end. Kenny got that all figured out.

I should be getting my modded crank, undercut trans, all trans bearings, studs (cylinder and main), cam (CX11) in the next week or so. My cases are done being cut down and have the magic windows between cylinder pairs so are ready for vapor blasting.



Also undertaking a side project of building a roller starter. Commercially available units are $800-1100 and I will be $400 all in for mine, so I can't complain. Also, none I have found had everything I wanted in one. Some were steel (too heavy) and some were gas engines which I was not interested in. My design is 13.25" wide and about 10" tall so will store very easily in the upright position out of the way.

This is where I ended up Saturday. All that is left is to get the rollers welded to the end caps and to the shafts and wire it up.

[bwaller]

If I may I'd suggest not making it too tall. By yourself it'll be way tougher to back over the first roller. It also tries to push the whole outfit away from the bike. Mine is similar, and I think it's a good layout.

Another couple suggestions, get a starter motor with a planetary drive. Secondly find good heavy flexible welding cable. It's amazing how lightweight cables heat & steal power.

There I hope I haven't pissed on your cornflakes!

[slikwilli420]

If I may I'd suggest not making it too tall. By yourself it'll be way tougher to back over the first roller. It also tries to push the whole outfit away from the bike. Mine is similar, and I think it's a good layout.

Another couple suggestions, get a starter motor with a planetary drive. Secondly find good heavy flexible welding cable. It's amazing how lightweight cables heat & steal power.

There I hope I haven't pissed on your cornflakes!

Not at all! Front roller is as close to the ground as it can be unless I make it smaller. The motor is a high torque tractor starter motor which seems to be what everyone uses. I definitely have heavy cables and will be running a solenoid for the foot pedal.