Topic: '75 550/590 Action Fours Piston Rings

[TheSaint]

Hi folks! Was hoping that one of the old-timers might be able to help me out with this one: I recently picked up a '75 550F with the Action Fours Stage 2 590cc kit installed. I found her sitting in a pole barn up here in tropical Minnesota (apparently, she's been parked there, unmoved for the better part of 27 years) so a re-build is definitely in order. The problem I have is that I don't know what size rings to buy for her. The pistons mic out at 60.98mm, are of the domed top variety, have the letters ART cast into the sides and are stamped 1.00 on the top of each (I'm assuming that this means 1mm over original size, right?) I'm under the impression that Action Fours used 61mm CB750 pistons for the 590cc kit, but that might just be hear-say. Any help would be greatly appreciated.

Thanks,
RD

[bwaller]

Post the ring groove width. I have a set of std 750 rings I'll dig up & measure for you.

[TheSaint]

Thanks! I'll post as soon as I get the measurements. Do you also want actual ring width? I should also mention that the pistons currently all have the old-school 1 piece oil control ring, thou I don't know if that makes a difference.

RD

[dave500]

the one piece oil ring makes a difference.

[Tews19]

Welcome. Any pics of her when yyou got her home prior to tear down?

[HondaMan]

From ART, with a 1.00 cast on it, they will be 1.00mm oversize rings, for sure. It does seem a bit off: if they were standard 61mm 750 pistons and rings (the usual 590cc kit), then the rings would have been marked "STD" or "S", or even "0". 

[dave500]

62mm pistons?,the area around the rings is less than the skirt,,measure at the skirt at 90 degrees from the wrist pin.

[bwaller]

I agree it seems odd that they be 1.00mm over, if so the stock sleeves are way too thin. Action Four had a great name for a while so I expect they used different sleeves if what you have is a 62mm piston. I never played with these middleweights back then, but ask Big Jay of APE fame, I'll bet he knows what Action Fours did with those engines.

For your info a stock CB550 sleeve bored for a 61mm piston leaves a thin wall 1.63mm thick at the tapered bottom.

I have a set of early #13011-300-013 rings. Both compression rings are 1.49mm, one piece oil ring is 2.8mm.

[TheSaint]

Thanks for all the reply's, folks! I think I've solved at least part of the mystery. I got in touch with one of the mechanics at a shop in St. Paul that specializes is vintage European and Japanese bikes (the place is named BlueCat, of all things...sounds more like a veterinarians office, but hey, Mpls./St.Paul is a weird place!)  One of their mechanics, who's been wrenching bikes for the better part of thirty years had a good deal of experience with Action Fours products back in the day. He told me that to his knowledge, AF never used stock Honda or Kawasaki parts for their kits. He seemed to recall that every 590 conversion that he'd done came with ART pistons, and all had the 1.00 stamp on the pistons, as well as the rings (but just like my pistons, mic'd out at 61mm). He also said that the pistons had a 1mm wrist-pin offset (towards the intake side), were domed, polished and relief cut (which mine have/ are) for the use with AF's own cams, which were physically larger than Honda's OEM units and provided more lift and duration. He also said that the pistons provided an effective compression ration of 11:1. He couldn't remember what application ART originally used the pistons for, but that they were not originally designed for Honda, however, worked with AF's set-up, thus the 1 over stamp. As for rings, he is fairly certain that stock Honda 750 rings will work, but he wants me to bring in the whole top end in to him tomorrow so he can spec everything out. The best part, is he's doing it for free! When I mentioned Action Fours to him on the phone, he went from being 'great, another kid with a bunch of goofy questions' to 'Holy Sh*t!!! Really! You've got an Action Fours 590 on your hands? Seriously? Damn, kid, bring that SOB in!!!' I must have triggered some pretty good memories for the old guy, eh? I didn't even know what Action Fours was 'til a week or so ago, and now I'm thinking I might have something really cool! I'll post more info and pics as soon as I can, and again, thank you guys! You all, and this site are priceless!

RD

[dave500]

good you found someone whos taken an interest and is familiar with it,i had a similar question.
http://forums.sohc4.net/index.php?topic=100076.0