Author Topic: So, I got some Yosh racing pistons (Read 4348 times)

Tretnine · « **on:** May 03, 2010, 06:10:57 PM »

Well, maybe a bit impulsive, but ebay had some yoshimura racing pistons that I picked up for an overbore on my 78 550k. I'm looking at street riding, so I'm hoping my compression won't be screaming and 'asplode' my motor. Anyone have any data on these little guys? Lots of relief area for the valves. Interesting...

Tretnine · « **Reply #1 on:** May 03, 2010, 07:10:32 PM »

Link added
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=120563558798

Tell me what I've gotten myself into...

Jerry Rxman Griffin aka MuthaF'er · « **Reply #2 on:** May 03, 2010, 08:44:34 PM »

good score. I'd say you got yourself into a better performing machine. Yosh isn't so radical it will take super special tuning to make it work. Just find a good cam and springs and hold on. Have MRieck do the head and you have a nice engine.

MoTo-BunnY · « **Reply #3 on:** May 04, 2010, 01:24:24 AM »

wOw - nice eBay score! I have seen other non-Yoshi sets go for much more than that!

If you keep hounding the 'bay, some verrrry interesting stuff turns up, from time to time

bwaller · « **Reply #4 on:** May 04, 2010, 06:47:11 AM »

I didn't look at first thinking this was another set of old used worn out pistons. Nice find. I went to a lot of trouble getting pistons made that aren't much different from these.

There are several guys here that use these 61mm Yosh jobs on the street, funjimmy comes to mind. I have seen subtle differences in these pistons so I expect Yoshimura offered some for street use and others for race use with more dome to bump CR. You may want to stick to stock gasket thickness and not remove any more material than necessary from the head or cylinders until you get an idea of the comp ratio.

Maybe someone who knows will recognize these.

Tim. · « **Reply #5 on:** May 04, 2010, 07:25:10 AM »

With a 61mm bore I think you got yourself into new sleeves, no? That's well above the stock tolerances for boring the stock sleeves out I think. Every 590cc kit I've seen comes with new sleeves.

You might need these too:

http://cgi.ebay.com/ebaymotors/HONDA-CB500-FOUR-BIG-BORE-DRAGBIKE-SLEEVES-POWROLL-/230441127953?cmd=ViewItem&pt=Motorcycles_Parts_Accessories&hash=item35a75c9011

I put one of these (actually 2 - long story) kits in my CB550. Was a great option for a stock rebuild. Couldn't do it much cheaper.

http://cgi.ebay.com/ebaymotors/Honda-CB500-Four-BIG-BORE-555cc-Performance-Rebuild-Kit-/390189085178?cmd=ViewItem&pt=Motorcycles_Parts_Accessories&hash=item5ad914f1fa

fastbroshi · « **Reply #6 on:** May 04, 2010, 07:41:26 AM »

Tintin, did you use all the rings that cam with it? I thought those one piece oil rings (for the bottom landing) were inferior the the three piece one.

Tretnine · « **Reply #7 on:** May 04, 2010, 08:08:11 AM »

With a 61mm bore I was under the impression you could run stock 550 sleeves but not 500 sleeves. It warrants further checking. Hannibal smith is dropping a 605 henry abe kit into his 550 and hasn't mentioned new sleeves, it's possible he got new sleeves. Anyone have any information on that? The plan is to have my head ported in addition to the pistons, but maybe if the CR starts getting too high I could run a 650 head, but I don't know how well that would work together. Seems a bit silly to low CR like that, but the street use and long term stability is the plan for this motor, not rebuilds and racing.

Hannibal Smith · « **Reply #8 on:** May 04, 2010, 08:16:49 AM »

No sleeves required here. Just a straightforward bore and hone.

I sent my stuff to APE, they are close and do this stuff all the time. They have done a tone of these SOHC cylinder boring jobs, so there is no surprises or learning curve action going on when you send them to APE.

bwaller · « **Reply #9 on:** May 04, 2010, 08:19:35 AM »

Stock 550 sleeves are ok up to 61mm. I'd be curious to know if these Yosh pistons will use standard CB750 rings too.

Tretnine · « **Reply #10 on:** May 04, 2010, 08:22:47 AM »

OOOOHHHH, Hannibal! You've got me pretty excited. I'm getting really close to doing that, too. Some of the VA boys on here showed me a machine shop that specializes in vintage bikes here in state that they really trust. It's going to be a long time before the whole works is painted, ported, polished, bored, honed and back together, but dammit, I'm all hot and bothered. I do think I'm going with APE HD studs. Originally, this build wasn't supposed to be so comprehensive, so I hope this gasket kit holds up...

fastbroshi · « **Reply #11 on:** May 04, 2010, 08:25:59 AM »

In fact, if you remember from the Gentleman's Express article, they initially went with a Yosh kit and were put off by how much oil the motor started using. Wether or not they were using the same kit as you remains to be seen, but I'd put money on it that their kit used similar rings, if not the same, to the ones shown in the Ebay kit.

Tretnine · « **Reply #12 on:** May 04, 2010, 08:30:51 AM »

Quote from: fastbroshi on May 04, 2010, 08:25:59 AM

In fact, if you remember from the Gentleman's Express article, they initially went with a Yosh kit and were put off by how much oil the motor started using. Whether or not they were using the same kit as you remains to be seen, but I'd put money on it that their kit used similar rings, if not the same, to the ones shown in the Ebay kit.

I read this, also. If there is a better (3 piece) oil ring I'll go with that and hope for the best. If that kind of oil consumption shows up I'll be more than a bit disappointed. There was also a discussion on how much better boring and honing has gotten since that article. All that can be done now is finish the build and check what kind of oil consumption there is when it's done. If the consumption is terrible... well, I'll rather dejectedly change it out. Thanks for the reminder, though, I'll be aware.

Ayrity · « **Reply #13 on:** May 04, 2010, 08:51:45 AM »

hey, did you decide if you were going to use your 550 head just ported yet? I am curious about doing this kind of mod as well, I have a650 cam shaft, and just looking for the right piston kit, cant find anything on ebay, you got lucky!

HawaiiMike · « **Reply #14 on:** May 04, 2010, 11:08:36 AM »

Hey if you're really worried about those pistons I have a fresh set of 59mm's and bored cylinders. We can trade and I'll worry about all that compression and burning some oil!

Tretnine · « **Reply #15 on:** May 04, 2010, 12:41:16 PM »

Quote from: Ayrity on May 04, 2010, 08:51:45 AM

hey, did you decide if you were going to use your 550 head just ported yet? I am curious about doing this kind of mod as well, I have a650 cam shaft, and just looking for the right piston kit, cant find anything on ebay, you got lucky!

For the moment I'm planning on using a ported 550 head, but I have to wait until these pistons show so I know what kind of CR numbers they'll be chucking out. Hopefully there is a bit of information that comes along with the kit. The other question is how to fit a 3 piece oil ring so I don't wind up with the problem this island maniac is talking about... which is oil burning. ;)The only place, it seems, anyone has heard of this problem is in the gentleman's express article, in real life, we'll see what happens.

Tretnine · « **Reply #16 on:** May 07, 2010, 07:40:21 AM »

And the box showed today. pop yoshimura racing parts. 590 cc, #4204 kit. Stock vs the new pistons.

fastbroshi · « **Reply #17 on:** May 07, 2010, 04:35:24 PM »

Tretnine, can you paste in the image codes from photobucket? We can see them all larger on the page that way.

mlinder · « **Reply #18 on:** May 07, 2010, 04:41:00 PM »

Quote from: Tretnine on May 04, 2010, 12:41:16 PM

Quote from: Ayrity on May 04, 2010, 08:51:45 AM
hey, did you decide if you were going to use your 550 head just ported yet? I am curious about doing this kind of mod as well, I have a650 cam shaft, and just looking for the right piston kit, cant find anything on ebay, you got lucky!

For the moment I'm planning on using a ported 550 head, but I have to wait until these pistons show so I know what kind of CR numbers they'll be chucking out. Hopefully there is a bit of information that comes along with the kit. The other question is how to fit a 3 piece oil ring so I don't wind up with the problem this island maniac is talking about... which is oil burning. ;)The only place, it seems, anyone has heard of this problem is in the gentleman's express article, in real life, we'll see what happens.

What's the bore on those again?

bwaller · « **Reply #19 on:** May 07, 2010, 06:45:29 PM »

Tretnine · « **Reply #20 on:** May 08, 2010, 05:56:36 AM »

I thought putting the thumbs on the page made it nice and clean looking. If you want the whole pic on page, you can have it. If you want bigger pictures, I might be able to turn up the quality on my camera, too. Let me know.

Tretnine · « **Reply #21 on:** May 08, 2010, 07:52:58 AM »

Here is a better side by side comparison. They are joined with a wrist pin. The deck height is almost the same, but the raised area is up about 2mm. The valve reliefs are about 1mm and 2mm deep.

lordwhimsey · « **Reply #22 on:** May 08, 2010, 07:59:20 AM »

They look great; I'm really jealous! What about the oil rings; what type and width are they?

Tretnine · « **Reply #23 on:** May 08, 2010, 08:06:07 AM »

I also smacked the crank case once or twice in my zeal. These bolts were in there tight... Anyway, here's a photo of that... if the raised portion is taken off, it should be alright, correct? There isn't nearly as much pressure down at this area of the motor.

Also, the FedEx guy dropped off $25 worth of stuff this morning. (Ebay, shipping included, so actually $2 + shipping)

A rim in pretty good repair, not perfect, but worth $1.

And a $1 gas tank with a dent and bad clear coat. BUT, it's got very nice honda emblems AND the chrome strips on it. Any ways to get around crappy looking clear coat? Other than that, this would be a very nice tank. It's also rust-free on the inside, so may wind up painted with cafe knee dents. There isn't rust on the inside, but there's some sort of sand or something. Probably old bee legs.

Tretnine · « **Reply #24 on:** May 08, 2010, 08:07:13 AM »

Quote from: lordwhimsey on May 08, 2010, 07:59:20 AM

They look great; I'm really jealous! What about the oil rings; what type and width are they?

They are 3 piece rings, I don't have any info on them yet, I could measure that later, but right now I'm off to get a tire put on this rim so I can slap it on my other bike, which is pretty much square.

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Author Topic: So, I got some Yosh racing pistons (Read 4348 times)