Topic: So, I got some Yosh racing pistons

[mlinder]

What was the shoulder to deck clearance on the old pistons?

[Tretnine]

The deck height from the top of the wrist pin bore on the 550 is about 14.8mm and the yosh high CR piston is 15mm, so only .2mm of a difference there, but the deck on the 550 piston is almost flat save for the valve relief areas. The yosh piston has a raise of between 1.5mm and 2mm, but the exact height is hard to measure due to the shape of my caliper. It came out close to 16.6mm.

[bwaller]

I don't know for certain but wonder if Yoshimura offered these as a race kit. I have seen 59mm Yosh pistons that did not have as tall a dome.

Here's a pic of a piston I had made (beside a stock one) and settled on a 1.25mm dome to get the 12:1CR I was looking for using thinner head & base gaskets. The effective piston dome with valve reliefs ended up 2.66cc positive.





I think your next move will be to determine what the dome on those Yosh pistons actually displace. Unfortunately you'll need to have the sleeves bored to check unless someone with the same pistons can help you.

[Gregorymoto]

Nice deal.

[Tretnine]

Here are some pics of the head. I'm wondering if this head is good enough to keep on using or if I should just get another one, since by comparison they're not that expensive. This is the only cylinder that has any marks on it, the other three look to be sound. Also, there is a very small nick on the valve bottom, I'm not sure if you can see it. I don't know how much tolerance to have with these things, so I bring it to you boys. (And girls)





and here is a picture of a cat, because my wife sometimes takes the camera and snaps cat photos when I'm not looking. This makes for an odd mix of photos on the camera: Motor disassemble, cylinders, cat, combustion chamber.

[MRieck]

 A lot of corrosion in the squish area. I wonder what the exhaust ports would look like after bead blasting?

[fastbroshi]

Looks like someone was beating on them right outside of the valves. 

Since you're getting ready to get your bore ship-shape:

http://www.aa1car.com/library/plateau_finish.htm

Interesting little tidbit about laser structuring, never heard of it before now.

[Tretnine]

I was just about to PM you saying I put some pics up. I shot this thing with oven cleaner, so you know, which is a trick I found somewhere on the forums here. It seem to work on the carbon well enough, but the product discolors the aluminum, I'm sure it's oxidizing it.  It cleans up alright with a brass brush and looks clean and smooth after. I don't know if this will negatively impact the head in any way. It should be taken into consideration when looking at the head.

[fastbroshi]

  When I last had my cylinder head off, I just chucked up one of those green abrasive pads in the drill and skimmed the head a tiny amount just to get rid of all the gasket crap.  Gave me a good idea of any nicks and scratches n' such too.   Some may gasp but I was getting the valves lapped and guides looked at anyway, so they skimmed it like .010" or something like that just to make sure the head was true. 

  Seriously though, the area right around the combustion chamber looks beat up. 

[Tretnine]

  When I last had my cylinder head off, I just chucked up one of those green abrasive pads in the drill and skimmed the head a tiny amount just to get rid of all the gasket crap.  Gave me a good idea of any nicks and scratches n' such too.   Some may gasp but I was getting the valves lapped and guides looked at anyway, so they skimmed it like .010" or something like that just to make sure the head was true. 

  Seriously though, the area right around the combustion chamber looks beat up. 

It's definitely beat up. If the opinion is that it's too beat up to use, heads can be found for $50-100. The problem is you never know if the valves are any good. Blarg.

[fastbroshi]

  You might be able to pick one up cheaper than that at the yard if they have them around you.  I think those divots might compromise the gasket's sealing being so close if not in the combustion chamber. 

  I hear you on the valves, I hear they can deteriorate and become pitted, especially the exhaust.  You could always disassemble and inspect.

[Tretnine]

Before disassembling the head, I suppose I should determine if it's worth using with all that marring. Opinions? Any way to know for sure?

When the local shop mounts rubber for my other bike, I'll get a list of yards from them and make some calls.

[fastbroshi]

  I wouldn't use it.  And since you have the head off, you might consider this.  I'm doing it to my next motor.

http://forums.sohc4.net/index.php?topic=24881.0

[Tretnine]

  I wouldn't use it.  And since you have the head off, you might consider this.  I'm doing it to my next motor.

http://forums.sohc4.net/index.php?topic=24881.0

Lord, do I need a garage. I'm at a point now where I really need to decide what to do. I've got these Yosh pistons I really like, but I'm not a fan of pouring so much money into the head... yet I want the performance. I would like to run either a ported 550 head or a 650 head, but I will need to get different pistons/crankshaft/etc. to run that head. If I already need to get a head, I could just buy a 650 motor from a scrap yard and pull the oil pan, tensioner, crank, head, jugs... etc and run a paulages style workup, but I'm daunted at the amount of work needed to complete that and since I don't have a proper garage...

This decision sucks.

[moham]

  I wouldn't use it.  And since you have the head off, you might consider this.  I'm doing it to my next motor.

http://forums.sohc4.net/index.php?topic=24881.0

Lord, do I need a garage. I'm at a point now where I really need to decide what to do. I've got these Yosh pistons I really like, but I'm not a fan of pouring so much money into the head... yet I want the performance. I would like to run either a ported 550 head or a 650 head, but I will need to get different pistons/crankshaft/etc. to run that head. If I already need to get a head, I could just buy a 650 motor from a scrap yard and pull the oil pan, tensioner, crank, head, jugs... etc and run a paulages style workup, but I'm daunted at the amount of work needed to complete that and since I don't have a proper garage...

This decision sucks.

it all costs money, brother. you're just deciding where to spend it...

[lordwhimsey]

I think you should just bore your cylinders, buy a slightly fresher 550 head, a 650 cam and stick the Yoshi pistons in. Don’t forget to put a Yoshimura sticker somewhere on your bike as this will make it go even faster!

If you’re not happy with the power, sell the pistons and bored cylinders on eBay and use the money to fund your 650 hybrid build.

[Tretnine]

I'm going to use these pistons. It's been decided and that's what will happen. But when you look at all the options out there you can never be sure what you're doing is what you want, there are just too many ways to go. Bore, hone, and pistons, better 550 head, porting optional.