Yosh Race Pistons: 2V 1000?

[49er]

The CPs are a better forging, better alloy aluminum, WAAAAYYYY tighter tolerances in the machining, narrower wrist pins so the PINS are lighter too, better pins, newer better ring style, anti-detonation grooves, lateral gas porting, & the pistons are lighter just due to the design shape & live longer & make more power! To me, for the $250.00 more to get 30 YEARS of better technology, it's a no brainer. If you can get a set of good, usable pistons for 50 bucks, go for it. Are the correct length pins available? Do they have an old style, DISCONTINUED ring groove sizing? Are the skirts collapsed? Two ring design pistons are designed strictly for RACING, not street use! They use a low tension ring set to reduce drag to free up power but on the street don't seal well for sustained mileage use. They were designed to be changed often. Do you want to replace rings often on a street motor. I know yours are a 3 ring design but I want others to know the purpose of 2 ring design pistons. My point is, used pistons are a crap shoot at best. If you get lucky & they are usable, they are still ancient in engineering respects. Way more power & durability is available with the new piston designs. Wisecos are still old design & heavy. Custom made & lighter pistons will make more power & your engine will live longer due to less weight reciprocating around inside. Ray.

Take heed guys. Ray is right. The modern forged ali pistons are superior to our 30 year old technology. Custom pistons, be they CP's , JE's and some others are lighter, stronger and more durable than OEM and Wiseco.
JE produced my pistons 2mm OS and at 10.5-1 CR to within 11 grams of my stock pistons (198 grams). Their piston pins weighed 9 grams heavier than the stock ones. You could have fitted them to a diesel piston. They were designed to run with pistons of varying CRs, probably up to 15-1. I replaced them with new stock pins and ground them back to match the circlip clearances. Saved 11 grams against the JE pin weight, leaving less metal removal off the pistons. The end result was a set of oversized pistons that were exactly the same weight as the stock 850 ones. The stock ones are a very light design anyway.

If you want an increase in performance with reliability, don't risk running second hand, high CR pistons.

 

[Billy Ricks]

A little off-topic, but here is a photo of one of my Cosworths I intend to use one day. I had a tough time sourcing rings for them so I sent the set to Total Seal and they recut the grooves to accept a set of their Gapless rings.

 

[rapidray]

What bore size are those Billy? I have a set of Cosworths also, BRAND NEW, flat tops, 80 mm bore, 18 mm pins for 16 valve. Ray.

 

[dardoonk]

A little off-topic, but here is a photo of one of my Cosworths I intend to use one day. I had a tough time sourcing rings for them so I sent the set to Total Seal and they recut the grooves to accept a set of their Gapless rings.

Good thought. I might have to consider talking to them about that on my "FleaBay, I sure hope they work" pistons

 

[Billy Ricks]

What bore size are those Billy? I have a set of Cosworths also, BRAND NEW, flat tops, 80 mm bore, 18 mm pins for 16 valve. Ray.

They are for a 700/750. 67mm with a .05 overbore. Not a typo there, .05mm. I got my set from Britt Turkington who had his engines built by Kelly Roberts back in the '80s. Kelly had the distributorship for Cosworth at the time. He had a few other sets at one time, not sure if he still has any or not. They were doing some pretty crazy stuff to the engines Britt roadraced. Center bored cams to lighten the valve train was just one of Kelly's tricks.

BTW Ray, I have two blocks with one liner missing in one and another with a busted liner skirt. I need to have one of the blocks made whole and probably nothing more than a clean-up to meet piston specs. Would you be interested in doing the work?

 

[rapidray]

PM me your # Billy & I'll give you a call. Ray.

 

[Guest]

One of the problems with these older pistons is rings. All of that old stuff used very wide rings. They are no longer available. Total Seal doesn't even have them. The guys over on the KZ boards just went through this.

We had a new set of Yosh GS pistons in house last month to have the block bored. I remember thinking "Hope this guy doesn't break a ring while putting this together".

Back in the beginning of this big bore thing, we had to build the pistons around existing piston rings.

If my memory serves me correctly, the 73 mm rings were Honda GL1000 Goldwing 4th over. Anyone with these old cast 1085s that can't find rings might want to try the Honda dealer.

Jay

 

[first timer]

One of the problems with these older pistons is rings. All of that old stuff used very wide rings. They are no longer available. Total Seal doesn't even have them. The guys over on the KZ boards just went through this.

We had a new set of Yosh GS pistons in house last month to have the block bored. I remember thinking "Hope this guy doesn't break a ring while putting this together".

Back in the beginning of this big bore thing, we had to build the pistons around existing piston rings.

If my memory serves me correctly, the 73 mm rings were Honda GL1000 Goldwing 4th over. Anyone with these old cast 1085s that can't find rings might want to try the Honda dealer.

Jay

thanks for the tip Jay, I'll be carefull installing my rings.

Could you have total seal recut your pistons for fit newer rings?

 

[Billy Ricks]

thanks for the tip Jay, I'll be carefull installing my rings.

Could you have total seal recut your pistons for fit newer rings?

It depends on the width of the grooves now. The Cosworths I have are new and never used. They had narrow grooves and Total Seal was able to recut and set me up with a set of their patented Gapless rings. The compression ring is actually two rings that you set the gaps up 180 apart to virtually eliminate leakdown past the rings. I don't know if he still works for Total Seal but I spoke to a guy named Ed Law when I had my pistons done by them probably 8 years ago. You might call Total Seal and see if Ed still manages the shop.

 

[first timer]

Yeah my pistons are the ones Jay talked about and are brand new with rings. I just wanted to know what my options were encase i did have to replace my rings. You think if i sent them a set of my rings (brand new) they could copy them? Maybe I'll give TS a call just to chat with them and see what can be done. I'll just be extra carefull installing the cylinder for now

 

[dardoonk]

I learned a little more from the PO on the "Yosh style" piston that started this thread. At first, it was thought to have been from Murdoch Engineering, but the ebayer looked into it more and feels they are more likely from Moriwaki Engineering. As he has used those as well. Back in the day the two companies worked closely together as one of the kids in Yosh's family was married into Moriwaki family.

The seller races Vintage bikes in the Heavy Weight Class and has used both brands without problem. His class is limited to 71mm bore, so these can't be used.


Jay, thanks for the advice on the rings, hopefully I can find something that works.

I'll let everyone know how they look and measure up after I get them

 

[rapidray]

It depends on the width of the grooves now. The Cosworths I have are new and never used. They had narrow grooves and Total Seal was able to recut and set me up with a set of their patented Gapless rings. The compression ring is actually two rings that you set the gaps up 180 apart to virtually eliminate leakdown past the rings. I don't know if he still works for Total Seal but I spoke to a guy named Ed Law when I had my pistons done by them probably 8 years ago. You might call Total Seal and see if Ed still manages the shop.

I might be wrong but I think Ed is at CP Pistons now. Ray.

 

[Billy Ricks]

I might be wrong but I think Ed is at CP Pistons now. Ray.

That's good info, the guy knows his stuff.

 

[Guest]

I might be wrong but I think Ed is at CP Pistons now. Ray.

No he's not

 

[rapidray]

Thanks Jay. See, I said "I might be wrong" & I was. Ray.

 

[Tarbash 27]

Just to kind of get back to the topic. Here's a set of NOS Yoshimura GS1000 pistons on ebay in UK. Just add 50% to the price to get our price in the US.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180308223068&sspagename=STRK:MEWAX:IT&viewitem=

 

[dardoonk]

Just to kind of get back to the topic. Here's a set of NOS Yoshimura GS1000 pistons on ebay in UK. Just add 50% to the price to get our price in the US.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180308223068&sspagename=STRK:MEWAX:IT&viewitem=

got mine today in the mail: Looks strikingly similar to those & appear to be in great shape. I'll post better pics when I get a chance.

 

[dardoonk]

Allright. I received my 73mm Moriwaki pistons yesterday and cleaned them up a bit, but I have a couple questions below. Overall, all four pistons look real good. The one pictured is actually the worst of the four. They are all in very nice shape, with the exception of a few small dings on the top edge. There is very little wear on the skirt (almost none). They actually look better than the pictures.

Below is a close up of this. It is a very close up shot, so use the ring gap and oil holes to give some perspective of the size of the marks. All of these are on the surface. Is this anything to worry about?

Another thing that surprised me is the shape of the compression ring. You can see in the picture below that it is an "L" shape. The piston groove is also cut in the same manner. The "L" points toward toward the top of the piston. By my caliper, I measure the thin edge of the ring at 0.0365" (.093mm). The total ring height is 0.0578" (1.47mm). The ring is 0.137" (3.458mm). I have never seen this style ring, but have limited experience in this area. Does anyone run these & when (and if) I can find new rings, how will they hold up on the street.

 

[Tarbash 27]

I dont know about the rings, but the pistons look to be in pretyy good shape to me. Once again, Im no pistonologist.

 

[49er]

Those "L" shaped rings are Dyke Rings. They were used on two stoke engines in the early 70's. They were fitted to the RD Yamaha engines. They are designed to reduce drag on the cylinder walls and the pressure of the ring passing over port windows. As cylinder pressure increases after combustion, the rings are forced hard against the cylinder wall as the piston decends. As the pressure reduces towards the bottom of the stroke (adjacent to the exhaust and inlet ports) the drag is reduced. On its way up again and after the ports close, pressure starts to increase for the next power stroke.
That piston is designed for racing and is not really suitable for road use, unless you are prepared to re-ring the engine on a regular basis.

You say that piston's marks are the worst. They appear to be casting flaws. If they had been caused by detonation or pieces of broken piston ring, the marks should also appear on the upper ridge edges and also across the piston crown/valve pockets. They probably won't cause any hot spots.