Yosh Race Pistons: 2V 1000?

[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.

[Big Jay]

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%3AMEWAX%3AIT&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.d...3AIT&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.

[hampshirehog]

Dyke rings were a good idea to stop ring flutter at high levels of piston acceleration. Previous to this the only way to stop flutter was to go for thinner and thinner rings.

However, Dyke rings do suffer with the drawback that they get rattled around considerably at high revs and, whilst they maintain a seal well, the ring and the piston ring groove get battered eventually resulting in failure of either the ring, the piston or both. Therefor it's the high maintenance option (ok for racers).

As far as I know the only manufacturer that persisted for a long time with Dyke rings was Bultaco but I don't think they've used them for a while now.

[dardoonk]

Okay, good info on the Dykes, now... Who the heck makes them or who will make a set for me?

[Nessism]

I had a Moriwaki big bore kit for (don't laugh) a CB400T. Took that bad boy all the way to 425cc!! This thread reminded me that the pistons used Dykes style rings - must be a Moriwaki characteristic. I have no idea where you would find rings like that. Maybe send the pistons to Total Seal and have them cut new grooves?

[dardoonk]

these are KZ pistons

Allright guys, I'm willing to try being a guinea pig, so we find some things out, so feel free to chime in here. It looks like I ended up with Kawi 1105 pistons & an 17mm wrist pin... Bad news... I'll either have to sell them, or just have some fun and figure out if this will work.

Bore = 73mm - No problem, I have an 1100G block
Valve cut outs = Bigger than I need, so I should be able to run high compression and a high lift cam w/out a problem
Wrist Pins = looks like I'd be best to bore them to 18mm - - Possibly, I could use nylon pin retainers if I can't get the stock clips to stay in place.
Compression ratio = who knows?? I may have to do a little milling to get it correct.

All that seems like stuff I can pull off, one thing I need to find out is whether or not the KZ and GS heads used the same valve angles.. This could cause problems with the reliefs already cut into the pistons if they are the wrong angle.

Does anyone know?? Thoughts or other potential problems?? I even considered running KZ rods, if they could be adapted to a GS1000 crank, so I am wide open here.

[first timer]

For laughs relist them on ebay with the correct info and see if they go for more then you paid. The Kaw performance parts crowd is hungrier then the gs crowd for parts. If they don't go for much have fun, just remember machine work costs lots of money nowadays.

First things first try to find some rings.

Talk to Stan Gardner he should know what you can do with a gs1000 crank