As the reader may realize, pistons are the basis of engine performance. So if you want or need piston kits now or soon, you will have to cope with CP's or JE's turn-around time which I am told is about a month. The good news? Gen I through 1100 piston kits in .5mm incremens in half point compression ratios. That's '81 to '83 750 from standard size through 87mm; that's 823cc, up to 13:1 compression ratio. 920 and thousand in 96mm (a full liter) in 11:1. Thousand (and TR1) up to 99mm (1065cc) 11:1 and 1100 in 99mm (1155cc) in 11:1. Frankly, these can be had in higher compression ratios, but 1) I must buy in quantity and I don't think I can stand behind the spares, 2) I don't want to be tempted to sell 14:1 hand grenades. Besides, I don't think that it would be possible to turn the engine fast enough to start. As always, having the engine torn down is an excellant opportunity for adding cam kits, carbs, and bending up a custom exhaust. 750 owners may want to go here. 920 riders can go here.   |   1000s   |   1100s   |   TR1 1004   |   TR1 1065

Keep in mind that while the American market 920s and Virago 1000s had combustion chamber volumes of 63cc, the Eastern Hemisphere TR1 had a more sporting 55cc. As a rule of thumb on the 96mm and 99mm pistons, reckon the TR1's CR to be a point and a half higher. Thus when looking at pistons that we have listed at 11:1, they will run about 12.5:1 in a TR1. There are many bikes in Scandinavia and Australia running this figure on pump gas without problem.

The maximum sizes that can be run in the various cylinders are as follows: 750s: 86mm (87mm will theoretically work with a copper head gasket but NO warranty). 750s have 20mm rod eyes althought the stroke and geometry was the sane as the bigger bikes which have 22mm rod eyes. Swapping out the rods (not an easy job) can open your ride out to enornaous displacenents, It is a matter of hogging out the spigots and - if you waanted to go fast - swapping out to larger heads (for the valves).
920s: 966mm - there is just not enough metal to go bigger. You can remove material from your case spigots and run 1000 cylinders.
1000s and 1100s: 99mm, not enough meat to go bigger. Later we will explore sleeving out 920 and larger motors to at least 105mm; this will probably be costly as I think only a plated-on bore can shed the heat fast enough for this much twin.

These pistons _require_ special head gaskets, and these are included in the "bare" kit ae well as with cylinders. These are high compression pistons and require greater holding power.

The risk fee I mention below is to cover my vulnerability. I must buy in quantities of four and I may have trouble selling the remaining pair. 99mm 11:1 for the 1000s carry no risk, but anything for a 750 is very risky. Anything 12:1 or higher is very risky. If what you want is just plain bizarre, I might require you to buy all four. Before I get too far afield, TR1s and 1100 Viragos seem to thrive under high compresssion: I'n heard of TR1s going over 14:1 reliably and 1100s coming alive at 12.5:1.

Coming up: piston kits with bored-to-size cylinders and an Athena gasket set. Figure an additional $400 for a 920. Thousand cylinders and gasket sets are costlier, so figure on $500 over the piston kit price.

At this point it may be a good idea to mention starting. All XV series bikes had marginal at best starting mechanisms. If your starter is weak, it is possible that it will spin without turning the bike's engine. See here.

Warning Warning Warning



The pictures above are of some 920 cylinders I had on hand. Note that the first two have no aluminum "dam" between the head gasket recess and that for the cam chain tunnel o-ring. These are blow-prone, and I recommend against even running an after-market cam with them, let alone a high-compression big bore. As near as I can determine, "good" cylinders (with barrier) were used in the XV920RH/RJ "Euro" and the XV920MK Midnight Virago. It appears that the good cylinders had a 5H1 part number and the bad were 10L. All our complete kits utilise the early style barrels. When I buy cores, I ask for pictures first, and when I do get fooled, I pitch the errors on the scrap alumium pile. TR1 owners note that this is a problem with your line as well. Finnish market '81s had good cylinders, Norwegian market '82s did not. You must check. One way around this is to get our complete kits with Virago 1000 cylinders - The compression is the same and the cylinder has a flat deck taking a single conventional head gasket.

JE Piston Kits
  • 86mm 12:1 or 13:1 with Head Gaskets
  • $685.00 for a kit to fit one engine.
  • 96mm 11:1 with Head Gaskets
  • $700.00 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $850 for a kit to fit one engine.
  • 99mm 11:1 with Head Gaskets
  • $815 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $965 for a kit to fit one engine.
  • Any size, any compression, any features as above.
  • Same price as above plus a "risk" fee.
JE Kits, Bored-to-Size-Barrels, Gaskets
  • 96mm 11:1
  • $1175 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $1325 for a kit to fit one engine.
  • 99mm 11:1
  • $1450 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $1600 for a kit to fit one engine.

I invite the reader to peruse the CP-Carrillo . Their pistons are low-silica, high-carbon and will not be as noisy while they warm up as the Arias were. These are quality pieces worth the extra cost. They may be of a better quality than your ride will ever test. If you plan on doing any racing, step up now. I consider myself fortunate that they decided to take on my lines. Due to their premium pricing, I will not keep any in stock - they will be special order only - figure four weeks. And if you want bored-to-size cylinders with them add two weeks.

CP-Carrillo Piston Kits
  • 96mm 11:1 with Head Gaskets
  • $975 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $1125 for a kit to fit one engine.
  • 99mm 11:1 with Head Gaskets
  • $1075 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $1225 for a kit to fit one engine.
  • Any size, any compression, any features as above.
  • Same price as above plus a "risk" fee.
Pistons, Bored-to-Size Barrels, and Gaskets
  • 96mm 11:1
  • $1350 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $1500 for a kit to fit one engine.
  • 99mm 11:1
  • $1500 for a kit to fit one engine.
  • As Above, plus Ceramic Crowns and Teflon Skirts
  • $1650 for a kit to fit one engine.

96mm kits come with early style 920 cylinders; 99mm kits come with Virago 1000 cylinders. Sorry, those are the only cylinders I handle. Recommendations? 86mm (805cc) 12:1 kits for the 750. 96mm 11:1 for the 920s (and possibly for the TR1). 99mm 11:1 for the Virago 1000 and the TR1. 99mm 11:1 for the 1100 Virago. All these with at least the internal milling for faster spin up. 750 kits are priced as the 96mm, 1100 as the 99mm. The cylinders you get from me will be gloss black with exposed fin edges. They go through multiple curing and heat treating cycles so that they do not smoke upon first start up. Keep in mind that these are forged pistons: they will be noisy when the engine is not warmed up. You might think that there is a problem, but once they reach operating temperature they will be no noisier than stock.

I realize that the reader can attempt to buy directly from JE or CP. They have both measured my heads, stock pistons, head gaskets, and connecting rods. I gave them cam specs and projected max valve size. They both have four piston minimums and sell them retail for more than I have them offered - unless you can prove that you are a merchant of automotive goods. It took six documents and multiple pictures for both. They will probably refer you to me.

And yes, I looked at Wiseco, Venolia, Mahle, and a few others. I stand by my choices.

The pictures below are mostly obsolete showing the Arias pistons we formerly carried. Some show claying and help to illustrate how performance pistons differ from stock Yamaha. As the new pistons trickle in these shots will be replaced.

Stock Piston on ScaleArias Piston on ScaleFront Arias at TDCArias at TDCArias Piston After ClayingArias Piston After ClayingArias Piston After Claying, Oblique ViewTop of PistonSide of PistonDifference in DomesA LOT More DomeDeck Height92mm Stock on top of Arias 96mmSide By SideCompare Domes and SkirtsArias UndersideSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of PistonSide of Piston