80-81 1196 Big Bore piston kit

[Do Lee]

I was looking through the parts area on Ebay for xs11's and came across a Big Bore kit for $150. I have been slowly rebuilding one of my MNS and need to a) purchase new rings, do a light deglaze of the cylinders while rebuilding the engine or b) purchase a BB kit. Wisco kit cost $500 + vs $150.... was wondering if anybody has purchased this kit and how the quality was??

http://cgi.ebay.com/ebaymotors/80-81...item20c5e29d07

[crazy steve]

Very good price.... but you know what they say; if it seems too good to be true, it usually is...

The one thing I would be concerned about is the pistons; $150 is really cheap for forged, I suspect these are cast. Might be fine, might not.

[ViperRon]

Make sure the kit you are getting is what you think. Could say complete kit with rings and you find its only one cylinder. I'd ask for a complete detailed list.

[WMarshy]

This kit can be used on any year xs right?

[Elevener]

It has a list.All four. And it ships from Japan. Like Steve says though, maybe not forged.

[WMarshy]

I sent a few questions to the seller and got a rapid response.

"Dear cruzinimage_co,
Hi, I am lookimg for more info about this big bore kit... Does this kit include 4 pistons? Are the pistons forged?
Thanks,

Wade
- wmarshy"


"Hello,
Thank you for your question. regarding piston kits. These are four pistons and head gasket include.all parts include in the picture.and these made by cast pistons.
Thank you again,
mitsuo

- cruzinimage_co"


So I guess my question to you guys is, are our stock pistons forged or cast? And, should I really care at $150 for a BB kit?

Set includes: pistons x4, pins x4, clips x4 sets, rings x4 sets and Head gasket
We produce this product in reference to (OE Number:3H5116310046)

[TopCatGr58]

Borrowed from another site!

Forged pistons are more durable than cast pistons will ever be. Cast pistons are very brittle, and are prone to skirt breakage as a result.

For riders that will take the time to do a proper break-in, and will discipline themselves enough to fully warm their engines before each and every ride, Wiseco pistons are a superior product to OEM. They are more durable under high-heat high-load conditions, less prone to skirt breakage from piston slap if the bore has a bit too much wear on it, and longer wearing than any cast piston will ever be.

Cast pistons don't require much in the way of special break-in, that's part of the reason they come as OEM equipment in two-strokes. Forged pistons, on the other hand, are a different story. A forged piston must be heat-cycled before it can be run hard, or you're playing roulette with your engine.

A new forged piston has to be heat-cycled several times to relieve the internal stresses left over in the metal from the manufacturing process. If this isn't done properly, the piston will distort and become out-of-round, causing it to wedge itself into your cylinder, more commonly known as a "seizure". A seizure with a two-stroke isn't a very dramatic occurrence, usually the engine just stops running. You re-plate the cylinder, rebuild the top-end again, and you're back in action. On a four-stroke, however, a seizure is often catastrophic. The four-stroke has more rotating mass, which creates additional inertia. So, when the piston seizes, the rest of the engine tries to keep spinning. The result is, more often than not, a snapped connecting rod, broken crank, and destroyed cases. A big bill usually follows.

To better understand why forged pistons are more seizure prone, you need to understand what makes a forged piston different than a cast piston.

A cast piston is manufactured by pouring molten metal into a mold. The final shape is machined to it's final exacting tolerances.

A forged piston is made by taking a chunk of metal, and beating it into shape with a die-press under enormous pressure. Like casting, the final shape is achieved through precise machine work.

The main difference between a cast and forged piston is the grain structure. A forged piston is beaten into shape, and as a result the metal stretches and compresses as the piston takes shape. The varied, elongated grain structure is like fiber reinforcing, and it makes for a very strong piston. Microscopic cracks don't readily propagate through the structure of a forged piston due to the high density and the irregularly spaced and sized grains. A cast piston, on the other hand, is made up of grains that are all the same size, because it starts out as a liquid that, after being poured into a mold, undergoes a controlled cool-down process that allows the metal to reach a near-perfect equilibrium right out of the mold. The highly regular grain size and distribution makes them more prone to crack propagation and failure.

The break-in of the two types is very different, because the metal properties are very different. The forging process produces a lot of internal stress from beating the metal into the intended shape. The stress is trapped in the metal of the finished part. A cast piston has lower internal stress, because it was able to seek it’s own internal equilibrium as the liquid metal flowed around inside the mold and then underwent a controlled cool-down. Since a cast piston has lower internal stress, it won’t distort nearly as much as a forged piston will when heated to a high temperature. The forged piston's propensity to distort when heated is the reason they require an elaborate break-in procedure.

To relieve the internal stress, and maintain it's correct shape, the forged piston has to go through a series of heating and cooling cycles. As it heats up, the grain structure will re-distribute itself into alignment to relieve any trapped stress. As it cools, the cylinder will contain and restrain the piston, maintaining it's shape. After a few heat/cool cycles, the internal stress reaches equilibrium, and the piston will no longer distort when heated in the engine. It will maintain it's shape for the rest of it's life.

Forging produces a higher grain density than casting, making the part much more durable under high-heat, high-load conditions. As long as you are patient enough to break a forged piston in correctly, you will have a piston that is more durable under extreme conditions.

Problems with Wiseco pistons are almost always caused by one of these three issues:

1. Improper break-in-This can be a death sentence for a forged piston.

2. Improper warm-up-A great way to cold-seize the engine. This also kills crank and rod bearings, not just forged pistons.

3. Cylinder-to-piston tolerances too tight-You can't just slap a Wiseco piston into a brand new engine with no time on it. Forged pistons require about .002" more cold clearance than a cast piston. Once it's time for the first top-end job, a cylinder will usually have loosened up enough for the forged piston to have enough clearance. Most Japanese two-strokes spec .002"-.004" clearance for the OEM pistons. Wiseco specs .003"-.005" clearance.

Another less common cause of problems with all pistons is when the person doing the top-end work doesn't drill the lube holes in the piston for an engine with a central exhaust bridge. A forged piston will actually tolerate this better than a cast piston.

Anytime you rebuild the top-end, you have to measure the ring end-gap, and file the ring ends if neccessary. I rarely have a set of Wiseco rings that don't need to be relieved slightly. If the end-gap is too tight, the ring ends will hammer the locator pin right out of the piston, with devastating results. Wiseco specs .004" per inch of bore size for their ring end-gap clearance.

All of these problems are caused by the mechanic that does the work, or the rider that's too lazy to perform a proper break-in or proper warm-up. You can't blame the product for your own incompetence (although that's usually what people do).

After all that, I'm thinking that our OEM pistons were CAST, so I would think that they would be okay, a definite price savings over Wiseco.

I have the WISECO 1179 kit, and I DID have a machine shop custom bore my cylinders to match the pistons, set the end gaps of the rings, and I did do a long slow gentle breakin procedure vs. the quick and dirty technique recently discussed on this site! They have never squeeked and have been fine for some 15K miles since the rebuild! But if I were to be doing it again and had found this PRICE, I think I would be willing to use the cast pistons instead. Yes, our machines are considered performance, but not RACING type stresses and our OEM cast pistons have seemed to work well for all of the models for 30+ years!

T.C.

[crazy steve]

Before there's a stampede for these, there's at least one other issue that needs to be addressed; compression ratio. The Wiseco sets are flat-tops I believe, and give a 10:1+ compression ratio (depending on which head you use). These pistons are domed if the pic is right (and listed only for the later motor with the larger combustion chamber), so you might need to find out the dome size and do a compression ratio calculation. If it gets too high, you may end up with a motor that will only run on race gas. It may be possible to shave the piston tops to lower it if need be, but that question needs to be asked before doing it.

As an alternative, you could have the combustion chambers machined larger, but that may be a bit tricky.

I'll note that cast pistons don't like high ratios or detonation....

[motoman]

After all that, I'm thinking that our OEM pistons were CAST, so I would think that they would be okay, a definite price savings over Wiseco.



T.C.

Original pistons are forged to go along with the radiused high performance shot-peened rods and chrome-moly rings. All that attached to a one piece forged crankshft attributes to the longgivity of these air-cooled motors, even with the abuse they have recieved over the years.

[TopCatGr58]

Hey Steve,

The Wiseco web site does NOT have photos YET of their products for the xs11. It's been 12 + years since I put my 1179 kit in, but I don't recall them being FLAT TOPPED, they did have the indents for the valves. IIRC from both previous discussions....they rate their obtained comp ratio per their use in the earlier model engines where the comb. chamber is shallower, and so the 10.25:1 ratio is obtainable. But with the later 80-81-82 engines, the comb. chamber is deeper due to the larger valves and reduced OEM comp. ratio for the emissions changes..9.0:1 vs. the 9.2:1.

Stock comp. is listed as 142 +/- 10 at sea level, and I'm at sea level, and after my breakin, I obtained values of 180+ psi, I don't know how to convert that value with our known bore/stroke to determine the comp. ratio that I got with the 1179 kit in my 81SH. I use Premium fuel, but because I didn't want to take any chances of burning holes in my pistons by "trying" to use regular and listen for KNOCK...but I might be able to run regular...just never tried it! YMMV, but I don't think he would need to worry about having to use racing fuel!

I haven't looked at the ebay ad yet, but I can't see them limiting themselves to marketing to just the 80+ year models vs. the 78-79, if they have the valve indents large enough for the 80-81 models, then there should be plenty of room for the smaller 78-79 valves.

T.C.

[WMarshy]

I will ask the questions Steve brought up...


"Dear wmarshy,

Thank you for your replay.I have stock more than 10 sets of piston kits.
Thnak you again,
mitsuo

- cruzinimage_co"

[WMarshy]

So, I asked the questions Steve brought up and this is their answer...

"Dear cruzinimage_co,
Do you know the dome size and/or compression ratio these pistons are expected to provide? Any idea if they are compatible with the '78-'79 XS1100?
Thank you for answering my questions and being so timely!
- wmarshy"

"Dear wmarshy,
Thank you for your replay. regarding some question.the dome size on top and compression are almost same as well as 80-81 pistons.these will fit to 78-79 models. but,different compression and piston top.
Thank you again,
mitsuo
- cruzinimage_co"

[trbig]

'78/79 piston on the right, 80+ on the left.









Wiseco piston on left, stock 80+ piston on right. Maybe hard to see, but the Wiseco piston isn't domed as high as the later models, but is considerably higher than the early ones.

[Rasputin]

There are also the RCE (Russ Collins Engineering) pistons that were available for these bikes that looked like these pics.

[motoman]

There are also the RCE (Russ Collins Engineering) pistons that were available for these bikes that looked like these pics.

Wow......some serious 'pop-ups' there, but without 'serious' cams to go with.......detromental and a waste at best.