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Old 02-24-2015, 07:20 AM   #1
motobene OP
Motoing for 44 years
 
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S3 225cc Kit on '14 GasGas TXT125

GasGas Pro riders, the info below has possible modification implications no matter what size machine you ride, so it's not just about the relatively few 125s out there.


Discovered: The cylinder though made from a GG25 casting is custom to the 225. The piston is a 250 piston with the 16mm wrist pin from the 125 instead of an 18mm wrist pin from the 250 to 300.

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KrAzY got his kit in from Ryan Young, and I'll soon be helping him install it. I plan to suck every bit of tech info I can out of the process.

The kit is comprised of a 250 top end modified in some way for the shorter stroke or not... we shall find out. It comes with the S3 Stars - insert - type head so one can futz with compression with different inserts.

The first question we have is why an A cylinder was paired with a B piston. Awaiting Ryan's reply as to whether that was an oops or intended.

I started out with GasGas intending to by a 225, but the owner backed out at the last minute. I bought instead a nice 280. Though I have briefly ridden two 225s, this opportunity will result in getting to know a 225 more deeply.

We'll update as we go.

motobene screwed with this post 03-04-2015 at 06:47 AM
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Old 02-24-2015, 08:27 AM   #2
Sting32
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{removed the quote}

you are the engineer, old buddy, check the clearances on that. I thought it was a piston that is modded, but that is a wild guess now I bet. where the piston pin is placed slightly lower from top of the piston, to fit stroke of 125??? but you will know more after this. I think Steve said the jug is just 250 though? I'm starting to suffer greatly with CRS... I think.
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Old 02-24-2015, 10:25 AM   #3
motobene OP
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Just had a discussion with KrAzY, and he updated me on info.

The S3 kits rom RYP USA is $600, and includes the cylinder, piston, rings, wrist pin, gaskets, head, and (I assume standard compression silver) Stars head insert.

Regarding piston-cylinder clearance, Ryan told KrAzY the matching of an A cylinder to a B piston is intentional by S3. That means the piston is a miniscule tighter in fit, as the cylinders and pistons get larger as the letters go up from A. I do love the very tight clearances made possible by water cooled plus modern manufacturing precision and piston materials, and I am not concerned by a tight fit. Trials is easy on top ends, with normal use being like a constant gentle break-in.

Sting, thanks for a clue on what's different. What exactly is modified and what is not has potential wide implications for us. It is POSSIBLE the 280 and 300 top ends fit onto a 125. It is POSSIBLE the S3 225 kit is also a 250 kit for a 280 and a 300. The center case part numbers are common across all models. It is possible the end of the left crank half is the same for 125 or 250 and up flywheels, so it is POSSIBLE whole ignitions will swap out though the flywheel mass is different on the 125, and the ignition maps differ over all sizes and models.

As I get deeper into this I will find out as much as I can. Need your help, however, to measure a 250, 280, or 300 piston, as I don't have one outside an assembled machine. I need the top of the wrist pin bore to the piston crown outer edge. I also need the piston skirt to the piston crown outer edge (how tall the 250 through 300 pistons are). Thanks.

Something has to give in the 5.5mm difference in the stroke between the 125 and the rest. For the piston to come up flush to the top of the cylinder at TDC, something has to be changed by half the stroke, by 2.75mm. Either the kit's piston crown is machined 2.75mm taller, or the bottom of the cylinder is machined off by 2.75mm, or the rod is 2.75mm longer on the 125 to begin with to make the cylinder top height common across ALL models. I did find the part numbers for the rod repair kits are different, so something is different between the rods. Maybe the length.

Let's say the rods are longer, and the S3 kit cylinder and piston are just a 250 cylinder and piston. That would be awesome! What will 'give' then will be the piston crown edge will come up short of the bottom of the transfer ports by the total stroke, 5.5mm (0.217") at the bottom of stroke. Most of the gas transfer happens in the top of the transfer ports, so that compromise is workable, but if the piston ends up flush with the transfer ports bottom on this conversion regardless of what non-cylinder stuff is changed, it means the kit cylinder is NOT just a 250 cylinder. It means the casting cores for the transfer ports are custom to the kit cylinder, even though the cylinder exterior has 'GG25' (instead of GG225) cast in.

As for the bore-stroke relationship of the 225 kit of 72.5 bore / 54.5 stroke = 1.33, it is interesting that the ratio is the same as the 300.

motobene screwed with this post 02-25-2015 at 07:37 AM
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Old 02-24-2015, 11:32 AM   #4
Sting32
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Quote:
Originally Posted by motobene View Post
Just had a discussion with KrAzY, and he updated me on info.

{Snipped above to save space}

As for the bore-stroke relationship of the 225 kit of 72.5 bore / 54.5 stroke = 1.33, it is interesting that the ratio is the same as the 300.
Not sure I followed this right, Ill reread, when I have time...

But to change the rod, you would have to split case, press crank apart, pretty sure this isnt done, and well, I am positive we wouldn't have anyhow. Steve helped with flywheel because that older one for the 125 was a heat weight, freeze flywheel ordeal I think... where as the 300's bolted on. this was back in 09, doing it on a pair of twin 06 125's in the "north central ks livery"

As far as I know, the kit is simply take off the barrel, piston, and head, replace with new parts, we removed the plastic crankcase spacer, where you have options now it seems? I think a while back we had to remember to order the 250 head, separately, as the older bikes heads, didn't have the inserts they do nowadays. Maybe the 125 insert technically fits into my 300's s3 head, and that would more than make sense, MFG can make one head and 4 different displacement inserts, then high, normal and low compression for each, instead of multiple heads and inserts...

I do know, or it was: gold insert is lower compression, I have one for the 300 not in use atm. I think higher compression was kind of an anodized red? Josh Nutch uses them. I will have one if I head to CO/NM I hope.
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Old 02-24-2015, 11:41 AM   #5
KrAzyOSUcOwBoY
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Great explanation. Clarification on the "A" cyl and "B" piston, Ryan said "no worries, piston and cylinder are matched by S3 on the kit." Interesting that the "over square" bore to stroke on the 225 is the same as the 300, as 'bene says "a mini 300." Really anxious to see how it rides at 200lbs geared up the 125 is fun but just a little soft.
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Old 02-24-2015, 03:44 PM   #6
Sting32
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Quote:
Originally Posted by KrAzyOSUcOwBoY View Post
Great explanation. Clarification on the "A" cyl and "B" piston, Ryan said "no worries, piston and cylinder are matched by S3 on the kit." Interesting that the "over square" bore to stroke on the 225 is the same as the 300, as 'bene says "a mini 300." Really anxious to see how it rides at 200lbs geared up the 125 is fun but just a little soft.
I believe Bene might have to recheck his figures, I think the stroke is smaller, I still think the piston is "special" to 125 to 225, but I surely don't know for sure.

Im checking the PDF (specs sheets) maybe gasgas changed more in the 125 since the 06?

according to specs, the 125 stroke is 54.5, the rest of the bikes are 60 (milimeters) with different bore sizes of course.
so I am still pretty dang sure they have made a special piston, with wrist pin just the 5.4 mm's further from the top of the piston than the other pistons...

So you cant use the 225 piston (kit piston) on the 300... but again I am NOT positive, just sounds like what I know from working with people that stroke v8's and stuff, you just get a piston that works when you get done.

I know this guy, created a 672 cubic inch Pontiac motor, from a 455 originally... but changing rods is a helluva lot easier on automobiles with split rods at crank-bearing end... still he just called a place they make a set of pistons with dimensions he needs when done.

Sting32 screwed with this post 02-24-2015 at 03:53 PM
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Old 02-24-2015, 04:20 PM   #7
laser17
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I thought the 200's and below had a smaller wrist pin diameter as well. Maybe the vertex or s3 web sites have the info. Im too lazy to check.
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Old 02-24-2015, 06:41 PM   #8
lineaway
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Bene, nothing really trick here. Just a big bore kit. Now back in `96 I think. Stan Hensley made Mark Manniko a short stroke big bore for the nationals. That year the stock Gasser was a 370. His was a 327. Might be where the 321 came from.
Just curious if you got the flywheel weight too?
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Old 02-25-2015, 07:11 AM   #9
motobene OP
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Never said 'nuthin' about changing rods. My comments were about speculating over same/different between models and the potential crossovers. The part number for wrist pin bearing is different, so maybe that accounts for the difference in rod repair kits? The S3 kit comes with a wrist pin but no bearing.

I could see a big project here, where I pull the 300's top end to replace the leaky base gasket. Then I can direct measure everything. Heck, maybe after a full season on the 300 I'll swap top ends again with the 280 at the same time? I love the 280
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Old 02-25-2015, 07:24 AM   #10
motobene OP
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Quote:
Originally Posted by lineaway View Post
Bene, nothing really trick here. Just a big bore kit. Now back in `96 I think. Stan Hensley made Mark Manniko a short stroke big bore for the nationals. That year the stock Gasser was a 370. His was a 327. Might be where the 321 came from.
Just curious if you got the flywheel weight too?
I remember them reducing that too-big bore then. Maniko was altitude riding so that was telling.

KrAzY called Lewisport to order the weight but the secretary did not have the application chart for models and year so she balked. Pretty sure it's just for the smaller Kokusan. There was one other available weight. My advice to KrAzY was to get the heaviest one available, as so far the only weakness I have felt in these conversions has been the need for more flywheel inertia (resistance to quick wind up). The two converted bikes I rode were hot rods, and I don't know if they had added flywheel weights.
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Old 02-25-2015, 07:30 AM   #11
motobene OP
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Of course it' s wait and see on what the KrAzY 225 actually feels like, but I could see the orange low comp head and the timing retardation trick. Sting, is that orange head you have for a 250? If so you should snap that up pronto, KrAzY.

When I ride my 300 at Sipapu I use the orange one for maximum mellowing of my former scalded dog.

Ideally all the mods to the 225 and my 300 can be done before the upcoming Palo Duro Canyon Texas event in a couple of weeks!
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Old 02-25-2015, 08:23 AM   #12
KrAzyOSUcOwBoY
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Talked with Lewisport twice so far and no traction yet. Sent off an email to Trialendurodirect in the UK asking about the difference in the 125 FWW and the 225 listed for an addl 10 euro and asking for a price including shipping in $US. No response form them yet either. Ready for more beans, but not wanting a fire breather.
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Old 02-25-2015, 08:59 AM   #13
laser17
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There was a very long thread on TC a while back on these conversions- essentially when the kit 1st became avail. The guy that everyone seemed to look to for advice was factory Kev at GGUK. He made several of the bikes (I think he was the one who 1st proposed the mod) and one thing I remember him stating was that the hot setup was mounting TWO of the small 125 style FWW's! evidently they can be stall prone w/o them. I took a quick look for the thread and couldnt find it - but maybe a better look will yield results. It was fairly informative regarding this mod.
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Old 02-25-2015, 09:20 AM   #14
KrAzyOSUcOwBoY
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I've seen that thread, in fact there have been a couple of them on TC. I'm not sure how you would mount the second FWW though.
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Old 02-25-2015, 10:00 AM   #15
laser17
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Can the big s3 FWW be used? I have one of those that it 20% lighter than stock and balanced if you want to try it - just have to dig through 3 ft of snow to get it. My buddy hacked off the 20% off the ID and then balanced it. It looks kinda rough, but works well. I liked it on my 250. Not sure it will fit the 125. MB probably knows.

laser17 screwed with this post 02-25-2015 at 12:58 PM
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