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Discussion Starter #1 (Edited)
Hi all -- I put in an intro in the General section. Will attempt to contribute more as time permits.

I guess most folks know already: the most straightforward way to get a bigger engine in a TW is to combine it with another 2xx series Yamamama engine. XT225, TTR225 & 230…there are some ATV engines from the same family. Huge thanks to those who have broken the ground in this experiment.

It so happened that I accumulated an extra TW200 engine, damaged on the left cover by too-close proximity to a rock. Then, a damaged XT225 engine came along for the cost of going to get it. Rich in Parts!!

The XT225 engine was ruined by this cracked intake boot that allowed the engine to run lean. The piston went sideways in the bore! Everybody run to check the boot on yer bike!!
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So, I could not resist the temptation to try building out a TW230. Performance improvement goals: Hoping for 18+ HP, but keep bomber reliability, indestructibility; no sacrifice in low end torque. Better power at highway speeds -climbing hills or passes at 55- 60 mph in loaded touring condition.

I’m going to be mixing a lot of parts. Can’t afford the dough to overbore, so it’s going to be a mere TW230 for now:
TW200 head with XT cam and a 6205 bearing at the chain end to replace the donut. Moderate porting, polishing, possibly reduce the length of the valve guide protrusion. TW countershaft, left case cover, stator, flywheel.

TTR230 70mm cylinder & piston, bought off ebay. The 2000 TTR230 came with a sleeved style cylinder- easier to tinker with later on. (The 2005 XT225 cylinder was not sleeved, was plated aluminum and is toasted- garbage)

XT lower case halves, balance shaft, rebuilt crankshaft & rod, transmission gears, intermediate shaft, shift barrel, 6 disc clutch, right case cover, cam chain/gear cover (TW has a crankcase vent on top of the lower case. XT vents through the cam cover so must use it.)

XT225’s came with a wide range 6 speed transmission. I gather that none of the others had the wide range. [edit: incorrect, see post 50 of this thread] More on gear ratios in this thread: http://tw200forum.com/forum/performance-customization/3889-tw250-six-speed-3.html. The extra TW engine would supply the countershaft- it’s currently being modified as in Ronnydog's thread.

Lets get to some specifics:

It appears that most builders have been milling out the case mouth- the aperture into which the cylinder skirt fits- perhaps using the TW case whole or half.

After exploring the cases and oil paths carefully, I decided the XT & TW engine case halves are identical with respect to oil circulation for the TW outer bearing. Instead of milling out the TW case ‘mouth’ into which the cylinder fits, I am going to simply use the already-bored XT225 case. In the case of this 2005 XT225, the cylinder was not sleeved; the whole cylinder including the skirt are cast, machined and plated aluminum. The cylinder walls are much thicker; the skirt OD is 78mm. The case mouth is 78.5mm; this might be interesting to those who are sleeving and overboring.
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This results in another question: I'm going to be using a TTR230 cylinder that came sleeved from Yamaha. The skirt OD is 76mm. That will result in a gap of half of 2.5mm or 1.25mm all round the cylinder skirt. Could there be issues with skirt support and heat transfer due to this gap? A 1mm press-on sleeve ring might resolve the issue.
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I have found some interesting anomalies. The balancing shafts are quite different. The XT balance weight is considerably smaller, but the shaft on the left case side is much larger and takes a different bearing. The bearing bore in the case is identical. Which balance shaft should you use? The XT shaft is probably designed and sized to go with the longer stroke crankshaft. XT is on the left, TW on the right.
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The flywheels I have are very different in many respects, although the extra TW engine is a 2000 with the older electrics. I'll be using the left cover & electrics from the bike's original 2004 TW engine, and am not certain the 2000 is identical. The flywheel inside diameter is very different. Thickness & flywheel weight is very different. The rotor cup depth is different. The crankshaft offset is different, although it seems to all work out when assembled.

[edit] have discovered that part numbers for 04 and 00 TW rotor (flywheel) are indeed different. Still doesn't mean anything from the XT will fit, but I'll have to take the left cover off the running OE 04 engine to find out what to use.

The builder is forced to use TW parts since they bolt into the essential TW left side cover. You MUST use TW flywheel & stator. I’m curious from those who have already gone down this road: I'd expect the flywheels to be matched to some degree to the crankshaft/piston for the XT (TTR etc). Have you noticed any extra or unexpected vibration issues?
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While I have all this metal apart, I'll be happy to take measurements for anyone.

The last questions pertain to results. The few threads that exist on this subject trail off without definate conclusions. Ronnydog experiences a flat spot at higher rpm’s and was going to look into changing out the cam. There was discussion & recommendation for polishing or carbs or.... The question is: has anyone found the right combination? Are we at a conclusive engine rebuild or are we still in full experiment?
 

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Just wanted to comment on your engine building post. I also am interested in a increased engine CC combo (naturally!). Your comments and questions parallel my experiences in the snowmobiling world. I spent years combining Polaris smallblock components in the same manner you are heading (boring/clearance case openings for larger cyls/pistons etc., matching ignition components, tuning). My favorite combo included a 440cc bottom end with overbored 600cc cylinders that accepted 700cc pistons! 135+HP. I can't wait to get my hands on some raw material! Best of luck.
 

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Discussion Starter #3
Progress is progressing!! The XT225 crankshaft is pressed apart for a new rod, rod bearing, & pin, plus the left side bearing that for some reason Yamaha doesn't list separately. Easy 6305J (J for open both sides) bearing, SKF at a bearings house $26. Transmission countershaft getting a snap ring groove cut in & spacer ring made.

Hope to hear from those who have already done a bore & stroke mod, wondering about several questions in original post.

Roy
 

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Mine is based on ttr cases and a lined cylinder. It's far from being a wedge fit but it is plenty snug. I will check the case mouth i.d. against the sleeve o.d. on mine. It's quite possible that the nikasil versions have a different case mouth diameter which would be handy info for those looking for donors.

Not sure what could be done about it short of a custom liner. I don't think you could retain a spacer ring reliably unless you pinned it in place somehow.

Quite a few conversions have been done on tw cases hogged out to diameter with die grinders. Not exactly an exacting process so maybe the slop isn't all that critical, but I feel ya.

Ronnydog's case mouths were done by hand on his smaller motors as well as his stroker. While he probably did his with more care than most I'm sure they have some wiggle room and I can attest to the fact that he's banged on every version of his motors pretty danged hard without issue.
 

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Discussion Starter #6 (Edited)
Thanks Lizrdbrth & Ronnydog ...nikasil huh?! Trademark name for electrodeposited lipophilic nickel matrix silicon carbide coating. So that's the coating on some Yamaha cylinders- this one happens to be out of the 05 XT225 and came with a relatively large case mouth.

I had noticed that the mill work was being done by hand and had the same thought that there might be some considerable slop. Agreed that a spacer ring could be potential trouble. Might be possible to pin it to the case rather than the cylinder. At the moment, I'm going to assemble it as is, though am also talking to some engine mod guys about it. One consideration is that the gap is so big it compromises the cylinder O-ring seal's seating area. It's a definite overlap, but not as much as usual.

So, you guys have used the TTR counterbalance shaft? Wha's that one look like- more like the XT? And the TW flywheel, stator etc? Those flywheels look to me as though they have been drill-balanced- possibly to mate with one specific crankshaft. Wonder how far Yamaha goes with balancing. TW & XT are not even close to a match, although it all bolts up.

I'm considering (only an idea) modifying the TW left side cover to accept the XT225 stator. Potentially a big job.

Super interesting project!!

R.
 

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I believe Ronny and possibly Sebastian have juggled balancers or at least studied them comparatively. Somewhere in an old thread I think Ronny weighed at least a couple of them.

The TTR balancer appears to be its own seperate aminal, as well.
 

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Discussion Starter #8
Got off the phone with LA Sleeve this afternoon. They generally confirm the big gap isn't anything to be concerned about. Will be using a larger cross section O-ring to seal everything up, but that's the only solution required. Partszilla messed up a shipment so everything is delayed.

R.
 

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Discussion Starter #9 (Edited)
1 day's progress

Amazing what can happen in a single afternoon once all the parts are in place. BBRP's Brian in Bellingham finished the crankshaft rebuild with new pin, bearings and rod. Circle F machine shop Dennis had the transmission countershaft done with a new snap ring groove and a choice of 2 spacers. Both of these guys are high octane moto racers and modifiers, great to work with. All the rest of the parts are on hand and waiting for assembly. These little gear sets are kinda cute. I'm more accustomed to working with bigger stuff, some of it too big and heavy for one guy to lift.
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Answers to several prior questions have accumulated; heaps of thanks to Ronnydog and Lizrdbrth for their help. Also thankyou's to LA Sleeve & BBRP for their patience with my q's. Everyone has agreed that the fairly large gap at the case mouth, 1.25mm all round, isn't something to worry over. I've installed a slightly fatter x-section o-ring, but it's generally agreed there's no penalty due to that gap. If I ever decide to overbore/sleeve this engine, the case will already be a known oversize. And I wondered about matching the crankshaft to the flywheel/rotor. Flywheels are NOT match-balanced to any specific crankshaft. Flywheels are balanced separately, so I can safely use the TW part. As to the balancing shaft, it's pretty likely to be matched to the corresponding crankshaft, so I used the XT balancer. Assembly was done on a test-each-part-as-installed basis, but no big glitches were encountered. For the most part, I'm assembling an XT225 engine- except that it has a TW 200 output shaft. Extensive parts comparisons were done at each stage. A couple of TW parts were substituted in where XT parts didn't fit.

The lower engine assembled; 6 disc clutch, 6 speed trani, TTR cylinder & piston. Last task is building out the head.
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Ron alerted me to the fact that the head internal parts are different. XT heads have springs on the rocker arms, keeping the rockers in contact with the cam. TW allows the rockers to free float. I also think I see a difference between the cams, though I have made no measurements yet. The difference is slight...do you see a longer 'open' duration on the XT cam on the right?
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I would have simply used the XT head with everything in it already but it suffered minor damage to the exhaust valve when the piston went sideways. So, all the XT guts are being installed in the good TW head.

Another change-out is the cam chain, totally different from TW. I'm using the XT crankshaft with cam chain gear, & chain guides. The chain is smaller & thinner than TW. Also ran across a difference in the heads; the XT head is different from the TTR one. Not the EOTW, but am mixing parts as needed.

No problems. Life gets in the way tomorrow, prolly be riding the new popper Sunday!

Roy
 

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Discussion Starter #11
Rip snorter

Well, it's a done deal. Have put about 250 miles on the new engine in the past 3 days. LOTS MORE POWER. Sustain 55-60 mph, actually pass slow highway traffic (ya ever done THAT wit yer T-dub?:D). OK, we were on downhill stretches. The 6 speed trani is perhaps just as impressive; I shift to 6th at 45mph. It's the XT225's wide range, so 1st is lower than before.

Still tinkering with the 2004 carb; put in a bigger main jet today, some lagging at various engine speeds, clearly needs to run more gas than the stocker. Nothing horrible, just details.

The best description I can give of the improvement: at highway 55-65mph, the engine is so quiet that most of what I can hear is tire noise. More soon.

Roy
 

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That's awesome! So you're saying the 6 speed has a 1st gear lower than the stock TW's? Thanks for keeping us in the loop on this.
 

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Good on ya, Roy.

After we spoke about compiling a list of all the mix-and-match possibilities I remembered there were a couple of different 6-speeds, as well. (3rd through 6th are all the same, and 6th=0.793):

XT225/TTR225 tranny: 1st=3.090. 2nd=2.000

TTR230 tranny: 1st=2.923 2nd=1.889

For comparison:

TW200 tranny: 1st=2.833 2nd=1.789

TW 5th=0.821 TTR/XT 5th=0.925

So either 6-speed will get you granny gears AND overdrive.

Other random junk:

The TTR225 vents from the top of the crankcase just like the TW rather than from the cam cover like the XT, but the clutch drives from the right side.

Yamaha killed off the kicker on all the XT guys same ss they did to us and the TTR never had one so you will need the early XT clutch cover if you want a kicker with the bigger clutch.
 

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Discussion Starter #14
The answer to the gear question is going to take some real work. Based on Qwerty's research, the XT225 low gear was a whopping 3.200:1. What I'm riding feels that low- first is back to a walk even with the Duro tire. The XT engine parts were 2005 so I've used that as a base year. Just looked up XT vs TTR vs TW for 05 and there's a difference in the first gear cog. XT is 34T and TTR is 38T. Normally you'd assume the higher gear count resulted in a lower 1st, but the intermediate shaft drive pinion must be figured in. TW 1st cog for the same year is also 34. The new trans feels lots lower than the original transmission. We'd need to look at each gear in the drive train and calculate everything out. Will attempt to do so soon. -- R.
 

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The answer to the gear question is going to take some real work. Based on Qwerty's research, the XT225 low gear was a whopping 3.200:1. What I'm riding feels that low- first is back to a walk even with the Duro tire. The XT engine parts were 2005 so I've used that as a base year. Just looked up XT vs TTR vs TW for 05 and there's a difference in the first gear cog. XT is 34T and TTR is 38T. Normally you'd assume the higher gear count resulted in a lower 1st, but the intermediate shaft drive pinion must be figured in. TW 1st cog for the same year is also 34. The new trans feels lots lower than the original transmission. We'd need to look at each gear in the drive train and calculate everything out. Will attempt to do so soon. -- R.
Interesting. My info shows the XT225 and TTR225 having identical gearing, then the XT gearing remained the same through the remainder of its run while the TTR changed when they began marketing it as a 230. My TTR tranny is an '01. Gotta count some teef and see what's what.
 

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Discussion Starter #16 (Edited)
Mhhhmmmm... likes I said, real brain work!! Using 05 as a base: TW 2nd pinion 19T driving the intermediate shaft. TTR 2nd pinion 18T. XT 2nd pinion 15T. Oww...this much thinkink is painful. Clearly not the same same, clearly with XT at an extreme end but not immediately logical. [Russ, I'm using partzilla.com's fiches as my references. Were dead on for both TW & XT parts.]
 

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Screen shots from the factory service manuals' "General Specifications" sections:

TW200. YFM and YTM versions of the 5-speed have the same gearsets as the TW so no options for the 5 speed guys:


I wasn't able to locate a download for the TTR230 but it appears we're good with both 225's having the goodguy ratios.


XT225:

TTR225
 

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Discussion Starter #18 (Edited)
Got it! The TTR225 had the same trans as the XT225. Cutoff year appears to be 05 when TTR225 was replaced by TTR230. TTR225 of 04 should have the lower 1st. At that point the transmission was changed from 11/34 (3.09) first gear to 13/38 (2.92). Qwerty's graphs used the more recent 230 gearing, leading to confusion on my part. Wheeew.
 

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Thanks for the info, guys. I was about to abandon the idea of a 6 speed because I didn't want to give up the low first gear. It appears, however, that I can have my cake and eat it too. I better start collecting parts before they become as rare as hens teeth.
 

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Discussion Starter #20
B-dub, the choice is far better than TW 5 speed. Any XT225, or TTR225 up to and incl 04 will have the lowest 1st. They also sport a higher top end; TW 5th is 0.821:1, on the 6 speeds, top is 0.793. A word to the wise: the 200cc engine had a hard time pulling the big duro tire in 5th. The 230 manages it better, but there's still no excess of power at highway speeds. My chain gearing is a tad high (for the monster tire) at 15/50 road. Satisfactory but would like to tinker with it more.
 
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