[ronnydog]

I am going to have a crank built 7.3mm longer stroke with the rod from a TTR225. The TTR rod is 1.15mm shorter than the TW rod. Can someone tell me what size spacer I will need under the cylinder,if the cam chain will fit, what the increased cc's will be?



Crank 7.5mm----------------------------+28cc ???

TTR 225 high comp piston and sleeve----+14cc ???

Web Cam--------------------------------+3cc ???

TW 200---------------------------------+196cc ???



Total CC's------------------------------241cc ???



Ronnydog

 

[uktw125]

Your new bore and stroke will be, 70mm-63mm this gives 242.3cc.



You will need a spacer equal to half the stroke increase, minus the difference in the shorter rod.

That is 3.65mm is half the stroke difference minus 1.15mm for the rod difference.

So the spacer needs to be 3.65 minus 1.15 equals 2.5mm.



Cam chain, I don't know.

 

[qwerty]

Bore and stroke determine displacement. Cam and compression ratio have nothing to do with displacement. Better figure this out. Better check into the crank/piston skirt clearance, too. Adding stroke to a high compression piston can easily get you in the compression ratio preferred by ethanol and diesel fuel--and the bike won't run on gasoline. Better learn the math involved and figure out what you're going to end up with before you build a very expensive paper weight.

 

[TWrider]

cam chain you'll probably have to go next size up. I know Tim used a stocker with a +5mm increase, but I think it was at limit. You're probably going to have to grind on the cases with that much stroke increase.

 

[lizrdbrth]

Has anyone out there cc'd a TW/XT head?



I'm also thinking that our small valves could actually become a plus to some degree on a stroker, as velocity would be up.



Thoughts?

 

[qwerty]

Has anyone out there cc'd a TW/XT head?



I'm also thinking that our small valves could actually become a plus to some degree on a stroker, as velocity would be up.



Thoughts?

Resistance to flow goes up exponentially with increase in speed. All else being equal, expect better off-idle and low speed torgue, less high speed torque. A stroker with stock cam, valves, and ports would be excellent for slow going with an ATV tire. The bike would definately lose top end since flow seems to be a top end limiting factor already. Pick your poison.



I once built a set of Chevy smallblocks for a guy using identical parts other than blocks, cranks, rods, pistons, and rings. They all made about the same horsepower, but at different RPM. The larger the displacement, the more torque and the lower the peak torque and peak horsepower rpm. If memory serves there was over 2000rpm difference in torque and horsepower peaks between the 283 and the 383 versions.

 

[lizrdbrth]

A 70 X 63 motor SEEMS reasonable enough. I need to get a chamber volume on the head if anyone's got that info.



A longer rod would be nice, but that info's hard to come by. Still digging.

 

[TWrider]

A 70 X 63 motor SEEMS reasonable enough. I need to get a chamber volume on the head if anyone's got that info.



A longer rod would be nice, but that info's hard to come by. Still digging.

The 200cc rod is longer...It would require a new(different) chain

 

[lizrdbrth]

Probably too much to hope for that there's a drop-in rod closer to 2mm longer. But it would kill three birds with one stone (Less piston skirt trimming, less rod angle, better long-term wear).



You gotta shim the cylinder and lengthen the chain anyway, might as well.



Using the TW stuff makes sense from an expense perspective, though. I suppose a TW crank could be stroked to the same limits and the TW rod used to a slight advantage with the appropriate spacer under the jug.



Compression ratio still a sticking point in terms of feasibility with common bits and pieces.

 

[RisingSun]

I am going to have a crank built 7.3mm longer stroke with the rod from a TTR225. The TTR rod is 1.15mm shorter than the TW rod. Can someone tell me what size spacer I will need under the cylinder,if the cam chain will fit, what the increased cc's will be?



Crank 7.5mm----------------------------+28cc ???

TTR 225 high comp piston and sleeve----+14cc ???

Web Cam--------------------------------+3cc ???

TW 200---------------------------------+196cc ???



Total CC's------------------------------241cc ???



Ronnydog

Is it safe? You need to get a hold of a importer. They have Big Bore kits for TW's in japan. Jug,Piston,carb,cam and cables.

 

[TWrider]

Is it safe? You need to get a hold of a importer. They have Big Bore kits for TW's in japan. Jug,Piston,carb,cam and cables.

what bore? 72mm?

 

[ronnydog]

what bore? 72mm?

70mm from the TTR225.

 

[qwerty]

I'm looking at 73x63 with a relign. I think that is reasonable. Sebastian has bore kits to 73mm. xr100.com used to sell tt-r engines to 250cc with the stock 230 crank.

 

[lizrdbrth]

If my guesstimate of the chamber volume is anywhere close to accurate, if at 70 X 58 you're near 9.5:1 CR, 70 x 63 puts you in the mid- 10's, by 72 X 63 you're bumping 11:1 and at 73 x 63 you're well past 11:1 CR with flat top pistons.



And if I'm wrong by as little as 2cc's, CR goes off the charts. Having that chamber volume is make or break if you're gunna know what will likely result.



Ronniedog and I are gunna round up all our heads and get this settled definitively.



Burette parties` are all the rage nowadays.

 

[macbig2k1]

I am going to have a crank built 7.3mm longer stroke with the rod from a TTR225. The TTR rod is 1.15mm shorter than the TW rod. Can someone tell me what size spacer I will need under the cylinder,if the cam chain will fit, what the increased cc's will be?



Crank 7.5mm----------------------------+28cc ???

TTR 225 high comp piston and sleeve----+14cc ???

Web Cam--------------------------------+3cc ???

TW 200---------------------------------+196cc ???



Total CC's------------------------------241cc ???



Ronnydog

Witch con rod do you want to use for this stroker crank?

73mm piston from Woessner

63mm stroke

-> 263,7ccm

Needed spacer plate:

2.60mm with TTR225 con rod

3.65mm with TW200 con rod



I recomment the longer TW200 con rod.

1. reason

The con rod angle is smaller (17.2°; 225 con rod 17.4°), this reduces the pressure between the sleeve and piston.

2. reason

You will need in both cases a longer timing chain -> not available from Yamaha or a other reseller, but I can deliver it.

A extendend chain does have 2 links more -> +14mm (7mm per link).

So, the maximum higth for a spacer plate with 2 link longer timing chain can be 7mm (14mm/2 = 7mm; both sides from the chain).

With this background info:

You will have with a 2.6mm spacerplate a bigger chain slack as with the 3.65mm spacer plate.

 

[lizrdbrth]

With this background info:

You will have with a 2.6mm spacerplate a bigger chain slack as with the 3.65mm spacer plate.

That presents a lot of variations in valve timing. How are you correcting it?

 

[ronnydog]

Witch con rod do you want to use for this stroker crank?

73mm piston from Woessner

63mm stroke

-> 263,7ccm

Needed spacer plate:

2.60mm with TTR225 con rod

3.65mm with TW200 con rod



I recomment the longer TW200 con rod.

1. reason

The con rod angle is smaller (17.2°; 225 con rod 17.4°), this reduces the pressure between the sleeve and piston.

2. reason

You will need in both cases a longer timing chain -> not available from Yamaha or a other reseller, but I can deliver it.

A extendend chain does have 2 links more -> +14mm (7mm per link).

So, the maximum higth for a spacer plate with 2 link longer timing chain can be 7mm (14mm/2 = 7mm; both sides from the chain).

With this background info:

You will have with a 2.6mm spacerplate a bigger chain slack as with the 3.65mm spacer plate.

I will use the ttr con rod with a 70mm Wiseco piston. Trim the top of the piston ?mm, add a spacer plat of ?mm and use the same chain. 242cc. What is your thought on this?

 

[qwerty]

That presents a lot of variations in valve timing. How are you correcting it?

On some of my old Honda stroker builds I had to drill new holes and make new timing marks. Sometimes I ordered cams ground a couple degress off to compensate. Sometimes running the cam "off" was done intentionally, like degreeing a cam on any other engine to influence powerband.



Properly engineering engine mods isn't nearly as easy as many amatuer builders think.

 

[macbig2k1]

That presents a lot of variations in valve timing. How are you correcting it?

There is no variation in the timing with more stoke and a 6mm spacer plate.



The 3.65mm length difference isn't a problem. It's like normal wear from the timing chain.

It is the best to set the cam sproket to a earlier valve opening.

 

[macbig2k1]

I will use the ttr con rod with a 70mm Wiseco piston. Trim the top of the piston ?mm, add a spacer plat of ?mm and use the same chain. 242cc. What is your thought on this?

NO!!!!!!!!!!!

You can not remove so much material from the piston.



The material on the piston is only 5mm thick.

2.4mm would be much too thin.