[joseimport1]

my new to me 1990 tw200 is a mongrel of parts between an xt225 and tw200

I'm disassembling the engine, and found out the cam chain sprocket is from the ttr230 or older model xt225 part number 2LN-12176-00-00

but the plastic that covers the sprocket is knackered and broken in a lot of places. these plastic pieces will end up on the bottom end. i don't think they would cause mayor damage (being plastic)

but I'm replacing it anyways.

my questions are:

1. do any of these family of engine's sprocket work? meanings tw200, ttr225, xt225 (newer and older), ttr230. they have different part numbers but appear to have the same amount of teeth and the same timing chain.

2. the teeth on my sprocket are good, a mechanic here just told me to remove the remaining plastic and to leave it bare. i don't see any functionality on the plastic pieces, could i just remove it?

 

[Mistervelocity]

They are not all the same as there are different pitched chains for some years. There is also some debate about timing advance, but I can't personally confirm that.
I'd probably follow your mechanic's advice and remove the remaining plastic. If you buy a new one just make sure it's the same part number.

 

[salabim]

Plasitic covering on the sprocket? Why would Yamaha engineers add that to the gear if its not needed ?
Could it be acting as an oil slinger of some sort ,maybe? Who knows?

 

[Fred]

Perhaps the plastic coating is to charge gear's harmonic frequency and thus lessen noise and vibration in part of the RPM range? Oddly my 2001, 2006 TWs, plus my TTR engine have bare metal cam gears lacking the plasctic coating.

R.E. ignition advance: Recently watched Engine Masters TV show did an exhaustive comparison of differnt octane fuels as well as alternations in timing with a V-8 as the test bed. Bottom line was timing changes from OEM base line did nothing noticsble to improve dyno curves. Same for 4 various octane levels from 87, 91,93 pump plus E85 and finally leaded 110 octane race gas. Just like no tangible benefit from additional timing advance in their engine there was no significant increases in horsepower or torque from different flavors of pump gas, with minor improvements from e-85 and leaded 10 octane race fuels. E-85's benefit was speculated to be to greater charge cooling in the intake tract due to the high alcohol content.
Point is if engine is not knocking on 85 octane in hot operating temps then nothing is gained by expensive fuels. Probably same is true for the 4 degree aditional advanced cam sprockets one sees for sale.
Often emperical evidence does not confirm commonly held beliefs.

 

[oldworld 124]

I also believe the sprockets that have the plastic were designed to help reduce the noise on the top end.
My newly rebuilt xt225 is a 2007 engine that has a different style of cam chain with an oem bare sprocket. It is very quiet. The rocker arms also have helper springs that pretty much eliminate the rocker to cam rattling.

 

[Ski Pro 3]

Perhaps the plastic coating is to charge gear's harmonic frequency and thus lessen noise and vibration in part of the RPM range? Oddly my 2001, 2006 TWs, plus my TTR engine have bare metal cam gears lacking the plasctic coating.

R.E. ignition advance: Recently watched Engine Masters TV show did an exhaustive comparison of differnt octane fuels as well as alternations in timing with a V-8 as the test bed. Bottom line was timing changes from OEM base line did nothing noticsble to improve dyno curves. Same for 4 various octane levels from 87, 91,93 pump plus E85 and finally leaded 110 octane race gas. Just like no tangible benefit from additional timing advance in their engine there was no significant increases in horsepower or torque from different flavors of pump gas, with minor improvements from e-85 and leaded 10 octane race fuels. E-85's benefit was speculated to be to greater charge cooling in the intake tract due to the high alcohol content.
Point is if engine is not knocking on 85 octane in hot operating temps then nothing is gained by expensive fuels. Probably same is true for the 4 degree aditional advanced cam sprockets one sees for sale.
Often emperical evidence does not confirm commonly held beliefs.

Just to clarify, when you speak of timing changes you saw on the TV show, that was VALVE timing, not ignition timing.
I'm unsure how you jump from ignition timing results and the 4 degree valve timing sprockets probably not having any measurable effect on performance.

 

[Ski Pro 3]

I also believe the sprockets that have the plastic were designed to help reduce the noise on the top end.
My newly rebuilt xt225 is a 2007 engine that has a different style of cam chain with an oem bare sprocket. It is very quiet. The rocker arms also have helper springs that pretty much eliminate the rocker to cam rattling.

How possible is it to add the springs to my 1999 TTR225 motor. It has a YFM250 cam in it. I think they just drop in, no mods needed, am I right?

 

[oldworld 124]

How possible is it to add the springs to my 1999 TTR225 motor. It has a YFM250 cam in it. I think they just drop in, no mods needed, am I right?

the rockers arms need to be removed in order to put on the rocker springs. Easy to do. Put them on the rockers and then re-install the rockers. The one free end of the spring just bucks against the inside of the head. NOT in the rectangular pocket above the rocker pin hole. I have the old springs from an original YFM250 head sitting on the shelf. I'll try to get the spring compression specs sometime. MrV has a tester.

 

[romtik - The Wide]

All cam gears should fit, except one: xt225(01-07), this one has different chain. Even some 4wheel gears will fit- YFM 250 and some more which I am not familiar enough with.
The timing may be different for each different part no. It will run, the differences aren't that big. If you want, you can file/grind different keyway to change the timing, if you want to chaae specific torque curve.
My gear has also chipped plastic and It seems to run without problems.

 

[Fred]

Ski, you are somewhat correct. I was just repeating the results from a rather lengthy technical show investigating primarily octane's effect on a non-knocking motor as well as varying ignition timing ( not valve timing) attempting to optimize output for each fuel grade well displayed on dynometer. Each fuel grade was dyno'ed through a suite of ignition timing settings seeking improvements using impressive engine management software courtesy of the race community. Not your father's ECU.
On-screen layering of the successive and cumulative runs showed very minor variations in the horsepower and torque curves for all pump gas , peak torque and horsepower measured values were up a few percent for E-85 and the race gas compared to the regular pump gas in a nominal 500 hp race crate motor.
The point being that running higher octane in our TWs for more power is likely to not yeild real gains. Emperical evidence sometimes trumps commonly held wisdom. I know some of you swear by hi octane to avoid knocking and make more power, maybe you just run lean mixture in hot weather.
As far as a new product advancing the TW timing sprocket 4 degrees I was thinking the science behind the benefit we'ld get from both opening and closing valves sooner could be a little better explained so as to form a better informed opinion.

 

[romtik - The Wide]

I think of cam timing as where in rpm band I want the peak to be. Of course it depends on much much more than just camshaft timing. And what works one one engine might not work on another one.