Ton up SR250: 100mph, 100kg, 30hp

About the rocker pads... I actually did the measurements with both versions of the rockers and came up with the same results. As with any good measurement, I took it several times then took the average - same for both. I did this because I always thought this particular bike made slightly more power than the black one and I thought it might have had something to do with the rockers - if the ratio was slightly better, the valves would get a little more lift = a little more air fuel mixture = a little more power. But this was not the case. Goes to show how accurate the butt dyno is haha.

Not sure about the 5.5mm valve guides, probably is. Thing is, Chris makes everything custom to each application anyway, so he'll turn some up in the right material and size. Yeah, I am happy with the decision about SS instead of Ti.

Current power falls off at about 7800rpm but will rev to 9000rpm. I basically want to be able to rev to 10000 and have power all the way up to 9500. I think this is achievable with the weight loss program.

Yeah, will be lightening the rockers - I covered this a few pages back in the thread :)

This amount of research is usually very unnecessary (unless rebuilding an engine to non stock spec) but I am treating it as an educational process and I am super passionate about it so it's all just really interesting to me! I have read a few posts on your blog too, looks like you take a similar approach!
 
The butt dyno is pure confirmation bias. Anybody who has ever worked with data acquisition knows this to be true.
 
While preparing and packing up the head to send away for machine work, I decided to see if I could remove the tach drive system entirely. The answer is yes. But then there is nothing for the tach-plug I have made to push up against and it sinks into the hole in the head too deep to form a seal. So I put it back in! It will not be driven anyway because the cam regrind I got was done on a non-tach drive cam (missing the worm gear drive). Anyway, if anyone was curious, this is what the assembly looks like...
 

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Why not just drill and thread a hole on the top side. Then make a aluminum plug with a flange and a plain hole? Worst outcome would be oil leakage in case the bolt unscrews and the plug comes off.

Hit me up if you want one done and I’ll squeeze it in at work.


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A cool day for the project yesterday - I went in and picked up the parts from the machinist/engine refurbishing mob!

The rebuilt crank looks amazing, nice to know the bottom end is fresh and strong when I put extra stress on it. He swapped out the bearing for a brand new one as well - this is a part Yamaha doesn't list on the spare parts program (rather it is a part of the crank half assembly), but he managed to source the correct one and replace it! Woohoo.

The bored up cylinder looks really nice as well, finished with the typical cross hatch honing. The guy said he shot for the middle of the suggested clearance tolerances and that came out at 0.075mm or something - pretty much what der_nanno suggested. He also explained the difference in these tolerances vs the factory specs for the factory piston... Also what der_nanno mentioned a few pages back. The stock piston is cast and expands less than a forged/machined piston like this new custom one is. He also said that because of that, the engine might be a bit noisier than stock when it is cold - until the engine gets to temp and the piston expands and comes into it's working diameter spec.

The machined starter drive gear looks great too. This actually ended up costing more than I thought - because it is hardened it couldn't just be turned down in a lathe with a bit, rather it needed to be ground down in the lathe with a grinding stone.
 

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Might need to pick your brains for the next job... Assembling the crankcases. Which sealant do you recommend? Yamabond #4? I heard 3 bond is the same product/manufactures the Yamabond. Anyone use anything else?
 
JadusMotorcycleParts said:
A custom plug could definitely be a solution! You work with CNC machines?

I got 3 of them at workHowever I would turn it manually in the lathe and mill since that would take way less time since our 5-axis ain’t running at the moment.

Just send me a drawing and your address and I’ll try to sort it out for you.


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JadusMotorcycleParts said:
Anyone use anything else?

I use Elring Dirko HT (red), with great success. Especially as it's a lot cheaper overhere and it comes off very easily with just a bit of Acetone. And a little bit goes a very long way, i.e. a tube will last you several engine cases.
 
Eleganten said:
Just send me a drawing and your address and I’ll try to sort it out for you.

I'll take you up on that! I'll need to measure things up and design it first so it may take a while before I get there. Cheers!
 
der_nanno said:
I use Elring Dirko HT (red), with great success. Especially as it's a lot cheaper overhere and it comes off very easily with just a bit of Acetone. And a little bit goes a very long way, i.e. a tube will last you several engine cases.

Awesome, thanks.
 
Been pretty quiet recently - been working on the custom for Lars. Now it is finally complete though! It came out pretty good for a 4month, 60 hour total (spare time after work) project. Really happy it is complete and can now get back to this. Lars was stoked too, which made the whole project sweet and well worthwhile.
 

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Thanks!

Now that the engine project is pretty much on track, or at least, things have been ordered and it is just a matter of doing the work, there is now time to focus on the chassis - wheels, frame, suspension etc.

The SR has notoriously poorly performing forks, so I have been focusing a bit on that first because it feels like that will be the most challenging. I have done a lot of reading and have been trying to weed out the good information from the bad and trying to decide what mods to do and for what cost/benefit ratio. Because eventually, if I come up with something good, it could be a nice product for all to have access to.

I have read a lot about the Race Tech cartridge emulators and they seem like the hot ticket for old RWU damper rod forks. But they are pretty pricey and I am not sure many people would be that willing to go so deep into their forks. I have also read through the Minton mods for forks for the XS650 and they seem like a good place to start - relatively small changes for good and cost effective results. I think I will try and find some looser fork seals to reduce sticktion, experiment with fork oil weight and volume, and also preload - which would require either spacers or some special fork caps with preload adjusters. For anyone interested, here is the Minton mods: http://www.650central.com/tech/mintonmods.htm

And here is good stuff about damper rod forks and the cartridge kits: http://www.racetech.com/page/title/Emulators-How%20They%20Work and here: https://www.youtube.com/watch?v=j3QYZEQoN_M

And I have listed the things that are adjustable on the fork.

Adjustable inputs:

Oil level
Oil viscosity
Preload on springs
Spring rate - single rate, double rate, progressive. Also spring length vs spacer length.
Valve emulators - on top of damper rods, requiring destruction of the damper rods (in essence removing their original function)
Add air valves - for air fork function

The air fork function is what I am least familiar with. I have a full-suss mountain bike with air shocks front and rear and adjust that every now and then, but still don't know why that method is chosen over others, or the advantages and disadvantages. If someone can elaborate on this, I am all ears, but at this point, because it is least familiar to me, it is less likely something I will do.
 
What size emulators would it need? They have to fit inside the springs and are usually the same OD as the top of the dampers rod.

I ask because there are other options than the RaceTechs, they don't have it patented or something. But you can't beat cartidges, the fundamentally improve the damping function.
 
I know the Ricor Intiminators (different internal cartridge emulator) are real popular with V-Strom owners but I think the smallest version is still 39mm. Cogent Dynamics also has the Drop in Damper Cartridge (DDC) and fork springs but I don't know what sizes they have. If you want to retain the OEM 32mm fork tubes, there's not much more that can be done than a stronger spring (maybe custom or from a CB360/400) a fork brace (you already have that) and different weight oil. Front end swaps are doable, but would look funny if you did not use a spoked front wheel (unless you swapped both front and rear wheels), but using a front end with a disk brake adds a better braking dimension.
 
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