Yamaha YZF R125 Forums banner
1 - 5 of 5 Posts

·
Registered
2008 YZF-R125 (180cc)
Joined
·
603 Posts
Discussion Starter · #1 ·
I'm starting a separate thread for this so I can just dump pics and progress without confusing my main bike thread.

This is a spare motor i bought as broken which I'm restoring to use in my main bike. The basic idea is to build the exact same engine as I have in my bike, but sort out a couple of issues.

Because of a scored little-end bearing I've had to get the tools to split the crank and replace the con-rod, for which there is a nice forged item ready to go in (it's a thing of beauty) .

scoring inside the little end from having to press the pin out.
Automotive tire Gas Bumper Machine tool Automotive wheel system



There's one thing though, namely since adding the 180 kit on my main bike I've always felt the vibrations were a bit off. Like it was happy to scream all day long at 8-10k before as a 125 but now it's kinda "reluctant" in that range. Some of that was fuelling and no doubt some of it will be due to the stretched timing chain on my main bike and probably quite worn bearings and basically everything from havign been beaten on relelntlessly for 28k miles.

So I'm hoping just freshening everything up will help a lot in general, but while I've got the crank in bits i'm measuring/weighing some stuff and seeing if i can do somethign about the vibration thing. It's looking liek the crank has a slightly weird balance factor whcih doesn't really make sense to me (hardly any counterbalance) but the bigbore piston is about 30g heavier than the stock and you can't tell me that doesn't affect the balance of things flying back and forth 80+ times a second, and must increase load on bearings, and may even mess with the counterbalance weight/shaft.

180cc
Automotive lighting Fluid Rectangle Font Fashion accessory


125cc
Material property Gas Audio equipment Electronic device Household hardware


So whilst I don't really understand the choice of balance factor, when it was 125 it worked great so my aim is to see if we can get it back to whatever the 125 balance factor was, and then hopefully it'll rev a bit more freely, even with the bigbore kit.

It looks like there's two choices - either drill some holes in the crank webs at the light end, effectively ging the heavy end more weight (i could prob do holes). Or adding weight to the heavy end, either by drilling holes and filling with lead/tungsten plugs (ha, nope), or be potentially welding on a small steel patch in just the right place.. seems preferable, but only if there's clearance to do so.

drilling the light end would be something like this:
Vehicle brake Disc brake Locking hubs Alloy wheel Rim



pics and measurements to follow, just wanted to get the ball rolling here.

The rough plan for this engine is all new internal bearings, new close ratio racing gearset, forged conrod, 180cc cylinder, stage 2 cam and for now stock head but freshly lapped valves etc, R15 super duty clutch like my current bike etc, brand new timing gears, chain and guides..basically all new internals...but all of that only works if i can get the crank apart and back together again, and straight, to within tolerances.

If it works out as planned that should make this a beautifully smooth big bore conversion :).

will follow this up with more pics once I've got them off the phone
 

·
Registered
2008 YZF-R125 (180cc)
Joined
·
603 Posts
Discussion Starter · #2 · (Edited)
crank progress in pictures...

what we're starting with..

Purple Pink Magenta Costume hat Cosmetics


lower timing gear and bearing removed
Sleeve Wood Electric blue Magenta Fashion accessory


trying to figure out the balance factor
Wood Machine tool Gas Automotive tire Engineering



Y-plate from 8mm steel to fit the webs and spread the load evenly
Wood Font Rectangle Gas Tints and shades


main plates either side..
Wood Gas Engineering Machine Table



Y-plate to support the back-side of the web
Gas Circle Metal Automotive wheel system Macro photography



that worked then :)
Automotive tire Rim Gas Auto part Cylinder


comparison of the stock rod vs the forged one going in
Sleeve Textile Electric blue Collar Denim


noticably wider
Tool Artifact Electric blue Font Spoon


the forged rod is a joy to behold.
Household hardware Tool Hand tool Auto part Nickel



[LOTS of measuring and calculating follows]
 

·
Registered
2008 YZF-R125 (180cc)
Joined
·
603 Posts
Discussion Starter · #3 · (Edited)
aaand fast forward a bit (ok a lot... and)...


so happy rn... i've been dancing around this problem for over a year now, and every "expert" I had let me down. A few months ago a dude (who I very much respected in terms of engine-building) stood in front of a machine-shop full of tools and told me they'd have to get it "sent out" to have this stuff done.. yet I was able to do it with my humble little workshop and a bunch of youtube videos?? wth.
 

·
Registered
2008 YZF-R125 (180cc)
Joined
·
603 Posts
Discussion Starter · #4 ·
built a tool to pull the new crank through ...
Crankset Automotive tire Bicycle chain Vehicle brake Bicycle part


cleaned up the cases...
Automotive tire Automotive lighting Crankset Motor vehicle Gear


unfrotunately that showed that most of the bearings weren't in that great shape...so, finally have almost all the new replacement bearings now. Waiting on one I missed...

Starting to look a bit more hopefull up in here :)
Rim Bicycle part Automotive lighting Motor vehicle Auto part


since all the pieces have been scrubbed clean, assembly can happening indoors now, which means it should be easier for me to keep it spotless, avoid rust etc during assembly.

As items come indoors they also get scrubbed before they go into the engine, so only clean/checked items go back in.
 

·
Registered
2008 YZF-R125 (180cc)
Joined
·
603 Posts
Discussion Starter · #5 ·
Looking rather engine-like once again. Internals rebuilt, all new bearings, everything silky smooth like new, clutch side is done now, I guess next up is stator side, timing chain and all that jazz. blimey that was pretty complex but I think we're back in familiar territory now :D

Automotive tire Motor vehicle Automotive design Rim Automotive exterior
 
1 - 5 of 5 Posts
Top