proper

I took the OKO wannabe carb apart to check for the things described here: http://www.miniriders.com/carby-and-tuning/26815-keihin-pwk-copy-carb-mods.html It turns out my carb is actually quite good: - It has the big hex drain screw in the fuel bow. That's good. - Has the required 8 holes in the main jet holder. I did find one hole that wasn't neatly finished. Drilled it out with a 0,8mm drill bit, sorted. - The big float valve is there. All good. - It has the 2 holes at the side of the float valve boss. - The D slide is indeed a low quality item. The chrome finish is lacking quality . But the slide from the 28mm Keihin is identical in size and fits my OKO without any problem. In fact, the whole assembly of D-slide, needle, spring, cable and cover fits on the Chinese OKO. Problem solved. The needle from the Keihin is thicker. Mental note to self: replace needle in case of problems. So far so good.

Another set back. The frame was standing on a hydraulic bike lift on the highest level. Yesterday I placed the rear wheel next to the lift, as I was planning to do some work on it. Imagine my horror as I entered the shop today, finding my frame on the verge of tipping over, and fully touching and grinding the work bench. It seems like the rear wheel touched the bike lift foot pedal, slowly but surely lowering the lift. At some point, the lift platform touched the rear wheel, preventing it to go lower on that side, tipping the frame towards the bench. It's really unbelievable this happened. Was it coincidence I ordered a fresh can of black metallic 2 days ago, and got it delivered today? The damage, of course, is right in eyesight. It will be difficult to repair this in a such a way you can never tell it ever happened. Repeat: I like bike projects, I like bike projects, I like bike projects. That's much better.

Thanks! The forces on that rocker roller are huge. Still, the inlet valve rocker seems fine. It has to be oil or temperature related. Anyway, I'm waiting for my valve shims to arrive by post. In the meantime the new red anonized footrests have been greased and mounted on the frame. I used a single copper washer to get rid of the axial play. Next up was the usual mayhem called rear suspension link system bearings. Just when you think you've had all of the rusty seized needle bearings cleaned, oiled, cleaned, oiled, loosened up the bearing, cleaned, oiled, cleaned and greased, and patched up all the shafts and bolts, another bearing seems to appear out of nowhere... But this has to the one job where you'll notice the biggest improvement while riding. (But a sorted front fork goes a long way too) The rear shock spring has been sand blasted, zinc coated and spray painted white. I used Motip Wheel spray, which should give a nice glossy petrol and scratch resistant finish. Mounted the new side stand on the swingarm. Greased all the moving bits, and some copper slip to the base. Took a while before I figured out how to mount that massive side stand spring. Luckily I had a spring puller tool, otherwise it would have been near impossible to get it done. Also, a new rubber chain guide plate, tyre guard and S3 chain tensioner are mounted. Need some fresh new nuts and bolts before the rear can be assembled. Pics will follow soon!

As much as I would like to say good progress has been made, the reality is I'm two steps back. I've handed over the exhaust rocker to my TIG welder, giving specific instructions about using minimum amps, and earthing the piece in such way, the current would not flow through the needle bearing. You can imagine my disappointment after I got the rocker back with a seized bearing with obvious signs of current passing through the roller. I have thought about grinding the shaft out again, to see what can be saved, but now the most sensible thing to to is just order a new rocker. What a bummer after all this work. Up next was the exhaust. Cranked up the air pressure to 4 bar, and it turned out to be leaking at at least a dozen spots. Most notably, all weldings of that additional damper box where cracked. I considered drilling out all the leaks, welding them up, and try getting the dents out, but it's just no good. Most sensible thing to do is just order a new exhaust. I needed a bunch of gaskets anyway, so Splatshop received another big order from me. They still have the best price on the parts I need, and their webshop is by far the best on the net for Sherco parts. Turned my attention to the swingarm. Looking at it, it just begs to be polished. Some local shop carried an angle grinder with adjustable speed. Just the thing I needed. After some fiddling, I got the hang of it: - Grind the surface with 120 grit flap disc on low rpm (maybe around 4000 - 5000). Even deep scratches can be removed easily. - Polish the surface with a combined grinding / polish flap disc. (http://www.cibo.be/en/products/gamma/flap-discs/rcd-conical?l=en) This disc is magic. Without any effort, the rough surface is polished to a dull shine. It's quite durable too. All kinds of small scratches can also be removed. - Treat the surface by hand with a pad of red Scotch Brite using Belgom Alu polish (http://www.thepolishingshop.co.uk/acatalog/Belgom.html). The whole surface turns black from the alu polish. - Using a big Polishing Mop in the hand drill a mirror shine appears within minutes. No polishing paste is used, just the Belgom applied earlier. I'll post some pics of your royal shineyness soon. Also tidied up the bash plate, but unfortunately the angle grinder speed control broke down.Need a visit to the shop to claim warranty. Greetings, Vincent

Thanks for that important information. I searched the web and found a site explaining the differences, and how to get them to work: http://www.miniriders.com/carby-and-tuning/26815-keihin-pwk-copy-carb-mods.html

@ralphy: Thanks Steve! @Copemech: The part of the rocker where the shaft/wheel is, has very thin walls. It's also made from very hard/brittle material. The cobalt had great trouble drilling the hole up 0,1mm. I'll guess pressing the new shaft could work if one hole is identical to the shaft size, and the other hole a bit tighter. Then I'll not risk cracking/bending the first rocker side wall. Also, if the shaft and the rocker are both from very hard material, pressing with 0,1mm hole size difference might not work. I'll see how I get along. Yesterday in the shop I wondered how to cut the cobalt drill bit, without going through 5 angle grinder cutting discs. For over 10 years I have a reinforced fibreglass cutting disc on my trusty wireless Dremel that has seen some pretty impressive abuse without obvious sign of wearing out. It cut the drill bit like butter.... (https://www.dremel.com/en_US/products/-/show-product/tools/426-1-1-4-fiberglass-reinforced-cut-off-wheels-5-pack)

I tried a 6.5mm drill bit first, since the original shaft measures 6.4mm. Still too much play. Then I tried a 6.6mm drill bit, and this looks to be about perfect. First, the holes in the rocker arm will be drilled to 6.6mm, then I'll grind a new shaft to the correct length from this cobalt drill, then TIG weld it back in the rocker arm.

Here's the DIY flywheel puller with M31x1 internal thread:

Now I'm tempted to replace the shaft with a piece of 6.5mm Cobalt straight shank drill bit offcut. It's hard as nails and has a smooth surface, and is available.

Here's the disassembled exhaust rocker. Pressed the shaft right out. Shaft diameter: 6,4mm Needle diameter: 1,4mm Roller inner diameter: 9,4mm The shaft is the only part showing signs of wear. And that wear is on one side only.

That's a real bonus! Thanks! Seeing that pic, I just know I'm gonna curse the day that engine has to get back in the frame....It's a tight squeeze.

What can I say? Welcome! It's a small, small world. Thanks for acknowledging the model year! We were right after all about the SPS mods. So far no questions. I'm going steady but slow. No need to rush. Received the M31x1 machine tap. Looks like a good quality item.

Cleaned the exhaust valves using a wire wheel on the Dremel: Cleaned the ports using the same method: Lapped the valves: The valves and springs are back in.

I've grinded the welds on the rocker arm, but haven't been able to get the shaft out. Need the big bench press. Got all the valves out. I found out my compression clamp works fine, but the half nuts seem to stick on the stem. A tap with the hammer before compression helps a lot. The head and valves have been cleaned of carbon deposits using ordinary paint stripper. This stuff works wonders on carbon, and doesn't eat the steel. Before: After: I needs another go, tomorrow. The exhaust valves have thick deposits, needing multiple treatments.

There's an update on the valves too. I increased compression force on the Clamp way beyond my comfort zone, and the half bits popped loose from the stem, covering half the workshop floor. Retrieved both. (Pfew!!!) There's quite some carbon deposits on the valves. Mating surfaces also have spots of carbon. Time for some valve lapping...

I haven't come around removing the cam needle bearing axle. First thought was to drill it out, but I'll try to just grind away the welds, and try to press to axle out, saving me the work to source a new shaft. Bearing dimensions appear to be 7mm shaft, 16mm Outer diameter, 6mm width. Bear (...) with me: A quick search did not reveil any replacement bearing. Unobtainium? Hopefully there's some designation left on the old bearing.

Edit: The new roller bearing will be mounted on a new shaft, welded in.

I re-read this great post by Vic: and realized I had skipped the step of checking the rocker arm bearing roller for deterioration. Indeed, the exhaust rocker roller has huge play, and can be twisted. This play probably accounts for the increased exhaust valve clearance. I had a quick peek at splatshop, and wasn't disappointed. It's not a cheap part. The rocker arm is fine, it's just the bearing roller needing replacement. So that's what I'm going to try. It isn't meant to be replaced, the bearing shaft is welded. (never seen such a perfect micro weld). I'll drill the shaft, and try sourcing a replacement roller, mounted on a precision 12.9 bolt. At the inlet valves I measured the following: Valve 1: gap 0,00mm Shim 1.26 Valve 2: gap 0,05mm Shim 1.26 Shim thickness was measured using a micrometer with a 6.34mm bearing ball in the shim recess. Double checked with the digital caliper. Here's the shim sitting on top of the valve stem. It took me a while to understand how to remove them. It turned out it only needs a magnet: Marked all the shims and valves postions: Piece of wood to compress the valve spring: I'm using a deep-throat bar clamp to compress the valve spring: But the spring will not compress. I'm afraid of giving it more pressure, as it feels pretty solid. Don't want to bend valves. Any ideas what's going wrong? The piece of wood is clear of the casing, the clamp sits directly on the valve. The stem doesn't move up in the cap.

The OKO arrived today. Actually looks pretty good, considering it's low price:

Story is that this particular Sherco has been used at expert level regional club championships. It's a Cabestany replica. The serial seems to point to a 2005 version? Yeah, I know, the crankcase needs fresh paint.

I might not like the meaning of this...

Popped the head off. Clear signs of threadlock on the camgear bolts. Must remember that. All looks well. Cam chain guides are like new. The cylinder head gasket looks fine too. Valves are next.

O well, I don't really mind what year of build it is. No reg papers, no serial (should there be any?). I'll give the OKO 24mm carb a try, because I'm curious what it does. In a couple of months time the bike will be ready to ride some entry level club trial. Can't wait to hear that bark again. Thanks again for your help. Appreciate it. Vincent

Well, at least it's a Keihin. And it has the SPS float bowl nut. Now I'm puzzled. Maybe it's a 2005 - 2008 version converted to SPS?

Thanks for that piece of information, Paul. Will check the carb tonight. That seems to be the best telltale. Last night I was thinking: what if I could 3D print a M31 nut. That would give the gear puller something to pull at. Probably not strong enough, but worth a try. Anyway, a M31x1 tap is on the way from China. If there's any interest in an affordable 320 flywheel puller, let me know. I'll only produce one batch of them.