konrad

In John Robinson's 2T tuning book, he classified an oil's load-bearing capability based on the results of Falex and ZN wear tests. In addition to two modern oils (Motul 800 and Silkolene Pro 2) the highest-rated oils were castor based. So for engines having the very highest specific power outputs (e.g. road racing) using a castor-based oil is not completely foolish. But a trials bike does not fall into that category. And castor's drawbacks are, as mentioned, quite a nuisance. At one point in my life I was very interested in the chemistry of combustion. I reasoned that castor oil could also act as a chemical supercharger since it is an oxygen-bearing fuel.

Beautiful restoration work! Same goes for your RTL250F. Will you ride these bikes? Or are they just for show?

That's what I would do. Thinking more about it... I use a synthetic ATF in the gearbox because I like how it makes the clutch feel. But clutch feel would be less important on the Explorer than a trials bike. Might be smarter to use a high-quality gear oil since the gearbox is so fragile.

That shift drum does not look too bad. It does not take long for the neutral detent to wear like that. Your EasyStart is slightly different (and better) than one I disassembled. On yours, the wires are soldered directly to the PCB. On mine, there was an insulation displacement style connector between the wires and the PCB. One of the wires pulled out of that connector.

Excellent! It's much easier to fix these bikes (any bike really) if you have another for comparison.

You can use a degree wheel if you want, but I don't think the "when" is much of an issue. What you need to test is that the Hall switches actuality do switch. Test each Hall switch independently by only powering them one at a time. The top of the pull-up resistor also gets connected to the positive side of your power source. Monitor the voltage between ground and the output of each SS543AT. You want to see the output swing from roughly your power supply voltage to roughly 0.5 volts (or less) as you rotate the flywheel. I would suggest using a battery rather than a battery charger as a power source. Any battery between 5 and 20 volts would be fine.

If you turn down the insert, will the "cover" still fit?

That wiring scheme is completely reasonable. Ground in the center was an assumption on my part. I'll also take this opportunity to mention that you'll need a pullup resistor (say 10k ohms) for the blue wire if you test the Hall sensors as I mentioned previously. Search "Honeywell SS543" if you need a datasheet for the Hall sensor.

Great you were able to get some test values from Chris, he's the best resource in the business! Regarding the early and late timings, that's my nomenclature -- not official Leonelli documentation. I was trying to figure out how the system worked. Pretty sure I used a degree wheel, and supplied the signals marked Vdd via a 5 volt bench power supply and turned the flywheel by hand. Hall-effect sensors can work at zero rpm. The position (timing) of the stator plate will affect the exact high/low transitions. The 3 identical stator coils provide power for the fan and are not related to the ignition. The coil wrapped in white glass-reinforced tape provides the high voltage for the CDI. There is one winding for high-rpm running and another for low-rpm running. One end of each winding is connected together and I think also connects to the chassis. So you should see a very low resistance from one of the charge coil wires (red or green or white) to the aluminum stator plate.

You have my sympathies! That has got to rank as one of the worst ignition systems ever designed! The "pickup" is actually a pair of Hall-effect sensors. You really need specialize knowledge and equipment to diagnose these ignitions, otherwise you just have to throw parts at it. I made some breakout cables to probe the signals and spun the system with my vertical mill.

trialshop.it to the rescue! I'm going to have to learn some Italian. https://trialshop.it/ossa-ricambi-originali/25217-biella-completa-tr280i/ I see it comes with the small-end bearing, just like the GasGas kit. This is unusual, so seems likely it is the GG part. 118mm for conrod center-to-center is probably a good number. I was guessing 120. Thank you. 5 micron (0.0002 inch) runout is perfectly reasonable. I have a dial indicator that has graduations every 0.0001 inch.

The short answer is: I would continued to use that crankshaft. The long answer is: I have not seen crankshaft wear limits for any trials bike. So we are forced to infer service limits from similar 2T engines. A trials crankshaft has an easier life than one in an MX bike or roadracer. The average piston speed is fairly low, but the piston is also relatively heavy. If you feel compelled to rebuild the crank, I probably would not replace just the big end bearing. Typically the rod, big end bearing and pin are all replaced at the same time. Like their gearbox, OSSA did not sell any crankshaft parts separately. As a point of reference, the complete OSSA crankshaft (P/N 3000020211) had an MSRP of $725 USD back in 2013. My best guess for something that would fit is GasGas TXT 250/280/300. They sell a connecting rod set (rod, pin, big end and small end bearings) as part number MT280212100. It has an MSRP of $266 USD today. GasGas also offers the big end bearing alone as MT32050GG-AIZ-1. MSRP of $35 USD. I have been very curious about the OSSA's connecting rod center-to-center length. Could you make that measurement for me?

Your rod side clearance is good. How much runout is 0.5 cents? Is that 0.05mm or 0.005mm? How much small end free play? Rock the rod side to side and measure movement at small end.

I've been working under the assumption that if the clutch slave cylinder is located inside the engine, the system will use mineral oil to mitigate cross-contamination of the seals. If the clutch slave cylinder is located outside the engine, DOT4 will be used to minimize the number of different fluids required for maintenance. Is this a bike that goes counter to my assumption?

trialshop.it is an excellent resource! Their website is the first time I have seen an exploded view of the OSSA gearbox. I must retract that statement. Upon closer inspection, it is for a TRS.

Interesting! You are absolutely right. I see that locker shaft is captive, with a through-hole, and a 14mm bearing ID. I'm getting the feeling that no two EFI OSSAs are identical!

Although I have not needed to replace a crank bearing, I believe so. This will probably be your best option: https://www.splatshop.co.uk/gasgas-main-bearing-with-seal.html Excellence work and many thanks for the write-up! That bike looks clean, I am surprised the motor is in such bad condition. 300 hours is getting up there. I have one bike with 500+.

Just so we are on the same page, I grabbed some images from the 2018 4RT manual. Here is what I think is going on: 1. Oil comes from the pressure pump and surrounds the outside of the oil filter. 2. Oil travels through the filter media and exits via the center of the filter. 3. Oil exits the filter cover and enters the generator cover. 4. Adjacent to the oil entrance in the generator cover is the PRV (excess oil pressure is vented to inside of the generator cover, eventually finding its way back to the sump.) 5. Oil travels through a passage cast/drilled into the generator cover towards the crankshaft big end. 6. Now I'm guessing... Some of the oil passes through the crankshaft and continues on to lube the piston and top end. (Or there's a different passage in the generator cover that directs oil on to those other locations.)

In all engines, oil flows towards the big-end bearing. When it escapes the big-end bearing, it returns to the sump. P.S. From my research, oil filters almost always flow from the outside to the inside. P.P.S. It seems that canister-type filters are the ones that have an internal bypass valve. So I'm guessing you won't find a bypass valve inside the 4RT's paper cartridge.

I assume you meant to write "...not swimming in it."

I am fascinated by these sorts of problems. But I'll start by saying the only motorcycle oiling system I've studied in any detail was for a dry-sump Aprilia vee-twin which was more complicated. So the following is conjecture. The block flow diagram below is for a 1977 Kawasaki KZ650. It represents my understating of the pressure relieve valve's place in the system. Its purpose is to prevent oil pressure from exceeding a preset limit. The bypass valve opens when the oil filter is clogged or when the oil is too thick (e.g. cold weather startup). The bypass valve can be external to the oil filter or internal. I would expect the 4RT to get 100% filtered oil under normal operating conditions. I suggest opening an old oil filter to have a look inside. If an internal bypass is present, there should be a spring and some type of valve. But if the bypass valve is external, and stuck open, I could see where your engine could still be running okay yet have no oil in its filter.

Some thoughts: 1. 260 miles before the first oil/filter change is a long time. Reviewing my old 4RT manual says the break-in period is 20 minutes. After which it implies the oil and filter should be changed. (Personally, I'll probably go more like an hour lacking any other guidance.) 2. Seems to me it was possible to install the oil filter backwards in that engine (and thus blocking all flow). 3. What transpired between the time the dealer said there was oil in the filter and you subsequently observing there was none? 4. Small 4T motorcycle engines sometime have no oil filter, so it's not the end of the world, but far from ideal. 5. The engine would have seized long ago with zero oil flowing. 6. I assume the oil looks used and oxidized, rather than like new (which would indicate it had not flowed anywhere). 7. I also assume that if you remove the tappet covers you will see oil. 8. If you are concerned about engine damage, you should submit a sample of the drain oil for analysis. In the US, I've used Blackstone Labs: https://www.blackstone-labs.com/tests/standard-analysis/ They can determine the presence of wear metals in the oil. I'm sure there are similar labs in the UK.

Now I understand my confusion. Apparently, Gael rode both a 2024 Comp and a 2025 FACTOR-E at Montpellier. Trial-club.com posted a video on FB. Here's a screenshot from the video.

What photos are you using for reference? Honda service manual are second to none. I still have a PDF manual for a 2107 260. It shows routing behind the bars. Maybe the 300 is different. It's worth investing in the manual. P.S. It's great to see women involved in this sport. If it weren't for my wife, I probably would not be riding trials.

This is an excellent first post! I sincerely hope you are not ChatGPT!