2012 Explorer 280i Rebuild

[SuperTeox]

1 hour ago, konrad said:

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?

I think that at this point, given that it has good tolerances, I won't open it, it's still an operation that stresses the materials, for me it's the first trial engine I've rebuilt so I'll follow your advice if they actually aren't as stressed as a MX

tried to figure out how long the TXT conrods are but I couldn't find this information, it would be interesting to find out which connecting rod it is, I saw that trialshop sells the complete "original OSSA" kit

thought about how to measure the conrod mounted:

less pin/2 , plus hole/2 make "circa" 118mm. before reassembling the engine I take all the measurements of the crankshaft and put them here

51 minutes ago, lemur said:

That's 5 micron 🤔 it takes some serious optical equipment to measure in microns considering the human eye can only see something 8 times that size.

with a centesimal analog comparator you have a definition of 0.01mm per division, when you turn the crankshaft you can see the needle moving within a division very well, sure 0.005mm is approximate but you can understand if it moves almost half a division

looking at some specifications of 2-stroke engines it's not bad to stay under 0.01mm of runout

Edited February 7 by SuperTeox

[konrad]

1 hour ago, SuperTeox said:

 I saw that trialshop sells the complete "original OSSA" kit

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. 

Edited February 7 by konrad

[SuperTeox]

small update: Sister found near home to be saved, it's a 2014! 

[konrad]

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

[lotus54]

I bought a 14 new.  Still one of my all time favorite bikes. 

I put a ton of hours  on it, at 300+ the cylinder/piston looked like new. I did sell it, since I wanted to try out an EM with clutch.  But since sold that (range was just too short) and picked up a 15 Explorer with 17 hours on it. I sold most of my spares with the 14 (darn it) but still have a few things. 

Edited March 19 by lotus54

[SuperTeox]

few more updates:

removed the ruined bushing from the crankshaft to make the modification to the plate with the ball bearing:

 

After a few attempts there was nothing to do, I took the Dremel and made a path to be able to take it with the puller. You need to heat, it's really tight on the crankshaft

I started to clean everything and create a few 3D printed parts to insert the seals and bearings:

 

 

I also disassembled the gearbox, I recommend you to follow this forum thread: 

Unfortunately, however, both the starter gear (also the counterpart on the starter shaft) and the gear drum do not seem to be in great shape at all:

 

trialshop has available both the drum and the gear on the shaft, I tried to contact Lamfos for the starter gear but unfortunately they are no longer produced and they don't have any more... If you have any info it would be great!

I'm also thinking of upgrading the crankcase and moving the ventilation pipe, to be able to use 450ml of oil instead of 350, it's the perfect time to do it since it's all disassembled and you just need to make a hole

Looking through the things that the seller of my Explorer '14 gave me incredibly I found this:

After a bit of cleaning work, unsoldered everything, resoldered, fixed the cables, here it is:

  

Fully functional (I don't know why it was in that condition), I change the battery and capacitor and I think I'll update the electrical system of the '12 Explorer to mount it

the kill switch input is controlled by the PIC which controls the 30 seconds of operation of the step-up power supply and after passing 2 diodes it is sent back to the ECU

The pick-up from the flywheel passes through an optical transistor that activates the system

It would also be easy enough to replicate as a circuit, but big payoff this time!

 

[SuperTeox]

1 hour ago, lotus54 said:

I bought a 14 new.  Still one of my all time favorite bikes. 

I put a ton of hours  on it, at 300+ the cylinder/piston looked like new. I did sell it, since I wanted to try out an EM with clutch.  But since sold that (range was just too short) and picked up a 15 Explorer with maybe 5 hours on it. I sold most of my spares with the 14 (darn it) but still have a few things. 

When I finished the '12 I think I'd completely disassemble the '14 so I can have a bit of fun, even if it's in perfect working order, I prefer to start again from 0 hours, I'm already buying some spare parts around

 

[konrad]

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.

[SuperTeox]

30 minutes ago, konrad said:

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.

Thanks for the information on the drum, so just remove any residue that could come off and put it back on.. I just need to fix the starter gear and I should have everything to reassemble the engine.

I also noticed from the pics on your website that your Easy Start is different.. I wonder how many versions there will be. 😁 However the wires were not welded well, easy to get a few shorts..

[konrad]

6 minutes ago, SuperTeox said:

...so just remove any residue that could come off and put it back on.

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.

[lotus54]

16 hours ago, konrad said:

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.

Adrian told me to only use Maxima extra4. 0-10

Edited February 22 by lotus54

[lemur]

15 hours ago, lotus54 said:

Adrian told me to only use Maxima extra4. 0-30

Is that Maxima extra4 full synthetic 4-stroke multi-grade engine oil that is available in SAE0W10, SAE10W40, SAE10W60, SAE15W50 and SAE5W40 🤔  ?

[lotus54]

2 minutes ago, lemur said:

Is that Maxima extra4 full synthetic 4-stroke multi-grade engine oil that is available in SAE0W10, SAE10W40, SAE10W60, SAE15W50 and SAE5W40 🤔  ?

Yes, that is it.  I made a typo on post (fixed)  0-10

[SuperTeox]

End-of-February update:

modified the engine crankcase to increase the oil capacity to 450ml by moving the ventilation intake behind the starter shaft (don't tell me about anyone who first closed the clutch cover with the starter return spring stuck 🤬😞)

 

the wall is thin so I thought of threading the hole m5 and using a bit of loctite, it's much better than hammering it in:

 

 threaded the original ventilation hole to m6 and added a stainless steel screw with a copper washer:

 

 

modified the gearbox plate by drilling a 4mm hole at the bottom right to allow oil to pass better on the left:

Water pump overhauled:
a small puller on the gear is enough to free it from the shaft, behind it there is a circlip and everything comes away magically:

  

used a Gas Gas seal instead of the original one which has a double lip and is perfectly compatible:  MT280210020 10x35x7.

install backwards, you don't need as much pressure to insert the gear into the shaft, be very careful when handling the seals especially when sliding onto the shaft!

unfortunately I'm still waiting for bearings and thinking about how to fix the gearbox so I moved on to cleaning components and finishing dismantling the frame:

  

here I was really lucky, thanks to the €35 puller on Amazon (the best money spent ever), first removed the bearing rollers mounted on the plate and then using a piece of soft aluminum (be careful not to ruin the thread of the steering column) I pulled the bearing race.
for the frame I used a slightly bent iron rod and knocked out the bearing race using the 3 grooves in the frame

I'm almost certain that it won't go so well on my Explorer, too lucky 😁😁😁

I was thinking of using Motorex Trial Gear Oil 75W... isn't that a good oil?

Edited February 29 by SuperTeox