2012 Explorer 280i Rebuild

[SuperTeox]

Hi everyone, as promised i'm sharing the entire 2012 Explorer 280i project to provide as much information as possible to those who need it.

Here is the bike before complete disassembly:

The bike starts (with difficulty) has good compression (forgot to test it before opening the engine), the gears are ok (neutral doesn't go in easily), the engine's electrical system works but nothing of the Explorer's additional system works; A 12V battery with flying wires that activates the pump and ECU has been added by someone previously.

The engine runs very very rich and makes a lot of smoke (the locomotive from Back to the Future III makes less smoke)

Before disassembling the bike i read all the various discussions on the forum and looked for as much information as possible (Thanks Konrad and your https://www.ossa-efi.com/) to understand how to act and what to look for before completely disassembling it.

After connecting the bike to K-scan (Thanks Lotus54) i managed to test the various sensors and discovered that the motorbike has 300h (assuming is the original ECU) and find the only one that gives wrong values is the engine temperature sensor (23°C instead of 11°C ambient with the bike stopped for weeks)

The time to dismantle the back of the bike, the exhaust, the shock absorber and the swingarm and... first problem!

a crack in the rear swingarm link!

ok, let's look for the spare part later hoping to find it.

Removed the additional tank (cool the quick no leak disconnection fitting), some electronics, removed the lower plate (there are some electrical connections in the front behind the plate stuck by the engine, just under the fuel pump), the reed valve and all the connections to the engine and here is the engine on the workbench (be careful not to pull the fuel hose that goes to the pump, the connection is weak and made of plastic)

For the moment leave the remaining parts of the motorbike assembled and dedicate to completely dismantling the engine to understand the conditions and possibly look for spare parts.

[SuperTeox]

ENGINE DISASSEMBLY:

After removing the water pump by removing the three screws that secure it to the crankcase and the coolant hose I removed the head to see the condition of the piston and cylinder:

ok it would seem that the gearbox oil has been leaking into the cylinder for a long time, really a lot of buildup but both the head and the piston don't look bad.

I removed the magnet side cover and removed the flywheel with a M27 x 1 right thread Puller. removed the coils but there is no trace of fresh oil here, it looks more like an old leak 

Switch to the clutch side and gearbox removal; I remove the clutch cover and remove all the screws holding down the disc spring and remove the clutch assembly (a lot of metal flakes here):

The clutch baskets remain integral to the gearbox and just remove the 5 screws (3 are hidden behind the clutch baskets) with a 3mm Allen key..... Ok..... simple! If only Godzilla hadn't locked them up! A screw gone (I would really like to talk to the inventor of the 3mm Allen key 🤐) and after two hours of testing, decided to drill the screw. Mission accomplished without disintegrating everything.

ok once the screws have been removed, just hammer lightly on the pinion shaft and the gearbox comes out of the crankcase.... maybe... After a day of trying and a pack of cigarettes, I decide to remove the vent plug near the pinion shaft and realize that behind the bearing there is the locking shaft!! with a 3mm hole!! (Konrad there is the fourth version of the locking shaft!) 
I removed the bolt inside the clutch basket (Be careful it's a reverse thread!!) with an 3mm Allen key (🤣) inside the ventilation hole and the gearbox came off with a couple of taps.

 

Edited February 1 by SuperTeox

[SuperTeox]

After taking out the gearbox and taking a quick look where I see the drum and the idler gear probably in bad shape:

I disassemble the cylinder by removing the four screws at the base and remove the piston. the cylinder is not bad at all, there are a few lines in the nikasil but nothing that you can feel with the nail, piston in good condition no sign of seizure only vertical lines probably from dirt pulled in in intake;

Once the engine has been disassembled, I will try to measure them to see how they are worn out:

The connecting rod doesn't seem to have vertical backlash but the main bearings don't seem to be in great shape, they make a lot of noise.
I proceed to remove the inner plate on the magnet side with an puller using long M5 screws (in the photo I didn't have M5 but I rethreaded some M6) the seal seems ok but I realize that 2 small Orings are missing (do any of you gurus remember if they are really there?) could they be the cause of the oil leak?

 

I realize that the crankshaft has an huge clearance almost 2mm lateral, a sign that the bearing on the right is definitely gone and I decide to completely extract the crankshaft from the crankcases
to pull I used what I had in the workshop, a minibike rim, a 3D printed centering ring, a 1cm thick plate and an M12 bar that I threaded 3cm long M10x1.25 which is the thread of the flywheel screw; It is necessary to heat the bearing housing from the outside with a heat gun to avoid the risk of ruining the crankcase by pulling too much

Once the crankshaft has been removed from the crankcase, it is necessary to first remove the gear from the shaft in order to be able to free the bearing.
The tricky part is to remove the gear, it takes a good puller and heat up a lot (not with a propane torch).
with my puller I managed to take the bearing in the Oring slot and in 2 seconds I pulled out the bearing:

[SuperTeox]

And here's who was probably leaking oil. Judging by the condition of the bearing, a 2-stroke engine has just been saved! 🤣

NO Orings found on the bearing, should there be?

[konrad]

1 hour ago, SuperTeox said:

NO Orings found on the bearing, should there be?

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+.

Edited February 1 by konrad

[konrad]

4 hours ago, SuperTeox said:

 (Konrad there is the fourth version of the locking shaft!)

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!

[SuperTeox]

7 hours ago, konrad said:

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+.

incredibly I found this on https://trialshop.it/cuscinetti-motore/122893-cuscinettoparaolio-arancio-motore-dx-ossa-tr280i/ and all the gaskets!

 

I have no idea if it is original or not but it already has the machining for the fixing pin and comes with a viton seal to be changed
It doesn't come with O-rings but I think that at least the internal one on the shaft should be put, I found a good quantity of oil here;
I don't know about the external one on the crankcase, it's much more difficult for oil to pass there

regarding the O-rings of the head I followed a discussion here on the forum and I bought the Gas Gas ones:

Internal Oring PN M01619215
External Oring PN M01619135

and also for the water pump seal I use the gas gas one which has a double seal PN MT280210020

yesterday evening I measured the cylinder and incredibly it is still 76.00 mm in the upper part and 75.99 mm in the lower part under the ports while the piston (it is a 75.95mm vertex) has dropped to 75.92mm.
I believe that the tons of oil that was leaking kept the cylinder in good condition... already found an original 75.95mm piston on nonstop which I think is fine given the non-wear of the cylinder. 

I also found an internal plate PN 54-3400020213 of the 2014 model to see if I can switch to ball bearing on the left side. 
the idea is to take a 6205 bearing and replace the grease with the Kluber Topas Isoflex NB52 which is used successfully (if every 2 or 3 years you change it) in rotax skidoo engines (it is also very easy to change this bearing)

now it remains to open the crankshaft and check the connecting rod and connecting rod bearing.. hoping it is a "normal" size 

[konrad]

6 hours ago, SuperTeox said:

incredibly I found this on https://trialshop.it/cuscinetti-motore/122893-cuscinettoparaolio-arancio-motore-dx-ossa-tr280i/ and all the gaskets!

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.

Edited February 2 by konrad

[SuperTeox]

I need an opinion on the crankshaft & conrod:
- conrod has Zero radial play.
- big end axial play 0.55 mm pass 0.60mm no pass
- big end bearing runs well without noise or visual defects
- conrod has NO color marks due to some heating
- just tested the truing with two dial indicators (without the main bearings) and it has a runout of 0.5 cents.

I think the tons of oil have preserved the crankshaft and I'm undecided what to do.

Do I separate or not separate the crankshaft to change the connecting rod bearing?

 

[lemur]

Conrod has zero play, I'd roll with it.  It will likely engine knock a little like an OSSA 🍀

[konrad]

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.

Edited February 6 by konrad

[SuperTeox]

33 minutes ago, konrad said:

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.

is 0.005mm. You're right I forgot to check the freeplay at the top, tomorrow I'll check

My sixth sense tells me to open and change the bearing anyway but it involves a lot of work and above all I am confident about finding the bearing but I would have no idea about the pin.

I haven't been able to figure out if it's a connecting rod of some existing bike or if it was custom made (there is no gas gas logo on the connecting rod and no code)

 

 

[SuperTeox]

I checked the freeplay at the little end of the conrod and it's 0.42mm ~ 0.45mm without applying too much force at the highest point, it shouldn't be bad!

[konrad]

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?

[lemur]

18 hours ago, SuperTeox said:

is 0.005mm.

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.