TDM850 : Oil consumption

(image)


A compilation about the theories on excessive oil consumption that may be experienced with the TDM850 (MkI & MkII) and also with the TRX850 & XTZ750 which all share the same engine design.

Output shaft - Part I (text by Nixey)

The issue of oil consumption is one that effects many TDM'ers. Here is what I discovered when researching this matter. This explanation was given to me by a long term TDM owner who has encountered the same issue and cured the problem.

On the output shaft behind the front pulley there is an oil seal, the oil seal has tags on the inside to stop it being pressed in too far, and blocking the oil return gallery from the starter motor. Some batches of TDM's (plus all derivatives of this engine) have an oil seal fitted where the tags are slightly too short and the seal partially blocks the oil return gallery.
This results in too high oil pressure around the starter motor and oil is forced out (when traveling at high speed) from the starter motor seal. The oil is such a fine mist it is un noticeable, a tell tale sign is to look at the bottom of the engine and around the inside of the kick stand.
If theses are oily and it is not chain lube then it's the seal that's causing it.

Dead easy job to do and very cheap.
Part number :
• 4TX (1996-2001) : 93102-35459
• 3VD (1991-1995) : 93102-35381
The TRX should use the same part as the 4TX, while the XTZ should use the same part as the 3VD.

Output shaft - Part II (by Dapleb / Carpe-TDM)

There are two oils feed holes one at about 7 and o'clock and another at about 11 o'clock (looking inboard from the LHS of the engine).
Indeed, as mentioned in the TRX article, if the spigots do overlap the oil holes, they would partially block the hole! It is possible to check if this is the case without removing the seal or buying a new one, as there is a reference mark (part code) on the outside of the seal which can be used to define where the 'spigots' (I'd call them 'tangs') are in relation to the oil holes.

Not convinced that the tangs and oil feeds lining up would cause enough pressure for the 'fine mist' of oil to pass the seal but its possible.

I also read an article on a TRX site about it being the SEAL itself that was at fault, as a new seal has more holes in....or something like that, which is utter bollocks.

I thought a few pics might be helpful (pics from a mkI) but same theory applies to all other 750 & 850cc engines :

(pics by Marco & DAV / Ouestlekeum)
The gearbox output shaft with the the oil seal in place :

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The gearbox output shaft without the the oil seal, showing the oil holes (orange circles).
The oil holes MUST NOT be lined up with the spigots.

(image)


The oil seal showing the four spigots :

(image)


Mark the spigots location on the outside of the seal :

(image)


Mark the location of the oil feeds on the crankcase then insert the new oil joint, make sure the marks DON'T line up :

(image)

1c - Output shaft - Part III (from the TRX newsgroups... Long but worth it...)

Thanks to Sandy for all those specs and oil flow drawings and along with some recent problems with a couple of TRX's and TDM's that all have high oil usage.

I might have found the answer, I certainly have found a design fault and a possible cause of early oil seal failure.

I am not 100% sure yet, but I think the problem with excessive oil use is in the design of the drive shaft oil seal.

It has four 2mm spigots attached to a standard 5mm depth oil seal in a 7mm journal, this allows a 2 mm free flow space between the output bearing and oil seal. In this space the oil flows from the bottom crankcase around the drive bearing then up through the top crankcase and then into the main shaft.........

IF one of these spigots blocks the oil gallery in the lower crankcase, the oil pressure builds up and escapes as a fine mist through the output shaft oil seal ( all lubrication still continues, so there is no risk of engine damage ).

Result.....No oil leaks ( or a very minor one that would be hard to spot ) and your oil level decreasing !

Cure ! refit a new oil seal with the spigots remaining clear of the oil gallery.

Two TRX's and one TDM have had new seals put in ( with the spigots away from the oil gallery ), and so far on a few 300 miles blasts, oil usage is nil and there is no fine mist oil leaks around the front of the rear shock and on the top od the starter motor. Which all bikes suffered from before.

Here is how to find out if you have a problem with the oil seal ( not a knackered engine ! )

Take a 20 to 30 mile high speed blast ( motorways are good for a long sustained run ), park the bike up with some clean white paper underneath the kick stand.

Look underneath and run your hand along the very top of the starter motor and see if you can feel a fine oil spray there, then run your hands around the front of the rear shock for the same oil mist.
Go indoors for a brew and then check the white paper for spots ( not a leak ) of oil.
If you have this, then order a new oil seal ( £9 inc vat ), it must be a genuine Yam one, it is a one off with those spigots or you will blow you engine up fitting a standard 7mm thick one.

It takes 40 min max to do ( no need to drain oil ).
Remove gear linkage, then the outer sprocket cover followed by the inner black ) sprocket cover. Loosen off the rear wheel and chain adjusters.
Undo and remove front sprocket. Then take out the 5 10mm bolts and remove the oil seal retainer plate.
Carefully pop out the old oil seal ( checking where the 4 spigots are on the back of the seal as it pops out ).

Refit new seal ( smear the outer edge with some Permabond or decent high temp gasket sealant ) making sure the spigots miss the lower and upper oil gallery near the final drive bearing.

Refit front sprocket, covers etc and then leave over night for the sealant to go off.
This can be done without draining the oil.
The Oil Seal costs £8.85 plus VAT ( if a bearing company did produce this seal it would be around 80 pence ! ).

Emulsion tubes (by Alan Eccles / Carpe-TDM)

I've got another theory on the 850s if the problem's not the oil seal but burning oil (usually a slight blue haze from the pipes or an oily smell picked up by the rider behind) :
Worn emulsion tubes and jets !!!

These tubes can wear oval in around 5000 miles if the engine is used gently.

The excessively rich mixture washes the oil off the bores and causes piston ring/bore wear resulting in excessive oil consumption.

Not a problem on the 900s as they use fuel injection

Valve seals (by tkphuah / Carpe-TDM)

Think I have known the reason for the high engine oil consumption.
The mechanic has dismantle the engine and found all the valve seals at the inlet ports are all badly worn out. But the valve seals at the outlet ports are still in good condition.
And all the valves are full of carbon....
Anyway have replaced all the seals.
Overhaul should be completed within these 2 days.
Should burn a hole in my pocket...
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