Hi!

Maybe you remember my "fuel pump" topic?
Well my first longer testride with the 907 was about 1300km on motorway.
The bike went really perfect & powerful, but there are 2 issues where I need your help:

1. The bike does not go faster than 210 km/h @ about 7500rpm with 15/39 transmission.
210 is enough for me, but why does it not go further? Shouldn´t be the maximum power on a higher rpm level?
OK- I had a backpack, but nothing more with me...

2. The cylinderhead on the rear side is still loosing some oil, where on the front side ist not leaking anymore.
It only looses (fresh and light coloured ) oil underneath the exhaust- between cylinder&head, and then of course drops down to the clutch and chain...

Since I have that bike (1993) it always was leaking underneath both exhausts-

I don´t like leakages at all- that also was the reason why I have stripped down the motor in winter time. Though I was successful on the front side I wonder whats up on the rear side. Off course I used new O-rings, silicon for all the copper studs and made a clean job to get the leakage fixed.

Are your 907´s leaking too? Is this "part of the game"?

So long
Gernot

on the 210km issue,that's still fairly fast,what tires do you use?
could be a speedo issue or maybe fuel supply or air supply problem.

On the oil leakage,persistant oil seepage generally is a warped surface of the head or the cylinder or both assuming all is is good

with a back pack you cannot expect anything more than 210kmh...

try in "perfect" conditions (i.e. tucked behing the fairing, leather suit, perfectly tuned engine, 20 deg.C, correct tyre pressure, etc etc) and in a good run you should see a little bit more.

To do the "in theory" declared MAX SPEED of 230Km/h with a 31/62 primery gear, 15/40 secondary gear (the standard) and a 170/60-17" tyre, the engine must rev over 8750rpm in 6th gear (28/24) which I see it to be quite difficult.

With the 15/39 the gearing is even too high and it is unlikely the engine can pull it.

I found that the 15/42 works much (MUCH) better, but I use the bike 99.99% on twisty roads (the Alps)


As for the OIL Leak, there are some oil passages in the Cilinders and the seal is made through a small OR wich sometimes leaks; I had the same on mune, and the only solution is Stripping the rear Cilinder and replace the sals making sure that during assemply the OR is correctly fitted; In any case mine has never beed very clean, not dripping oil but not dry neither...

mine leaks a little after a good long ride, i keep sayn im gonna ride it without the fairings on and after getting her home running her up on the table and looking for where she drips from...........


doug hunt

you can always clean it off then spray it with a good powdered type spray deoderant to track it down effectively

repeated leaking is almost always a problem with the head or cylinder surfaces that enclose the seals

Hi Ynot,

the leaking is part of the game. Mine leaks at the exhaust side of the rear cilinder. not much, so I don't mind.

about the speed. I've tried my 907 a few months ago and achieved 220 km/h on the clock pretty easy with rather wide textile clothing and back pack.
I think with my racing leathers and helmet down in the tank I'll reach 230/240 on the tacho. But the Italian correction will give max 220 km/h for real.
This doesn't mean I'm satisfied with that
my 907 needs a fully tune up with setting the TPS, vacuumbalance, camshaft timing and so on.

Bertus

Oil leakage:

Like most have said, get use to it. The cylinder heads do not have head gaskets but rather use a raised part on the cylinder and a recess in the head for sealing the cylinders, metal to metal. O-rings are used for the oil and water passages. I have tried almost everything. I even used o-rings with the same outside diameter but thicker in roundness. Didn't work. I have tried myself about 5 different times and had two dealers try but no luck. I had the engine rebuilt and whatever they did it has stopped the leaking. Something to try the next time you take the head off is to relax or remove any bolts that connect the cylinder to the frame when you torque the heads down. The mechanic that rebuilt the engine told me that the oil and water passages are not high pressure. That is why they tend to leak out and not mix oil and water between passages. If you look closely, the cylinder has the recess the o-ring sets in and the head is flat around the passage. So it's a matter of tightening the head down EVENLY.
du907

The space between cyl-head is 0.35mm.
Having an idea of having Oring also outside of the cavity original rings lie,
in 0.40mm thickness. Could this work or stupid idea?

maybe instead of using O-rings the use of X-rings is a solution.
as pressure builds up the lips of the X are pressed outside, where the O-rings are pressed inside due to the contact angle of the O-ring to the mating surface.
it is just an idea, but could work.

Bertus

x-rings could work, but the surfaces still need to be flat and square and the ring needs to be sized correctly and torqued down properly

Would a switch fr original Orings to Xrings be better?

don't see a down side

I've googled a bit and found a lot of X-rings both in NBR as in Viton quality.
so, I don't think there is a dimensional limitation.

Gert, the load in the X-ring by the oil pressure is totally different as on a O-ring. The O-ring need a lot of compressing to withstand the oil pressure.
the design drawback in the cylinderhead is that there is not a back up.
the recess where the O-ring lies in is not deep, so the ring can move a little out ward. the X-ring's lips are forced by the oil pressure to move outside, so helping the compression force. the edge radius of the lips of a X-ring is much smaller as on the radius of a O-ring.
in a motor chain, yours probably as well, are X- or Z-rings nowadays common, replacing the O-rings which where used in the past. if there was no improvement, O-rings still would be used.

Bertus

I would say so.
https://www.tradcom.com/JPBC/0_5StartPa ... 30|3876797),sel(3874355|3877184|3874390|3874630|3876797)

this is where I found the X-rings in Viton quality. I'll have to work on the heads these winter anyway, so I'll use these rings and see what's happening