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[xt600]

Hi all, any engine experts here?
Last year I rebuilt the top end of my X25XE but within a short time it was burning oil. This happened mainly after a period at idle, at traffic lights for example, blue smoke and that telltale smell.
All seems to point at stem seals, but I had replaced all these! What could've gone wrong? 
I've just started stripping the engine again, and with the inlet manifold off I can see what looks like traces of oil sitting on top of some of the inlet valves. Is this normal, or should they be perfectly dry? All the plugs look black, and some slightly oily, but prior to stripdown I ran the engine at idle for 15 minutes.
Any help/suggestions greatly appreciated :-)

[RallyArde]

One "easy" option would be the crank case breather, unless you already havenīt clean up the breaher box behind the block and the valve above plenum?

https://www.omegaowners.com/forum/index.php?topic=90653.0

There are good instructions for cleaning it up by the way

[xt600]

One "easy" option would be the crank case breather, unless you already havenīt clean up the breaher box behind the block and the valve above plenum?

https://www.omegaowners.com/forum/index.php?topic=90653.0

There are good instructions for cleaning it up by the way

Thanks, yes I did look at the breather box and it all looked really clean, no sign of blockage. Before I refurbed the top end there was no oil burning at all, in fact never needed a top up between changes. My suspicion is that stem seals have popped off, or damaged somehow. I've heard of stem seal retainers, but can't find anything to fit this engine...

[Nick W]

I think you've damaged at least some of the valve stem seals. That's quite easy, as they're small, and buried quite deep in the head.


How did you push them into place before fitting the valves?


The bad news is that to fix this properly, the head will need to come off again.

[xt600]

I think you've damaged at least some of the valve stem seals. That's quite easy, as they're small, and buried quite deep in the head.


How did you push them into place before fitting the valves?


The bad news is that to fix this properly, the head will need to come off again.

I bought a special tool to remove the old ones and place the new ones. It went very smoothly I remember, all seemed to push into place nicely. I'm guessing maybe they have popped up with the valve movement for some reason. Yes, I'm resigned to the fact it's all got to come apart again, so I've bought a new gasket set. I'm guessing I won't need to skim the heads again though....

[Doctor Gollum]

Quick question before you blow it all apart...

Have you removed and cleaned the intake pipe between the air filter housing and the front variable intake valve?

It's not unusual for oil from the breathers to drain to the bottom as the crank case fumes cool and condense. (These fumes are what produces the oil that you see in the throttle body). Over time you end up with a fair sized puddle at the bottom of the y pipe. A decent full throttle pull width start to draw this oil into the intake and consequently the valves.

[xt600]

Quick question before you blow it all apart...

Have you removed and cleaned the intake pipe between the air filter housing and the front variable intake valve?

It's not unusual for oil from the breathers to drain to the bottom as the crank case fumes cool and condense. (These fumes are what produces the oil that you see in the throttle body). Over time you end up with a fair sized puddle at the bottom of the y pipe. A decent full throttle pull width start to draw this oil into the intake and consequently the valves.

The plenums are a slightly different set up as this is in a Vectra, not Omega. When I redid the top end everything including breather pipes were all cleaned, although weren't too bad anyway. Also, before my rebuild, it burnt no oil whatsoever.

[Doctor Gollum]

If the breathers vent into the plenum then they will put oil into the intake. Ironically, the cleaner the breathers are, the more crankcase fumes they allow into the intake.

So unless it's consuming enough oil to blow smoke rings, I would leave well alone.

[xt600]

If the breathers vent into the plenum then they will put oil into the intake. Ironically, the cleaner the breathers are, the more crankcase fumes they allow into the intake.

So unless it's consuming enough oil to blow smoke rings, I would leave well alone.

I don't like the smoke, every time I leave a set of lights or roundabout. I also hate the smell, which is most evident sitting in slow moving traffic. It never did this in the 10 years before I did the top end work, so it has to be down to something I did wrong, or defective seals perhaps....

[Doctor Gollum]

If the breathers vent into the plenum then they will put oil into the intake. Ironically, the cleaner the breathers are, the more crankcase fumes they allow into the intake.

So unless it's consuming enough oil to blow smoke rings, I would leave well alone.

I don't like the smoke, every time I leave a set of lights or roundabout. I also hate the smell, which is most evident sitting in slow moving traffic. It never did this in the 10 years before I did the top end work, so it has to be down to something I did wrong, or defective seals perhaps....

Then I guess you're going to be rebuilding it again.

[TheBoy]

It does sound like one of the stem seals hasn't sealed.  Crankcase fumes would not produce that amount of exhaust smoke.

[xt600]

It does sound like one of the stem seals hasn't sealed.  Crankcase fumes would not produce that amount of exhaust smoke.

I'm so hoping so! Started stripping the engine so will soon find out...

[xt600]

Got the first head off and discovered damage. Markings in the head surface, marked bore and tiny nibble out of the piston. I'm guessing maybe a piece of ring broke off?

[Nick W]

Got the first head off and discovered damage. Markings in the head surface, marked bore and tiny nibble out of the piston. I'm guessing maybe a piece of ring broke off?

More likely to have been something that fell in before/as you refitted the heads. Not that it matters, because now you have an engine that's not worth reassembling as it, and almost certainly isn't worth repairing.

[xt600]

Got the first head off and discovered damage. Markings in the head surface, marked bore and tiny nibble out of the piston. I'm guessing maybe a piece of ring broke off?

More likely to have been something that fell in before/as you refitted the heads. Not that it matters, because now you have an engine that's not worth reassembling as it, and almost certainly isn't worth repairing.

Can't think how, I was super carefull! Do you not think it could be a piston ring breaking up?  The scoring isn't deep, wondering if it's worth sticking in a new piston and rings as I'm thinking this could probably be done from underneath after dropping the sump, or does the crank have to come out on these?