Don Terrill’s Speed-Talk

I'm experiencing a cloud of blue smoke coming from the engine immediatly after I decel from mid to high rpm. Engine produces high amounts of vacuum during a decel event and I already ruled out the PCV as being the source.
So I assume either the valve guides or the seals. What is the most likely ?

I had that issue with a SBC. Leakdown test turned out ok so I could rule out the rings. PVC system looked to be functioning good. Replaced the valve seals as it was the cheapest and most likely fix. Of course it turned out to be worn guides in my case.

Roundybout wrote:I had that issue with a SBC. Leakdown test turned out ok so I could rule out the rings. PVC system looked to be functioning good. Replaced the valve seals as it was the cheapest and most likely fix. Of course it turned out to be worn guides in my case.

Yes, similar here. Compression is ok, as good as it was after running in. Was also thinking on doing new seals for the same reasons.

Did it start to smoke again immediatly after new seals ?

I would bet guides.

Carnut1 wrote:I would bet guides.

Care to explain ?

You can't rely on leakdown tests nor can you rely on compression tests.
You learn this when you pass the tests, pull it apart to find broken ringlands.

Very common with turbo engines.

joe 90 wrote:You can't rely on leakdown tests nor can you rely on compression tests.
You learn this when you pass the tests, pull it apart to find broken ringlands.

Very common with turbo engines.

This is not a turbo engine.

Belgian1979 wrote:

Carnut1 wrote:I would bet guides.

Care to explain ?

On an engine that the valve stem is bathed in oil or submerged when the throttle is leaned on the change in vacuum pulls oil past the loose guides.

Do the rocker studs go into the intake port?

Belgian1979 wrote:

joe 90 wrote:You can't rely on leakdown tests nor can you rely on compression tests.
You learn this when you pass the tests, pull it apart to find broken ringlands.

Very common with turbo engines.

This is not a turbo engine.

I know it's not a turbo engine but it doesn't affect the fact that those tests are unreliable.

Taking a look at the plugs tells you more.
Nobody has suggested it yet?
You can't do either test without pulling the plugs and you don't even take a look at them?


You haven't done anything yet?
You're just asking.

I don't know if it's guides ect..... but I do see what is common between these comments.

With no LOAD, the ring tension itself, and mainly the second ring is doing the oil control.
If the second ring is overly worn, worn barrel face, or lost tension, for whatever reason, you could get a situation like that.
Good compression, leak down test OK.. but eats oil anyhow.

496blaze wrote:Do the rocker studs go into the intake port?

Yes, but they have silicone on them

Carnut1 wrote:

Belgian1979 wrote:

Carnut1 wrote:I would bet guides.

Care to explain ?

On an engine that the valve stem is bathed in oil or submerged when the throttle is leaned on the change in vacuum pulls oil past the loose guides.

I understand that but right now I cannot conclude to a loose guide. I remember they were within tolerance when built.
Any check that can be done with the heads on ?

It could be valve stem seals, valve guides or a leaky inlet manifold gasket allowing oil to be sucked into the port. I would try checking the tension on the inlet manifold bolts first. What type of valve stem seal do you have? Viton seals are the better ones. Teflon seals don't stop the port from becoming wet. 'o' ring seals as in factory seals on SBC are pretty useless on a performance engine. Silicone on rocker studs does not seal the threads. Try using Loctite on the threads going in the head.

modok wrote:I don't know if it's guides ect..... but I do see what is common between these comments.

With no LOAD, the ring tension itself, and mainly the second ring is doing the oil control.
If the second ring is overly worn, worn barrel face, or lost tension, for whatever reason, you could get a situation like that.
Good compression, leak down test OK.. but eats oil anyhow.

In that situation there is still the first ring to prevent the oil from going up imo