Smoke on Deceleration

[K Sykes]

I have a 3.0 stock engine that was rebuilt about 30k miles ago. I recently noticed that i can get oil smoke on deceleration - highway speed, downhill, in gear with a big puff when I open the throttle a bit. Don't see smoke on startup or acceleration. This sounds like classic valve guide wear to me, but I am confused given the relatively recent rebuild. Couple of questions;
1. Is there any other possible explanation for the smoke? For example, could the oil tank ventilation behave that way? The oil is not overfilled, but I have converted to EFI,so not sure if the vent hose angle is exactly the same as stock and I do see a bunch of oil residue in the throttle body.
2. Is there any way to test the valve guide wear without pulling the heads?
3. If it is the guides, can I just send the heads out for new guides and a valve job and not worry about the rest of the motor? I realize that you can't be expected to diagnose my engine over the internet, but that's the path I am thinking if it's the guides.

I dumped a ton of money into the car on the rebuild, and I don't think I can justify spending much more but if it's just a matter of the heads, it seems like that could be done for around $1k if I take them off myself.

Any thoughts are welcome

[86911tlcab]

am no engine expert, but had a similar problem with lots of smoke on decel that various mechanics told me was likely due to sticky rings...i had one cylinder with near zero compression...good hunting...

[faverymi]

In my very, very limited experience what you described happened to me because of worn valve seals and/or guides.

Leak down and compression tests will get you more answers.

If in reality is seals and guides any machine shop should be able to do the job without a hassle and very affordable. If you are whiling to take the engine apart.

[matt demaria]

Smoke on decel is classic rings; smoke on accel is guides.

[KTL]

Oil residue in the throttle body is common because of how the oil tank is vented. The engine case vent hose provides positive pressure into the oil tank and that has to be relieved. So the other hose coming off the tank goes into the throttle body and the engine then sucks in that oily air.

If you overfill the tank, you'll know it. The engine will puke oil smoke like a fog machine....

[Lapkritis]

Originally Posted by matt demaria

Smoke on decel is classic rings; smoke on accel is guides.

backwards

[Steve@Rennsport]

Originally Posted by Lapkritis

backwards

Not always,...

The very first thing the OP should do is perform a leakdown test to record the numbers and observe/listen for any leakage from the valves and oil tank.

I've seen plenty of "rebuilt" engines that used a lot of oil due to poor ring sealing as well as improperly fitted guides.

One must determine where the problem is.

[Lapkritis]

Originally Posted by Steve@Rennsport

Not always,...

The very first thing the OP should do is perform a leakdown test to record the numbers and observe/listen for any leakage from the valves and oil tank.

I've seen plenty of "rebuilt" engines that used a lot of oil due to poor ring sealing as well as improperly fitted guides.

One must determine where the problem is.

Agreed as in not always but as far as classics go... vacuum in the intake on decel sucks hard on those stem seals.

-Andrew

[Aurel]

How was the engine broken in after rebuild? In order for the rings to seat properly, Wayne recommends high and low rpms, using the engine compression for deceleration will help the rings seal well in that situation. If the problem persists, maybe using a thicker oil would help.

[K Sykes]

Most of the way through dropping the engine. Leak down test once I get it on the stand.

[Ramathorn]

Hmmm is running overly rich a possibility i.e. 10-11 ish:1?

[K Sykes]

So engine is out and heat exchangers and intakes off so I can see the valves and guides, at least a little bit. Overall they look ok, nothing obviously grimy with carbon/oil etc. What does look off to me is #4, which is clean as a whistle, with a sheen of oil on it. the rest look more like the second picture, with a bit of carbon deposit on a slightly dirty looking valve. Is the #4 picture evidence of valve guide leakage?

#4 (noticed what looks like a crack on the aluminum snout in the pic, not a crack, wiped off with my finger)


#5 and the rest pretty much look like this, or have a bit more carbon particles.

[Lapkritis]

Wow, that's freakishly clean. Wondering if you're washing down the rings... that could cause cylinder wear.

[K Sykes]

It has an oily coating - if it's washing the cylinders, it with oil not gas - think it's the source of my smoke, but curious what others thought.

[K Sykes]

Originally Posted by Ramathorn

Hmmm is running overly rich a possibility i.e. 10-11 ish:1?

I don't think so - I run MS2 EFI with a wideband sensor, have a pretty good idea of my AFR's and when I'm getting smoke it's pretty lean ~ 15:1 or thereabouts.

[Lapkritis]

I would bypass the vent back to intake for the crankcase if your tb is oiling up. Clean as much oil out of the intake as you can and see if it persists. I wouldn't pull it out until I did the basic testing first. Full workup of leak down, compression for starters.

-Andrew

[K Sykes]

All good advice, but it's already on a stand. I am going to try to do a leakdown to see if rings or valves are an issue, but it will be cold, so mainly looking for differences from cylinder to cylinder. I don't think it's oil from the ventilation anymore. There wasn't that much and as you can see from the pics, the intake walls are spotless. I'm tempted to just pull the heads and get the guides replaced since I am so far into it already, but not keen on spending more $ on tools to handle getting the cams off and then back on and re-timed.

[K Sykes]

A bit more data. I have the heads off and while doing the teardown, did a leakdown after pulling the rockers. Short answer #2 and #5 were excellent (less than 5% cold), but the rest leaked like a sieve, but all through the exhaust valves. Half the plugs were fouled, half perfect, but unfortunately got scrambled by an errant elbow, so I don't know which is which. My plan at this point is to go ahead and get the heads cleaned up, valve guides replaced and what ever else is needed. Couple of questions;

• The piston tops are pretty carboned up, can I clean them without removing them from the Cylinders?
• Any way of evaluating the rings/cylinder condition wth the pistons in? (I am assuming it's better to leave well enough alone there - I had ~30k with no smoke so I am guessing they were seated ok after rebuild)
• Every thing else looks pretty good (camshafts, rocker arms, tensioners), any "must do's" given the heads are off and the chain covers are open?

There are a bunch of oil leaks I am going to try to cure. Rocker arm seals, torn cam o-ring, intermediate shaft gasket, maybe main seal under crankpulley. Anything else??

[KTL]

Fouled plugs can be indicative of the guides if they are oil fouled. Were the plugs oily?

Piston tops are just going to carbon up again. It reaches a point where it stabilizes and you're likely already there.

I'd leave the rings alone. But you can look at them rather easily by sliding the cylinders off. You simply have to use a good adjustable ring compressor on the pistons to reinstall the cylinders. And don't worry about the ring orientation. Simply rotate them to the typical spacing when installing new. They'll rotate themselves to whatever position they want as the engine runs.

A must do with the heads off is have the valve seats cut, if you're replacing any valves. You need to do this to ensure the valve seals well against the hardened seat ring in the head.

Those seals for the cam cover plate in the chain housing should be replaced. The paper one gets destroyed anyway, so that's a given. But reusing an old o-ring would be asking for a leak. If it was a relatively new ring, i'd not worry about reusing it.

IMO the crank seal is better left alone if it isn't leaking.

[K Sykes]

KTL - thanks for the response

The plugs were black and wet, so I assume oily. I am hoping it was guides as at this point I've done most of the work.... and I don't want to go down the re-ring path.

I am going to just replace all the seals I've opened up. I was just surprised by the cam o-ring, it should have been pretty obvious it wasn't in right when doing the rebuild.

I'm going to be taking the crank pulley off to install a trigger wheel in anticipation of doing an EDIS ignition since I already have MS2 doing the fuel, so I'll get a look and see if there's a leak there.

One thing that's really obvious with the engine on the stand is that I (and I am guessing a lot of other people) were blaming leaks on the case seal and lower valve covers when the source was much higher up on the engine. I can really see now how something like a rocker arm seal can travel down to the bottom of the engine and show up on the case seal or a valve cover nut...