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Christian S. Hansen
Experienced User
Username: enquiring_mind

Post Number: 39
Registered: 4-2015
Posted on Monday, 27 July, 2015 - 05:37 pm:   Edit PostDelete PostView Post/Check IP

1955 Silver Dawn SUJ128. Are there any tests to determine the more likely cause of oil consumption from, I am thinking, either inlet valve seals, or past the rings? Uses about one quart per 300-400 miles and under normal conditions I do not see smoke clouds in rear view mirror, however recently while letting warm engine idle for maybe 10 minutes while chatting with a pedestrian, and then upon pulling out into traffic again, to my concern I did notice a cloud of exhaust smoke and took mental note.

Then tonight while descending a hill, throttle closed, but at freeway speeds (50-60 mph) with a car following, I could clearly see my exhaust illuminated by that vehicle's headlights, and then as a test I accelerated and saw a larger cloud of smoke. Typically headlights of following cars show exhauast that is not so noticeable during daylight, and under these circumstances (throttle closed) I would imagine the suction of the engine to be pulling oil past the valve stems. Any thoughts to test the likely causes, and indeed both may be likely, but do I attribute that descending hill, throttle off exhaust condition, as valve seals?

In past with Jaguar XKE, I found their overhead valves and fibre seals to be susceptible to that exact scenario, that is, loading up via the throttle closed suction when going down hill, and then emitting a noticeable cloud upon acceleration at the bottom. Happened once with a motorcycle cop observing, and ending up chatting with the judge about it.

Any ideas on how to separate the two possible causes here?
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christopher carnley
Unregistered guest
Posted From: 86.181.212.64
Posted on Monday, 27 July, 2015 - 06:04 pm:   Edit PostDelete PostView Post/Check IP

Very likely the string seals are worn. There are service tools to permit the replacement without the removal of the cylinder head.
If the valve stems and guides are within normal wear tolerances, avoid the use of modern garter seals, Rolls-Royce had a lot of problems with seized valves and consequently damaged pistons, in later models.

(Message approved by david_gore)
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Christian S. Hansen
Experienced User
Username: enquiring_mind

Post Number: 40
Registered: 4-2015
Posted on Tuesday, 28 July, 2015 - 11:05 am:   Edit PostDelete PostView Post/Check IP

Christopher...
A couple of things to note;
1) Thanks for bringing that to my attention. I had forgotten. I have that tool for my 25/30. It fits thru spark plug opening with a curved end that keeps the valve from falling down? I wonder if it will also work on the Dawn head? That would be serendipity, eh?
2) Is there any test to verify which of the possible causes is the culprit, or is it SOP to simply replace the seals and see?
3) May I presume no hard feelings carried over from the past? OK?
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christopher carnley
Unregistered guest
Posted From: 86.181.211.235
Posted on Tuesday, 28 July, 2015 - 05:31 pm:   Edit PostDelete PostView Post/Check IP

No,1 Possibly.
No,2 Suck it and see.
No 3, Not sure about the (OK?),but I leave bitterness to other people.

(Message approved by david_gore)
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 342
Registered: 5-2015
Posted on Wednesday, 29 July, 2015 - 08:15 am:   Edit PostDelete PostView Post/Check IP

A method for holding valve shut while replacing valve guide seals all makes.

Rope. Remove spark plug wind piston down a bit. Thread rope into the cylinder. Wind piston up to keep both valves shut.

Whay hey.


To check the rings. With engine assembled. Take plugs out and fill cylinder with compressed air. 120 psi plenty. Listen at oil filler cap for rings. Exhaust for leaking exhaust valve and carby toot for inlet valve.

Make sure that oil drains from rocker box properly.

Exhaust valve seals are sometimes not used. Because its blow not suck.

Start up smoke is oil that has drained through the inlet and EXHAUST valve stems over night. Some of the valves will be open and the oil lies on the piston. The shut valves will also have oil behind them.

Not a lot of oil. Maybe an oil can squirt total but its surprising how such a small amount of oil can make that much smoke.

Modern seals with the spring and lip seal work well. But maybe a bit too well for this engine resulting in maybe seized valve stems.

Actually a USA quart for 300 to 400 miles isn't that bad for a 1950s engine.

Jaguar XK engines were about 1 pint Imperial 20 fluid ounces to 150 miles, before the factory considered that oil consumption was excessive.

Also one must also consider the seepage.( polite word for oil leaks)
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Christian S. Hansen
Experienced User
Username: enquiring_mind

Post Number: 41
Registered: 4-2015
Posted on Wednesday, 29 July, 2015 - 04:00 pm:   Edit PostDelete PostView Post/Check IP

Robert...
Thanks for the tips. I did not really think that the oil consumption rate was that bad, but it was the visible oily exhaust smoke developed in those limited certain circumstances that got me concerned since it creates "environmental bad vibes" from the other drivers, and adds to the argument that "those smokey old cars need to be banned". During daylight driving, and looking in the rearview mirrors from the driver's seat I never notice exhaust. I'm not sure what it looks like from the vantage of the other drivers, so until I start getting rude hand gestures and verbal threats to report me to the EPA folks, I suppose the issue is in the "still benign, but plan to get around to it someday" stage!
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 345
Registered: 5-2015
Posted on Thursday, 30 July, 2015 - 04:31 am:   Edit PostDelete PostView Post/Check IP

Is the exhaust tail pipe oily.
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Christian S. Hansen
Experienced User
Username: enquiring_mind

Post Number: 42
Registered: 4-2015
Posted on Thursday, 30 July, 2015 - 07:43 am:   Edit PostDelete PostView Post/Check IP

Robert...
Interesting observation. In past I have noticed that vehicles that are "smokers" tend to have dirty rear ends due to the backdrafts swirling and pulling the oily exhaust back onto the vehicle. I had observed over time, and when washing the vehicle, that the rear is absolutely clean and thus exhibiting none of those additional tell-tale signs of excessive exhaust. The insides of the exhaust pipe ends (dual exhaust) are slightly dry sooty, but not oily. When starting the vehicle in the morning and during initial idle, there is no excessive, or even noticeable, exhaust other than moisture due to condensation effect, like seeing your breath, on a chilly morning. Other than that, nothing untoward.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 348
Registered: 5-2015
Posted on Thursday, 30 July, 2015 - 08:41 am:   Edit PostDelete PostView Post/Check IP

Condensation makes oil smoke look worse.

Try this.

Run engine on idle. Then capture the exhaust gas in a black plastic dustbin liner.

Leave liner closed for 30 secs then open and look for damp. The damp is condensation and if smoke is left then thats oil smoke. Very unscientific but easy to do.

I used to do this to customers cars to show them that the smoke is actually steam. Or vica versa.

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