SD 240 Engine: Oil Consumption, Valve Stem Seals

C

Carl Childers

New member
I have a Silver Diamond 240 engine in a 56 S120 truck that uses oil and smokes. A leak down test shows all cylinders are good and the motor sounds and runs strong. I have had other brand motors in the past that did this and replacing the umbrella seals on the valve stems fixed the problem. Looking at my shop manual it shows the valve train but no stem seals. I also have noticed stem seals listed for this motor on the aftermarket.

Did IHC use stem seals on this motor from the factory?

Is there maybe something else I am overlooking that may be causing the problem?

Any help or opinions on this would be appreciated.
 
I think umbrella seals used to come in the FelPro gasket sets, at least years ago. But I don't think the parts books show any stem seals as original equipment.

I suspect that a leak-down test wouldn't show anything for valve stem to guide wear. The leak-down testing has the piston at top dead center, with both valves closed. So as long as the valves are seated, the compression wouldn't be lost through the guides.
 
Thanks, it helps to have a second opinion and thinking about it the valve guide musts really be worn to let that much oil in. If the bottom end checks out then I need to decide if I want to spend the money on an automotive machine shop to go through the head or just swap the motor entirely for a good SD 220 that I have although I'd be giving up a few cubic inches if I do.
 
Or swap a used head in better shape and keep the 240. The other option, as long as it's running well, is to just keep it the way it is, do a little mosquito fogging, and add a little oil on occasion.
 
You mention leak down test (uses compressed air into the cylinder through the plug hole and indicates what % of the pressure is being lost). Can you describe the method you used to verify or measure compression.
only experienced mechanics actually use or true leak down testing.


Rule number one on intake valve guides being the cause of smoking or oil usage. Exhaust guides are seldom if ever the cause of oil usage. The oil is effectively sucked past the intake guide at high manifold vacuum conditions like idle, coasting, and cruise power settings. Under power and loaded conditions there is not enough vacuum to have a significant effect on oil usage.
older engine used crude oil control in the valve train. An oring to seal the spring retainer against the stem, usually had a second groove on the stem or like Paul mentioned, umbrella seals that slide on the valve stem and cover the top of the guide. neither of these methods will do any good if the oil drain back from the head area is bad and the guides are flooded with oil.

Smoking under power like a hill or long periods of high throttle, would likely be rings.

I'd go through some deep sleuthing of possible causes before pulling the preverbal trigger on any fixes.
 
Thank you for that detailed response. I am not a pro mechanic but I have been doing it as a hobby for over 40 years now. I'm not saying I'm great but I do have a grasp of the basics. A few years back I bought an actual leak down tester as I learned they are able to tell you a lot more than a compression tester will. I had very little leakage in any of the cylinders. Just to be thorough I did do a compression test too and got an average of 140 lbs. per cylinder which I felt was pretty good for an old motor of unknown mileage. No leakage past the rings or valves or leakage to adjacent cylinders made me think it must be valve guides.
It does seem to smoke its worst at idle. I am open to any suggestions you may have as to where to look or what to test next. Again thank you for your help.
 
Hi Chris,
I didn't intend to infer that you were not experienced but in the majority of situations that leak down testing is brought up by a form member, it is miss used for the standard methods. Im glad you know about that and it makes it easier to discuss things when there is a good knowledge base to begin with.

My recommendation is to remove the valve cover and verify that the oil drain back system is functioning as it should. Even consider running it while the valve train is exposed and watch oil movement drain back and over all amount reaching the valve guide areas. While I may not know the SD series of engines as well as others, they are very similar in design to many others of a similar vintage.

If you can not see an obvious cause, umbrella seals are an cheap and easy to install alternative. You can buy them based on valve stem diameter and OD as associated with valve spring ID. Remove the rocker assembly and use your leak down tester to pressurize each cylinder, remove the valve springs and install the seal, one by one.
 
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