Diesel engine knowledge

[sv.antea]

I have replaced all the gaskets and seals on friends low hour Perkins 4-108, including installing a snake oil rear oil seal (two pieces of teflon and graphite impregnated rope purchased online for $120). I am experienced mechanic and tend to work meticulously. I am very embarassed, that despite my efforts the engine started leaking right away again, from several locations. I may not have used the best (only the most expensive) gasket sealant, but that is another story.
Now I know Perkins is notoriously difficult to keep from leaking oil. From the start I intended to soup up the marginal existing PCV (Positive Crancase Ventilation) system. Just have't got to it yet. I am hoping, that reducing the crankcase pressure (created by piston blow by), oil would be discouraged from escaping.
Two ways to go about it. The simple one may be to make positive connection (hose) between the crancase space and intake manifold and then install a filter instead of the existing screen/mashroom. The resistance of the real filter (like the washable kind from auto supply stores) could create enough suction to keep the crancase below ambient pressure. (I have done that with some success on my boat's Universal M-25)
The fancier solution would be to make and install a veturi between the manifold and the filter and so increasing the suck.
Now, the question is: How sensitive is a diesel engine to resistance in the intake? If it is not, the right amount of suction can be gotten by some kind of adjustable throttle. Any suggestions, comments from the diesel experts?

[DeepFrz]

I have heard on here that the Walker Air Sep works well with the 4-108. Helps keep the engine room clean.

[sv.antea]

Thanks, DeepFrz, I'll google that. It may answer my questions.

[sailorchic34]

I know the yanmar gm's has a restriction on the connection to the intake manifold. If perkins has the same thing, drilling it out a just a bit will provide more savaging without dinking with the intake.

I had oil leaking from my yanmar two years ago, caused by broken rings on one piston. I drilled out the restriction on the breather and that helped with the oil leak till I took the engine apart.

If there is enough pressure leaking by the rings, you can pull the oil fill cap off while the engine is idling. If there is smoke coming out the oil fill or pressure releasing when the cap is removed, then there is high blowby. A tight engine will have no smoke and no real pressure in the crankcase at idle (with the oil fill cap off).

[sv.antea]

Thanks Sailorchic34, here's what evolved over several decades on my boat (see picture), though for different reason. The brand new Universal M-25 had these pinging hickups at idle when I first started it. Turned out that the PCV hose was occasionally delivering drops of lube oil into the intake, which caused the sporadic pinging. When I disconnected the PCV hose, the pinging stopped. Than I thought an real air filter would be a good idea, just look at the fazzoo accumulated on it. So I run the crankcase blowby through air/oil separator (the little fiberglass cannister aft of the valve cover has copper wool in it, the hose from the valve cover is connected to the bottom, the intake T to the top. It is probably reducing the crankcase pressu as well. The fiberglass tube from the filter to the manifold is just a straight tube, no venturi. But a venturi there would probably lower the crankcase pressure further.
The Perkins may need a little more agressive PCV. The question is, is it worth the experiment to build the venturi, or would it work to simply put some kind of restriction between the filter and the point where the PCV connects to the intake.

[sv.antea]

Try and try again

[sailorchic34]

Ah, the original intent of the PCV, positive crankcase ventilation valve was to make the crankcase have a bit of back pressure to prevent outside dust and dirt from being sucked into the crankcase breather. back in the pre PCV days it was just a u- tube pointing down to the road on cars.

Your system is actually very nice and a step up from a PCV valve.

Now my engine two years ago had an issue where oil was leaking from around the valve cover bolts. That was my oh ^&**( moment. My problem was that all the rings on one piston were broken. The engine was hard to start, but once it ran it seemed to run fine. Then it started leaking oil out from odd places.

Really your system is about as good as it gets for a diesel. There just is not enough manifold vacuum on a diesel. So a venturi is not going to get you there. You don't want to mess with a throttle/damper on the inlet as that's going to effect combustion.

I assume you've cleaned out the catchment tank copper wool between the valve cover and intake, of any oil in it.

Exactly where is the oil leaking from. Does the engine start easy?

[donradcliffe]

The classic leak locations on a 4108 are the rear seal, front seal, and the pan gasket. They may also leak from the valve cover gasket, but that's too easy to fix to mention.

[model 10]

I believe the air oil seperator mentioned does not decrease blowby or crankcase pressure. What it does is recycle the oil back into the crankcase. I think the best you can hope for is almost no crankcase pressure, not a low pressure.
I would be curious where these leaks are, what kind of sealant you used and does the "snake oil " rear seal leak?

[sv.antea]

SailorChic, you are right of course, diesel would be sensitive to intake manifold pressure, and I do remember the pipes dangling under the car, spewing nasty fumes. And yes, the diesel was leaking from the rear oil seal, and every other possible joint. It is little better now, just the rear seal, the timing cover and a bit from the water pump">raw water pump. The blowby doesn't seem bad, starts beautifully, sounds good but leaks. I am embarrased to say, it's been a while since I was routinelly rebuilding engines, so figuring some new snake oil gasket cement was worth if. I bought this expensive red stuff at a local auto store. Didn't read the directions. How hard it is to use gasket cement?
Well, as we were waiting for some parts, the assembly of the engine was taking some time and to my consternation, the gasket cement seem to be running out of the joints. Now I read the directions and there I found that it is a two part system, you are supposed to paint the components with a hardener and then apply the red cement and assemble. I ran off to the autoparts store, but they didn't have it, said they didn't carry it and it had to be special orderd. But they assured me, that it works without the hardener, that they use it on their race car. Oy. So the rest of the engine was assembled using the hardener, but the crucial parts around the pan and seal were already assembled, flywheel and transmission on. Now I will have to take the engine appart again. But this time I want address the crankcase pressure. When it comes to 4-108 leaks, every bit helps.

[Allan S]

Following.

[sv.antea]

Thanks Guy, as you see in my first picture, I have built such an air/oil separator for my Universal M-25. It works well. What harm do you figure slight negative pressure, if it in fact can be achieved over wide range of speeds and loads, could do?

[model 10]

Originally Posted by sv.antea

What harm do you figure slight negative pressure, if it in fact can be achieved over wide range of speeds and loads, could do?

That's just it, I don't think you can get it (low pressure.) You probably could get 0 pressure at idle if the engine is in good shape but there is going to be blow-by at power unless you did an amazing ovhl. If I read your post right, you only re-sealed the engine. So if you have blow by, let it blow into the intake like Perkins designed it.
Gasket sealant with a hardner? That is pretty cool. Many helicopter transmissions are sealed from the outside with a sealant like that. It works. However you put it on the outside because you would never get it apart again if you used it on the mating surfaces.
Anaerobic sealant seems to be most favored these days, looks like Lock Tite but it does not dry completely. I've used it on both gaskets and metal to metal and it comes apart very nicely.

[sv.antea]

Ah, yes, thanks Guy, that was what they called that red snake oil. Anaerobic sealant. And the product on the shelf doesn't say you need the primer/hardener part, and in fact they didn't have it in stock. I only found out about it when I read the fine print. I call it snake oil, but it was made by reputable company and it was recommended to me. Just not sure what the deal is with the primer, hardener or catalyst, forgot what they call it. If you were using it, I take it there was no hardener with it?
Back to the venturi. It should create drop in pressure at the tap point, in fact proportionate to the RPM, without creating appreciable drop in pressure at the manifold. I had no luck finding formulas for puting some numbers on that phenomenon. Hence my question.

[model 10]

The primer for that stuff is like perfume for a pig so not having any was not the problem.
I think you are barking up a tree with the pcv idea. You go ahead and persue that idea and some other guy is making a real seal that does not leak, between the 2 of you the Perkins will be a modern wonder.