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Crankcase Breathers

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budk1953

budk1953

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I'm leaning over the fence with this since it involves a triumph engine. There was discussion in the spridget forum regarding performance upgrades and crankcase breathers so I'll just copy my post:
I've been reading these posts with great interest as my 79 midget seems to leak oil only when on the road (I can let it run for hours at an idle w/no leaks). I'm planning on changing suspect gaskets soon and this seems like a good idea. I've got a Weber and aluminum valve cover w/plugged holes. I know one hose should be installed in the valve cover but where should the second hose go? I've found a source with a good selection of crankcase breather filters (clamp, plug-in, threaded connection). Any suggestions?
 
[ QUOTE ]
You have a Triumph engine in a MG?

[/ QUOTE ]

Beginning with the 1975 model, the Midget used the Triumph 1500 engine from the Spitfire. Several "failed" during testing as outraged engineers at the factory fought the decision. Fact is, BL didn't have the money to engineer and certify two engines for the new emission standards, and the 1500 won out over the 1275.
 
Thanks Paul,

Don't tell JBird theres MG's running around on Spitfire engines, I learn something new every day. Usually on most vehicles the vent from the valve cover would be connected in some fashion to the back of the air filter housing(s) to be reprocessed through the carb(s)and back into the combustion chamber. I do not know exactly how that is accomplished on a 1500 engine though.
 
This sure sounds like a crankcase breathing issue. Cannot recall if that engine used a PCV valve, but it must breath some way.
 
Fix the venting system first. If that does not solve the problem look to the rings. If your piston compression rings are leaking you will have too much pressure in the crankcase and this will also cause oil leaks. I had a AH 3000 with this problem. I would recycle the oil from the catch can back into the engine a quart per day, only drove a few miles to and from work. After putting in new rings the problem was solved. WHen I worked for Fairfax County we had a 70's Ford police car that used 48 quarts a day, also hundreds of thousands of miles. This car was driven 24 hours a day. I fixed that one by putting to plates on a new car and giving it to the officers:smile:. They were not happy! The new car was a 383 Plymouth with 2 bbl carb and single exhaust. The old car had a NASCAR 428 engine with 4 bbl carb and dual exhaust.

Phil
 
Any gas engine requires some sort of ventilation. At least a small amount of gas will escape around the rings even if they are in good condition.
Now if the vent hole is plugged you are going to get high pressure in the crank case, and it will come out somewhere. Usually with some of your oil.
I am not exactly familiar with the American version of the engine however there are a couple of ways which the unwanted gas pressure can be relieved. Your engine probably had an PCV valve at some point which most likely was hooked up to the intake manifold.
When the carb and manifold were replaced, this was "lost"
Probably the best way to solve this would be to get a catch bottle and a breather.
Also, if it isn't leaking at idle, you may not need to replace the gaskets. I would get a breather first, and see if the leaks continue
Yisrael
 
My Spit has a breather hose from the valve cover to the air cleaner.
 

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I agree with Yisre.

If you have the port in the intake manifold I would install a PCV valve there and run a hose to the top of the valve cover. In a factory installation there is a baffle inside of the valve cover to block directly impinging oil from entering the hose. This is lsualy flipped off of the rockers. There is usually another hose that runs from the engine to the air filter. The air is drawn into the engine through the air filter and than sucked into the intake manifold to be burned. the PCV valve meters the air flow based on manifold vacuum.

Phil
 
With the breather/bottle set up you usually run a single line from the valve cover to the breather/bottle and the breather/bottle will have a filter cap on the top. You usally run a slightly larger line to the breather/bottle. The PCV set up does NOT reduce the power of the engine. I am planning on replacing the draft tube on my TR3 this winter with a PCV system.

Phil
 
Bud,

On the late federal Midgets, at least on my last one w/ the 1500, the stock valve cover vented through a hose to a fitting on the forward side of the ZS carb above the bypass valve. There was a plastic restrictor between the hose and carb fitting. Ideally, without excessive blow by, this arrangement should generate a slight vacuum within the crankcase, collect and burn crankcase fumes.

With no vent, you will get pressure in the crankcase potentially pushing oil out of your seals, dipstick tube, etc. I would consider taking a step back a few decades and installing a draft tube from the valve cover, simply venting overboard under the car. Without anything drawing fumes from the crankcase, air should never be sucked in this vent tube and I don't see a need for a filter, in fact it would probably get plugged with sludge, condensation, etc.

Good luck. W
 
There have been a couple of posts on negative crankcase pressure and the need to vent the engine. ISTR that the consensus was that a catch can setup is far from ideal and that the winner is a simple PCV system as on the TR4A.

The factory TR4A PCV uses a PCV valve between the side port on the valve cover and the vacuum port on the intake. The TR4A valve cover oil fill cap is not vented and the road draft hole is plugged.

This sets up a negative pressure on the engine crankcase so all blowby as well as normal gases are drawn from the engine, metered by the diaphram in the PCV, and sucked directly back in to the intake and reburned.

The later TR4 setup routed the valve cover gases through a flame trap (one way valve) and then pulled into the carbs off idle.

Early 4s shared the open system of the TR2-3B with the crankcase venting directly under the car through the road draft tube on the side of the engine.

The rule is that they have to breath.
 
This is the standard setup in post-75 Spitfires too, which use the same 1500 engine.


The valve cover vents to a carb connection that also serves as a purge vent for the charcoal (evap loss) cannister(s).
 
I checked out the engine and the only venting is thru the side of the valve cover to the weber carb set-up. All the emissions were unhooked by the PO. I did notice the last time I drove the car in addition to the oil leaks the dipstick was halfway out. I need more venting for sure. I can take one of the plugs out of cast aluminum valve cover and either do the breather set-up or just run a tube as suggested earlier. I did find a good canister if I go the breather way - a stainless steel bar mixer - if I change it later I can use it over. /ubbthreads/images/graemlins/thirsty.gif
Any additional comments are appreciated. Now I know where to get my 1500 engine questions answered.
 
Click on the attachment if you want to see one type of Midget crankcase ventilation.
 

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[ QUOTE ]
I checked out the engine and the only venting is thru the side of the valve cover to the weber carb set-up. All the emissions were unhooked by the PO. I did notice the last time I drove the car in addition to the oil leaks the dipstick was halfway out. I need more venting for sure.

[/ QUOTE ]

No I think you need to find out why you are getting so much pressure. The dipstick was probably blown out of place by the pressure.

1. find out if the vent is really connected, ie is there a plug in the cover? where is it venting to? the manifold side of the carb or the air filter? if you are conected to the filter side, and there a straight hose, there should be enough venting. If it is hooked up to the manifold side, there needs to be a valve there (the PCV) and possibly this is pluged up or broken. now since you have a non standard set up it is a bit hard to guess what may be there but if there is a pcv valve, it most likely will be a plasic bit conecting between the hose and the manifold.

2. if this is not the case, you have WAY to much gas being blown by, and you should find out why. But lets hope that #1 will solve the problem! Otherwise, I suggest that you bring it to a good competent mechanic and get them to check the blowby on all four cylinders and find out where the leakage is.
Yisrael
 
I think you are running a Weber DGV on that engine. Are you sure that the valve cover is being vacuumed by the Weber. I was not aware that the DGV had a vacuum port on it. It is possible that what you are hooked up to is nothing at all. Try pulling the valve cover end of the hose off and see if you feel any vacuum pressure with the engine running.

I vote for a simple draft tube hanging down beneath the engine. That way you accomplish two things, suck a small vacuum on your engine and rustproof the bottom of your car.
 
Bill, the car belongs to BudK, not to me /ubbthreads/images/graemlins/confused.gif
I also a somewhat confused as to exactly where and what is hooked up, which is why I suggested that he check exactly were the hose he says is there is conected to (on both ends!)

When I bought my Herald, it had a hose just hanging off of the valve cover. Considering the amount of work it took to clean the front end of the car, I really don't recomend that. An engine with a real draft tube also has a conection to the air filter to supply clean air to the crankcase.

Given that it is somewhat unlikely that the Weber setup has a port for a PCV, then if the valve cover is really hooked up, then most likely it is to the filter. But until Bud gives us a bit more info, we are all just guessing.
Yisrael
 
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