engine hiss, PVC on 1500 midget

[recordsj]

I have a 1500 mg midget with weber dgv carb.
I noticed that after I turn off the engine there is a hiss, I then noticed the sound was coming out of the dipstick (it was sucking air in). So I put some sealant in the dipstick cap to seal it up when it is in place. Is there any issues with doing this? Should this be sealed?

Should there be any engine breather?

I looked, but was wondering why does the 1500 not have a PCV system for the engine?

 

[jlaird]

Yep. got to have a breather.

What it really means is that valves and or rings need renewed.

It is time to rebuild the engine.

 

[recordsj]

so you are saying that if I remove the dipstick and put my finger over the hole and feel a vacuum, it means that the valves or rings need to be renewed?

I do have a connection between the valve cover and the carburator which has a check valve which provides a vacuum, I assume this is not the same thing?

 

[recordsj]

so where is the breather supposed to be? Is it the connection between the valve cover and the carburator?

 

[jlaird]

No not a rebuild with a vacume, the eng pushing air out, you said out, lol.

A vacume must be caused by smog stuff. Only reason I can think of and yes I think the dip stick is supose to have a sealing plug thing on it to prevent outside air comming in.

Yes your breather is the hose between the valve cover and the carb, not as falmilar with the 1500s but you prob have another breather as well.

Sounds to me like all is good but for the dip stick seal.

Come on 1500 guys, a little help here.

 

[vagt6]

Correct me if I'm wrong, O' ye 1275 gurus, but a (mostly stock) 1275 is supposed to have a bit of vacuum in the crank case in order to be happy.

The 1275 crank case should register about 3-7psi of vacuum (via a gauge tap in the side plate of the engine) with the engine running at idle. This should keep the oil in the crank where it belongs and not leaking out past the rear crank journal.

As for crankcase breathing issues on 1500s and other LBC engines: here's a link to Paul Tegler's site that's very helpful: https://www.teglerizer.com/triumphstuff/emissions/emissionsresearch.htm

Be sure to read the .pdf file on boat engine crankcase venting, very informative.

Anyone else??

 

[recordsj]

on the dipstick tube I feel a vacuum (not air being pushed out), would your diagnosis still be the same?

 

[vagt6]

on the dipstick tube I feel a vacuum (not air being pushed out), would your diagnosis still be the same?

I don't know. Maybe Hap or Jack or one of the Spridget gurus could answer that one. Sounds reasonable, but I don't want to assume.

Jack??? Hap??

 

[jcatnite]

A vacuum at the dipstick is ok bud. I am envious that your engine is that tight. I haven't run across a 1500 yet that didn't puff a bit from the dipstick. The check valve in the system holding the vacuum in the block. The hiss you hear is the air whistling past the dipstick once the noise of the engine is gone.
JC

 

[recordsj]

cool, thanks!

 

[recordsj]

should I seal the end of the dipstick then? I figure I would place some RTV silicon in the cap of the dipstick (let it cure first), so when I place the dipstick into the engine the cap would seal.

 

[jcatnite]

I would just get the little felt seal next time you are making a VB or Moss order but I wouldn't be too worried about it.
JC

 

[recordsj]

might be a stupid question, so if the engine wants to suck air in, where is the air going? I assume it would be going past the piston rings then out through the exaust pipe?

I have already placed some RTV silicon in the dipsick cap (but haven't driven the car yet), is there any problem in having a positive seal with the RTV sealant like this as opposed to a felt seal (which would filter air coming in). Or does the engine need to "breath" with the felt seal?

 

[jlaird]

Must be going out the engine vent system.

 

[recordsj]

what do you mean by engine vent system?
i have a 1500 midget

 

[jcatnite]

Well, you said that there was a hose running from the valve cover to a port on the carb. That is the beginnings of an engine vent system.
Every engine has some amount of leakage past the rings on the piston each compression event. You are having 16000 of those a minute at 4K rpm. These gases are pushed into the block by the pressure of combustion. These vapors are harmful to the oiling system and lead to oil breakdown and sludge buildup. What engine manufacturers have done for years is connect the block back to the intake where a vacuum exists. (this is the hose that runs from the valve cover to the carb) These vapors are recycled through the combustion cycle and hopefully the majority of them go out the tailpipe. Also, if you didn't have this system, pressure would build up in the crankcase and push oil out all the seals in the engine. You would have more drips on the concrete than pampers has diapers. So the air is going out the tailpipe. The RTV won't hurt anything but I doubt it will last. If you see it getting loose peel it off. You don't want that getting sucked into the engine where it can stop up the oil pump screen. If you really want to test the theory, pull the hose from the carb and plug the hole in the carb. Start the engine and let it idle. You should feel a slight pressure at the end that is attached to the valve cover. That is called blowby and possible some windage from the rotating bits inside. That pressure is what the vent system is trying to recover. The fact that everything connected gives you a vacuum at the dipstick is a bonus. You might be able to fiddle with orifice sizes to throttle back on the "engineered vacuum leak" we have discussed on this thread. Although, I bet there are other things your Midget needs that are a higher priority.
Sorry for the long post.
JC

 

[racingenglishcars]

On most American cars the vacuum supplied to the crankcase from the inlet manifold is reduced using a PCV valve. (positive crankcase ventilation) Manifold vacuum can be rather strong and could actually pull a seal in if not regulated somehow. The PCV valve also helps prevent an open air leak into the inlet manifold. I had once an old Datsun with the A15 engine and also an Opel Rekord. They just used a small vacuum hose from the manifold to the valve cover. Sometimes, especially with the PCV, crankcase breathing is helped by allowing fresh air into the valve cover or another place on the engine. This reduces crankcase vacuum, but allows good breathing.

4 cyl

8 cyl

 

[AweMan]

Actualy it is P.C.V. {Positive Crankcase Ventalation} It`s function is to evacuate fumes { both oil and fuel} from the crankcase and reburn it. The clear path for vacuume to be in the crankcase is via the oil drain back passages. To have a Negative Pressure { Vacuume } in the crankcase is normal! Yes you should do your best to seal the dipstick. There should be a P.C.V. valve inline on the hose that goes from the fuel intake system to the Valve Cover, {not sure if this hose is connected to the Valve Cover on an MG or not} Make sure this valve is free, {working properly}. It should rattle when you shake it.
People that remove these P.V.C. systems from thier engines create more problems that they ever solve eg. oil leaks.
You have vacuume in your crankcase so that suggests your P.V.C. system is in working order. The question is, is the P.C.V. Valve working properly? If not, it could create an excessive negative crankcase pressure eg. Stuck wide open. Stuck closed would create NO vacuume in the crankcase at all.
Hope this helps somewhat.

 

[jcatnite]

The 1500 doesn't us a PCV valve. It orignially used an orifice and a pressure balance between the block and the vapor collection canister. The cap on the valve cover isn't vented. The system probably worked when it was new but as the engines wore the increased blowby will overwhelm the system. Also people have trouble with the small lines stopping up and many remove as much of the emisions system as possible. The only place fresh air could get in would be through the seals (the rear is a scroll seal anyway). But I agree, that he has nothing to worry about given the current indications.
JC

 

[recordsj]

any idea if I should add a PVC valve to my engine then?

Also I noticed that from the previous owner they have disconnected the vapor canistor in the system, which I guess I should reconnect for possible other issues?

All I have connected between the valve cover port to the intake manifold (right below the carb) with a hose which looks like some kind of check valve inline on the hose....