|
|
Post by tommydp on Jul 4, 2013 11:37:38 GMT
Ok, I know I've been into the engine breathing system before but.. My white one has done almost 200 000 kms and the engine is 100% original. It has never been rebuilt. It uses quite a bit of oil, no surprise really. As mentioned before it runs really well. Pulls like a train and even idles smoothly  I've driven behind it myself, and there are no clouds of blue smoke or nasty smells. This is an "everyday car", so i'm planning to drive it as is until a rebuild is really needed. When the engine is fully warm there is some metallic rattling, which I suspect is due to bearing wear. At least the noise is the same as when starting from cold until the oil light goes out. I have cleaned the strainer and pick up btw. Oil pressure is within specifitations. Anyway, until the engine really needs a rebuild (I once drove a mk 1 for 30 000 kms with the same noise, only much worse) I'm looking into ways to get the oil consumption down. It seems some oil finds its way through the PCV valve too. There is steel mesh inside the tappet cover "can" and you can blow through it easily, no restriction at all. there is always some oil in the PCV valve. I don't recall this on earlier 1800s, except the blue one of course which has had all the problems possible... Question is: How on earth can oil through the PCV valve be avoided when there is full manifold vacuum suction through it at idle, and I suppose other conditions too, as trailing throttle?? Or is something wrong with the valve? Another thing that points to oil being sucked through the PCV valve is that the two middle cylinders have more oil in them than the two outer, after idling. Yes oil, not fuel. As we know, the valve is in the middle of the manifold, closest to cylinders 2 and 3. OK, no intention of another lengthy thread as the car runs like a dream! I just wonder if the PCV valve is supposed to pull full manifold vacuum at idle. I'm thinking of fitting a catch tank between the tappet chest cover and PCV valve to monitor the situation.. Any experiences with this? Regards, Tommy |
|
|
|
Post by dave1800 on Jul 4, 2013 13:06:14 GMT
Hi Tommy I understand that the later systems that did away with the PCV and fed through the carb which exerted a reasonably constant vacuum (depression) vastly improved oil consumption problems. However, from past experiences I guess you probably won't want to swap carbs etc as the car is running well. At idle and under light load when the manifold vacuum is at its highest (and trailing throttle) the PCV should be fully closed. If it wasn't it would weaken the mixture. As you open the throttle this weakening effect is proportionately much less so not an issue. I think what you are seeing is at higher engine rpm you are getting positive crankcase pressure from ring blow by and this is forcing the oil via the PCV into the inlet manifold and burning it. Oil in the PCV is unfortunately quite common on older engines. Maybe you could build a trap so the oil runs back into the engine? Regards David Question is: How on earth can oil through the PCV valve be avoided when there is full manifold vacuum suction through it at idle, and I suppose other conditions too, as trailing throttle?? Or is something wrong with the valve? Another thing that points to oil being sucked through the PCV valve is that the two middle cylinders have more oil in them than the two outer, after idling. Yes oil, not fuel. As we know, the valve is in the middle of the manifold, closest to cylinders 2 and 3. OK, no intention of another lengthy thread as the car runs like a dream! I just wonder if the PCV valve is supposed to pull full manifold vacuum at idle. I'm thinking of fitting a catch tank between the tappet chest cover and PCV valve to monitor the situation.. Any experiences with this? Regards, Tommy |
|
|
|
Post by tommydp on Jul 4, 2013 13:35:15 GMT
Ok. If I understand you correctly, there is something wrong then. When idling, if I remove the hose at the tappet chest cover/ can there is full vacuum there, ie suction through the PCV valve at idle. your finger will be stuck when blocking the hose.
If the valve is supposed to be closed at idle I guess there would be no suction through this hose when idling?
Perhaps this is why I never get the lifting pin test right, and always fint the middle plugs lighter when they should be darker? Perhaps it's down to the diaphragms I've got through ebay (for Minis). They appear thinner and more fragile than the original stuff I had in the "old days"?
Just some thoughts..
Obviously, there is some oil getting past the piston rings too, however I find this suction through the valve strange. As you say, it runs great so I'm not touching anything:-)
Regards, T
|
|
|
|
Post by threelitre on Jul 4, 2013 14:02:37 GMT
Tommy,
I don't know the details, but the diaphragm and spring loaded valve in there are supposed to meter the flow, so that not too much is fed through the inlet manifold. I remember it was never fully closed, so a vacuum would be found if you close the pipe with your finger. I had two cases of a leaking diaphragm and there was always some suction (and wrong air) at idle. But the valve should open and close, so that a certain amount of flow is achieved. It may be worth checking if it is clean, seating well and the diaphragm is in good condition. The amount of oil surely relates to the wear in your engine. Can you feel some (pulsating) pressure from the venting hose (at the engine end) when disconntected?
Regards,
Alexander
|
|
|
|
Post by dave1800 on Jul 5, 2013 0:01:01 GMT
Try connecting your vacuum gauge and taking some readings of the manifold pressure either side of the valve. As Alexander has noted there will be some vacuum at idle as you won't get a perfect seal of the valve but it should be minimal or the mixture setting will be wrong. regards David Ok. If I understand you correctly, there is something wrong then. When idling, if I remove the hose at the tappet chest cover/ can there is full vacuum there, ie suction through the PCV valve at idle. your finger will be stuck when blocking the hose. If the valve is supposed to be closed at idle I guess there would be no suction through this hose when idling? Regards, T |
|
|
|
Post by threelitre on Jul 5, 2013 7:36:05 GMT
Notice to Tommy: When you use your gauge, take care that all other hoses are connected as they should be. If you just plug the vac-gauge into the engine-side of the valve, you'll just read the same vacuum as is in the manifold. To take a useful measurement, the vacuum gauge needs to be inserted into the hose using a t-connector. When you block the hose to the engine (as with the finger), there will always be full vacuum, as there is no flow!
But I doubt that actually something is wrong, as in this case you'd notice the engine running weak (i.e. bad) at idle.
Regards,
Alexander
|
|
|
|
Post by tommydp on Jul 5, 2013 8:51:32 GMT
Thank you David and Alexander!
I'll have a go with the vacuum gauge later. Seems like the valve is OK then. After all the idle rises and gets more rough when I open the oil filler cap, which "the books" state is an indication of the valve working as it should.
Regards, T
|
|
|
|
Post by dave1800 on Jul 6, 2013 2:19:57 GMT
If you read the various MGB forums it would appear that the later system venting through the carb improves high oil consumption and has no moving parts. I recall one individual wrote that he had made a large oil trap and poured it back into the engine at the end of a long run! You say the idle rises and gets more rough when you open the filler cap so it does seem to be working. Not sure whether it should get more rough though, but if it is then taking in oil perhaps this is the reason. Now if you get the blue car running properly you can overhaul this engine  Regards David Thank you David and Alexander! I'll have a go with the vacuum gauge later. Seems like the valve is OK then. After all the idle rises and gets more rough when I open the oil filler cap, which "the books" state is an indication of the valve working as it should. Regards, T |
|
|
|
Post by tommydp on Jul 6, 2013 6:50:21 GMT
If i set the mixture richer it will rise and run smoothly when I open the oil filler cap. Otherwise, the mixture seems fine, though I'm not able to judge by the lifting pin on this one either.. It always seems to weak.
I will rebuild this engine once, on my own. Apart from the rattling noise this seems to be a very good engine.
|
|
|
|
Post by dave1800 on Jul 6, 2013 9:13:19 GMT
If the mini diaphragms are weaker that would tend to restrict the flow of crankcase at high vacuum as the valve would in theory close more easily. Try making the car run smoothly when you open the filler cap by richening the mixture. If you record the number of flats you can always reset it. I would always go on the slightly rich rather than weak setting if there is uncertainty. If you've not already seen this article it describes the PCV and crankcase breathers quite well and flags up the issues. HERE Now we have some new members, perhaps some of them can throw light on your blue car problems? Regards David If i set the mixture richer it will rise and run smoothly when I open the oil filler cap. Otherwise, the mixture seems fine, though I'm not able to judge by the lifting pin on this one either.. It always seems to weak. I will rebuild this engine once, on my own. Apart from the rattling noise this seems to be a very good engine. |
|
|
|
Post by dave1800 on Feb 20, 2015 3:34:52 GMT
There are numerous reports on the internet about problems with direct injection on petrol (gasoline) engines with build up of carbon deposits on the inlet valves. There are numerous reasons being quoted but the one that seems most logical to me is that that there is no longer any fuel to wash off the oil on the back of the valve that emanates from the crankcase ventilation system and leakage via inlet valve oil seals. Apparently some engines are requiring expensive head restoration after relatively low mileages as everything is so crtical nowadays there is little tolerance to issues like this and it is sufficient to put some engines in limp home mode sometimes without warning when drivers are in tricky overtaking situations, if the anecdotes are to be believed. It seems that this is not a big issue on diesel engines that have had direct injection for many years. I recall that every 1800 cylinder head I have removed revealed quite substantial build up of burnt carbon on the back of the inlet valves probably from poor valve stem seals and fouling from the crankcase breather system. This had little impact on the "wonderful" performance. Looking at the Mk1/Mk11 engines the PCV is situated on the inlet manifold closer to cylinders 1-2 so I wonder if these inlet valves suffer more than 3-4? Later cars did away with the PCV and vented into a constant depression take off from the carb so should provide a more even spread of oil on the stems, and maybe foul up the carb in the process! Maybe if anyone has an engine apart it would be worth having a quick look. I guess Tommy is the best person to ask if he is not too snowed in and it is his thread. regards David |
|
I've driven behind it myself, and there are no clouds of blue smoke or nasty smells.
