Why am I getting an oil leak there?

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#1 Post by **Umquat** » Wed Mar 12, 2008 4:03 am

I may have mentioned this before but recently I\'ve got a little more concerned about whats going on. Ever since the first month of ownership (about a year ago), I\'ve noticed what appears to be a small weep of oil between the block and head from about number 3 backwards. After a decent run, there would be a thin sheen of oil running back towards number 6. Today after a 40 mile round trip I got back to find that there was a more noticable sheen of oil, which on arrival at around number 6 cylinder then dribbled down the side of the block. I recently have also seen what I think is a compression ratio drop across the board of about 10-15psi (at least since the last time I did a compression test anyway). What I cant figure out is this. The oil leaks on the side of the engine where the push rods come up. The engine still seems to be in reasonable rude health. I managed a comfortable if slightly vibrational (wheels need balancing) 80mph most of the way there, and back, and once home the engine ticked over smoothly and didnt run on when I turned the ignition off. It maintains good temperature with the needle sitting right in the middle of the gauge. The water hasnt needed topping up since I replaced the radiator and all the hoses and it is completely clean (ie no mayonaise) I\'m still concerned however that possibly the head isnt sitting right (maybe as a result of the over heat that occured when the radiator leaked). However I would\'ve thought that I was more likely to be loosing coolant rather than forcing oil out Besides I can\'t exactly see why oil would be being forced out from this location anyway. I am considering removing the head anyway to check on the general state of the internals, but I\'d like any advice as to what could be causing this somewhat perplexing and worrying problem. Regards Gavin P.S. If I can get a decent camera shot I\'ll post some images of the problem <edited><editID>Umquat</editID><editDate>39518.9618171296</editDate></edited>

#2 Post by **Alec** » Wed Mar 12, 2008 12:49 pm

Hello Gavin, there is no real pressure at that part of the engine apart from the drilling that takes the oil to the rocker gear. It might be an idea to check the head torque, nothing to lose by doing it, and also check the rocker assembly to ensure that the oil way is clear. Alec

#3 Post by **David Withers** » Wed Mar 12, 2008 1:26 pm

Gavin, are you sure the oil isn\'t leaking from the cylinder head cover joint at the rear of the engine, out of sight, then running down and forward?  You wouldn\'t expect the oil to run in this direction but I feel sure I recall an instance of it happening.

#4 Post by **Umquat** » Wed Mar 12, 2008 1:56 pm

Right. If the weather holds I\'ll try and check the cylinder head bolts at the weekend. I seem to recall that I need to remove the rocker gear to check the ones down the nearside of the engine, so I\'ll check the oil ways at the same time. Regarding the rocker cover joint, I have a solid alloy rocker cover, which I replaced for that very reason - it actually leaked from all directions! The gasket on that is clean. I can imagine however that it could leak forward as you say so I\'ll check this. Incidentally I have noticed on a high speed runs that I get a small amount of oil expelled from the vent hole in the top of the alloy rocker cover cap, which then trickles down the fins on the rocker cover and to the back of the engine. Its not excessive - more annoying really as its the only proper shiny bit under the bonnet <img> Best Regards Gavin

#5 Post by **Mike Stevens** » Wed Mar 12, 2008 6:47 pm

Hi Gavin,
There is naturally oil \'mist\' in the engine while running.  With the standard rocker cover, and depending on model, this is normally vented back into the inlet manifold.  Does your super-super rocker cover vent in the same way, or just through the cap?
Your oil leak.  Assuming the engine isn\'t pumping oil (you\'d know \'cos the plugs would foul up), the only high pressure oil feed to the head is via the hole at the back to supply the rocker shaft.  (OR, via an external feed pipe whether you like them or not!)  This oil drains back down the holes adjacent to the push rods, (and lubricates the tappet blocks on the way).  This is where your oil leak is and by the sound of it, it is not a pressure leak.  It is possible that in the past the head has been removed, and knowing how difficult these can be, maybe something was forced in the joint there to free the head.  In that location, it wouldn\'t damage the fire-rings around the bores, but could leave some score marks on either head or block where the gasket is and where the oil drains down.
The oil obviously then works it way backwards \'cos a) it\'s hot and b) it\'s blown back by fan and forward motion, (especially at 80 MPH!).
As you know exactly where the leak starts, it may be possible to see a gap above/below the gasket at that point.  A small dental type mirror may help with that.  If you can see something, you may be able to clean up the area and seal it with something.  Not a permanent fix I know, but might give some more clues.
I hope this gives you something to think about!
Cheers,
Mike.

#6 Post by **Umquat** » Wed Mar 12, 2008 7:04 pm

The rocker cover on my car has a breather pipe like the conventional one. At one stage I had it connected back to the carbs as with the standard setup, but as with the original rocker cover it didnt run particularly well, so in the end I connected the carbs together and vented the rocker cover to atmosphere. I seem to recall that I still got a small amount of seepage even when the breather pipes were connected up. The only thing I get out of the breather pipe now as a rule is a small amount of moisture after startup. The plugs are a decent colour with no oil fouling. I think this is the first classic I\'ve owned where the plugs are actually the colour recommended in the back of the Haynes! Cores have a slightly red tinge, but that\'s the colour of my fuel additive! As I\'ve got a spare engine on the way, I might whip the head off that, get it cleaned, crack tested, skimmed and rebuilt, then drop it on the current block. In the mean time I\'ll check the head torque settings and make sure that none of the upper oilways are blocked. Regards Gavin 
<edited><editID>Umquat</editID><editDate>39519.5906134259</editDate></edited>

mikeyb · #7 Post by **mikeyb** » Thu Mar 13, 2008 2:39 am

Hi Gavin,
My 2500s is doing the same thing with oil leaking apparently from around numer 3 backwards. I had thought perhaps the head gasket was blowing oil out but I cant find any of the usual symptoms, still runs perfect!
I do have the external feed to the head, which I have yet to fully investigate, and decide whether to keep or not.
It could be its weeping from there, and running forward as david suggests, although I like the idea of checking the torque just to make sure, and cleaning the oilways.
Mike

#8 Post by **Umquat** » Thu Mar 13, 2008 3:50 am

Well I\'m glad I\'m not the only one with this problem.. If you discover why its happening before I do let us know.... and vice versa Regards Gavin

#9 Post by **David Withers** » Thu Mar 13, 2008 2:55 pm

Gavin,
I wonder if the change you have made to the breather system is leading to a slightly positive pressure in the top cover (from piston blowby) instead of a slightly negative one as I think you\'d have with the standard system connected to the engine intake.  If so, this supports my thought that oil may be seeping past the cover joint at the back (i.e. low) end.

#10 Post by **Umquat** » Thu Mar 13, 2008 3:11 pm

Its possible Dizzy, but I would\'ve thought that there was sufficient
breathing of the rocker cover to stop any pressure build up. Certainly
if I rev the engine, I dont feel a massive amount of positive venting
from the pipe to atmosphere, and as a result I would\'nt have thought
there would be any significant pressure at the join between the head
and block. 
 
Anyway its one more course of action I can check. First things first, get those head bolts checked. 
 
Automotive mind is else where today.... Wifes eurobox has gone in for
its MOT, and I\'m a little concerned its gonna fail on a couple of
points. Might have to devote some time to that instead. 

 

Regards 

 

Gavin