DB18 Crankcase Oil Leak

Post Reply
clevitt
Posts: 53
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

DB18 Crankcase Oil Leak

Post by clevitt » Sat Jun 09, 2018 9:43 pm

My DB18 has always had a small oil leak from the bottom of the bell housing, usually seen when parking after a run. This has recently worsened, and the engine required a 2 pint top up after a 50 mile run a fortnight ago.
I believe that the oil is leaking from the crankcase rear cover into the bell housing, Is there anything to be checked before resorting to engine dismantling for further investigation, and can anybody advise me how the cover seals the rear flange of the crankshaft?
Chris

qantasqf1
Posts: 82
Joined: Mon Mar 07, 2016 10:13 pm

Re: DB18 Crankcase Oil Leak

Post by qantasqf1 » Sun Jun 10, 2018 8:41 pm

Chris, 2 pints on a 50 mile run is a big leak! Are you certain the leak is from the rear main bearing because the seal must be very badly worn and usually they wear very little at all. If it is worn then some serious work needs to be done, I’m afraid. Sealing is effected by a machined thread that’s part of the crankshaft. The crests of the thread are machined back slightly to a given diameter and they run in a plate that’s bored at its centre to give a minimal running clearance. Any oil that tries to get past is ‘wound back’ so to speak, by the thread and returns to the sump. The plate is fastened to the rear of cylinder block by about 8 bolts (I can’t remember the exact number) and to access it the gearbox, bell housing and flywheel have to be removed. I know from your description it’s unlikely that the flywheel is leaking, but I would definitely check the FF oil level just in case because they are far more prone to oil loss. Checking the rear main bearing seal is a last resort! Maybe using a higher SAE engine oil would help.

Steve.

Soundmike
Posts: 26
Joined: Thu Mar 17, 2016 8:54 am

Re: DB18 Crankcase Oil Leak

Post by Soundmike » Sun Jun 10, 2018 9:35 pm

I guess if there is heaps of blowby creating crankcase pressure, the oil could be blown out! Rings/ major overhaul may be required......

Petelang
Posts: 176
Joined: Sat Feb 13, 2016 10:23 am
Location: Nottingham
Contact:

Re: DB18 Crankcase Oil Leak

Post by Petelang » Sun Jun 10, 2018 10:16 pm

Are you sure it's not overfilled? If the level is too high it will increase leakage. Maybe the wrong dipstick?
Peter
Peter Langridge
Cloud Nine Classic Weddings, Nottingham.

clevitt
Posts: 53
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

Re: DB18 Crankcase Oil Leak

Post by clevitt » Mon Jun 11, 2018 8:55 pm

Many thanks everybody: the oil is definitely from the engine as both gearbox and FF maintain their oil levels.
After a short run to bring the engine up to temperature, I can see a film of oil emerging from the offside bell housing cutout, and also feel some oil inside the other two cutouts. However, the problem is probably exacerbated by a leak from the rear of the rocker box and one from the where the oil feed pipe enters the cylinder head via a 90' elbow. So I need to address these two leaks first, by fitting a new rocker box gasket and resealing the elbow.
Has anybody managed to stop leaks from the rocker box, which the rearwards slope of the engine makes difficult ?
I also have to own up to changing from SAE 30 to 10W-30 at last year's oil change, so maybe I should revert.
Thank you Steve for the explanation: I do draw some comfort that should it be necessary, I can gain access to the rear cover with the engine in situ.
Chris

Db n j
Posts: 144
Joined: Sun Mar 13, 2016 8:55 am

Re: DB18 Crankcase Oil Leak

Post by Db n j » Sat Jun 16, 2018 7:57 pm

Chris,

Think you are on the right track in sorting out the 2 current leaks, as they could pool at the back of the engine / flywheel area.

Make sure the other outlets are also clean - petrol-pump, oil pressure sender, oil filter/block etc, and maybe even the coil clamp bolts ?

I had a worrying leak which was from the oil filter block, which tracked along the sump gasket and dropped from the bottom of the flywheel, and gave us the same worry that it was from the crank-seal.

Not an expert on oil, but the original is like treacle !

let us know the result.

clevitt
Posts: 53
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

Re: DB18 Crankcase Oil Leak

Post by clevitt » Tue Jul 10, 2018 10:17 pm

It is now 3 weeks since I fitted a new rocker box gasket, and can no longer feel a film of oil on the rear face of the cylinder head, so one source of the leak has been sorted. At the same time I resealed the elbow a second time with RTV (first time using Wellseal was unsuccessful), but I am still seeing some seepage from where the elbow mates with the cylinder head. Problem here is that with the elbow tight into the head, the downward part of the elbow points at 7 rather than the 6 o'clock that it is required to connect the feed pipe that runs vertically from the block.
I was hoping that some careful bending of the pipe would sort this, but the pipe seems to be made of steel rather than the expected copper.
At the same time, I am still seeing oil at the bottom of the bell housing, so I am now contemplating bringing forward the planned autumn oil change and reverting either to SAE 30 or possibly 20W/50. Hopefully this will reduce the leakage to a level that is acceptable for a 66 year old car.
I had an interesting email dialogue with the owner of a DB18 engined Dingo Scout Car, on which the lower circular bell housing hole is fitted with a threaded plug ( military spec? ). This causes any oil leaking into the bell housing to,pool in the bottom and then be dispersed as an oil mist through the oval cutouts after being picked up by the starter ring gear. I can see some oil on the chassis members around the fuel changeover valve and the battery carrier on my car to support his theory.
I didn't spot the leak from the oil pipe elbow until I removed the Bakelite cover over the spark plugs, so it is probably something that most engines experience and I should just live with?

Post Reply

Who is online

Users browsing this forum: No registered users and 3 guests