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Engine oil drip through crankcase breather pipe

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After a complete rebuild, the engine in my TR3A drips oil ostensibly through the crank-case breather pipe. This happens apparently while driving and especially some minutes after stopping, making soon a small pool of oil under the breather outlet. A friend with another TR3 states that this was common in his car, until the oil level dropped to slightly above the minimum mark in the oil dipstick.


For me, it is difficult to understand how he oil finds its way from the crankcase up through the breather pipe, even in the case of some pressure build-up.


Do you have any experience with this situation? Can it be improved? I am reluctant to leave the engine dripping until the level drops, and especially to keep the level so close to the minimum.


Thanks for your comments.



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Hi Jesus,


I have not heard this to be a common problem, and I am surely not experincing this myself, driving a 59 TR3.


I would think that you have a stopped up crankcase breather system or excess crankcase pressure due to excessive blow-by at your rings.


You should be able to test it, the blow by (rings), by doing a dry and wet compression test.


If you do not know the procedure please refer to this link:




Good luck!




Edited by e_ingemann
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When running, there will be a cloud of oil mist in the crankcase and, with the pistons flying up and down and gas leakage past the piston rings, there is a sort of pumping action which results in some of the mist being blown into the breather where it can settle, either running back to the sump or, if it is beyond the elbow, to the ground.


To reduce this dripping, some people advise running the engine with the oil level slightly below the full mark on the dipstick - but it is important to check the oil level more frequently.


Engines which have just been re-built will tend to blow more until the piston rings have bedded-in.


If you are very concerned about the car marking its territory, the answer is to fit an oil catch tank.


Most of consider that with all the other oil drips from the TRs engine, gearbox and overdrive, the answer is drip trays &/or old newspapers or cardboard! Remember, oil on the underside should be considered as providing added protection against corrosion!


Ian Cornish

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Jesus, oil returning to the sump from the rockers and camshaft runs down the inside of the block and can seep out through the breather pipe entry hole. Leakage then drips down where it appears to be coming from the breather pipe.


This leak can be stopped by sealing the pipe into the block with polyurethane or similar.


Also check that the leak isn't coming from the fuel pump, which also shows near the breather pipe.





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Jesus - My neighbour rebuilt the engine for my 1958 TR3A in 1988. I gave him all the new parts. He put in a new matched set of pistons, rings and liners I had bought from Peter Hepworth in Yorkshire. This was the last new matched set he had with 1991 cc displacement. I did not watch ny neighbour re-build it because I was away on a business trip so I can't say for sure.


I had the dripping you describe, right from the first time we ran the engine. The engine ran fine but I cannot say if the liners had been honed. If they were not honed, then the new rings did not "bed in" as they should. I had to add a litre of 20W50 Castrol every 600 miles (900 km). I ran the car like this (it ran fine) for 94,000 miles and I always had what you describe.


I suspect that the liners may not have been honed before assembly and I was getting blow-by.


In 2007, I decided to re-do the engine and an engine rebuild shop told me I had been running the carbs too rich and this was washing the oil past the rings and that I needed a new set of rings. He honed the bores and checked everything dimensionally and everything was within tolerance. So I put it back together myself with new rings and bearing inserts.


I have driven 9.000 miles (15,000 km) since 2007 and I use Castrol 10W30 with no more dripping. I also rebuilt the carb throttle shafts and have adjusted them to get the correct air/fuel ratio.


Hope this helps.

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This used to be a problem on all the 4-cyl TR engines I've had, so that I couldn't tell how much was being blown out and how much burned. Eventually, I was told to only fill with oil to halfway between min and max mark. Problem solved and on my current engine, rebuilt 11,000 miles ago I think I've only added a couple of pints (apart from oil changes).

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Thank you for all the inputs.


The engine was completely refurbished and among other, got new pistons and liners. After receiving all the pieces from the machining shop, I assembled everything taking a lot of care with weights and dimensions. I think the liners were correctly honed (see pictures below) and the rings gaps were checked to be within tolerances.


The car has run less than 30 miles after rebuilding (engine less than one hour, probably), and I am using a specific running-in oil. Surely, I still need to drive the car longer to check other oil drips and eventual malfunctions.



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Jesus - Your cylinder liners seem to have been honed with the correct honing angle between 30 deg. and 45 deg. with the sloped criss-cross pattern we see. Many TR owners say that you must run in the engine at 2000 RPM for a certain time to bed in the rings to the liners. Or drive the car at 2000 RPM for the same length of time (I forget exactly) and this hopefully will solve your problem.


Check that the carbs are not set too rich.

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