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MG TD TF 1500 - Pressurized rocker cover?

O.K. so this is my problem. According to local mg specialist when fitting the rear crank seal modification the engine in my 1250 TF appears to have had a major overhaul from crank up.( bought with no history) The bores viewed with my camera still have the bore marks indicating recent attention. Virtually no carbon deposit on the piston tops. The problem I'm having is that the "breather " pipe from the rocker cover to the front carb is sending a good deal of oil into the front carb air filter. So much so that after a shortish journey (10 miles) it's dripping from the bottom of the air filter cover. Carbs rebuilt and problem was noticed before doing so. Where would you start looking. I'm thinking a pressurized rocker cover but if so why? Any advice or help appreciated.
JK Mazgaj

Check that the tappet block cover has the correct casket with holes to allow the crankcase to vent.
Also,as you still have the honing marks still visible in the bores, you may have to run it in a bit to seat the rings.
Ray TF 2884
Ray Lee

I agree with Ray - I suspect the rings are not yet seated. Use a good procedure for breaking things in, and the seated rings should reduce the internal pressure.

Tom Lange
MGT Repair
t lange

It is nothing to do with pressurisation, it is oil splash. I had the same problem and put a kink in the copper pipe that sits between the two small rubber hoses so that any oil that gets in there runs back down. You can buy a small 15mm copper fitting from Screwfix that is used where domestic pipes cross over each other and this has the right sort of kink.

Jan T
J Targosz

I think that covers all the main causes. As long as the crankcase vent tube is open and working the vent tube to the front aircleaner is almost superfluous. I ran without one for the first 500miles - after that, little sign of oil at all.
Dave H
Dave Hill

Thanks for that Jan T however I don't understand the pipes you mean. The hose I'm referring to runs from the front offside of the tappet/rocker cover to the rear of the air filter on the front carb. As stated the oily liquid is dripping from the bottom of the air filter cover and when pulling off the pipe concerned has obviously had similar oily liquid.Not an enormous amount but enough obviously to result in discharge through the bonnet side fins and accumulating on the chassis below the carbs.
JK Mazgaj

I believe the original layout had two short lengths of hose with a section of rigid pipe between them rather than a single length of hose.
As I am almost to that stage of my rebuild I was considering using just a hose as the pipe is missing from the parts that came with my “kit”. Jan’s explanation has just persuaded me otherwise.
Chris
C I Twidle

Can anyone confirm this original layout to which Chris refers?
JK Mazgaj

On TFs originally, there is a metal pipe(slight crank in shape) to just miss the carb. bell. at the ends of which are short rubber pipes. The rubber piping connects the Rocker Cover and the Vokes Air Cleaner. The clips (4) used were Jubilee 'O' Size type which are very hard to obtain.

However,I don't think that explains your oil in air filter issues.

Cheers
Rob Grantham
Rob Grantham

Thank you Rob for that information. Thinking on have wondered whether it's a combination of things including the fact that the carb. obviously "sucks". I'm going to review all the suggestions including isolating the hose/pipe referred to to see exactly how much is being dispelled.
JK Mazgaj

The TD has a restrictor washer in the air filter/vent to prevent high oil consumption, see WSM plate A34.
I do not have the original vent pipe on my TF so do not know if they had the same.
Ray TF 2884
Ray Lee

The only way pressure could force oil out of the breather tube is if the level of the oil was higher than the tube hole. The same applies to carburettor suck. Run the engine without the connection to the air filter and you will find oil readily eascapes. I have a cork that I block the stub in the tappet cover with if I am tinkering with the carbs with the air cleaners off. There should be a small baffle inside the cover to prevent splash but it doesn't work too well.I attach a photo showing how I have angled the connector pipe up so oil can flow back into the engine and not into the carb.

Jan


J Targosz

Ray,

No restrictor washer in original TF vent pipe.

Cheers

Rob Grantham
Rob Grantham

Thanks again Jan. I've actually got some of those 15mm pipe bits left over from when I was building. Cars are much more fun-well sometimes. Always amazes me how what on the surface are minor changes in design seem to occur in classic cars as they develop.
JK Mazgaj

Here's mine. This is supposed to be as original even with Jubilee clips. The jubilee clips are new directly from them, but they haven't made them with the cheese head screws, as original, for some time now. If you have originals, save them!!

PJ Jennings

There is an article somewhere that explains that when stationary this pipe 'relieves' pressure in the cover via the air cleaner but when the car is in motion the pipe on the Tappet chest cover, with its lower end in a low pressure area below the car, has a bigger effect on removing oily fumes to the road surface below. Not considered PC these days!
Chris
C I Twidle

I run pancake style air filters on my '53 TD and vent the rocker cover to the atmosphere through a small filter (see image attached). Is there any reason why I couldn't/shouldn't eliminate the filter and just run a tube from the rocker cover to the back of one of the pancake filters? If not, should I put some kind of restriction in the tube to prevent oil from being sucked out of the engine and into the combustion chambers?

Thanks.

Jud

J. K. Chapin

There is no significant suction in the air filters, unless you get very close to the venturi area.
Dave H
Dave Hill

This thread was discussed between 07/08/2018 and 12/08/2018

MG TD TF 1500 index

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