MGTD Smoky Engine

[Candellara]

Chaps,

Advice required as a bit of head scratching going on.

A friend is rebuilding an MGTD and is having engine "issues"

Bottom end was rebuilt by a well established engine builder - crank, bearings, re-bored, new oversize pistons, rings etc. Head rebuilt by reknowned MG specialist - guides, seals, valves etc


Everything went together ok but, the engine is pretty smoky :-( On idle, it's ok but increase revs and lots of blue smoke. The engine is most smoky upon throttle depression or constant throttle opening at circa 3k revs.

We've checked compression and all is ok across all cylinders and there's no excess crankcase pressure etc.

Suspected stem oil seals so took head off and sent this back to specialist. They've looked at this and said all is ok - but they changed stem seals as a precaution


Is it a case of allowing this thing to run in as it was rebored with new pistons / rings? Oil is Classic 20/50 - should we change to a straight 30?

Any advice?

[classicaholic]

Are you sure its not running rich? what are the plugs like?

[Candellara]

classicaholic said:

Are you sure its not running rich? what are the plugs like?

That's a good call and it's something that I also suspect. Not knowing too much about SU's - is the mixture fairly easy to adjust on these carbs?

[Candellara]

OK, had a quick look at the mixture. Yep, running very rich and a huge improvement in the volume of smoke already

Also, rear main seal is very leaky (although new). I guess running straight 30 as opposed to 20/50 will help?

[paintman]

Worth a read:
http://www.britishclassicmotors.com/3301.html

[Candellara]

paintman said:

Worth a read:
http://www.britishclassicmotors.com/3301.html

Thanks - big help

The majority of the smoke has now gone :-)

Carbs still need setting up correctly as I think it's still too rich - but we're on the right track


Question though. There is a fair amount of oil being lost via the rear crank cork seal. Does this take a while to "swell" and therefore the oil drip from this seal gets better as time elapses?


We're thinking of changing the 20/50 oil to SAE30 - will this help?

[RayTay]

Fit electronic contactless ignition. The timing is always right with a big spark.

[davejf]

In theory it should expand and not leak as much but they are notorious for leaking. I’m surprised being recently rebuilt by the pros it wasn’t suggested to fit a Moss oil seal which is uprated and is supposed to be much better. Not sure how easy that is to fit now.
I’ve not looked at oil weights etc but I would stick with the 20/50. It’s what I use in mine and most cars that age will use it. Don’t know how the single weight oil compares but as I’ve not heard it used much I would expect it to be inferior in such an engine.

[Candellara]

davejf said:

In theory it should expand and not leak as much but they are notorious for leaking. I’m surprised being recently rebuilt by the pros it wasn’t suggested to fit a Moss oil seal which is uprated and is supposed to be much better. Not sure how easy that is to fit now.
I’ve not looked at oil weights etc but I would stick with the 20/50. It’s what I use in mine and most cars that age will use it. Don’t know how the single weight oil compares but as I’ve not heard it used much I would expect it to be inferior in such an engine.

It was a US import last year and it has a Chevrolet seal apparently but it still leaks quite heavily - certainly much more than my old E Type.

I wasn't involved with the rebuild but it has a Chevy seal and a cork seal?

[davejf]

Ah ok. Not come across what the Chevy seal is. Maybe not the right size?
I would have expected that to help. These cars always leak, but how much are we actually talking about over how long?

[Candellara]

davejf said:

Ah ok. Not come across what the Chevy seal is. Maybe not the right size?
I would have expected that to help. These cars always leak, but how much are we actually talking about over how long?

I'll find out and report back

[paintman]

No idea what the seal type is but is there a possibility that the surface it runs on is worn/damaged?

If so it might be worth considering a speedi-sleeve of appropriate size.
I've used them for while & my RRC has a couple on it - steering box output shaft & crankshaft front pulley - & very good they are too.

Plenty of info online & youtube.
http://www.skf.com/group/products/seals/industrial...
Random youtube: https://www.youtube.com/watch?v=daKqbFvZnjY