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MG MGB Technical - Valve Seal question

Here is a stumper that I'm sure someone has seen before. I rebuilt my engine last year, had a machine shop do the machine work and he assembled the head as well as fitted the pistons, con rods, and crank. I have had very good luck with this guy and understand he has had experience with MG's in the past. Here is my problem. I have about 500 miles on the engine since rebuild and it will still smoke for the first 2-3 minutes of operation after it has sat for more than a couple of hours. After that initial warmup it clears up. Runs like a top other than that. At first I thought it was just the rings seating in but after 500 miles, I need to move on! My second guess is that my guy left out the oil seals on the valve guides which (I think) would allow oil to run down the guides into the cylinder. It is blue smoke by the way and again, it only occurs after it has been sitting for several hours. Anyone out there have any ideas? Without removing the head, can I pull the valve springs off and check? Any other possibilities or tests?
Tony Mason

What year car?

Does it have a PCV valve on the manifold?

If so is there oil in there, under the diapragm?

Could also be oil sucked out of the tappet chest cover with the later carb breather pipes.

You'll not see if he has left the seals out without removing valve springs - can be done with soft rope in the cylinder to support the valve but it is a bit of a pain.

Look to see whether he has fitted the seals on the stems below the caps - some people do!

Even though you have done 500 miles it could still be oil from the bores.
Chris Betson

Tony. I recently had to pull and dis-assemble a rebuilt engine with 3K miles on it due to an oil line cracking. Not all of the blackening of the rings had worn off, showing they were not fully seated yet. On my own 79, with about 4K miles on the rebuild, it gave a puff of smoke on start up for the first 2K plus miles. I suspect, but have no way of proving, that the use of modern oils delays the ring seating significantly and this is the root cause of the problem. I had to take the 79 through emissions last month and it saled through. No CO reading at either cruise nor idle and very low HC readings--2 ppm at cruise and 74 ppm at idle with a standard of 220 ppm. So, at this point, I would not worry about your engine, but would suggest you drive it more and see what happens. By the way, the engine that had these low readings has .040" over pistons, a CB camshaft, Mike Brown Cylinder head, Peco exhaust with aftermarket cat and a Weber DGV on it. Great engine at full throttle, but the Weber 32/36 is not enough carb for it. Now that is is fairly well broken in and has passed emissions, perhaps some carb swapping is in order to see what it can do. Les
Les Bengtson

Tony-
It might be oil getting past the seals on the intake valves, but Les is right about today's modern oils. While they're superb at reducing wear, by the same token they're too slick to allow for a quick break-in of the engine. Use the cheapest reprocessed oil that you can find until the rings seat (2,000 miles at most). If you still suspect the seals on the intake valves, here's a simple test that you can perform: once the engine is warm, downshift at high rpm, and close the throttles. The vacuum in the intake system will draw oil into the intake ports if the seals are bad. Look over your shoulder to see if you see gray smoke.
Steve S.

On the oil theme - I was advised not to use synthetic oil in my new (rebuilt) engine for the first 5000km (3000 miles) - precisely for the reason that it delays "run in". Trust you aren't using synthetic oil, Tony.

BarryQ
73B
B.J. Quartermaine

The stock "B" valve stem oil seals are small "O" rings stuffed under the valve keepers - inside of the
valve spring retainers. This arraingment still allows a small amount of oil to splash onto, and then run
down the valve stem and trickle past the guides and onto the backs of the hot valves. The result is a
poof of smoke upon a hot re-start (from oil being cooked on the exhaust valves) as well as a noticable
consumption of oil (from oil being constantly sucked down into intake valve stems).

IMHO, a better designed seal is the "umbrella" type - as they encapsulate the entire upper portion
of the valve guide and actually wipes away most excess oil off of the valve stem during valve travel.

FelPro stem seal # SS 70373 - ( for Chevy Vega 4 cyl 140, '86-92 Ford 351W ) - just happens to
fit the "B" engine as though they were originally made for this application, and in my real-world
experience, provide a much better and longer lasting seal than the original "O" ring type seals.

They come 8/set and are made of some sort of rubber (neoprene?) with two, metal retaining rings.
List = $18, but they usually go out the door for $12. Cheap. No machining required.

You'll have to remove the valve retainers and springs, and then install them by placing a steel washer
on top of each seal (to avoid damaging them) while gently tapping them in place using a deep socket
and small hammer.

Some engine builders put them on the intake valves, only. Other engine builders install them on
both intake and exhaust valves.

Of course, your valve guides should not be worn-out and must be in proper condition for any of
this to work.
Daniel wong

Tony, the seals that Daniel are talking about are outstanding. At the suggestion of many folk on this site two years ago, I did this after my rebuild. I was adjusting my valves after about 1000 miles and found bits of the original seals (New) crunched up in the valve springs. I did the Fel-Pro seals and have had no trouble at all.
Steve C.
Steve C.

Tony-
Daniel is right about the Fel-Pro seals. I've got them in my engine, so I can testify from experience that they do in fact perform just as well as he says that they do. Definitely a very real improvement over the OE seals.
Steve S.

I've heard nothing but good things bout these umbrella seals. Any problems using them on a dual valve spring motor?
Baxter

Baxter -

The Fel-Pro seals do not interfere with dual springs or high lift cams.

On my own car, I've got the dual, heavy-duty valve springs (Moss # 423-455) as
well as a vintage, high-lift, Isky cam (.435/.430 lift).

The Fel-Pro stem seals fit, clear the spring coils, and the spring retainers do not
bump into them at full valve lift.

No problem-o.
Daniel Wong

In my view the fitting of the later seals may lead to insufficient oiling of the valve stems and premature wear of the guides as well as potential valve sticking.

Oil should not "dribble" onto the hot exhaust valves unless the guides are worn. At 0.7 to 2.5 thou clearance the oil film should be mainly retained by capilliary action, even when hot.

I would never fit full stem seals to my engines and would not recommend them to others.

Interesting to note that the Rover V8 fits seals under the caps of the inlet valves only - the exhausts get no sealing whatsoever.
Chris Betson

Thanks guys. I haven't be on line for a couple of days and now see all of your great comments. A couple answers. No I haven't used synthetic oil, just the cheap Wallmart brand. It is a multiweight with an SG spec so your comments make sense. The seals I had with the gasket set were cap type seals. The reason I questioned it at all was my bag of gaskets, when I reassembled the engine, still had those. At first I thought maybe we had a double set or those were the old ones but then I started second guessing the longer I saw the smoke. One of the comments perked me up a bit though. I de-smogged the engine and connected the breather pipe from the lifter cap up to a common connection with both carbs and the carbon cannister. I didn't install a pcv valve. Could that be a problem? I piped up my midget the same way several years ago and haven't had a problem with it so assumed I had it right.
Thanks again for the help.
Tony Mason

Tony,

Disconnect the pipe to the tappet chest from the carbs and see whether the oil burning stops.

Excessive vacuum from the carbs will just pull oil up from the chest - where is the connection made?

Is there a lot of "suck" with the engine at idle?
Chris Betson

My V8 had this problem, and it's about 11K since the motor was rebuilt. Hot restarts after, say, 15 min of sitting would produce huge puffs of blue smoke. Suspecting exactly what you say -- bad valve seals -- I had the whole valve train pulled apart and inspected bit by bit. The mechanic -- whose judgment is widely regarded as impeccable -- pronounced that it was in absolutely perfect shape, seals were perfect, everything was perfect. Then we talked about oil ... stupidly, I have been running Mobil 1 ever since the rebuild. Apparently that's exactly the problem; the motor can't break in properly using such an ultra-slick lubricant.

You might want to just route your hose from the tappet chest cover to the air cleaner. There's some suction there -- should be sufficient for the purpose -- but it's not as strong as that at the vacuum ports on those SU carbs.
Ted

Thanks! I'll check this out again. I might experiment with a PCV valve too.
Tony Mason

The running in process is actually quite brutal - if you imagine the surface of the newly honed bore it is a series of V shaped valleys and peaks.

As the rings slide over this surface, the sharp edges of the rings need to slice off the tops of the peaks cleanly to produce a smooth surface with the remains of the valleys to hold oil and lubricate.

Eventually the bores and rings wear down to a perfectly matched pair of surfaces.

What happens if you use a synthetic oil or friction reducer is that the peaks, instead of being sliced off are bent over into the valleys and are work hardened - this leaves a rough irregular surface that retains more oil and therefore you get more oil burnt and more blow by into the crankcase which blows more oil mist into the breather system to be burnt.

Hence - use the cheapest oil or special running in oil until the bores are run in - you want the oil to aid the process - its most important job is to cool and wash away the debris so make sure you change it and the filter after the first 500 miles. Also make sure you drive the car normally during the running in period.

The first 20 mins of running after rebuild is crucial not only for the bores but the cam also. It should be run up to 2,500 rpm and held there for 20 mins.

I also give my engines a good burst up to 4,000 once fitted to the car to aid the bedding in process, at higher revs the rings are forced out against the bores ensuring a good seal.
Chris Betson

This thread was discussed between 12/02/2003 and 14/02/2003

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