MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Burning oil after rebore

I have just had my XPAG TD 9287 rebored to +100" (= 1350cc). It runs fine, but with clouds of blue smoke from the exhaust! Any suggestions what is wrong before I take it all to bits again? All the spark plugs are equally oily, so the problem is with all 4 cylinders. Have I done something stupid fitting the rings to the new pistons, which are the 3-ring type? The oil control rings consist of 4 parts which I assembled as follows: a lower thin scraper ring, an central spacer, a locking ring which fits into notches in the spacer, and the upper scraper ring.
Mark Martin

How many miles since the rebuild? It's pretty normal to burn a little oil while the rings are 'bedding in.' The engine may also run a little hot until broken in.

Follow the recommend break in procedure, and the oil burning should go away after a few hundred miles of driving. If the engine was professionally rebuilt, I'd call the rebuilder for advice.

P.S. that assembly procedure for the oil control ring sounds right to me, but there are a couple of different types. The correct procedure should have come in an info sheet packaged with the rings.
Mark B.

One should use 30 wt non detergent oil for breakin
Run about 300 mils then change to same oil, change filter and 300 again then to regular oil. The smoke may last for 300 to 400 miles then stop. If the non detergent oil is not used the rings may take a long time to seat. Just been there and done that.
Ellis
carlton

Take a look at the o rings on the top of your valves ??
R Matthews

<<<snip>>>
30 wt
<<<snip>>>
Okay

<<<snip>>>
non detergent oil
<<<Snip>>>
Nope
Blake

Thanks everyone for all the advice and info. I have only done about 20 miles since the rebore, I was afraid to do any more in case there was something wrong. As it seems to be working fine with no nasty noises I will run it a couple of hundred miles and see if things improve. I don't think it is the valve oil-seals, as I also had the head "unleadded" by George Edney, and the vales were fitted by him.
Mark Martin

Martin; My advise about non dergent oil and 300 miles twice was not from a novice. It came from the machinist and a hbbist who has many cars. The machinist races his own cars in dag racing and must know what he is doing. Miine quit smoking after about 200 miles and has stopped the oily spark plugs. I had to change and clean plugs several times. Luke to you
Ellis
Ellis Carlton

PLease pardon incorrect spellings. I get in too big of a hurry.
Ellis
Ellis Carlton

My TD smoked a fair amount for the first 250 or so miles after recent rebuild, esp. after idling for a bit and then reving. Smoke free now. Some years back my 280Z engine smoked like a mosquito fogger after rebuild- seems the "machinist" put some of the rings in upside down. Not sure if the new rings are moly or chrome or what, but I would just drive it for some time before pulling it down. I personally think break-in driving should be somewhat normal, but without any lugging or really flogging it. No synthetic oil either!
George Butz

Mark.......from your email it appears that you increased the cubic cm. capacity of your engine by 100 cc. Not as stated +100". Did you mean you rebored to .010" oversize? Did you put in .010" oversize pistons? If you did'nt that could be the problem.
I have not done the math to see what a .010" overbore does to the dispacement.
If you told the machinist that you wanted a 1350cc engine and left it up to him to determine the bore size, it could all be wrong if he did'nt do the math right to determine the bore dia. and what size pistons you should use.
Heard all this before. You, have to gauge all this stuff before you put it together. Don't assume or trust your machinist to be correct, ever.
colin stafford

I admit my experience is somewhat limited in this area, but doesn't the machinist always wait to bore the block until AFTER measuring the replacement pistons?

The way it's happened for my previous couple of rebuilds, the machinist measures the worn bores on my block, and tells me the mimimum size overbore pistons to buy. I'm sure you could go over that, but I never have. I then have the new pistons sent to his shop, and he doesn't do the actual boring until he has the pistons in hand and precisely measured. That way he can get the tolerances exactly right.

Just boring to a block to a specification seems to be a recipe for problems, since you can't really guarantee that the replacement pistons you get will exactly match the specification.
Mark B.

To amplify what Ellis Carlton said about oil for running in, consider what is in the oil to understand what you want to use.

Modern detergent oil has additives to keep soot in suspension (dispersant) and to neutralize acid. Both of these additives are always beneficial. Also, an anti-wear additive, usually zinc dialkyl dithiophosphate (ZDDP) is added. Any oil marked as SJ or SL will have all of these additives. The acid neutralizing additives are especially important because modern gasoline has oxygenators to combat unburned hydrocarbon emissions, and this additive is going to put sulphur dioxide (sulphur a natural trace impurity in gasoline) into your crankcase. In the presence of water vapor (also always present) this will turn into sulphuric acid, which is not going to help anything. Without this additive, your best defense is changing oil very often, like 300 miles as recommended by Ellis.

Multi-grade oil, i.e., 10W-30 will also have a viscosity index improver additive to resist thinning at high temperatures. Synthetic oils need much less VI improver as their viscosity is naturally less affected by temperature. A 10W-30 synthetic oil probably has no VI improver additive. It is just SAE 10 oil that does not thin out at high temperature.

During break in, you really don't want the anti-wear additive because you want the piston rings to wear to fit the cylinder. If you use an oil that has anti-wear additive, this is naturally going to take longer. Therefore Ellis's recommendation to use non-detergent oil at the very beginning (no anti wear additives) and to change it very soon (get the acid and soot out of there) is right on the money. After the initial 300 miles I would consider whether the rings have seated yet or not. (Make this determination based on is it still burning oil excessively.) If ring seating is accomplished, I would change to a detergent oil at that point. If not, I would repeat the non-detergent oil to continue encouragement of seating the rings.

Now regarding the intiial question about the cloud of blue smoke. Here's hoping you finished the cylinders with a 240-320 or so grit hone. If you rebored, this will have been done by the machine shop as the last stage of fitting the pistons. However, If you just took the pistons out and fit new rings or even used the old rings without honing the cylinders, you are in for disapointment. Most likely the rings will never properly seat and you are going to be burning oil like it was going out of style for a long time. The honing leaves a slightly rough surface necessary to cause the rings to seat, but this roughness also wears smooth in time.

Bill Vatter

Mark,
My TF was exactly the same as you describe, but emitting blue smoke on the over-run ie going down hill with the foot off the throttle. After 1000 miles it got better with almost no smoke now. I was advised that for the first 500 miles I should use running in oil, which is what I did. At the next oil change I used Castrol.

What seals did you use on the valves stems? I used the modern Ford type 'top hat' seals but you must have the guides machined with a locating groove to stop them moving up and down with the valve stem.

I have just fitted a Lucas Leystal head to my TD and also used these seals ( supplied by George Edney ) and there is no smoke at all despite the block being over bored to + 100thou.

David Tinker. Wales UK
David Tinker

Thanks for all the info! I have only managed about 100 miles due to other commitments, but the smoke is much reduced already. To answer some of your questions:
The re-bore was done by George Edney. He supplied the pistons, and converted the head to unleadded at the same time. So I'm sure all the work was OK, the only source of problems would be my ham-fisted assembly! The bores were "rough finished".
The bores are now 0.1 inch oversize, for which standard pistons are available. This equals 2.7181 inch or 69.0397mm diameter, so if my maths is correct it's now 1347.7cc.
I think I'm using non-detergent oil. It's Halford's 15W50 Basic mineral oil, "suitable for pre 1980 cars". It does not name any detergent on the label like the other Halford's oils do. No one in the shop knew of course!
Cheers, Mark Martin.
Mark Martin

Why not bore it out to 72mm dia and make your engine a 1500cc XPEG. and stick in stock pistons. At least it won't be a bastard size motor.
Not sure what rough finished bores are, but most engine builders run a hone up and down the bore to develop a cross hatched finish. I have never had a rebuilt engine that suffered from the "blue smoke syndrome".
colin stafford

Colin- minor problem with your 1500 idea- there is that water jacket thing between 1/2 and 3/4 on the XPAG block. Moss has had pistons from .010 to .12 for many years. Any larger and it perforates. Of course- what is the actual displacement of the XPEG- not exactly even 1500? Personally, I am a rather proud parent of two oversized bored T-series motors- maybe when they are older I will tell them they are really displacement challenged bastards! Haha. Seriously, just read Smokey Yunick's autobiography- his research and microscopic study of bore finishes and hones really interesting. Still applicable today.
George Butz

This thread was discussed between 01/03/2003 and 11/03/2003

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.