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MG TD TF 1500 - Expert engine help neded

My refreshed 1951 XPAG engine (new rings, bearings, valves, honed cylinders) is smoking excessively when the engine is revved up. The smoking has gradually increased as the engine has been run (only about 2 hours running time). I removed the head and found the combustion chamber and piston heads covered with clean oil (not burned). The pistons are .100 over. Here is what I've measured:

Cylinder Diameter
#1 2.722 in
#2 2.723 in
#3 2.721 in
#4 2.724 in

Compression
#1 132 ft/lbs
#2 140 ft/lbs
#3 138 ft/lbs
#4 130 ft/lbs

I had a local shop (no mg experience) put in the valve guides (steel) and valves. Are the bore diameters too large for .100 over pistons?

Thanks

Tim
TD12524

TW Burchfield

Tim, The stock bore is 2.61811. Did you check for taper of the cylinders? If there is no taper I would run it to seat the rings. Just my opinion,by no means an expert. Tom
tom scott

Thanks Tom. I took measurements at there different depths in the cylinder and didn't find any taper. But that is with the piston in the cylinder so I couldn't check the very bottom of the cylinder. A friend just told me that he thought old MG engines needed 1,000 miles to seat the rings. That seems like quite a few miles. But I'm open to new info.

Tim
TW Burchfield

Did you fit the rings the right way up? If you fit them up side down they will not function well.

Maybe the rings need a 1,000 miles, but after burning off the assembly oil, there is no need for excessive smoking.
Willem van der Veer

What are you using for valve stem seals?

Jim B.
JA Benjamin

Are you using running in oil or at least a classic oil of the correct grade. A modern sythetic would be a bad idea.
Dave H
Dave Hill

Willem, the rings had a step (notch) in them that was supposed to face down. I certainly tried to install them per the directions.

Jim, I initially used the stock o rings that came with the head gasket kit. I'm going to install the Felpro umbrella seals mentioned in the archives.

Dave, I'm using Castrol classic 20 w 50 oil plus zzdp additive.

Does anyone think the cylinder bore measurements are excessive?

Tim
TW Burchfield

Tim,

Perhaps wishful thinking, but it could be that the valve stem seals were not put in correctly. When the engine has been sitting for some time, look at the top of the spring retaining washers. There should be oil still on top. If it has drained away, it has gone past the collets and the O ring and down the guide. If the head is off the car, set it down (and perhaps pack one side up a bit) so the valve retaining washers are horizontal. Put some kerosene on top of the washers and see if it runs through ... It should stay on top if the seals are in their proper place.

Good luck.

Bob Schapel
R L Schapel

Tim

I suggest you download this doco it will provide the specifications that you require;

http://www.ttalk.info/XPAGEngine.pdf

Clearances should be adhered to regardless of your bore size.

Graeme
G Evans

Tim, I had a similar problem with the rebuilt engine in my TF. I initially ran it before the car was drivable, that is,under no load. The suggested method was to drive the car up to 30 mph then slowly increase the speed under load, back off and repeat a few times.
Regards, Don TF 4887
D J Walker

Tim, I don't think the bore measurement is excessive. I know of cars that used a lot of oil when first rebuilt until the rings seated. It may well take a 1000 miles. These engines are proven reliable and will give many years of service. A little blue smoke is nothing to worry about. Tom
tom scott

Tim,

When I first started driving mine it smoked like a chimney - simply a case of seating the rings. In my case it took several hundred miles. Hopefully that's all yours is too.

Gene
Gene Gillam

Once many decades ago I had a shop rebuild a Morris Minor (948cc) engine. They fitted new rings on original pistons but the car smoked like a train and it did not cure over some mileage. A second tear down found excessive taper in the cylinders which they overlooked on first go round. A rebore and new pistons totally cured the problem. The new pistons were Covmo brand with a second scraper ring below the wrist pin.
John Quilter

The only way to know piston to cylinder clearance is to measure each piston (I think 90 degrees to the pin), and compare to its own cylinder. There is often a lot of variation from piston to piston. The shop should number, measure, and match each piston to specific cylinder when doing final hone. I think you would have bad piston slap noises if excessive enough to cause oil burning. I recall certain rings (chrome?) take a very long time to seat, and the final cross hatch finish on the bore is crucial.
https://www.hastingsmfg.com/ServiceTips/compression_ring_installation.htm

Many years ago a machine shop put at least one ring in upside down in my 280Z motor, and it smoked massively and of course never stopped, so hope that is not the problem. George
George Butz

Thanks everyone for the excellent advice and comments. I'm months away from having the car on the road but I'll report back after driving it for a while.

Tim
TD12524
TW Burchfield

adding zddp is like setting elephant traps in Illinois..I haven't had any elephant problems since I set the traps. Regards, tom
tm peterson

Then I would keep setting the traps.

Tim
TW Burchfield

This thread was discussed between 27/10/2015 and 28/10/2015

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