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MG TD TF 1500 - Rings

When I had the sump off I observed a few things.
The bearings are all perfect.
The cam shaft looks brand new.
The lifters have no wear.
The cylinder walls look fine.
I had the head completely rebuilt a year or so ago.
The rockers show no sign of wear.
Mind you that these are the observations of a mechanic with very, very limited experience.
Now I could not see the rings.
The compression is not horrible but not great.
I believe I have a good deal of blow-by. My crankcase seems to be highly pressurized. It has turned my new front and rear seals into oil vents. Yuck. My breather pipe looks like a second exhaust when I drive. The valve cover vent spits oil regularly. Fresh oil at an oil change becomes black from the blow-by very quickly.

I am considering putting a PCV valve on the breather, back into the intake manifold along with an air cleaner. T
But that is just treating the symptom and not the disease.
I am trying to avoid pulling the engine.
So here is my question.
Can I change rings without pulling the engine?
A fellow in my club did it with his Spitfire.
TIA,
Mort
Mort Resnicoff (50 TD-Mobius)

Mort, what is your compression? Does it get higher if you put about a teaspoon of oil in the cylinder?
The pistons have to go in from bottom, but I don't know if this can be done with the crank in place. Another thought is that your rings are frozen. You may want to try soaking them with marvil mystery oil,or a mixture of acetone and ATF.
-David
D. Sander

Mort, pushing the bare pistons up through the bore and then putting the rings on is a common technique. After putting the rings on the pistons you just use a standard ring compressor, push them down in and bolt them on to the journals. It takes a bit of fiddling with the crank, but you don't have to remove the mains. Here's a view of #4 just before shoving it down. Bud



Bud Krueger

Before you try to push the piston up through the bore (while still on the connectiong rod) you must insure that you do not have a ridge on the top of the bore.
If so, the ridge must be removed first.

Jim B.
JA Benjamin

Right, Jim. I've always done it as a step in a honed cylinder. Bud
Bud Krueger

Bud, were your pistons three or four ring? I am wondering if you could use the same technique for a four ring piston.
Jim Merz

Mort the pistons come out through the bottom, with the
crankshaft installed.
You will need to use a glaze breaker on a 1/2" drill motor, to resurface the bores.
Inspect the piston ring lands for wear.
Hastings piston rings are regarded as the best.
Len Fanelli

Each brand of piston rings has its champions. Last year I had to re-ring an engine which I had rebuilt and into which I had put Hastings rings. The rings were properly fitted and installed: ring gaps were perfect, ends were staggered, and all went together fine. But they never seated in 2,000 miles of driving, despite careful breaking-in; the car burned oil at a disturbing rate, was down on power, and had a lot of blow-by.

Visually there was nothing wrong - I lightly honed the bores and fitted Deves rings, and had absolutely no problems - in 500 miles or so the engine felt great, higher compression and leak-down readings, no blow-by, and plenty of power.

Motor oils, brake fluids, piston rings, - that's what makes horse-races: differences of opinion. I just do what works for me

Tom Lange
MGT Repair
t lange

Jim, mine were three ring. I see no reason why the same technique wouldn't work with four rings. I'm guessing that the bottom ring will come out of the bore before the big end of the rod contacts the block. Bud
Bud Krueger

Good comments above. Yes, can be done with engine in place. However, you will have to pull the head to remove the top ridge completely. It is very difficult to hone and so on and keep the crank completely clean. Putting the pistons back in looking up from the bottom is really, really tough. Did this years ago, never again. It worked for a few miles- I didn't know to remove the ridge.. George
George Butz

I used to be a big fan of Deves rings, in instances like this especially, when the engine was fairly worn but it was desirable not to rebore it. But the company seems to have changed hands a few times since, and I can't swear they are the same product they used to be. I used some on a Gravely Walking Tractor recently, but that isn't a terribly good test.

Oh Len, why do you specify a 1/2" drill for glaze breaking?
kylemorley

The blow-by you are experiencing as well as the (somewhat) lower compression, can also be explained by a burnt valve coupled with a leaky valve guides.
As dave noted, after running a compression test, try a SMALL squirt of oil in the lower compression cylinder.
If the compression increases it may well be rings. If not you may have a bad valve.

Just because the head was rebuilt does not guarantee that the valves sill not burn in the future.

Jim B.
JA Benjamin

Kyle, the 1/2 inch drill motor is needed for the power, & low speed for the glaze breaker , not a hone, but an abrasive to deglaze the bores, or give a fresh surface for the rings.
Jim, burned valves & worn valve guides do not result
in blow by, blow by is only a result of piston & piston ring damage.
Len
Len Fanelli

Thank you all for your comments. As usual they are invaluable for a novice like me. I am encouraged to proceed.
When I get home I will run another compression test both dry and wet.

A few more questions please.
I have the proper drill. What tools are recommended for honing and ring compression and are there any good articles on the process.
Thanks again,
Mort
Mort Resnicoff (50 TD-Mobius)

Mort - you will certainly need a cylinder hone and a ring compressor (although some folks use hose clamps to fit the rings). Both are available at NAPA. Be sure to get the size that will go down to about 3". The most important thing is to check and see if there is a ridge at the top of the cylinder. If it is enough that you can catch a fingernail on it, you will need to take the engine apart and re-bore it (I don't remember how many miles you have). If a very small ridge, a ridge reamer will remove it. If no ridge, you are fine.

Tom Lange
MGT Repair
t lange

I'm all for DIY, and pretty foolhardy in what I will attempt, but ridge removal is one of those jobs where a bit of experience comes in handy. Ridge reamers are deceptively simply devices that can turn on you in the blinking of an eye. So if you decide to do an in-the-car ring job, try and find someone who is familiar with the process and the tool to help. If you can't, just go slow and it should work out OK.
kylemorley

I just checked, to be sure, Mort, since I have not used them in many years.
I have both a ring compressor and a ridge reamer if you want to drop by.

Jim B.
JA Benjamin

Adding oil to the cylinders for a "wet" compression test will, in my experience, always give a higher reading. The question I have is how much higher should it be over a dry compression test.

Also, over time and high mileage cylinders can develop a taper which interferes with piston ring sealing. If excessive, and I do not know what excessive is, the only solution is a rebore and/or sleeving the bores.
John Quilter (TD8986)

This thread was discussed between 17/11/2013 and 19/11/2013

MG TD TF 1500 index

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