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MG TD TF 1500 - Replacing TF1500 rings in situ

Hello from New Zealand. I want to replace the piston rings in my 1955 TF1500, engine bored to 40 thou oversize. I have had the engine out twice to get the Moss rear crankshaft seal kit to work properly and cannot face taking it out again. Questions are can I simply remove the sump and head, then remove the pistons by pushing the rods up through the bores. From what I seem to be reading from various threads is that the rods will fit up through the bigger bore. Presume that if they won’t fit I can just push the pistons up far enough to replace the rings ( 3 ring pistons) then push them down again.
Is there anything particular I should watch out for apart from reinstalling the gaskets and seals carefully and plenty of pain killers for the sore back I will get as I do not have a full hoist. Any suggestions gratefully received. Thanks
Paul
P Hicks

Lots to say. Yes, the rods will fit up thru a 1500 block, so it is indeed humanly possible to do rings in situ. You have to turn and wiggle each rod past the crank throws - that being said, it's REALLY no fun. I would remove the engine.

New rings. Hmm. Symptoms? If smoking, it could be valve seals also. Smoking is not usually cured with just rings - if the cylinders are worn tapered they are enlarged at the top, so new rings will never seal.

Also, since there is usually a significant ridge at the top of the cylinders, it will break the rings when you try to remove the pistons out the top, so rings will need replacing also. If you are lucky enough not to need an overbore, you will need to de-glaze the cylinders with a cross-hatch hone, to try to encourage the new rings to seat.

And you might as well check the rod bearings while you are there, and if they show wear you must mic the crank to be sure you can maintain good oil pressure. If the rod journals are out of spec, you might as well drop the crank too, for measurement of the mains; the timing gear has to come out for that.

So yes, it is easier in both the short and long runs to remove the engine, is my experience and opinion.

Tom Lange
MGT Repair
t lange

Paul, first why are you condemning the piston rings?
Len
Len Fanelli

Pulling and replacing the pan is very difficult. Besides what Tom says, you have to measure ring end gap and adjust if needed. Also change to ARP rod bolts. I replaced rings in my TD in high school, and proved not removing the ridge will break things! I'm also curious as to why you are replacing them, especially after the engine was just out. George
George Butz III

Hi guys, sorry for the delay in replying. Thanks for your comments.
It is rather an odd situation with my engine. It has all been rebuilt about three years ago, rings bearings, rebuilt head, rear oil seal kit etc. We have used the car quite a lot and it is a superb little machine ( one of the rare original RHD 1500s) .Recently we were out in it and noticed a slight noise from the engine. Took the head off and found the head gasket was giving out. Planed the head and replaced the gasket.
Some time later I noticed some fumes coming from the crankcase breather pipe. The exhaust gases showed no signs of smoke at all and it still runs brilliantly. I did a compression test. cylinders 2,3 and 4 all on 150psi going up to 200 with a few drops of oil down the bore. Really good oil pressure.
Number one cylinder was 135psi, but also going up to 200 with a bit of oil in it..
Plug seems pretty clean, so I am pretty sure there is some gases getting past the rings in cylinder one. It is not a major problem but it really annoys me.
Basically I want to pull that piston out and see if a ring may be broken. My health really precludes me taking out the engine again hence the reason for my original question.
I do find the car is a difficult beast to work on, having been used to much earlier cars (which generally seem to have much better mechanical access) for most of my motoring life.
Thanks
Paul
P Hicks

Just for the helluvit, since you removed plugs and checked the compression finding one cylinder slightly down, replace plugs, run engine once more, then remove plugs and recheck compression.

Unscrewing plugs, after running for a long period of time, can break bits of carbon loose that can wind up on exhaust valve seats creating a slightly low reading. Briefly firing the engine up after breaking plugs loose and burning out the trash will ensure a more accurate test.

Gus, from Popular Science, suggested that at least 60 years ago. I hope Popular Science was available in New Zealand way back when, lets say, the past 150 years (no longer in hard print, sigh).

I feel your pain as I rebuilt my honey's 1466 TD with the most expensive pistons money can buy, only to open it back up a year later finding broken ring lands on the pistons- BRITTLE FRACTURES. Maybe they were cast out of scrap and pop cans in India. It was only run on premium gas, too.
JIM N

Hopefully Tom L will chime in with his recommendations regarding piston rings. I recollect a company in Los Vegas (Deves ??) that makes rings for our XPAG/XPEG.

Tom knows!
gl rombough

Word of caution on just replacing rings from experience long ago on a BMC A series engine. Make sure the cylinders are measured for taper. This was not done in my case and new rings on original pistons never seated properly resulting in high oil consumption and smoking. Had to be corrected with a rebore. Cylinder scoring is very evident, taper, not so much.
John Quilter (TD8986)

This thread was discussed between 10/09/2025 and 31/10/2025

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