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MG TD TF 1500 - Piston removal

Did I imagine it or did I read a thread where it was just possible to drop pistons in a XPAG via the bottom end? I appear to be over pressurizing in the sump and a stuck or worst a broken ring is suspected. Couldn't immediately trace the thread via the archive.
JK Mazgaj

The connecting rod will not pass through the cylinder bore so removal is through the bottom of the block. Some have asked if it was possible to remove them with the crank in place and the answers were mixed on that question. Not easy at best and replacement even worse as I imagine it would be near impossible to get a ring compressor in there. Removing the crankshaft is pretty much an engine out of the car job.
L E D LaVerne

To echo what LaVerne says, it IS humanly possible to remove a piston from the bottom of the engine, but it is a huge hassle, and rings are often broken in the manipulation.

The only way to re-install pistons with the crank in place is to insert the rod and piston without rings, push it out the top of the block, install the rings, use a ring compressor on the rings, push the piston and rod down, and then bolt back up to the crank.

If you have a known problem requiring removal of pistons, it is MUCH easier and safer in the short and long runs, to remove the engine and do it that way. You will no doubt find other things that need fixing whiule you are there, which can only be a good thing.

Tom Lange
MGT Repair
t lange

I can confirm what Tom says. That is exactly how I replaced my pistons and rings. The worst one is no.#1 piston due to the web on the block. I have also read it depends on the oversize involved whether it is doable or not.
Regards
Declan

Declan Burns

And for my information, what about pistons with an extra oil control ring below the piston pin? Can they be pushed up far enough to fit all the rings?
John Quilter (TD8986)

JK,
have you done a blowby check on all cylinders?
Also check that the tappet cover plate gasket has the holes to let pressure vent out.
I have changed pistons from below, it is a bit fiddley but do able.
Ray
Ray Lee

When I stripped my spaghetti (don’t you love autocorrect) - xpag (+20 bores) just for the hell of it I removed them past the crank. Lots of back and forth rotation of the crank was needed and I did manage to scratch a journal. Luckily it needed freshening up. I can’t imagine doing it in reverse!
C I Twidle

To expand further my problem started after a winter (2017) lay-up. The car wouldn't start so time being at a premium I had the car collected by local MG/Classic car specialist. The car was successfully started but during the test run by the garage it became obvious that oil was appearing through the body side vent on the off-side (RHD). I was advised that this was due to the common problem of crank leak via the bell housing. Accepting this diagnosis I agreed to the rear crank seal conversion. In hind sight this diagnosis was illogical. In fitting the seal it was unfortunate that time was not taken by the garage with the crankshaft out that the pistons were not checked. A subsequent report on the engine stated that it was obvious that exstensive previous work had been completed including a rebore and new crankshaft. Having therefore now spent time thinking on the problem and realizing that the oil leak was infact coming from the front carb via the rocker breather (didn't happen before the 2017 lay-up) my conclusion was excessive pressure in the sump caused by a piston ring problem. Could well be a stuck ring.That to me being the only thing that might happen after turning the engine off in the autumn of 17. As the engine has so recently been removed by the garage and my reluctance to "trust" their expertise it's down to me to explore possibilities. Obviously the easiest way possible before plunging into engine and gearbox out.
JK Mazgaj

I did the rings and bearings almost 50 years ago in a car park with the help of a pretty knowledgeable amateur bush mechanic this way. (Or rather I helped him). 40 thou oversize and no real issues that I can recall. Having recently had the sump off with the engine in the car, getting the cork gaskets at the rear of the crank in exactly the right place is a pain though. Cheers
Peter TD 5801
P Hehir

I have removed and replaced the pistons twice in the last year without removing the engine or crankshaft, with .060" over pistons.
IMO:
1)Remove them 1 at a time, do not try to remove 2 on one rotation of the crank
2) Remove # 2 last, and install first, when close to the bore tilt the piston upright or parallel with the bore.
3) If the chamfer at the bottom of the bore has been removed as a result of boring oversize the 4th ring if used must be a 1 piece ring, you can compress it with your fingers. It can not be done with a 3 or 4 piece oil ring even on a 3 ring piston.
No the 4th ring below the wrist pin can not be installed with the piston pushed above the block.
4) Remove the head first, if the bore is perfect with no sign of wear, I would remove the pistons / rod assembly with the engine in the car.
5) Deglaze the bore with a BALL TYPE HONE.
6)The ring to ring land clearance when NEW is .001-.002". Wear limit when pistons must be replaced is .006" with new rings. ( I would use new ones perhaps at .004")
When replacing pistons I always ceramic or thermal coat the piston crowns, and dry film coat the skirts.
Hope this helps!
Len
Len Fanelli

My update.
Following advice from here and elsewhere I've carried out the following tests.
Compression test (cold) range from 3 pots just over 130 to one at 140 psi so considered good.
A blow by test ( at a compressor setting of 95 psi) only resulted in forcing the piston down and thus opening valves allowing air to escape via inlet ( hear it from carb) or outlet (hear it from exhaust pipe). Turning and holding the starting handle reduced this escape to virtually nil.
The only other "clue" I have as to rocker area being pressurize is that whilst my dash guage shows a fraction over 40psi a secondary guage attached from block to head shows around 75psi.
So the next question is could my problem lay with a fault in the oil pump/filter area.
God this is so frustrating!!!!
JK Mazgaj

You will need to read my earlier entry reguarding my problem and why I was asking about piston removel for the above to make any sense.
JK Mazgaj

This thread was discussed between 20/05/2019 and 01/06/2019

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