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Re: Trying to change a Piston with Engine and Crank in Place (TD)

To: <>, "Bob Howard" <>
Subject: Re: Trying to change a Piston with Engine and Crank in Place (TD)
From: "Ernie Betts" <>
Date: Fri, 10 Dec 1999 11:06:01 -0500
Put the piston with rod in from the bottom.  It will go up far enough to the
top to put the rings on with a compressor, slowly tap back down and then
connect the rod bearings and cap.  Changed several that way with engine in
car and that's how I've done with engine rebuild.

-----Original Message-----
From: Bob Howard <>
To: <>
Cc: <>;
Date: Friday, December 10, 1999 9:48 AM
Subject: Re: Trying to change a Piston with Engine and Crank in Place (TD)

>Hi Bob,
>  I am pretty certain that the piston went in from the bottom at the
>factory, probably pre-connected to the rod.  But, with the crankshaft in
>place you're going to have a very difficult time getting a ring
>compressor in there and getting the piston to enter the cylinder. I gave
>up on the challenge, removed the piston from the rod and pushed piston in
>from the top.  In the original casting, there was probably some
>chamfering that made piston insertion easier. Once an engine is bored,
>though, that chamfer is gone.
>  Somewhere I read that rods being in backward is a bad thing, and an
>explanation for it. Of course, I forget where any why, but a dim memory
>tells me that it had to do with the oil squirting out of the drillings
>and lubricating wrist pin or piston or cylinder wall....
>  I would turn them around. That, of course, brings up the further
>problem that you may not know if the front of the piston is facing the
>front of the engine. Is the head still off? Can you see any markings on
>the piston tops?  It could be that he is 180 degrees out with both piston
>and rod, so all you would have to do would be to remove bearing caps and
>rotate the rod. That sure would be nice, and easy. And unlikely,
>according to Mr. Murphy, discoverer of Murphy's Law.
>On Thu, 9 Dec 1999 23:44:32 EST writes:
>> As several list members advised, I was able to remove the piston and
>> rod from
>> the bottom past the crank. I found this had to be done on the
>> camshaft side
>> of the engine and it's a bit tricky. The crank rotation, piston and
>> rod all
>> had to be manipulated in order to "sneak" the assembly out. Once out
>> I could
>> not get a socket to go over the wrist pin clamp bolt because it's so
>> close to
>> the rod. Horst Schach in The Complete MG TD Restoration Manual
>> suggest using
>> an open end wrench, but my wrench couldn't get a good enough grip on
>> the bolt
>> and it started to round off the head. So next I tried grinding down
>> the
>> outside diameter of my 1/4 W socket as far as possible, but it still
>> wouldn't
>> fit. I then used the flat side of my Dremel cutting wheel to grind
>> down the
>> ridge on the rod adjacent to the bolt head. This provided just
>> enough
>> clearance for my modified socket to fit over the bolt head. This did
>> the
>> trick and I don't believe I removed enough metal to cause any
>> balance
>> problems (I hope).
>> Now does the new piston go in from the top or the bottom? I can
>> envision the
>> piston going in from the top and pushed down just far enough to
>> allow the rod
>> and wrist pin to be attached from the bottom. Now that I can get my
>> socket on
>> the pinch bolt, I could tighten it with an extension. Or should the
>> rod and
>> piston be assembled and then installed from the bottom the same way
>> they came
>> out? If done from the bottom, can you get a ring compressor in there
>> past the
>> crank? If not, can one compress the rings with ones hands?
>> By the way, the shop manual seems adamant about the rods being
>> assembled with
>> the pinch bolts on the right hand side of the engine. Naturally the
>> DPO had
>> them in the other way. Should I turn all the connecting rods around
>> the right
>> way or leave them alone?
>> Thanks for all the advise. You should see how badly the old piston
>> is beat
>> up. No matter how I get the new piston in, it's got to be a big
>> improvement.
>> Bob Donahue (Still stuck in the '50s)
>> 52 MGTD - under DIY restoration NEMGTR #11470
>> 71 MGB   - AMGBA #96-12029, NAMGBR #7-3336

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