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

Subject: Re: Trying to change a Piston with Engine and Crank in Place (TD)
From: Bob Howard <>
Date: Fri, 10 Dec 1999 08:54:23 -0500
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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