Oversize Pistons?

n-engelbert at terrans.net n-engelbert at terrans.net
Tue Aug 10 14:28:56 EDT 2004

I've got my donor motor out (229k miles) at a local machine shop and the
guy I'm working with wants to bore it since he can "tell just by looking at
it" that it needs to be bored.  There is a definite ridge at the top of the
cylinder, but there are remaining hone marks from the bottom of the stroke
to about 1/4" below the ridge.  I've asked him to measure the bore for me,
but he has yet to do that.  I'm in Chicago, but the working is going on in
Dayton.  The only oversize pistons I've been able to find are through the
worldpac distributors for at least $880 for the set.  Boring and sleeving
the bores is going to run me about $700.  Are there any other options out
there, like using the 7a pistons and boring out to 82.5mm (walls between
cylinders too thin?), or is there a cheaper source for .50mm over pistons,
or should I take the block somewhere else for a second opinion?  I'd like
to just hone the block and put new rings in, but I don't know yet whether
I'm over the wear limit for the engine.  It burned no oil prior to

Also, what is the proper style of valve guide for the 3b head?  I ordered
027 103 419 from Rod at The Parts Connection, and the machinist says that
with the shoulder that is on them, that they aren't the correct parts, but
he can lathe them down to work.  Something about the ones that are
currently in the head are ~.330" and he needs ones that are ~.450" which is
8.5 and 11mm respectively.  I see that the worldpac sites show a 8.5 and an
11mm guide, with the 11mm one without a step/shoulder.  Are these the ones
I need?


Nathan Engelbert
83 UrQ DA900453
89 90q
91 200q20v donor

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