So how bad is it to have a 0.009" taper in your cylinder?

[Jim Green]

On Fri, 25 Mar 2005 17:44:07 -0800, Tyson Varosyan <tigran at tigran.com> wrote:
> The engine is an MC that came out of an '87 5000T. I tore the block apart
> because the #1 cylinder had low compression. I found that the head gasket
> around the #1 cylinder had failed and that no other damage was apparent.
> Given that the block was torn out of the car, I decided that it may be a
> good idea to take it to a shop and get new rings and main bearings changed
> out. The guy at the machine shop measured the cylinders and said that they
> will need to bore the them, which means new pistons, etc, etc... However, he
> said that the taper in the cylinders was only 0.009" between the radius at
> the top of the cylinder and the bottom and that the rest of the engine
> looked to be in very good shape. The walls are smooth, no groves, the oil
> looked nice, etc. The taper he said was too great to just do a simple ring
> job, but was not too catastrophic to absolutely require a rebuild.
> 
> I am now a bit torn. With the motor already out of the car and torn apart,
> it is tempting to throw some $2500 at it and get new pistons, get it bored
> out, balanced, get the crank and rods nitrated, etc and pretty much build a
> race motor. On the other hand, I could just have them "deck" the head, throw
> a new head gasket on there and call it good.
> 
> What do you guys think? Is 9 thousandth of an inch worth a rebuild or should
> I just snap it back together and call it good?

Don't touch it other than some new seals, and put it in the car. 
Please don't waste $2500 on rebuilding an MC!  You may have a little
extra blowby, but it's a turbo motor, so it's going to be more by
nature anyways.  I've seen many more success stories with junkyard
blocks thrown in and beat on, than freshly rebuilt bottom ends.  It's
just asking for trouble for no reason.  Trust me, save your money for
a possible 20vt buildup someday.  If I ever have to buy new pistons
and rods, it's going to be because the factory pieces will not hold up
to 30lbs of boost and 20 valves.  The MC is built like a freaken tank,
I'm convinced the 10v head will not flow enough to even make it wink
at failing.  Now having said that, there's a turbo bolted to it that
made 455 whp on a Javads 20vt, so we'll see just how much that bottom
end can really take.  I need some wood to knock on.


-- 
Jim Green
'89 90tq
'89 80q
http://www.mswanson.com/~jgreen/car_home.html