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From: Ray Frazier
To: alpine list
Subject: Bad motor
Date: Tuesday, October 21, 1997 5:29PM
>As I was driving to a rally last Saturday in my S3 it made a really bad
noise. the >noise was a deep clunking noise that got considerably
better when the clutch was >engaged. I stopped immediately and called
the tow truck. being an eternal >optimist(I have to be with three MGs
and an Alpine) I thought it was probably the >clutch coming apart or
maybe a transmission problem. When I got a chance to >inspect it when I
got home however it sounded more like I had thrown a rod so I >pulled
off the oil pan and looked around. at first I didn't see anything but
then I spied >some metal bits around the no. 4 crank journal. I pulled
off the bearing cap >expecting to see a spun bearing but there was only
minor scoring on the bearing >surface. I then looked up at the journal
and was shocked at what I saw. there was a >crack all the way through
the crank. apparently the crack was jagged enough that >the crank was
operating as a unit so the engine would still run.
>
> Also while I have this motor apart what would be some engine mods
that I could >do to it to give me a little more horsepower. this car is
a driver so I don't want to do >anything too radical, just give it a
little more pep. The car seems to be pretty much >stock except for it
having the twin sidedraft stombergs of the later series cars.
>any advice on pitfalls to look out for would also be appreciated as I
have only had >the car a couple of months and will be trying to make
sure everything is up to spec. >inside.
Well, this is the way many of our engines will end up in the long run.
A small stress riser that exists on the crank, will form a crack that
will
propogate aross the part eventually.
You may well have had the crack for 20 years, and it just let go.
Getting a new crank shouldnt be too tough. Try the parts guys.
Curt?
They seem to keep used parts too.
The 3 main motor IMO requires a little more magic than does
the 5 main motor, this is to assure that the motor will last
longer than the old one did.
Get one that has a maximum of .020 undercut on both rod
and main journals, as the journals size contributes considerably
to the strength of the crank. That is, select one that will allow
a max of .030 regrind.
When you get your new crank, have it cleaned and magnafluxed.
If it passes have the webs shot peened.
The shot peening relieves surface stress risers, and puts the whole
cranks skin in compressive stress.
This will prevent something on the outside like a scratch or an
imperfection in the die from propogating through the crank.
Have the crank balanced, and match piston and rod weights
to assure that the reciprocating parts are also balanced.
I know this sounds an awfull lot like a race motor, but these
opperations are relatively inexpensive and are a cheap
insurance policy toward keeping the motor together.
Cam and compression are easy ways to bump performance on a rebuild.
I would put in a milled down series V head on the early car.
Why?
The series V head has better ports and bigger valves than all other
models.
Also there are a bunch of corroded heads around, that could be cleaned
up without welding by taking a good swath across the face.
Cheap performance.
Jarrid Gross
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