Rocky has a great point there, that I missed in reading the email. Little
nicks and scratches don't mean the other parts are okay. It doesn't occur
to me that someone would consider reusing the adjoining bits without
remanufacturing them after an engine goes away. But that's only because I
learned not to do that the hard way many motorcycle races ago. Doesn't
mean that I really remembered it under all circumstances.
Sure, at trackside, you do about anything to salvage the weekend and make
some laps. But even if the only symptom is a slightly stuck piston (as in
my Radical two weekends ago) doing the teardown means measuring and
perhaps replacing all the other stuff that might be at end of life.
As is typical, I forgot that lesson last week and reassembled my engine,
only replacing the pistons and honing the cylinders. When I ran the engine
on the dyno there was a tiny pinging sound above 7,000 RPM. Tore it all
apart and found the piston in the previously seized bore was lightly
touching the head.
Stretched rod.
Damn. I had a reason for not tearing everything down. the rod bolts are
stretch-to-yield, which means you can only torque them once, and I
couldn't get replacements in time to race this weekend. Guess what, I'm
still not racing this weekend, and I have a complete rebuild to do,
including probably replacing that piston, even though it was just a light
graze--only hard enough to clean off the carbon. And this time I'll check
the piston/head clearance even after I make sure all the rods are good.
There may be an exception to the "check and replace everything" rule. The
new rods I'm eventually going to put in this engine make Carillos look
like a bargain. But they're titanium. According to a mechanic who has been
using them in motorcycles for some time, you can salvage these rods after
an engine goes boom, even when it's a big boom (and bike engines rarely go
quietly, especially when they're between your legs). They fish through all
the broken bits to find the rods (which nearly never break--titanium rods
be very strong), clean them up, straighten them, and stick them in the new
engine. The grain structure of Titanium makes that feasible, and the price
makes it necessary.
-----Original Message-----
From: Rocky Entriken [mailto:rocky@tri.net]
Sent: Friday, April 12, 2002 11:38 AM
To: andrew stark; fot@autox.team.net
Subject: Re: engine weight/things that go boom
I have no specific answers to your second question. I'd imagine if you
mill
the block/head you'd be lightening some, but lightening is not the real
purpose for that. However, IIRC you do have to stay with the stock cast
iron
block (no aluminum blocks a la drag racing allowed).
On Q1, however, what you describe sounds "normal" to me. One question is,
what caused the engine to blow. I've blown two engines lifetime, and
determined in both cases it was a rod bolt or rod cap that let go. When
that
happened it threw the piston up into the head with considerable force,
shattering the piston (which is better than cracking the head! Good that
the
piston was able to absorb the majority of the force.)
I'm surprised the rod seemingly survived, but probably it really didn't.
Look close. It's probably bent (even a little and it's toast). The
wristpin
does not surprise me at all. That's a tough little piece of metal. In one
of
my blown engines there was a silver-dollar size hole in the side of the
block (the old cartwheel dollar, not the Susie or the Sac), but no
evidence
of a wristpin anywhere. I figured that as the pin, now free of the piston,
fell, the crank came around and baseballed it out the side. In the other,
the wristpin was in the pan and looking pretty pristine -- but no, I did
not
re-use it.
Remember when all that happens, your engine likely was not at idle --
maybe
6000-8000 rpm. Think about it, that means your engine is rotating
something
like 100+ times per SECOND! Things are pretty violent in there, and when
it
lets go it lets go violently. Parts and pieces are suddenly crashing into
each other and few survive the impact. The piston may take the first hit
and
if its aluminum it shatters pretty easily. Total loss is hardly rare, it
is
expected. And then all those bits flying around inside the cylinder does
the
cylinder walls no good (it can probably be sleeved). If the piston came
off
the crank, probably the crank journal is bunged up (that can be welded,
resurfaced and fixed -- if the crank isn't bent or cracked). Everything
else
in there from valves to rod bolts gets replaced. I felt lucky on my two
blown engines that the head did not need repair. On one of them, the top
of
the flattop piston was jammed into the head intact (everything below the
top
ring was gone) and when I pulled it out of the head there was a neat
imprint
of the headwork, sparkplug and valves.
No, I'd say the damage you describe is pretty much what would be expected.
To me the surprising thing about a blown engine is that the "BOOM" never
really happens. Rather, if you are alone (as I was both times) it is
sudden
silence. The engine's roar is suddenly ceased. First time, when I holed
the
block, it was "what's all this smoke? Omigod, it's me!" Second time, when
I
did not ventilate the block, it was just silence and the tach at zero.
--Rocky Entriken
----- Original Message -----
From: "andrew stark" <whitedog72@hotmail.com>
To: <fot@autox.team.net>
Sent: Friday, April 12, 2002 5:30 PM
Subject: engine weight/things that go boom
> Two weeks ago I ran a SCCA super school in a Gt-4 EXP. I made the first
> day, but 2/3 of the way through the second day the engine came unglued.
Made
> a big boom! education by fire and all that stuff. Needless to say I did
not
> complete school. In hopes of running the IRP school I am helping the
owner
> of the car install a new engine.
> Two things about the engine I am very surprised by are.
> 1: the piston completey exploded taking the cylinder wall with it. There
are
> no pieces of the piston bigger than a quater left. The rod, rist pin and
> valves seem to be relativly ok with just nicks and scraps in them. My
> question on this is. Is this a rare thing to have this kind of total
loss
> on piston?
> 2: The blown engine and the new engine appear to have been lightened. It
is
> very obvious that alot of meat has been taken off the block. These two
> engines were so light that I could pick up the long block without a
> struggle. I am not a strong guy so this amased me. While looking at this
the
> wheels started turning in my head. " My Gt-6 is very nose heavy by
nature
> because of the brick #$#!house of an engine sitting up front. So my
second
> question is can a Triumph engine block be lightened??
> Thanks
> Andy Stark
> 72 EP GT-6
>
>
>
>
> _________________________________________________________________
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