> Date: Fri, 14 Jun 2002 12:18:37 -0700
> From: "BORDER,RYAN (HP-FtCollins,ex1)" <ryan_border@hp.com>
> Subject: [oletrucks] GM V8 Engine questions
>
> Do GM big block and small block engines share the same output shaft and
> bellhousing mounts? (Will a tranny from a small block bolt up to a
> big-block)?
The small and big block Chevy V8s have the same bellhousing pattern,
flywheel pattern, and side mount location. But a big block will not fit
in many small block powered vehicles, because the engine is a couple
inches longer, wider, and taller. On TF trucks with stock steering, the
engine will need to move to the passenger side about 3/4 inch to clear
the steering, and the engine usually wants to sit forward about half an
inch or so so the heads will clear the firewall. The front block mounts
from a small block (as used originally to mount the 265/283 in TF
trucks) will not fit a big block. And if you try to use a big block
with the original bellhousing mounted to the original crossmember (for a
manual transmission setup), then you'll find that the steering and
exhaust will be interfering with eachother. Been there, done that. Big
blocks work best with an automatic tranny, side engine mounts, and a
rear tranny crossmember mount...just like they were mounted in newer
cars/trucks.
The small block 400 is externally balanced, and has a special weighted
flywheel. The 454 is also externally balanced, and uses a different
special weighted flywheel. The 283/305/327/350 and 396/427 all use the
same flywheels, so you can use a 350 flywheel on a 396, but not on a
454, for example.
Also, the small block got a different flywheel bolt pattern and balance
in the mid 80s, so the 87-up 305/350 flywheel will not work on the big
blocks.
> What is the typical cause of "rod knock", and what is the usual repair
> entail?
The usual cause is a worn rod bearing, and the usual cure is taking the
engine completely apart, getting the crankshaft reground, and the rods
resized...but we usually wind up reboring and putting in new pistons,
replacing the cam/lifters, and doing the heads...because it usually all
needs to be redone by that time. Usually a simple little rod knock
repair will end up costing $2000 or so, unless you pull the engine and
do the disassembly/assembly work, in which case it'll only cost about
$1000-1500. Or, you can try to patch it by just replacing the bearing,
and have it start knocking again after awhile, and then spend all that
money later. If you haven't messed around inside engines much, you will
probably want to take parts to a machine shop you trust (ask around in
town to see who has a good reputation) so they can help you decide what
to do. Honest machine shops will generally recommend that you do all
the work, but they will tell you what is probably ok to use as-is.
"Good looking" cylinder bores with 0.005" or more taper will not make
for a long lasting engine! You get into a judgement thing; you have to
decide how much money to spend based on how long you want the engine to
last, and this has to be determined by how much money you have, and how
long you will actually keep the engine.
But don't feel you have to replace everything, I've been running the 396
in my truck for 6 years after doing a half-way complete rebuild...it was
starting to knock, one of the rod bearings was going, and I had the
crank reground, resized the bad rod only, had the block honed (it had
quite a bit of taper, but less than 0.010"). I also replace the cam,
lifters, timing chain, cam bearings, and had the heads redone with new
valve springs. Now it has some interesting piston knocking noises at
times, but since I don't drive the truck too often, less than 5000 miles
per year, it's lasted this long and still works ok. I spent more than
$500, but less than $1000 on it, but instead of lasting 100k miles, I
only expect it to last between 25 and 50k miles.
> I'm on a little detour here on my project- as I have apparently
> over-estimated the abilities of my air-cleaner: my small block has done it's
> best impression of the wierd kid we all knew at the playground... it ate
> sand. I caught it very quickly (hopefully before real damage was done) as
> the carb went to hell immediately. Head's are off, bores look OK to my
> untrained eye, but it's going to be a real bear to completely clean. Any
> bright ideas short of stripping it completely down and having the block,
> heads, and intake manifold tanked?
No, you'll have to take it apart to get it clean. You would want to
have a machine shop hone the block, to see if it's ok, because you can't
really tell about the scratches in the bores until you hone it. You
might try running a light duty drill powered hone thru the bores and see
how it looks, but if there are noticable vertical scratches in the
bores, it will need to be honed with a real (machine shop) hone, and
possibly rebored if it's too bad.
> Sigh.
yeah....
> Before putting a ton of effort into it, I am considering just dropping a
> big-block into it. I think I've found a 454 cheap, but owner says it has
> "rod knock". How scared should that make me?
that should make you check your bank account, if you don't have another
$1500 to spend fixing it and another $1000 for the swap, then you might
want to keep the engine you have now. I would buy the 454 anyways,
because I collect them...but you may want to wait until you have a lot
of pennies saved up, because it seems that big blocks cost more $$$ than
you think they will.
> Found a Caddy502 which was also of interest; until I started pricing parts
> for it. An oil pan with the rear sump (required for installation) cost
> almost as much as the engine, for instance.
>
> Ryan.
Yeah, oddball stuff can cost a fortune to swap in. That's why everyone
runs Chevy 350s, they're cheap! and they work.
Jim F
59s in AZ
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