Repair or replace engine 75 Eldorado Convertible

[Tpicks55]

Im to the point of looking at the engine. Do I overhaul my old engine or should I go with a LS1 replacement?

cost either way?

resale value better or worse ?

[The Tassie Devil(le)]

Rebuild your original engine but to 1970 specs. if you can.

Parts are available, and a lot easier, and cheaper than trying to slot in any other engine.

The big problem is going to be fitting everything on top of the Front Wheel Drive.

There is a crowd here in Australia fitting an LS engine into a '74 Eldorado Convertible, but they are going overboard in converting the car to Rear Wheel Drive.

Bruce.

[2011DTS]

Rebuild, Bruce is correct the 472/500 motors and transmission were developed together. There are several firms that will rebuild your 500, as Bruce says to 1970 (increased horsepower) standards and you will not be disappointed, IMHO.

["Cadillac Kid" Greg Surfas 15364]

putting a puny LS motor into a full sized eldo is not something I personally would consider an option. Rebuild your motor, and don't worry about going to 10.5:1 compression like the 1970 500. First of all it will barely run on 93 octane and any HP increase (approximately 15 over the 9:1 you get with flat top pistons) would not be noticeable. The semi myth of compression ratio increases HP is just that. With an increase in compression ratio you CAN increase efficiency leading to lower fuel consumption, but actual HP is determined by how much air and fuel you can flow through the motor.
Resale with anything but an original motor goes in the toilet, and realistically you are going to have to do some research with local machine shops as far as the cost.
Greg Surfas

[TJ Hopland]

Whats wrong with it now?   Does it even need a full rebuild?   These were a good design and well built and typically very well maintained for much of their lives so even if they got less maintenance later in life they usually still survive in pretty decent overall shape. 

[Big Fins]

Why anyone would take a Cadillac engine out and put anything else in its place puzzles me. I'm not sure anything but a 425/455 Olds would even bolt up to the THM 425. Even then, you throw the entire car out of balance.

I also echo the question, what's wrong with it? Does it have over 100,000 miles on a poorly maintained engine? Is it out of the car already? Oil burner? Leaker? 

[Tpicks55]

Has over 100k miles, smokes, but runs decent.  It has leaks as usual due to it setting for 25 yrs.

[Big Fins]

Then it's worth pulling and going through it. Get a good machine shop to disassemble it and evaluate the internals. These are stout engines. Maybe a simple honing, re-ringing, bearings seals and the heads gone through. Because you're going to have to pull the transmission with it, have it resealed and new soft parts put in it.

Much easier to pull these as a unit than trying to separate them in the car.

[35-709]

I would rebuild it to stock specs, in 1971 and forward those engines were built to run on Regular gas, not Premium.  Unless you are going to street race or drag race it, the difference in horsepower will be negligible for a road car.  Yes, the earlier engines had big HP numbers but much of the decrease in advertised HP numbers was due to an across the board industry change from gross horsepower ratings to net ratings, and some of the early attempts at pollution control which can be eliminated in the rebuild if wanted. 
Both of my 472s ('71 and '73) run fine on 89 octane non-ethanol, except on road trips I run regular pump gas if non-eth. is not available.  One way or another, they both have plenty of stomp.  My opinion. 

[James Landi]

Your engine smoke may disappear with some "fixes," and over time and with use. Have you soaked each cylinder with Marvel oil, have you taken  a vacuum test, and next,  a compression test? One piston may have stuck rings. My advice, look at every diagnostic  method to eliminate unnecessary expense.  Except for the timing gears and seals, the basic block is very durable, unless, you're looking to restore the car to like new condition and so, in that case, all parts, engine included, are subject to renewal.   

[TJ Hopland]

How many miles and what sort of driving have you done with it recently or since you have owned it?  If its been sitting a lot just driving it may help the smoke which then would just leave external leaks to deal with which is a lot cheaper than a total tear down involving machine shop work.

Compression test and then adding something like the marvel and retesting is probably worth doing and its pretty easy on this car since the engine sits up pretty high and the plugs kinda point out at you.  Let us know if you want to do that yourself and need advice on how to do it.  Its really not that difficult and a compression gauge is like $50 these days. 

[Jeff Rosansky CLC #28373]

Is it new to you, and has just been sitting?
For what it's worth, our 55 had been sitting for years. I had more oil smoke out of the breather than out the exhaust.
Marvel's, heat cycles, and a few hundred miles freed them up.  Now it just leaks.

If you do go LS, keep the original engine for the next owner.

[bcroe]

I would never rebuild an engine if it has good
compression and no strange noises.  Most of my
engine problems have been with new rebuilts.

I would first get a new timing chain set on it. 
If compression is OK but it smokes, check the
seals on the valve ends.  These can be changed
without even removing the head, by cranking each
piston to the top of stroke to prevent the valve
from falling into a cylinder. 

Personally I like engines that burn the cheapest
unleaded gas, like yours.  But a higher compression
set of 70 pistons could add some power, if you can
find and afford good enough gasoline.  Changing to
a different engine will bring a very long list of
problems.  good luck, Bruce Roe

[Tpicks55]

I have owned it since 2012. It was sitting in a storage area for 25 years prior to me.  I havent driven it much due to it being apart in various stages.  It is finally ready to tackel the engine.  I know I should have done it first.  I could try the marvel oil o see if it helps.  I need to find a good shop to do the work but my luck with outsourced projects is bad around here. 

Thanks for all the advice it is appreciated.  Tony

[bcroe]

Getting another 70s car, the first thing I worry
about is changing out the timing chain set, before
this time bomb can wreck my engine.  Immediately
after that is tires and ALL of the brake system, so
I will not wreck.  The exhaust and fuel system may
soon need attention.  And the transmission must be
gone thru, installing a cheap seal kit can avoid
a catastropic failure as a clutch piston fails to
maintain pressure. 

There are a lot of sealed ball bearings that may
fail from dried out grease, but are easily replaced. 
good luck, Bruce Roe

[TJ Hopland]

IS the rest of the car ready/safe to drive?  If so I would try to drive it a bit and see what happens.  The internals may fix themselves just by some use and fresh fluids.  If the engine isn't clean clean it and that way you can better see where leaks are coming from. 

[Jeff Rosansky CLC #28373]

Put at least 500 miles on it before you decide to do anything major.