[GMCnet] identifying a Cadillac "500"

[Dan Borlase]

So I'm off to look at a Cadi 500 tomorrow...at least I'm told it's a 500cid (1975)...
There seems to be some ambiguity in identifying a "500" verses a"420".
Can you "500" boys help me understand identifying marks so I do not buy a "pig-in-a-Polk".
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[Larry Engelbrecht]

IIRC, the 425 S code has some sort of "lump" sticking up around the distributor. The 500 S code (and 472 T code) that I have seen do not have this. Also, the 425 has a single plane intake as opposed to the dual plane intake of the 472 and 500. This, of course, is assuming the engine is not a mutt build of parts of various motors. The 368 has very short (in height) exhaust ports. The 425 crank flange has more lightening notches than the 472 and 500 cranks. Maybe get a copy of how to identify Cadillac motors.

The above are merely my recollections.
--
Larry Engelbrecht

San Diego, CA

'73 26' ex-Glacier

TZE063V100319 03/07/73

[Dan Borlase]

Thanks Larry...I'll continue to "investigate".

[Larry]

Dan Borlase wrote on Mon, 27 January 2014 21:50

> So I'm off to look at a Cadi 500 tomorrow...at least I'm told it's a 500cid (1975)...
> There seems to be some ambiguity in identifying a "500" verses a"420".
> Can you "500" boys help me understand identifying marks so I do not buy a "pig-in-a-Polk".

Her ya go, check this:
http://www.cad500parts.com/tech/EngineIDPages.pdf

and if it is still in the car, check this:

http://www.gmcmhphotos.com/photos/g3558-identifying-cad-500-donor-cars.html
--
Larry :)
78 Royale w/500 Caddy
Menomonie, WI.

[Dan Borlase]

Larry...thank you...this will be a big help !! I understand that the earlier years were more "preferred" though I'm not clear on why...Does anyone have any good reason why a 1975 would not work well in our coaches??

[James Hupy]

Dan, I believe that part of the attraction of the early cad eldo's was the
front engine cradle . It simplifies the swap into the motor home. Some of
the earlier engines had much higher compression, and some still hold onto
the belief that high compression and alcohol blended fuels are compatible.
I don't happen to be a graduate of that school. But other opinions will
vary, sometimes a great deal.(GRIN)
Jim Hupy
Salem, Or
78 GMC Royale 403

[Larry]

Dan Borlase wrote on Tue, 28 January 2014 11:08

> Larry...thank you...this will be a big help !! I understand that the earlier years were more "preferred" though I'm not clear on why...Does anyone have any good reason why a 1975 would not work well in our coaches??

Dan, you are welcome. Some say the early years are better, some say the later are. Personally, for our application I don't think it makes a particle bit of difference. You just cannot mix some parts from early to late and visa versa. Unless you want a high compression engine (10.5/1) and don't mind burning high test gas, you need to stay with the 71-76 engines. The 1970 472 and 500's had the 10/1 compression, so I'd avoid that one. The 70-76 472 and 500 eldos had the correct intake, and exhaust manifolds. Also had the correct oil pan. Only the 70-73 eldos had the correct motor mount. 500's from rear wheel drive Cad's will work, but you have to find the motor mount, exhaust and intake manifolds to make it work with our front wheel drive. If you can find a 71-73 eldo, IMO, that makes the best donor car. Has almost everything you need for the swap.
See this for more info:
http://www.gmcws.org/Tech/Caddy_Swap.pdf

--
Larry :)
78 Royale w/500 Caddy
Menomonie, WI.

[Ken Henderson]

Don,

Don't let the front motor mount be a deciding factor. IIRC, MTS sells a
suitable front mount. OR, it's easy to make your own. The one I made has
served me well for several years now -- and allows the use of your Olds
engine mount, which is probably in better shape than any Cad mount you'll
find (the Cad design holds oil on the rubber). It may even lower the
engine just tad. I haven't measured the difference, but I didn't raise
the hatch as much as most do.

http://www.gmcmhphotos.com/photos/g5259-cad-500.html

Oh yeah: Larry probably knows better than I, but I thought the 68-72 mount
was the one that works.

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com

On Tue, Jan 28, 2014 at 12:59 PM, Larry wrote:

>
>
> Dan Borlase wrote on Tue, 28 January 2014 11:08
> > Larry...thank you...this will be a big help !! I understand that the
> earlier years were more "preferred" though I'm not clear on why...Does
> anyone have any good reason why a 1975 would not work well in our coaches??
>

> ...

>
Only the 70-73 eldos had the correct motor mount.
>

...

[Larry]

Ken Henderson wrote on Tue, 28 January 2014 16:01

> Don,
>
> Don't let the front motor mount be a deciding factor. IIRC, MTS sells a
> suitable front mount. OR, it's easy to make your own.
>

> http://www.gmcmhphotos.com/photos/g5259-cad-500.html
>
> Oh yeah: Larry probably knows better than I, but I thought the 68-72 mount
> was the one that works.
>
> Ken H.

Ken is right, it is the 68-72 mount that is the one you want. NOT the 73'. And it is The Cad Company in Alburquerque, New Mexico that has a mount for the 500 in a MH. MTS does not. It is not in their catalog, you have to call and ask about it. If you have the equipment and skills, Kens mount is the one you want. JMHO

--
Larry :)
78 Royale w/500 Caddy
Menomonie, WI.

[Dan Borlase]

Thanks guys...I'm going to see this eng. to morrow and will make sure it's a 500. It is a 75 model year which as I understand is a lower compression than some. The man says its complete so we will see if that is true. obviously I will have it completely rebuilt which should make someone happy as the coach is FOR SALE.
Why build an eng. for it...because a dead coach is a worthless coach, even if it is a full body off reconstruction, stretched to 29.5'.

[Bates]

The Cad Company no longer sells this mount. Is there another source?

[gene Fisher]

This might help
http://gmc49ers.blogspot.com/2013/12/good-news-for-gmc-ers.html

Erf

--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Ken Henderson]

Bates,

Since I only received your one-sentence message, I can only assume that
"mount" refers to the CadCo front motor mount for the Cad500. If so, this
and following photos may help; they show the one I'm using, which allows
use of the Olds isolator, in the original crossmember holes:

http://www.gmcmhphotos.com/photos/cad-500/p32488-060-cad-500-front-mount-w-olds-rubber.html

The main reason I designed and built that mount was because the Olds
isolator ins inverted from that of the Cad -- it deflects oil away from the
rubber instead of collecting it. I saved the cost of having the Cad
isolator rebuilt -- immediately and frequently in the future.

Ken H.

[Bates]

Yes, I am looking for the front mount for a Cad 500 in a GMC using the Olds rubber. I was hoping someone was selling them. If not, I will attempt the
fab per your photos. Thanks

[John Biwersi]

Some suggestions and information regarding the 500 Cadillac engine. First, get a copy of the book titled Big Inch Cadillac by Doc Frohmader. Lots of
great information and sources. As for front motor mounts , the wish bone style that works very nice for the conversion was used on the 68-72 Cadillac
Eldorado. It is wise to get the rubber portion of these remolded. Steel Rubber Products has in the past done this remolding. An advantage of this
mount is it is very compact which is beneficial when working around the final drive. I can sell you one of these for $75 plus shipping. It needs to be
remolded. I don't know what Steel's current pricing is for remolding. You will be able to find out on Monday. Another thought for you is to use the
the wings of the 68-72 mount and adapt them to the motorhome Olds motor base similar to Ken Henderson's design. If you proceed with the 500 cadillac
swap, I suggest you seriously consider a shaft rocker arm system. If you stay with the original T stand design then you should get a retainer plate
installed in the lifter valley which will prevent the lifters coming out due to a valve train failure. If the lifter comes out, the engine oil
pressure drops in a heart attack second. I know of 2 members on this forum that probably will support this suggestion. For information purposes, I do
have an original Cadillac Port injection manifold, throttle body, and fuel rails for the 472 and 500 Cadillac engines for sale.

[Don Jeffers]

John Biwersi wrote on Sat, 23 August 2014 16:33

> I do have an original Cadillac Port injection manifold, throttle body, and fuel rails for the 472 and 500 Cadillac engines for sale.

Sending PM.

Don and Susan Jeffers