1956 Cadillac 365 Heads, should I have them redone?

[Christopher Petti]

Hi gang,
  I have my 365 apart because I had to do some repairs. I have the heads off and was wondering if a head job would be a major improvement? The engine ran great when I took it apart. I have cleaned the heads but was thinking of putting hardened valve seats in and improving them. Has anyone done anything to the heads on their 365 and was it a major improvement in the way the car ran? I'm at a cross roads. I can put the car back together now and not spend the money. OR! since the labor is already invested should I just have the heads redone and wait a few months to reassemble it? I'd love to hear your comments.

Chris

[dplotkin]

 
If I had the heads off a car I would without hesitation send them to a machine shop and have them freshened up with a nice three-angle valve job, new valves if needed, and new springs. As for hardened valve seats, that is a debatable subject. I have come to believe, based on discussions with lots of knowledgeable folks, that hardened valve seats are unnecessary for a low RPM low-load and low-use engine such as that in your car. The bennefits of hardened seats come in high load, high usage such as towing a trailer or hauling *ss down a interstate every day pulling grades or a lot of weight.

There is a small but real risk of damage to heads in installing them, many Corvette guys and other owners with rare heads would never take the chance.

Dan

[Dave Shepherd]

To add ,the seats issue would only apply to the exhaust as doing the intake is unnecessary.

[CEC #20099]

Re: 56 heads. These were very prone to CRACKING. Have them Magnafluxed or pressure tested before any more $$ are spent.
c chleboun #20099

[Walter Youshock]

Have them done now.  No sense putting them back on and then taking them off again next year.  While you're at it, you can more easily detail the firewall.

[Christopher Petti]

I was talking to my HAMB buddies and Studedude explained to me that Cadillac heads have a lot of nickel in them. He said the hardened valve seats aren't needed because the ethanol gas we have today doesn't effect the 365 heads at all. Any truth to that? I'm planning on doing a triple grind and opening up the exhaust ports for breathability. I'm also planning on smoothing out and polishing the interior of the intake manifold.

[dplotkin]

Never heard of the nickle thing.

I doubt you will much notice any improvement in performance resulting from porting and polishing on an otherwise stock engine. Especially a 285 HP 365 behind the "controlled coupling" Hydra-Matic in a 4,000++ Cadillac. There will be a scientific improvement in flow, but it will get lost in all that transmission fluid and weight. The porting & polishing routine works best with a package that includes bigger intake & exhaust and more carburation among other things; and even then the bennifits don't really materialize until high RPM's, speeds Cadillacs seldom go. Remembering that an engine is ostensibly an air pump, incremental improvements in air flow don't add up to much on an engine as naturally restricted as the 365.

Having said that by no means do I oppose the idea of hot rodding a Cadillac, but I didn't get the idea that is what you set out to do.

Dan

[Dave Shepherd]

Never heard of the nickle thing.

I doubt you will much notice any improvement in performance resulting from porting and polishing on an otherwise stock engine. Especially a 285 HP 365 behind the "controlled coupling" Hydra-Matic in a 4,000++ Cadillac. There will be a scientific improvement in flow, but it will get lost in all that transmission fluid and weight. The porting & polishing routine works best with a package that includes bigger intake & exhaust and more carburation among other things; and even then the bennifits don't really materialize until high RPM's, speeds Cadillacs seldom go. Remembering that an engine is ostensibly an air pump, incremental improvements in air flow don't add up to much on an engine as naturally restricted as the 365.

Having said that by no means do I oppose the idea of hot rodding a Cadillac, but I didn't get the idea that is what you set out to do.

Dan

Agreed, no reason to do any head work on a stock engine with the carb and intake/cam combo, it will have little or no effect on performance.

[Christopher Petti]

OK, dually noted. I want to hot rod it but I just don't have the funds for that. Maybe once I've driven the car another 50k milles. Thanks guys. Here's another question a little off topic. I bought motor mounts from Rock Auto and they are larger than the originals. They go on the outside of the engine casting rather than the inside like the originals. They don't fit correctly. I was thinking my engine needs to be pulled foreward to get them to fit in because they are off by 1/2 and inch from sliding into the slot in the frame. I'm thinking of forking over the dough and gettting a set of originals. I don't think my transmission mounts slipped and the engine moved rearward while I was propping up the engine. Maybe I should start a thread? See if anyone else has had this issue. Wouldn't be the first time I got generic parts from Rock Auto.

[J. Gomez]

Chris,

Words of caution, the 1956 motor mounts are not the same as the 1957..! The 1954-156 are the same per the MPL 146 2934.

I know this first hand as I purchase a set from a local auto parts which they cross reference to be the same for 1956-1961 and found after installing them the drive shaft was too high.

The 1956 motor mount are slightly higher (can’t recall off hand) than the 1957-1961 ones, the later one fit but it places the tranny to tilt higher at the tail just a few degrees.

I’ve notice Rock Auto list the same part for 1956-1961 but nothing for 1954-1955 , so that is incorrect.

Just as FYI

[Christopher Petti]

Thank you for your comment! Youre always a big help! I'm goign to take them off tonight. Hopefully send them back if I can find the reciept.

Chris,

Words of caution, the 1956 motor mounts are not the same as the 1957..! The 1954-156 are the same per the MPL 146 2934.

I know this first hand as I purchase a set from a local auto parts which they cross reference to be the same for 1956-1961 and found after installing them the drive shaft was too high.

The 1956 motor mount are slightly higher (can’t recall off hand) than the 1957-1961 ones, the later one fit but it places the tranny to tilt higher at the tail just a few degrees.

I’ve notice Rock Auto list the same part for 1956-1961 but nothing for 1954-1955 , so that is incorrect.

Just as FYI