How do they engineer the mating of 2 diff. metals?

[Cad1]

Just curious, like the 4.9 with the aluminum block and the iron heads I believe it is; how do they keep the same expansion rates during thermal-cycles or is there a degree of difference in expansion that is acceptable?

Cad1

[TDK]

Cad1,

I'm not certain if the 4.9 has cast iron heads.

But a quick ramble regarding thermal expansion of metals and very loosley applied to engines.

The values for metals are around 10 x 10^-6 per degree centigrade or about one thousandth of a percent change per degree.

So, if the metal temp was at 250f on one part but not the other (let's say at 0f for some really dumb reason). That results in length change of about a 10th of a percent. That would be less than a 64th of an inch on a ten inch piece of steel. Significant sure - but only if one part was really hot and the other really cold (not very probable with successful engine design and coolant circulating). I'm certain the coolant/combustion engineers are frothing about the details just about now...

Aluminum and cast iron do have differant rates of expansion, but its managable. Galvanic corrosion is usually more of an issue.

Regardless of the possible differances in the thermal expansion rates of aluminum and iron, the coolant's job is to collect/distribute the engine's heat and of course pass it to the raditor for cooling. The temperature differentials and resulting expansion-contraction rate differentials of the two metals or assemblies - should be minimal for the temperatures normally experianced at the gasket area.

And I would guess as you did - that the gasket technology is all about handling any expansion/contraction issues.

Considering that aluminum heads have been around a very long time with cast iron blocks, I would guess that the aluminum block and its "thread holding" capabilities might be more of a concern with thermal cycling - given the high stresses to begin with.

However, IF Guru posts on this interesting subject - then forget all of the above generalized BS and go with what he saz regardless...

[Scotty]

Bbobynski, has somewhat covered this subject already. Someone else brought this issue up as a potential flaw in the NS relative to the bolts. The dissimilar metals issue and the potential for electrolysis and corrosion is a good question, and bbobs answer should calm your fears. This is one reason why keeping the coolant fresh is important. I hope this helps, Mike

http://caddyinfo.ipbhost.com/index.php?sho...5&hl=dissimilar

[Matt]

I just spent about 40 min reading through all the links posted on this subject. I think any one who comes to this post should do the same. If you enjoy learning from this site as much as I do you will love this posted topic. Sit back, take your time, learn with a laugh or two, you will love it.

[navion]

I remember the post that Scotty is referring to.

That guy must have thought that The Cadillac 4.9 and N* were the first in history to use both aluminum and iron or steel in an engine. If memory serves, aircraft engines were using aluminum cases and steel cylinders as far back as the twenties. Probably farther than that.

If this was an issue then it as been a long time being found out! I thought that the guy was a troll. As far as I know, EVERY car manufacturer has at one time or another used some combination of aluminum and cast iron. Aluminum heads & cast blocks. Aluminum blocks and cast iron heads. Probably millions of them in service now. This fellow thought that Cadillac was venturing into unknown territory.

The tone of his post looked to me like he was trying to start trouble.

I don't think that Cad1 is doing anything other than asking a question.

Britt

[Scotty]

Not at all Cad1 is just curious. I was trying to help with a good post by Guru on dissimilar metals..

[navion]

OOPS!

If I gave the impression that Cad1 was trying to stir up trouble, I apologize. I think that he was asking a legitimate question.

I was referring to the guy who posted about the N* aluminum block with steel bolts. & I confess, I didn't go back and read it. I was trying to go from memory & I forgot that my memory is bad.

Anyway, I was sounding off on the other guy, who sounded like he had an axe to grind, not Cad 1.

Britt

[Scotty]

On the contrary you have a good memory, that guy was trying on my patience and said some annoying things and it still took quite some time to remember the details so that I could find the post through the search function. I suppose that is good that I can forget the annoying part of the thread BUT still remember bbobs excellent seminar on dissimilar metals....

When I went back it appears that some of his posts were removed so the thoughts are at times choppy..

[Cad1]

Thanks for the feedback. I can see those posts are going to take some time to read through. I tried a search but wasn't sure what it would be called. I guess galvanic corrosion in a car motor is similar(maybe) to what happens on a boat motor. Those little metal blocks that sit above the prop to cull all of the deterioration to one central location. That piece of metal gets all corroded and discolored while everything else stays nice and clean. Maybe it is a magnet, I can remember for sure.

The reason for the head gasket leaks is b/c of not maintaining coolant and adding supplements before the orange coolant came around, right? Not why I started the topic but those other posts bring up the question.

That link of posts reminds me of the flame battle on the old forum. Man that was a drag. One reason I like the caddy board is b/c we don't flame the crap out of people like on other boards. We disagree from time to time but still get along well.

Cad1

[navion]

Cad1,

The metal used for galvanic corrosion protection in boats is zinc. It is a sacrificial metal that will act as the point where the electrolysis attacks the propulsion unit or hull if the hull is metal. It must be kept clean and free of paint. (I have seen several that the owner painted "because it was corroding!")

Needless to say they had other corrosion problems shortly after that.

If you have a boat that remains in the water (especially salt water) these sacrificial zinc's should be checked regularly. If the boat is hooked to shore power, then this multiplies the eroding of the zinc (or other metals, if the zinc is not kept clean.) I have seen propellers that looked like lace doilies because of the electrolysis.

In Caddies, the 4.9, 4.5 & the 4100 engines are more prone to damage by not having the coolant changed and treated regularly. However, the N* benefits greatly also.

Take care,

Britt

[Cad1]

"The system is designed so that the iron liners sit slightly proud of the aluminum deck surface."

-Does that mean it sits above or below the surface? It sounds like above but it must sit below to prevent the overcompression as mention in the last sentence.

--------------------------

"IF all the aluminum is at the same temperature then RELATIVE movement in the joints is avoided. Relative movement in a joint will scrub and tear the gaskets."

-Does that mean there is relative movement with the 4.x engines but there is a special gasket that doesn't scrub or tear? What is the material for the gasket, brass?

----------------------------

I need to re-read it again but had to say thanks for such a throughout post. I feel like I can apply for a thermal job at GM and ride it to the top of the company?

[JasonA]

I thought I read somewhere that the cooling system supplement was originally intended as a "head gasket lubricant" on the 4.x engines due to a lot of movement with the head gasket due to different metals.

It sounds odd to me...in theory, the coolant should have little interface with the head gasket itself. But for some reason, I thought I read it here somewhere. Am I senile...at 26 years old...already??

[67coupedeville]

Thank you Guru for such fantastic information, I can finally explain to people that Duramax diesel engines are not going to "blow up" as so many people have told me because they have cast heads and aluminum block. Great info, thanks again.

Spence

[Scotty]

I did not know that they made aluminum pistons. They must weigh a lot less than a forged piston. When the pistons and rods are lightened thereby lightening the rotating mass, in what way does that effect the engine performance? Thanks Guru

[67coupedeville]

Uhh....Duramax diesels have cast iron blocks and aluminum heads I believe....

Yea I had that BASS ACKWARDS!

Spence

[JasonA]

I was flipping through the channels Sunday afternoon and caught some of the F1 race on CBS. The onboard telemetry recorded repeated 19,000 RPM upshifts on those engines. Not much iron in those babies, huh?!

[Bob D]

I was flipping through the channels Sunday afternoon and caught some of the F1 race on CBS.  The onboard telemetry recorded repeated 19,000 RPM upshifts on those engines.  Not much iron in those babies, huh?! 

Not much stroke in the crankshaft, either....LOL.

The crank stroke is dramatically reduced to allow that RPM. Piston speeds in an F1 engine are not that much higher than some production engines at redline as the piston speeds are the critical, limiting factor. So, they reduce the stroke considerably to allow that RPM. They also use a pressurized air pneumatic valve "spring" to eliminate valve spring surge and fatigue. Pneumatic valve operation is pretty much mandatory as the RPM goes over 12,000 or thereabouts.

What's spinning that compressor? Chain? How much hp is it robbing? What level of psi is required for that pnuematic valve train?

Questions, questions..

[JasonA]

The crank stroke is dramatically reduced to allow that RPM. Piston speeds in an F1 engine are not that much higher than some production engines at redline as the piston speeds are the critical, limiting factor. So, they reduce the stroke considerably to allow that RPM. They also use a pressurized air pneumatic valve "spring" to eliminate valve spring surge and fatigue. Pneumatic valve operation is pretty much mandatory as the RPM goes over 12,000 or thereabouts.

Wow. Fascinating!