[Skip Fix]

So does the different expansion rate of an aluminum block affect main clearances needed? Steel cap on aluminum block cause movement?

[GTOGEORGE]

Originally Posted by Skip Fix

So does the different expansion rate of an aluminum block affect main clearances needed? Steel cap on aluminum block cause movement?

Thats a good question.........!


GTO George

[Skip Fix]

Probably overthinking it but curious minds want to know

3" main if that matters.

[JSuchma]

Originally Posted by Skip Fix

So does the different expansion rate of an aluminum block affect main clearances needed? Steel cap on aluminum block cause movement?

Not exactly the same question....... but I have always wondered if you have to adjust the clearances if engine parts are machined in the dead of winter or during a scorching summer. On top of that, as Skip knows down here in Houston
the temps can fluctuate 20 to 30 degrees in a matter of hours during the seasonal changes. It has to affect the expansion and contraction of the metals involved during machining. In fact, cast iron blocks and heads sweat down here due to the fluctuation in temperature and humidity.

[steve25]

It’s my understanding that a steel cap on Aluminum is not the issue, but the added main bearing clearances are needed to be well on the safe side of not pinching a main bearing bore.

Thick areas of Aluminium absorb heat much faster then thinner sections will, so the upper area of the main web that the crank bore passes thru will expand more .
This combined with how the cooling front to rear of the block veri’s can make the crank bore shift around from web to web enough to call for that added .0005” of clearance over that of a iron block running .0035” already.

[PAUL K]

The answer is probably not, but we tend to set all our aluminum block builds of on the tight side. We also set the rod bearings towards the minimum suggested clearance when using aluminum rods and have had zero issues. One set of aluminum rods had more than twenty years of hard service and the rod bearings looked reusable when the engine came in for a freshen up.

[PAUL K]

Originally Posted by JSuchma

Not exactly the same question....... but I have always wondered if you have to adjust the clearances if engine parts are machined in the dead of winter or during a scorching summer. On top of that, as Skip knows down here in Houston
the temps can fluctuate 20 to 30 degrees in a matter of hours during the seasonal changes. It has to affect the expansion and contraction of the metals involved during machining. In fact, cast iron blocks and heads sweat down here due to the fluctuation in temperature and humidity.

All clearances are spec'd assuming 70° (or something like that by the SAE) ...... so technically the clearances need to be checked and adjusted for that temperature. I can't think of anything on an automotive engine rebuild that would change enough to make a big difference. Your best chance would probably be checking an aluminum rod bearing clearance in a sub zero atmosphere.... But not sure that would make enough of a difference to matter, or whom would be attempting that.

[JSuchma]

Originally Posted by PAUL K

All clearances are spec'd assuming 70° (or something like that by the SAE) ...... so technically the clearances need to be checked and adjusted for that temperature. I can't think of anything on an automotive engine rebuild that would change enough to make a big difference. Your best chance would probably be checking an aluminum rod bearing clearance in a sub zero atmosphere.... But not sure that would make enough of a difference to matter, or whom would be attempting that.

Thanks Paul K.
Now I can put that thought to rest after all these years of wondering.

[Skip Fix]

So what clearances Paul? 0.002-0.0025 for mains?
I guess saddle could grow larger and get looser or grow down from expansion to steel cap and pinch things tighter.

[Jack Gifford]

Originally Posted by Skip Fix

... Steel cap on aluminum block cause movement?...

I don't think it's significant. But I've tried to minimize it on my aluminum blocks by making the center three main caps of aluminum alloy (2024 & 7075).
I feel that bearing "crush" is more of a concern than clearances in aluminum blocks or rods.

[PAUL K]

Originally Posted by Skip Fix

So what clearances Paul? 0.002-0.0025 for mains?
I guess saddle could grow larger and get looser or grow down from expansion to steel cap and pinch things tighter.

Hi Skip, if the we were shooting for .002 to .0025 on an iron block, I'd try to get it between .002- .0023 if it was an aluminum block. Our target clearance is based from the parts being used and the intended application.

[Skip Fix]

Thanks Paul.

And Jeff you are right about the humidity in the shop. I added dehumidifiers this year. When it has been cold then a warm moist front blows in, my cars in the shops are dripping with water-as in it will drip on your face if under them. Surface rust and that white powdery stuff on aluminum just being in the shop! Tractor rear tires are filled with water for ballast for the front end loader and they sweat so much it looks like you threw a 5 gallon bucket of water on them!