Technical Liquid Nitrogen-Valve Guides

I have Silicon Bronze valve guides to press in an iron block. Would like to cool them enough to slip in [small afraid of deforming], freezer doesn't seem to be quite enough. So thought dry ice; but to be sure liquid nitrogen ought to do it. Too late to call any suppliers to see if liquid nitrogen available to general public. Thoughts?

 

I would think a few days in the freezer would be enough.

liquid nitrogen should be available and any gas supply house.or dry ice.

what are your thoughts? Hopefully just slip them in without pressing ?
I guess to avoid honing and machining afterwards ?
Would you still not have to trim them to length?

sorry just intrigued and confused. Help a fella out!

 

Installation of guides isn't finished until honed or reamed, especially today with the corn gas.

 

Just looked into it here in Canada you don’t need any special license to purchase liquid nitrogen. But you do need to buy the container!!!

 

Put rubbing alcohol in a pail with the dry ice. The alcohol will transfer the cold much better then the air between the chucks of ice and not freeze. I did that in a shop we were pressing pins in a very tight hole. A few minutes in the juice and the pins fell in. After we were done I spit my chewing gum into the bucket and a few seconds later I could hear it crack. Liquid nitrogen will hurt you., like fingers falling off.

 

If you use liquid nitrogen you will need to cool the parts slowly. Metal cooled to quick will crack.

 

Make sure there's some setup to stop the guides at the right depth.

 

I use rubbing alcohol in dry ice works fine.Did it on my old Farmall Cub long time ago

 

Wonder how that stuff plumbers use to freeze pipes would work? Liquid Nitrogen doesn’t sound safe to me.

 

I've used co2/halon fire extinguishers to shrink parts, don't know if it'll work for this application. Use thick gloves and keep bare skin away from the nozzle! Put small parts in a bin or jar so you don't blow them across the garage.

Oh... and don't use an extinguisher you rely on for future fire safety.

 

Sometimes it's easier to heat one part, rather than cool the other part enough to make the same difference in size. Sure, cast iron probably changes size with temperature less than the valve guides, but there's a definite limit to how cool you can get something. -273.15C is as cold as anything can go, while you can heat cast iron until it melts at +1200C or something like that, should you want to. Joking aside, it's way easier to heat things than to cool them down once we get below about -50C.

 

There was a prison used made by Goodson. Thayer a engine building tool supplier that you spray on and and is meant for valve guides and piston pins. I’ve done 100s of guides this way. You need to measure the id/od and make sure you have the correct interference fit. Shrinking is fine but may not be necessary. And as mentioned you need to have a stop so you don’t go to far or not far enough. If shrink /expand and have to make a small adjustment the braking force to move it will be greater and potentially cause more problems.


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Back in coll-edge I saw liquid nitrogen poured into ordinary thermos bottles.
Great fun freezing erasers and shattering them.

 

We use dry ice sometimes. I am pretty sure that you can buy liquid nitrogen if you want to, but dry ice should get the job done for ya.

 

Holes for the guides are .4375, guides measure .4395 to .4398. So about a .002 press and length is to size. Made a set of pliers with a depth set for guide height. Went to freezer to get some ice and experiment with alcohol and found a bag with some dry ice in it so I took some and dropped a guide on it to see how much shrink it will do. I took an ice cream sandwich while I was there too!

 

Not to avoid sizing ID or length. Just so they don't self broach any material off of the OD on the way in.

 

Usually you need to also heat the heads or block, its kinda' a two part process. Freezing the guides alone may not be enough to shrink them enough to fit.

 

I would also make a punch to act as a mandrel, loose inside ID with a shoulder to drive them in.

 

Dry ice is approx -40F (-40C, same at that temp). The alcohol solution with dry ice is best way to transfer the cooling.
You can also heat the head to add additional clearance.

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Well my dry ice experiment was a dud, cause it wasn't dry ice! The ice cream sandwich was good. Tomorrow I will find some real stuff.

 

Damn! Now I want one and there are none in my freezer.

 

Sorry bout the sandwich. I got the dry ice today, $3.00 a lb, so should know something by tomorrow; meanwhile another sandwich is doable

 

I like ice cream!

 

Tried the dry ice and alcohol. Coldest the guide got was about 1°, good for about a .001 reduction on diameter. Went and checked the freezer temp and it turned out to be about 1° so the dry ice is more or less a wash. So I called Airgas for liquid nitrogen, yes general public can get it but you have to have special container, available for purchase at over $200. Cryro- something container. Not thrilled with that cost I found "freeze spray" aerosol can of Liquid Nitrogen, claim -60° in 3 seconds. We will see what it can do, got a 10 oz can coming tomorrow. I wonder how long it will last, good for warts and skin tags too. Back to the freezer for an Ice Cream sandwich.

 

Up date.. Tried the Freeze spray, 3 second hit. Temp got down to -34°, good for another half thou. I think it will be enough, at least to make me feel more comfortable. Made an alinement/depth bushing so gathering up the gallunes to start pressing. Time for ice cream

 

I'll take one with vanilla only please.....

 

Now you got my shop inspector wanting one too and I still don't have any.

She is pouting and getting grumpy.

 

Did you start with the guide at room temperature for the 3 second spay or out of the freezer. You may get a bit lower temp if you pre cool the guide in the freezer.

 

Great idea I will give that a shot! Thanks..

 

Why do I get the feeling your shop inspector is going to be getting the boss ( your wife that is) involved in this.


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