Freeze Plug Press Fit

jrmach · May 7, 2019

So a customer came to me with concerns that his new freeze plugs he just bought for 2 engines he is building are to much oversize.
I tend to agree
BUT,I am not a race guy
You can see in the pic these are not ordinary freeze plugs
There are 4 of them per engine
Cast Iron Block,Aluminum Freeze Plug,,for sprint cars

So first thing I did was make plug gauge to see exactly what the hole size is
consistently all 8 holes are the same,
also all freeze plugs measure the same
problem is,they will be almost an .008 press fit.
These Freeze plugs are roughly 1.625 diameter and .500thick that presses in
Thoughts please

TDegenhart · May 7, 2019

Those don't look like freeze plugs. The ones I am familiar with are domed disks or cups that are tapped into place against a shoulder, then the dome is collapsed to expand the plug into the block.

Tom

jrmach · May 7, 2019

TDegenhart said:
Those don't look like freeze plugs. The ones I am familiar with are domed disks or cups that are tapped into place against a shoulder, then the dome is collapsed to expand the plug into the block.

Tom

They are Freeze Plugs with I believe a 13/16-14 thread

john.k · May 7, 2019

Dont look like plugs with a hole in the middle.............are you sure they arent installing tools for the cupped plugs?.............But I do know many race cars have the plug holes tapped ,and plugs screwed in ,so they cant be blown out......But the screw ins generally have a hex socket hole .Or sometimes square.

Hodge · May 7, 2019

Looks more like part of a tool for installing cam bearings

workin stiff · May 7, 2019

Shove em in, they will be be fine. Threaded holes are for circulation.

GregSY · May 7, 2019

I think normal freeze plugs might tolerate an .008" oversize as they can 'crush' in a little. But those things are a lot thicker wall and I don't see them crushing. They kinda look like someone's good idea that ain't so good.

I guess my first question is 'why' are they made that way? Are they supposed to be less likely to blow out or? Or are they yet another race part that does more bad than good?

If I had to use them, I'd turn them down to maybe .004" over, and press them in with plenty of LocTite.

jrmach · May 7, 2019

GregSY said:
I think normal freeze plugs might tolerate an .008" oversize as they can 'crush' in a little. But those things are a lot thicker wall and I don't see them crushing. They kinda look like someone's good idea that ain't so good.

I guess my first question is 'why' are they made that way? Are they supposed to be less likely to blow out or? Or are they yet another race part that does more bad than good?

If I had to use them, I'd turn them down to maybe .004" over, and press them in with plenty of LocTite.

Was thinking along those lines too

I will find out tomorrow what the use is for.I do know freeze plugs are not really there for freezing really,,,they are holes where the foundry gets the sand out after casting.Obviously this guy is doing some kind of special plumbing for some reason,,,My hunch is .003 would be great with loctite,,,but certainly not .008

magneticanomaly · May 7, 2019

They look like they have 1/2" pipe thread in middle. Look like anodized aluminum. .008" interference on 1 1/2" diam is too much or an essentially solid plug..would be OK with a drawn cup plug. If you turn them down for a reasonable fit of .003" or so, I would still worry that since Al has higher coefficient of expansion that iron, they will squish when the engine heats up, and end up loose on a cold day. I'd get some standard cup-type plugs, they even come in brass. If you NEED that pipe-thread port, tap the block for a standard pipe reducing bushing.

Milland · May 7, 2019

Factor in that the Al will expand roughly twice as fast as the cast iron, and I'd be concerned too. And are those hard anodized? It might save scraping material off the plugs if the interference was less, but at .008" it might be sheared off during the press.

jrmach · May 7, 2019

Google helped,,I found them here,,,Aluminum Freeze Plugs with Return

They mention slight press fit with a drilled and tapped hole next to them that the engine builder has to do which a button head screw will make sure the don't come out.
So I am thinking .0025 press with loctite will be about right ?

strokersix · May 7, 2019

If you are going to the trouble of modifying these parts, why not just make new ones out of steel? Avoid the dissimilar material problems of aluminum against cast iron.

jrmach · May 7, 2019

strokersix said:
If you are going to the trouble of modifying these parts, why not just make new ones out of steel? Avoid the dissimilar material problems of aluminum against cast iron.

Simple answer,I was not asked to do that

LKeithR · May 8, 2019

jrmach said:
..Simple answer,I was not asked to do that...

Simpler answer. If your customer is not open to recommendations then just stuff them in the damn holes and
let him worry about the outcome. For as long as I have been in business--going on 50 years now--I have always
tried to offer suggestions when I felt a customer was going down the wrong path. If they're willing to look at other
ideas then (usually) everybody benefits. If they don't want to listen then I simply do as I'm asked and let them
deal with the consequences...

Milland · May 8, 2019

LKeithR said:
If they're willing to look at other
ideas then (usually) everybody benefits. If they don't want to listen then I simply do as I'm asked and let them
deal with the consequences...

Exactly. But if the second, only after you write down the consequences and have them sign the note.

Clive603 · May 8, 2019

Milland said:
Exactly. But if the second, only after you write down the consequences and have them sign the note.

Can't see that working. Its always Your fault when His idea doesn't work.

Send him down the road. No way is that job even worth half the time you have already spent on trying to figure out if and how it can be made to work. (Something I do with monotonous regularity, so you aren't alone.)

Website says that plug needs a screw at the side to ensure its fitted properly. Translation "We are a subsidiary of Bodgitt & Break It Engineering Inc and haven't got a clue what we are doing. But our stuff sure looks pretty." Three Dutch keys per plug might work but why trash the block for a bodge.

Only way to do it right, especially with a hose hanging off it, is to thread the hole in the block and screw a plug in. Short thread so add strongest Loctite.

Core (freeze) plugs are the way they are because not only are they cheap, effective and easy to fit but also machining the hole needs pretty much no attention to tolerances. Four wins on the production line. Far too much variation in factory blocks for one size fits all press fit.

Clive

Larry Dickman · May 8, 2019

Why would you need freezeplugs in a race motor? The Antartic 500?

.008 sounds reasonable. Pack the plugs in dry ice/ alcohol overnight and drop them in.

magneticanomaly · May 8, 2019

200 deg F temp diff will shrink them less than .005" . Clive has got it right.

Milland · May 8, 2019

So .008" interference at room temp, and what will it be at operating temp? (another 215F or so)? And into a thin wall of a cast iron race-prepped block?

If the block were Al I guess I'd take the matched CTE and higher ductility and go with it, but in a material that grows roughly half as much and is usually brittle you'd have enough hoop stress that I'd be worried.

Are we sure those plugs weren't meant for Al blocks?

jrmach · May 8, 2019

OK,talked with an old friend that has been building engines all his life.There is no VooDoo going on here,,especially with small block Chevy in Sprint Cars.There are benefits in circulation and cooling.Very common in Sprint circles I am told.
YES,the best way would be to thread the engine block to accept a threaded plug he said,and a lot of folks do that,BUT,for whatever reason the current engine builder (not my old friend the Guru of engine building)wants to do it the press fit way.
YES,.008 is too much !!!
He recommended .004 and at that use dry ice and a sealant,,,NOT loctite.
Also make sure both surfaces are not too smooth,as you get more surface area due to the peaks and gullies of a rougher surface.
And either pin it or button screw the edges to make sure they don't back out
Sounds like a lot of work huh ?well race engines are a lot of work
got to remember these engines get rebuilt quite frequently
My initial question was .008 too much press ?
Not the politics behind the part.YES,.008 is too much
I am not a race car junky,but have done work for all kinds of race vehicles like boats,cars,motorcycles,snowmobile and these folks do all kind of little mods to get that extra edge,,,I have no idea,I am a Machinist not racer,,my gut told me that was too much press
So that is what is behind the part

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