Spigot Swell At Operating Temp

[bugguy1967]

It's standard practice for my machinist to cut cases to approximately .010" larger than the cylinder skirt O.D. So for example, the 94mm cylinder is 97.25mm, so he'll cut to around 97.5mm.

With my 96mm cylinders, we need to retain as much case material as possible, so he's thinking he'll only bore my case .005" larger. My question is how much do you think the bore shrinks at full operating temp? I like the idea of the cylinders being as tight as possible so the case helps to support the cylinder skirts when the piston is at BDC.

[mark tucker]

the bore dosent shrink!! the case opens bigger and the cylinder open bigger...but the cylinders do not open as much as the case does. you can dial bore gauge each cold then do it again hot to see how much more the case opens. but remember that these are bored bigger for a reason... many casea and heads are not the same spread..(bore spacing) due to whoo ever doing the work and what there using...so if you do them tight be sure to make sure the heads are right so there is no cylinder missaliginement or cocking... miss alinement can be a bitch when she wants to be.

[busdaddy]

But the case doesn't get warm as fast as the cylinders, you'll probably want to warm it up before tearing off down the 1/4 mile. If they'll grow more than .005?, don't know, but As Mark says it's also about head alignment.
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[bugguy1967]

Ok, I wasn't sure. I know things expand, but I thought the bore might expand inward.

This isn't for the 1/4 mile, so no worries there.

How important is it for the head's walls to transfer heat from the cylinder side walls? They shouldn't touch, if there is looseness machined-in for alignment purposes, so. Wonder hw important it is...

[nsracing]

\Expand inward? \what the hell?

I do 0.005" clearance for my bores. \but you have to machine the register w/ precision. I cannot be bastard cut on one shot like most shops do.

[modok]

The lower skirt of the cylinders have a small step right at the flange that locates the cylinder, then the lower area is slightly smaller. It is relieved the way it is.... so that it does not touch the case.
I don't think it matters if the gap is .002 or .005, but it is like that for a reason,
That's a no-touchy zone. No touching. It doesn't like touching there.

[modok]

So why. Because Ford. Ever try to take an old flathead ford apart....you'll see. Many had slip fit thinwall cylinder sleeves, and slip fit guides. They are all jammed solid.
If you HAVE a small gap....that gets slightly bigger or smaller as it runs or heats/cools or ect......what can happen is dirt, schmoo, gunk, oxide, or little bits of stuff WILL get in there when the gap opens up, then the gap tries to close.....and smashes the stuff in there. Over time it may actually build up stuff between the cylinder liner and the block and make the bore tighter on the ID, and ruin the heat transfer from the liner to the block also, and you try to replace it.....it's stuck. Unsatisfactory in all respects.
So that s why it is better design practice to have parts either touch solid, or they float with several thou gap.
None of this gently touching some of the time tickling baloney, because, don't be a ford.

[bugguy1967]

Alright, cool. Thanks for clearing things up guys.

[hobbybob517]

Where did you get 96mm p&c's?

just curious it seems an oddball size
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[UK Luke 72]

Think he's using thick wall 94s opened up, not sure on the pistons... A different OE application.
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[mark tucker]

there isant a lot of heat generated in that part of the cylinder fast unless your running a 90mm stroke , I think you will be fine with that clearance. I wonder what clearance they use for the 94 cylinders that are machined to fit the 92 case size.???
if your sure the bore spacing on the heads and cylinders is the same .010" should be fine.005 would probably be ok too( I think that's where I put mine, but that was oh so long ago).I also use copper head gaskets that in my opinion transfer cylinder temps to the head better as well as sealing better too.