Author Topic: A Wallaby of my own.  (Read 252115 times)

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Re: A Wallaby of my own.
« Reply #885 on: December 18, 2018, 09:04:27 PM »
If .001 works for an iron piston in an iron sleeve then youll need double that for aluminim pistons in iron sleeves.    So .002" at the crown and .001 at the skirt.
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Offline b.lindsey

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Re: A Wallaby of my own.
« Reply #886 on: December 18, 2018, 10:08:49 PM »
That sure sounds a lot more reasonable Dave. Guess it may depend on expected run times too though.

Bill

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Re: A Wallaby of my own.
« Reply #887 on: December 18, 2018, 10:54:27 PM »
That sure sounds a lot more reasonable Dave. Guess it may depend on expected run times too though.

Bill

That will depend on the temperature.    I have a few more references, but Aluminum has a Thermal Expansion Coefficient that is double that of iron, hence my comment that it needs to be more gap than an iron piston.

....But .0015 sounds right now doesnt?

Dave
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Offline b.lindsey

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Re: A Wallaby of my own.
« Reply #888 on: December 18, 2018, 11:13:39 PM »
The cylinder sleeve can expand some too, just at a slower rate. At least that my thought. Now the Porsche engine may need some further thinking.  :)

Bill

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Re: A Wallaby of my own.
« Reply #889 on: December 18, 2018, 11:32:34 PM »
It does.   so here's what I did.

A chevy 350 with AISI 4032 alloy pistons that are 4.155" need 0.0042 nearly maximum clearance as per some looked up references..   I rounded that to 0.001" / inch of diameter.

AISI 4032 Hypereutectic has a Linear coefficent of expansion that is 0.781 that of 6061-T6 aluminum.   That said....the 6061-T6 needs 1.28 times as much clearance...or about 0.00128"/inch...assuming the pistons are heated to the same temperature.

Now...practically, I doubt the model pistons get anywhere near as hot as a hard working Chevy 350...    so.....0.001" to 0.0015"/ inch of diameter would seem fine on a water cooled, low compression ratio model engine.   

See Cletus!    You can count on the good ol country boys....

Dave
« Last Edit: December 18, 2018, 11:41:08 PM by steamer »
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Re: A Wallaby of my own.
« Reply #890 on: December 18, 2018, 11:37:34 PM »
The cylinder sleeve can expand some too, just at a slower rate. At least that my thought. Now the Porsche engine may need some further thinking.  :)

Bill

That might require a mule motor to sort out...though I'd start with 0.0015, or use 4032 alloy and run the same percentage clearance as the real engine did.

Dave
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Offline Dave Otto

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Re: A Wallaby of my own.
« Reply #891 on: December 19, 2018, 12:43:24 AM »
Hey Dave

Attached are a couple charts that you and the other guys might find useful.

Dave
« Last Edit: December 19, 2018, 01:27:11 AM by Dave Otto »

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Re: A Wallaby of my own.
« Reply #892 on: December 19, 2018, 01:09:44 AM »
Hey Dave

Attached are a couple charts that you and the other guys might fine useful.

Dave

Interesting!     These charts confirm ETW's numbers!!!    :lolb:

Dave
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Re: A Wallaby of my own.
« Reply #893 on: December 19, 2018, 01:24:47 AM »
ETW's comments about the piston fit.      My rings are going to be .04 thick x 0.045 wide, and I'll have 2 of them   I'm wondering about some oil control holes in the skirt like J E Howells V twin.   

Then again, I Just make them as is and experiment later...

Dave
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Re: A Wallaby of my own.
« Reply #894 on: December 19, 2018, 11:31:51 AM »
Hi Dave,

I would go along with the Westbury piston clearances. It's the rings that do the sealing. while the piston is there to take the combustion loads. I am a firm believer in generous piston clearance with an aluminium  ringed piston. Clearance will ensure good lubrication of the piston skirt and so prevent rubs and seizures. I ended up in a ditch. beside the track, a couple of times due to seized pistons.

Hang loose, as they say

Mike
« Last Edit: December 19, 2018, 12:59:46 PM by Vixen »
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Re: A Wallaby of my own.
« Reply #895 on: December 19, 2018, 06:00:55 PM »
I agree Mike at least at the crown...it can get a bit tighter at the skirt.
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Online Roger B

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Re: A Wallaby of my own.
« Reply #896 on: December 19, 2018, 06:57:14 PM »
I agree as well although it is difficult to really know the clearances unless you have some quite precise bore measuring equipment. Outside diameters are relatively easy and if the bores have been finished to a plug gauge you have a chance of knowing what is really going on otherwise it is just feel  ::) I have also tried measuring the clearance by sliding a feeler gauge between the piston and the bore but that also has uncertainties  :headscratch:
Best regards

Roger

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Re: A Wallaby of my own.
« Reply #897 on: December 19, 2018, 07:04:46 PM »
A snap gage will get me pretty close I think.
Dave
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Offline Tennessee Whiskey

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Re: A Wallaby of my own.
« Reply #898 on: December 19, 2018, 08:32:14 PM »
Snap gage is way “close enuf” . Like I said, we used a thou and a half feeler gage to see if it was “go-no go” . Which got me to thinking: how many of y’all have used “Plastigage”? Hey man, what’s the candy bar of choice this year  8). Sorry, trying to kill two rabbits with one shell  :lolb:.

Whiskey Out
Eric

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Re: A Wallaby of my own.
« Reply #899 on: December 19, 2018, 09:34:29 PM »
Snap gage is way “close enuf” . Like I said, we used a thou and a half feeler gage to see if it was “go-no go” . Which got me to thinking: how many of y’all have used “Plastigage”? Hey man, what’s the candy bar of choice this year  8). Sorry, trying to kill two rabbits with one shell  :lolb:.

Whiskey Out
Eric

That hasnt changed any.....8-)
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