Today's Message Index:
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1. 07:41 AM - Re: Barnstorming Carnival Springfield, OH July 19-20 (Baldeagle)
2. 08:50 AM - model A engine (bender)
3. 09:04 AM - Re: model A engine (tools)
4. 09:27 AM - Re: model A engine (Brett Phillips)
5. 09:34 AM - Re: model A engine (tools)
6. 09:47 AM - Re: model A engine (tkreiner)
7. 11:48 AM - Re: model A engine (tools)
8. 12:57 PM - Re: model A engine (Brett Phillips)
Message 1
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| Subject: | Re: Barnstorming Carnival Springfield, OH July 19-20 |
Hope to see some of you Ohio guys here for this one.
Also, we're doing our annual fly-in at Hagarstown, Indiana in connection with the
Model T Ford Club of America the following Tuesday, July 22, on the way to
Brodhead. Here's some info from last year:
http://henryshoosiers.com/hagerstown-antique-plane-flying-circus-model-t-museum-driving-tour/
At least three Pietenpols already planning attendance at Hagarstown, the Rudolf
Air Camper, Frank Pavliga's Sky Gipsy, and Bob Coolbaugh's new Air Camper.
-
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do not archive
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Message 2
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So I have my engine torn down.
The #1 piston scuffed pretty much all the way around.
#2 has scuffs all the way down the skirt perpendicular to the pins.
#3 has very light scuffs but same as #2
#4 is ok.. but the last failure it was scuffed like #1.
the clearance is just under .003 piston to wall.
I have new pistons and I'm thinking of opening the clearance to about .006
the temps and oil pressure have been great. And the fact that it has happened to
all 4 cylinders has me thinking is not a hot spot is just a clearance problem.
I'm going to put it back together but thinking the engine could go in my AA
truck and I know of a little continental in town if things don't work out. I
hate to think that way because I know there are A's that have been flying safely
for years and I prefer the A. I guess I can run it hard on the ground and see
if opening it up takes care of the problem.
Jeff Faith
sdf
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| Subject: | Re: model A engine |
Hey Jeff,
Did you ever check the ring clearance? I imagine the whole set would have the
same clearance and could cause this problem.
.02
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| Subject: | Re: model A engine |
A few random thoughts:
I assume you have checked the ring end gap. I had to file most of my rings to
get them right.
I've also heard rumors about recent production Model A pistons that had the alloy
a little off, causing expansion problems, but can't verify that info, so take
it with several grains of salt.
.006" at the skirt seems like a lot for a liquid cooled engine, but a little piston
slap when cold is definitely preferable to scuffing or seizure.
Have you considered using the AA truck to break the engine in for a couple thousand
miles? That might be almost as much fun as flying it, and a lot less pucker
factor.
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PLEASE DO NOT ARCHIVE!
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| Subject: | Re: model A engine |
Even more thoughts...
Have you checked the clearance for EACH piston? Depending on the manufacturer,
each one could be a few thou different just due to quality control (think Chinese
pistons here...).
Even good manufacturers have tolerances and they get exceeded on occasion.
Did you change the pistons last time? Perhaps you just coincidently wound up with
the right size piston in that #1 cyl this time.
This whole measuring consistently and accurately down to .001 or less is FAR LESS
than trivial and matters.
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| Subject: | Re: model A engine |
When I ran a Thermal Expansion on your piston, I came up with some numbers that
you might want to consider...
Assuming these are 4.00 in. diameter aluminum pistons, with a Coefficient of Thermal
Expansion of 13.1 uin/in/F degree, you run the calculation like this:
4.00 x 13.1e-6 x Temp, and you get the expansion of the piston. For 150 degree
rise, the diameter of your piston grows by .00786 inches.
Perhaps speaking with some of the Model A guys to get the proper clearance would
be the best starting point, as the numbers don't lie, and at 200 degrees, the
increase in diameter is over .010. It will help a lot to determine the running
temp of the engine and set your clearance - and ring gap - sufficiently to
provide .0015 to .002 clearance AT RUNNING TEMP.
Best of luck with this; let us all know how it turns out.
--------
Tom Kreiner
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| Subject: | Re: model A engine |
Wouldn't those expansion calculations be for if the piston was a solid piece?
Nearly 7 thou expansion at a rather low temp seems excessive.
Also, pistons don't generally expand evenly, which is why modern pistons are cam
ground.
Lastly, I did just find a 1931 reference to tolerances used in the manufacture
of the Ford A, and it mentions .002 MAX.
Now, I do know it's common to simply overbore to address issues like these, but
if .002 is the manufacturers recommendation, and most chevy guys seem to indicate
about.004 is alright (for the MUCH higher horsepower and rpm ranges of v8
small blocks) for street engines... something just doesn't add up. I think factory
specs are about .003 max out the door. The .007 and up clearances seem
to be used mostly by guys really hot rodding the engine, not producing 50 hp...
Besides ring end gap, have you checked the fit of each piston in several locations
in the cylinder? Perhaps your block is tapered... Checked in several clock
codes to try and find out of round? Perhaps a six pack of beer and a google
search for a car club in your area to find someone with a bore gage you can
play around with to help determine exactly what is going on. Also a good micrometer
to double check the pistons.
Also, are you using forge or cast pistons? Cast need more clearance.
I just hate over boring (honing) without really knowing, because that will shorten
the life of the engine.
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Message 8
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| Subject: | Re: model A engine |
A big part of this problem is that most pistons today are not pure aluminum, but
are instead made from a very high silicon (hypereutectic) aluminum alloy. Low
silicon aluminum pistons would require more clearance than the hypereutectic
version. Just how much more is hard to say. Most of the modern piston alloys
are semi-proprietary, so it is very difficult to conjure up the proper clearance
without some help from the manufacturer or some unfortunate practical experience.
I should also point out that it is actually the FORGED pistons that
usually require more clearance for expansion. This is primarily due to the fact
that most (not all) are not made from a hypereutectic alloy. For all of the
above reasons, the factory Model A piston clearance really only applies if original
Ford pistons are being used. (FYI, original style Ford pistons had split
skirts to allow for expansion, and they were known to shed large hunks of skirt
on occasion).
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PLEASE DO NOT ARCHIVE!
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