04-30-2017, 05:03 PM | #1 |
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239 bore.
If a standard piston is 3.185, what is the optimum bore size at bottom of cylinder ?
How much wear at bottom and how much taper is allowable at top of bore for just a reasonable runnning engine that will never see a lot of miles. ie, fitting new pistons into an existing bore. |
04-30-2017, 05:40 PM | #2 |
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Re: 239 bore.
I don't know the specs off the top of my head, but there are several things to consider. Taper, how egg shaped/out of round the bore is, ridge at top of the cylinder, etc. Ridge must be removed or there is a good chance of breaking the top ring.
Per Repair Manual, Ford, Mercury & Truck, V8 Engines, 1937 to 1947, Ford Motor Company, July 7, 1947: Ware limits Bore out of round - .003 max Bore taper - .006 max Bore ware - .006 max Piston to bore - .005 thickness gauge 1/2 wide 6 to 10 lbs pull Last edited by JSeery; 04-30-2017 at 07:04 PM. |
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04-30-2017, 08:09 PM | #3 |
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Re: 239 bore.
Side note: I thought the 3.187 bore was for a 221 cube flattie? A 239 flattie would have 3.375 bore? Correct?
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04-30-2017, 08:11 PM | #4 |
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Re: 239 bore.
OOPS...I was waaay wrong - sorry!
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04-30-2017, 09:38 PM | #5 |
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Re: 239 bore.
a 239 stock engine is 3 3/16" inch bore (3 /.187") using hasting steel vent rings I have gone way past the books engine tolerance specs, ran strong and no smoke, good for around 40,000 miles
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04-30-2017, 10:17 PM | #6 |
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Re: 239 bore.
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04-30-2017, 10:30 PM | #7 |
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Re: 239 bore.
You need to use a bore gauge and check the taper in the bores frist If you have 6th taper all you are doing by putting new pistons and rings in is adding a band aid to the problem.
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05-01-2017, 07:10 AM | #8 |
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Re: 239 bore.
As a quick inspection, see how much ridge there is at the top. As someone said you need to remove it to prevent breaking rings. Wear typically occurs more at the top due to the ring pressure. Someone said with just new rings you're putting a band aid on it but if funds are lacking and you just want it to run reasonably well, new rings may do what you need. If this is an 8ba and this far apart, new bearings might also be a good idea.
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05-01-2017, 08:06 AM | #9 |
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Re: 239 bore.
To get a close idea of your taper all that is required is square up one of your existing rings in the bottom of the bore and measure the end gap.Do that three times starting at the bottom then half way up and last at the top under the ridge compare your findings as to end gap and you can calculate the taper as the end gap increases with the formula of PI. Every .001" increase in bore will give an increase of .00314" end gap.
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05-01-2017, 08:37 AM | #10 |
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Re: 239 bore.
Interesting approach Ronnie.
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05-01-2017, 08:53 AM | #11 |
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Re: 239 bore.
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05-01-2017, 09:03 AM | #12 | |
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Re: 239 bore.
Quote:
Thanks Ronnie Bruce
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05-01-2017, 09:43 AM | #13 |
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Re: 239 bore.
I use the same technique as Ronnie. Probably obvious but use a piston to push the ring into position to make certain it's square in the bore.
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05-01-2017, 01:10 PM | #14 |
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Re: 239 bore.
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05-01-2017, 02:00 PM | #15 |
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Re: 239 bore.
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05-01-2017, 02:07 PM | #16 |
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Re: 239 bore.
The setting gauge for the bore gauge isnīt a to fun investment either...but if you canīt trust what you measure itīs not much good either.
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05-01-2017, 04:16 PM | #17 |
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Re: 239 bore.
First you need to be consistent.I have grown up using measuring equipment.Telescope measuring is a good way to get a measurement but then you need a micrometer to read the gauge.You now have 2 investments.Most non machinist people don't know how to use a telescoping gauge.I have seen some struggling and not liking the results.It takes 10 seconds to get the size done.If you are fiddling around you are doing it wrong.
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05-01-2017, 08:29 PM | #18 | |
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Re: 239 bore.
Quote:
Last edited by Bored&Stroked; 05-01-2017 at 08:35 PM. |
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05-02-2017, 02:10 AM | #19 |
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Re: 239 bore.
Ronnie, thanks for good trick.
Frank, absolutely zero ridge , I cannot understand it on a standard bore. Block is in shop now to get a guy to measure bore. Have another Q, are (mushroom) intake and exhaust valves identical ? I have a box of stainless valves that look almost new here. Are these Ok to use in a standard block ? ie no hardened seats . |
05-02-2017, 08:59 PM | #20 | |
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Re: 239 bore.
Quote:
With that said - I've taken apart many rebuilt flatheads where all sorts of intake versus exhaust combinations were used - so I don't know if it actually makes any difference. I don't know if there were different alloys or material properties between the two different valves from Ford. Anybody know the details? B&S |
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