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The absolute 'MINIMUM' cylinder wall thickness.... If you had to stake all your worldly possessions on getting this answer correct, I am asking this question regarding overheating due to cylinder bores that are too thin. What would you say the absolute minimum wall thickness an A-6015 Model-A Cylinder Block should be bored/worn/eroded/whatever to that you would GUARANTEE that a rebuilt engine would not overheat as a direct result of too thin of cylinder walls?
This is not a trick question, but a sincere question regarding giving someone sincere advice about. I honestly am not looking for 'He Said/She Said' answers about someone who got away with...., -but instead I want to discuss Ford's engineer's design tolerances, and what we would feel comfortable in giving sincere advice about. Thoughts?? |
Re: The absolute 'MINIMUM' cylinder wall thickness.... The largest original replacement Ford pistons I have seen are 0.060 oversized
I haven’t done any measurements, how thick is the uncooled cylinder wall area below the water jacket? |
Re: The absolute 'MINIMUM' cylinder wall thickness.... I have had .125 in one of mine before. Don't recommend it but it worked.
Mike |
Re: The absolute 'MINIMUM' cylinder wall thickness.... I know for the flathead V8 the recommended minimum cylinder wall thickness is .100.
And of course you have to look for core shift so you would need to check all points of the bore with your sonic meter and accept nothing thinner . I don't know if core shift is a thing with model A blocks but it sure was with later V8 blocks in the 70's . |
Re: The absolute 'MINIMUM' cylinder wall thickness.... I have one at .125 . Runs like a watch.
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Re: The absolute 'MINIMUM' cylinder wall thickness.... Brent
There are too many variables to your question, too thin a wall will cause other issues. If memory serves, 1/16" of calcium/rust build up equates to multiple inches of cast iron in regards to thermal transfer to the cooling water. That said, I would think the condition of the cooling system and especially the water jacket of the block would need be cleaned in order to perform satisfactorily. I have done the acid soak in preparation of filling with aluminum, amazing what came out. In a low performing motor less than 1/4 hp per cu in displacement the peak cylinder pressures will not be affected by the reduced sealing capacity between the 1/2 and 3/4 cylinders. .125 oversize reduces this web by 33% (from 3/8" to 1/4") if the bores are not moved away from the web. This is where the games of adding a wire to support the gasket comes into play, just another patch. Another issue with going big on the bores is finding pistons and customs cost a ton, sleeving is less expensive if you do not need a forged piece. I have seen blocks break just under the water jacket separating the top and bottom, it took a load of nitro but still broke all the same. Best of luck, John |
Re: The absolute 'MINIMUM' cylinder wall thickness.... In 1959 I had a 29 coupe that was already over bored to .080 and drove it everyday at least 8 miles each way to high school at speed limit. At that time the speed limit was 65 mph on rural roads in Texas. Never ran hot, even in Texas hot summer time. The car caught fire and burned, sold the chassis to another model a guy that had a 31 body and he drove it for, unknown to me, many years.
Ed |
Re: The absolute 'MINIMUM' cylinder wall thickness.... Schwalms supplied a "touring motor" via Snyder's to me bored to 0.125 over. It has done 30000 miles since. Runs usually at 145. Deg F even though a 160 deg thermostat is fitted. Stat. starts to open exactly at 160 in a lab test. It is a vintage Precision housing and stat. It replaced a Snyder's stat in the upper radiator hose which also sat on 145 deg using the same temperature sensor. So I suspected the guage reading but an IR gun and a mercury thermometer in the radiator all read 145.
My wife's Tudor also runs too cool. It is 80 thou over and has a 160 stat in the upper hose. No extra holes drilled in either stat for better flow when shut. No engine pans on either car and Roadster has an aluminium 2 blade fan and the Tudor a 6 blade from, I think, Bill Stipe. Both radiators run tap water and a green anticorrosive from Repco. I thought Jim Brierly mentioned an even bigger bore than 125 thou on race engines. SAJ in NZ |
Re: The absolute 'MINIMUM' cylinder wall thickness.... This thread is going in a direction of "I have done this and gotten away with it..." which is NOT what I intended this thread to be. To me, this is much akin to saying I have driven 100mph several times without receiving a ticket, therefore it is ok to do this regularly. Again, no one in their right mind would stake all of their earthly possessions guaranteeing they could do it again and not be cited for speeding.
So let me reel this back in. Kurt pretty much nailed it when he asked about the factory wall thickness and piston sizes. According to my prints, the wall thickness on a std bore was 0.250" thick from the factory. As I was looking at my 10/01/1929 A-6015-A print, it mentions "Diameters for Reconditioned Engines ..." and goes on to list 1st Oversize of 3.876" (--0.001 oversize), 2nd Oversize 3.880" (--0.005" oversize), 3rd Oversize 3.905 (--0.030" oversize), 4th Oversize 3.915" (--0.040" oversize), and 5th Oversize 3.935" (--0.060" oversize). Now this information was list in October of 1929, so this information was not listed because the Agencies had engine already on their 5th rebuild, -but was listed to provide guidance on the maximum overbore the engineers deemed prudent. Therefore, the minimum cylinder wall thickness they allowed was 0.220". As mentioned above, many engines have seen very sloppy machine work causing cylinder bores to be machined off-center, and even slanted from perpendicular with the crankshaft centerline. As many would agree, this potentially causes the cylinder wall thickness to be less, -as does rust pitting or core shift during casting. Why I am asking this is I have recently had some discussions with a few hobbyists (-and one engine rebuilder) who are having overheating issues that potentially are being caused by cylinder wall hot spots. I have a sonic tester that I try to scan the bores, and because my tester defaults to metric, I just use 5mm on the tester as my minimum thickness baseline. That basically meant I felt could safely bore to 3.975" using 0.100" over pistons with a fair amount of certainty that I was not going to have a likelihood of cooling issues. With the manner in which many Model-As are being driven (-higher speeds, lugging, greater loads due to overdrives, etc.) in today's environments, the importance of not having cooling issues are greater than ever. Therefore with the above said, I need to establish what that threshold of wall thickness needs to be for me to properly warranty an engine. Granted, no one wants to spend $500.00 to sleeve a block back to 3.875, ...but they also complain when their block was bored too thin causing heating issues. So, what should that number be that if any cylinder wall in their block is beyond a certain minimum thickness, then they understand there is no warranty? Since Ford engineers stated 0.060" was to be the maximum overbore, is the minimum thickness number 0.220"?? |
Re: The absolute 'MINIMUM' cylinder wall thickness.... I've always figured that 1/8" is about as thin as a person should go when calculating to a bore job. Some sleeves are 1/8" and some are as thick as 3/16" and in some cases the sleeve is about all that is left to repair a corroded, cracked, or a bored through cylinder wall. A good ultrasonic check of thickness will give a general idea of how much corrosion there may be lurking in the water jacket but it can miss some spots even if a tight grid pattern is followed. This is all if the block didn't have any issues with core shift during the casting process.
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Re: The absolute 'MINIMUM' cylinder wall thickness.... OK, I am not a machinist by any stretch of the imagination. But, even to me when dad said the Model A could be bored to .125 that was way to big for me. I 'think'-and this is my opinion-if you stick with the .060 that would keep the walls thick enough to not risk any cracks, hot spots etc.
Again just my opinion-I know you were looking for actual numbers. Mike |
Re: The absolute 'MINIMUM' cylinder wall thickness.... Hi Brent! The sand casting process is not a precision one, and it was my experience that my sand cast designs were at the mercy of the pattern maker's best effort and the actual casting process. Sample castings were destructively measured and dimensions feed back to the engineer for structural and functional analysis. If found acceptable, the engineering drawing would be revised to reflect the actual dimensions. Did Ford do this???
I recommend that you survey some Model "A"engines that have been cutaway, and check their cylinders for wall thickness and bore size to analize their original wall thicknesses. The limiting walls have to be those between Cylinders 1&2 and Cylinders 3&4. I am assuming that Ford engineers did a structural stress analysis, a thermal stress analysis and a thermodynamic heat transfer analysis to determine their 0.060" oversize piston is serviceable. So as a business man, I would not recommend boring cylinders more than 0.060" as Ford limited by service piston size. |
Re: The absolute 'MINIMUM' cylinder wall thickness.... Just how many people do you think have ever measured that thickness? I think not many, less than 1%. So how do you expect to get any exact answers? People above have said that a 4" bore (.125") will still allow the A engine to run cool, what more do you expect? I have raced my B engine on the Bonneville salt flats with a 4" bore with no heating problems. In the old days guys raced them with at 4.060". This required off-setting the bores to gain head gasket sealing between 1&2 and 3&4 cylinders, many did this. Racing puts a lot more heat into the block than driving to the local market. Get real!
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Re: The absolute 'MINIMUM' cylinder wall thickness.... I don't know the average original cylinder wall thickness but I do know that the distance between the pairs of cylinders is very narrow. A person can have issues getting the cylinder head gasket to seal on large bores. They made some gaskets for larger bores but man that little strip of gasket between pairs ain't much.
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Re: The absolute 'MINIMUM' cylinder wall thickness.... Something else to consider besides a barely adequate cooling system design is that higher efficiency motors do run cooler
Partly because of the flow characteristics in the cylinder to more completely empty and refill it One last observation if the paint below the water jacket is starting to discolor or peel the paint it is CV more than likely a mechanical clearance issue than a wall thickness concern J |
Re: The absolute 'MINIMUM' cylinder wall thickness.... Quote:
Bob, I agree with you however the print shows the finished thickness size to be 0.250". It does not give a + or - tolerance with that number. Based on the sheer quantity of blocks that were cast, and based on the methods Ford used, my guess their QC was very close on these measurements. I do have an ultrasonic tester that we use to verify wall thickness, and the tester is calibrated to be within 0.001±" of what the display screen reads. As far as the "limiting factor between 1&2 and 3&4, the bores are siamesed in most of those areas, so generally speaking I don't think that area is affected much except the upper 2" where the temps are the hottest. I think your logic about 0.060 makes sense. There is less than 3% difference in cubic inch displacement between a standard bore vs an 0.060" overbore, so the benefit there is negligible ...however sleeving back to 3.875" and the rigidity and/or heat transfer you would gain by properly installing sleeves would likely be huge with regard to cooling. Quote:
As for Bonneville and a 0.125 over engine, I agree that it has been done successfully however I can refer you to an engine rebuilder whose customer has a 0.060 block that appears to have a couple areas thin enough to produce 'hot spots' for his customer. The amount of lost revenue and time this issue has caused this rebuilder dealing with this troubling. |
Re: The absolute 'MINIMUM' cylinder wall thickness.... Brent, I’m not an expert by any means but would like to see if I can condense the comments. You seem to want an opinion and short of talking to the engineer that did the original blueprints anybody’s opinion is going to be biased based upon their own experience. If, theoretically, based upon sound engineering princeaples, a number (over bore/wall thickness) was put forward, there would be some that got a less than perfect original casting that would have failed. On the other hand, you could get get an exceptionally thick casting that would tolerate a much bigger overbore. If you are looking for a hypothetical number based upon original blueprints, that’s a commendable question for sure but there are very few (if any of us) qualified to answer the question in an unbiased opinion. Real life experience is all we have to go by. I’m not saying that your question is unreasonable or unanswerable but few if any of us are qualified to answer it.
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Re: The absolute 'MINIMUM' cylinder wall thickness.... .125
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Re: The absolute 'MINIMUM' cylinder wall thickness.... "Granted, no one wants to spend $500.00 to sleeve a block back to 3.875, ...but they also complain when their block was bored too thin causing heating issues."
Spend the 500 bucks. |
Re: The absolute 'MINIMUM' cylinder wall thickness.... Quote:
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