Cylinder wall thickness

[tubman]

There is a thread going about rebuilding an 8BA. The O/P has decided to build a 276" engine. The last post on that thread was for "19Fordy" who said :

Originally Posted by 19Fordy

Thinner walls can create more cavitation which means more heat.
Follow JWL's advice.

Not wanting to hijack that thread. I will start another one, because I would like someone ("19Fordy" if you want, but anyone is welcome) to explain this to me. I do not understand how the thickness of cylinder walls can cause cavitation. I am a great fan of 3 5/16" pistons, and am just finishing off a 258" (3 3/4 stroke) engine. I would think that a flathead with a 3 5/16" bore would have cylinders walls at least as thick as most modern engines with "thinwall" castings. There have to be literally thousands of 1/8" overbored flatheads out there (I had a 276" in a '36 myself), and I seldom hear complaints about overheating with a properly built clean engine.

[51 MERC-CT]

Originally Posted by tubman

There have to be literally thousands of 1/8" overbored flatheads out there (I had a 276" in a '36 myself), and I seldom hear complaints about overheating with a properly built clean engine.

And this seems to be the answer to the conundrum, without over heating, there should not be cavitation. I'm certainly not going to worry about it.

[Low-Blow]

Originally Posted by tubman

There is a thread going about rebuilding an 8BA. The O/P has decided to build a 276" engine. The last post on that thread was for "19Fordy" who said :



Not wanting to hijack that thread. I will start another one, because I would like someone ("19Fordy" if you want, but anyone is welcome) to explain this to me. I do not understand how the thickness of cylinder walls can cause cavitation. I am a great fan of 3 5/16" pistons, and am just finishing off a 258" (3 3/4 stroke) engine. I would think that a flathead with a 3 5/16" bore would have cylinders walls at least as thick as most modern engines with "thinwall" castings. There have to be literally thousands of 1/8" overbored flatheads out there (I had a 276" in a '36 myself), and I seldom hear complaints about overheating with a properly built clean engine.

I certainly appreciate you asking for further explanation, or clarification of this. I am definitely a novice at this, and have realized that there are differing opinions when it comes to building these engines. I can honestly say that it has clouded my mind a little. I realize that this is my engine, and in the end will be built like I want it built. But, I certainly would not want to do anything to compromise the integrity of it. I am glad that I have found this site, where folks are willing to share their opinions and expertise. And, I sure hope that no one would take offense if I did not follow each suggestion. After all, that would be impossible right?

[tubman]

You're on the right track here. I'll go out on a limb and say that there were a lot more overheating problems in 8BA's caused by incorrect timing and by 1/8" overbores. Getting the proper ignition on one of these is probably the most important tuning consideration.

[redmodelt]

Ok this is murky waters for me but what was the largest oversized pistons Ford sold for this engine? Wouldn't Ford engineers have figured out what was the largest size the bore could have gone to before issues would arise?

[tubman]

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I'm no expert, I think Ford may have offered pistons for up to a .060" overbore. However, they were working in a production environment where core-shift on a small percentage of blocks would have dictated the overall maximum. These days, we have the luxury of sonic testing so we know exactly where we are with any individual block, which allows us to take advantage of a favorable situation. Without sonic testing, overboring this much is a crap shoot, albeit one with the odds heavily in our favor.

[Ol' Ron]

In the past I've run several 3 7/16 engines. One was a track engine and the other a street engine. This engine was assembled while i was writing my book and some of the pics if that engine is in my book amd that was 25 years ago, and is still running. In the esrly days a 3/8 X 3/8 flathead was very common 296 ci and I had one of them running untill last year.Engine is still in good condition was replaced by a 294 blown engine. At present I have a 280ci in my truck which is a stock Merc bored .145 over. The 59 and 8ba engines were quit thick, but time will take it's toll on the water jackets and sonic testing would ba a good idea.. PS I love thoes 258 engines, have a new one going in the roadster. Have to save up the money to buy the pistons. Damn the prices are getting out of hand, It's becoming a rich mans hobby.

[tubman]

"Ol' Ron" - Speedway has Offenhauser 4 ring 3 3/4" X 3 5/16" pistons for $149.99 (rings are an extra $60). They have two reviews, both very positive. I think Speedway is trying to clear out the Offenhauser pistons to make room for their new Chinese ones. Just a suggestion.

I'm thinking about ordering a set myself just to have "on the shelf". (I have an "extra" std bore 8BA.)

Oh yeah; free shipping on orders over $100.

I know what a lot of folks think about Speedway parts, but I don'r see how they could screw up a set of Offenhauser pistons.

[Ole Don]

My two cents worth, and worth every penny. I think cavitation may be mixed up with steam pocket. The flatty I built used fifty year old 3 3/8 pistons in a newer block. I told the machinist I wanted .004 clearance, and that is what it was. As we loaded it to my truck from his shop, he slid his fingers in a water jacket and down the bore and he said "I sure hope you know what you are doing, this is awfully thin." It ran like gangbusters and only got hot in heavy traffic.

[rich b]

Originally Posted by tubman

I know what a lot of folks think about Speedway parts, but I don'r see how they could screw up a set of Offenhauser pistons.

Pretty sure Speedway has licensed the Offenhauser name for use on some of their own products.

[Jason in TX]

Ol' Ron - I love reading your replies. I wanted to say thank you for your posts and let you know that you are appreciated.

[FlatheadTed]

If your worried about over heating get a radiator with a extra row in it ,90% of overheating is the Radiator ,

[Ol' Ron]

Thanks guys for your comments and especially any help getting this engine built. The roadster is bilt for antique racing as a fun car for the gang, especially my Grandaughter which has a kead fot. I have a racing crank assy thad I would have used at Danbury. we were limited to 258 ci stock valves. So acceloration off the cornors were the Key to winning. a good driver also helped. as the engine man I learned that the best combination of parts were the late 38 to 41 cranks and 21A rods. At first we used Jaann's pistons but these hit the heads. so we ran .100" piston clearance. Then we started lightening the pistons. I was amazed at how much wecould take off of them. Had a fixture for the milling machine tha had a wrist pin mount for the piston and using a 2 1/2 hole saw cut the skirt off up to the wrist pin boss. I was supprised they did't break. WE never balanced thes engines. One guy had a tach and said he was turning over 5k. We were running 542 rear gear.

This engine will have a new port and larger valve and another carb. And yes it will be balanced. I'll have some pics for youse guys soon.

[flatheadmurre]

Cavitation on cylindewalls are not related to heat issues as much as that the lack of weight...
I have experience with diesels and the thinner cylinderwalls erode from cavitaion and it´s from vibration...high frequency vibrations causing it.
More meat in the walls dampen the vibrations better.

[40 Deluxe]

Originally Posted by tubman

There is a thread going about rebuilding an 8BA. The O/P has decided to build a 276" engine. The last post on that thread was for "19Fordy" who said :



Not wanting to hijack that thread. I will start another one, because I would like someone ("19Fordy" if you want, but anyone is welcome) to explain this to me. I do not understand how the thickness of cylinder walls can cause cavitation. I am a great fan of 3 5/16" pistons, and am just finishing off a 258" (3 3/4 stroke) engine. I would think that a flathead with a 3 5/16" bore would have cylinders walls at least as thick as most modern engines with "thinwall" castings. There have to be literally thousands of 1/8" overbored flatheads out there (I had a 276" in a '36 myself), and I seldom hear complaints about overheating with a properly built clean engine.

Cavitation is caused by vibration, particularly from detonation. Late model Diesels in pickups need special coolant to deal with this. By design, a Diesel engine is always running in detonation. That's how you get the 'Diesel clatter'. A properly tuned and maintained flathead will not have this problem.
Here's a question for discussion: While we worry about thin cylinder walls causing overheating, how THICK can a cylinder wall be and still cool? Suppose our flatheads had inch thick cylinder walls? Two inches? Would the heat of combustion transfer to the coolant quick enough to avoid melting the pistons? What is the ideal thickness?

[Ol' Ron]

Now that's a good question. I till experiment woth these engines, but they're getting harder to find and buying parts is gettingso expensive that even if you could find the holy grail of power for the flathead, nobody would be interested except by a few racers. My new port deesigh, if it works, would onlu improve performance bu 10 or 13 percent. but the expense of doing it wouldn't be worth it for a street machine.

[revkev6]

Originally Posted by Ol' Ron

Now that's a good question. I till experiment woth these engines, but they're getting harder to find and buying parts is gettingso expensive that even if you could find the holy grail of power for the flathead, nobody would be interested except by a few racers. My new port deesigh, if it works, would onlu improve performance bu 10 or 13 percent. but the expense of doing it wouldn't be worth it for a street machine.

Ron, are you still playing with the flow bench?? I literally use the time when I can't sleep as my engineering time for building a better flathead

care to share any pics?? flathead port work is just art to me.

[GB SISSON]

I am not exaggerating if I say I have spent at least a full year of my life building flatheads with my head on the pillow between 2am and 4am. I have no idea what 'normal' guys think of at that time...you know, after they get up to pee. And another thought. You guys who have worked with your hands all your lives will get this. You can actually tell a thin wall or a thin board with a pinch of your fingers. You just can.

[40cpe]

GB, we might be brothers. When I was a teenager building a hot rod (in the '50s, no internet to research, no one near who had ever done it) I literally had solutions come to me in dreams. I guess it comes from concentrating so hard.

[GB SISSON]

Originally Posted by 40cpe

GB, we might be brothers. When I was a teenager building a hot rod (in the '50s, no internet to research, no one near who had ever done it) I literally had solutions come to me in dreams. I guess it comes from concentrating so hard.

I'm not some kind of nut but I have wondered if heredity has anything to do with it. My dad was an insurance guy who couldn't start his lawn mower but HIS dad ran Sisson's Grage in Wareham Ma and had the Ford franchise sold Model Ts. He drove a 1908 Buick from Boston to Miami so he knew how to fix stuff. There must have been early ancestors who chipped out the flint hatchets while other cave dwellers cooked the mastadon hocks or threw the spears. Anyway it's in my blood. Working on mechanical things that is....