Model A engine overbore 125+?

R

Richie R

Member
Bore sizes?
Had a test bore done on my early 28 model A engine, at 100. over it looks like the pitting will not quite clean up in the bad cylinder when taken to 125.
As I planed using insert Snyder's rods, I could use the other insert rods they sell for running standard Chev pistons?
Anyone using oversize Chev pistons in their "A"?
The rods are designed for 283 standard pistons, at but at 125. + overbore it will be over 4 inch so what pistons do I look for then? 327 or 350 maybe?
The block is going to be tested for wall thickness first and offset grinded to keep the gap as big as possible between the cylinders but looking for info from someone experienced in running such a large overbore.
Thanks Rich
 
colin1928 said:
Sleeve it back to std
Click to expand...

Hi Colin
Yes I was given that a option, liked the idea of a engine at .125 over. Brings the motor up to 207 ci or so.
The crank is still going to be machined this week so I know what undersize inserts to buy.
Just sitting back at the moment looking at ideas for the block. Have another rebuildable engine I am picking up next week.
 
Have the one bad cylinder sleeved with a 1/8" sleeve and bore all the cylinders at .100. If you use a 1/8" wall sleeve and leave a ledge at the bottom for it to sit on it will bore to .100 with no problem.
 
I am currently running my A at 4.000 bore. It is a huge amount of stock to remove, but the A block will take it . By my calculations it increases the displacement to about 215cu.
It runs fine above an idle.
Terry
 
I use 283 pistons with insert rods. Get 283 pistons, not sure 327 would work. they are made for a longer stroke. Advice put the pistons with the front mark to the back. Model A engine has the cylinder bore centers off center to help with piston slap. 283 pistons have wrist pins off set to help with piston slap.
With both together you have way to much off set. If you turn the piston around you have just the right amount.

The A engine has about twice the off set as a 283.
 
I have had .125 pistons in my touring car for 11 years with no problems. I do use a high capacity 4# pressurized radiator to help with the cooling needs. I will get on the freeway and go if I need to make up some time and the heat will build pretty fast. I have heard for years that an engine bored to .125" will overheat...I do not know if that is true. When I built this engine, I was advised to upgrade my cooling capacity for the way I described I wanted to drive. For the average Model A owner running .125" pistons, I think a good condition standard radiator would do the job if you drive at reasonable speeds.

I typically will choose 283 Chevy pistons in engines for touring engines and those that I know will be pushed hard because of the narrow ring sets. I have been told by my suppliers that the narrow rings will seal better under extreme loads. I only use 283 Chevy pistons in engines that finish at .080" or under. If I need to run with a larger bore and maintain the narrower ring set, I will install a set from Egge. Note that they have the narrow and standard ring widths available in their oversize pistons so you need to specify what you want when ordering. Call them to verify their stock. 800-866-3443 Check out their website: http://www.egge.com/
Personally, I find their website lacking the details you will need to research their product offerings. When I first considered using their products, I called them and obtained very helpful assistance that has served me well. Their pistons have performed well with no issues to date. Good luck with your build, hope this helps.
Good Day!
www.durableperformance.net
 
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302 chevy pistons are 4 inch bore and same stroke as a 283 , you will have to make sure they are flat-top and not domed
JIMI
 
I've found that anything over .080 will overheat. Maybe my bad experience but some blocks are a little thin in cylinder wall casting and I would never use a block bored to .125.
 
I do have mild overheating issues. I thought it from my less than perfect radiator. This only happens on longer drives at higher speeds. Never around town at lower speeds.
Terry
 
i run a couple of my engines at 4" and have never seen them run hot. they used to race them at 4.060" with no problems. i would bore it to 4" and not worry about the pits.
 
Jim Brierley said:
i run a couple of my engines at 4" and have never seen them run hot. they used to race them at 4.060" with no problems. i would bore it to 4" and not worry about the pits.
Click to expand...


I never had a problem with over size pistons. I had one engine that was bored .155 over size in a 30 pickup. 7-1 head, hot cam, big valves, down draft. It never run hot.

My take is they run cooler. The heat gets through the cylinder walls faster. Plus they are more efficient, produce more power with less throttle.
 
Agree with everything above.

There is an easy way to get just the right 283 pistons, or should I say 283 style pistons.
Contact John at Pete's Auto Machine in New Mexico 505-836-3110.

He will provide custom made 283 style short skirt modern style pistons with the wrist pin hole situated so that you can use stock Model A rods, saving the considerable expense of diff. rods.
You will get the pistons, rings, pins, and snap rings all for 250.00

Tell him Ken and Dave from Texas sent you.

You will not be disappointed. Set your piston to wall clearance to .0035. Remember cyls 3&4 run hotter so those pistons expand more. Usually they come machined to match that spec but check the clearance with a feeler and hone a bit from the cyls. as needed. Be sure to use a feeler long enough to get down to the skirt; the very upper part of the piston is slightly less in diam. The worst assembly jobs are where someone just shoves the pistons in the holes and calls it good. Also check ring gaps. I have seen this step skipped with resulting disaster.
Should be .022 top ring .016-.018 second ring

The tops of the pistons are spec for the stock height of the block. If the block has been decked, you may need to cut the piston tops. No big deal. Supposedly original A pistons were proud of the deck by .030 or something. I have never actually seen anything official from the archives that would verify this. In todays racing world you would be told to keep the pistons level with the deck....not to have anything protruding into the 'quench' area, else your HP can suffer.

I have installed 3-4 sets of these babies and they are sweet and simple and save the expense of new rods
 
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Small pits won't hurt a thing.
I have built 3 engines with 4.030 bore and one with 4.040.
All ran cool. I use only Ross forged pistons. There are at least 4 other manufacturers
of forged pistons.
Putting cast pistons in a high performance engine is idiocy.
 
tbirdtbird said:
Agree with everything above.

There is an easy way to get just the right 283 pistons, or should I say 283 style pistons.
Contact John at Pete's Auto Machine in New Mexico 505-836-3110.

He will provide custom made 283 style short skirt modern style pistons with the wrist pin hole situated so that you can use stock Model A rods, saving the considerable expense of diff. rods.
You will get the pistons, rings, pins, and snap rings all for 250.00

Tell him Ken and Dave from Texas sent you.

You will not be disappointed. Set your piston to wall clearance to .0035. Remember cyls 3&4 run hotter so those pistons expand more. Usually they come machined to match that spec but check the clearance with a feeler and hone a bit from the cyls. as needed. Be sure to use a feeler long enough to get down to the skirt; the very upper part of the piston is slightly less in diam. The worst assembly jobs are where someone just shoves the pistons in the holes and calls it good. Also check ring gaps. I have seen this step skipped with resulting disaster.
Should be .022 top ring .016-.018 second ring

The tops of the pistons are spec for the stock height of the block. If the block has been decked, you may need to cut the piston tops. No big deal. Supposedly original A pistons were proud of the deck by .030 or something. I have never actually seen anything official from the archives that would verify this. In todays racing world you would be told to keep the pistons level with the deck....not to have anything protruding into the 'quench' area, else your HP can suffer.

I have installed 3-4 sets of these babies and they are sweet and simple and save the expense of new rods
Click to expand...


I agree I have also used those pistons. They work well. It saves buying $500 rods. Stock 283 piston will not work with out new rods because the piston pin height is different plus the pin dia is smaller then a Model A. Petes piston are ready to go on stock rods. They also take the narrow rings
 
Thanks everyone, all good advice.
Thinking I will just have it taken to .125 for now and not worry about a few pits left behind.
I guess the small pits left behind will just fill up with carbon with use.
I also like the idea of forged pistons too, don't know if I can purchase as sets of 4?
This engine will be running a performance high torque regrind cam but non counterbalanced crank (early beaver tail style)
Full insert, standard oiling system.
 
Terry said:
I am currently running my A at 4.000 bore. It is a huge amount of stock to remove, but the A block will take it . By my calculations it increases the displacement to about 215cu.
It runs fine above an idle.
Terry
Click to expand...

Thanks Terry

215cu, great!
I did calculate it to roughly 207 or 8 but more use to working in the metric system.
We changed to metric for everything in between 1970 to 1975, they were still teaching imperial measurements in my first year in school in 75 then changed mid year to full metric.
I don't remember it but my parents reminded me of it years later.
 
I just finished a similar build a few weeks ago. Block bored .125 over (small minor pits left, nothing noticeable though) used oversized intake valves, all inserts, touring cam, counterbalanced, VA clutch setup and a 6.0 head on it. No issues thus far and runs great, power for days. It will hit 45-50 without trying, honestly afraid of how fast it will go but time will tell. I wanted to run the 283 pistons in mine but was unable to find a set at a 4.0 bore and was told they aren't made. Good luck with your search and build and let us know if you find 283 at a 4.0.
 
I spoke to John at Petes auto machine last week, a real pleasant and knowledgeable man, I have a clean .90 over bore with some heavy piston slap. alas they do not have them for that size, I have been directed to EGGE and have been told they maybe able to machine a set to fit, as anyone tried this.
 
if anyone can do it Egge can do it.

and to KMeredith87 John at Pete's Auto Machine has a .125 over 283 style piston, I just bought a set, call him
 
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