Model A to bore or sleeve

T

trctrdr

Member
I just purchased a model A block which has been bored .095 O.S. for some reason. I'm thinking of boring to .125. It looks like the space between number 1-2 and 3-4 will be pretty small. I don't want to have problems with blowing head gaskets as I'm planning on a 5.5-1 head as well as touring cam, model "C" crank, B rods "B" carb. on a bored out "A" manifold and lightened flywheel. Not really wanting to build a "hot rod" just would like to have a little left at 55 MPH.
Also will be installing a F-150 O.D. trans.
Any thoughts?
 
I've been running my engine with an 0.125" overbore for years with no problems.

If you haven't looked at the dyno sheets at http://www.modelaparts.net/dyno.htm/dyno.html, do so before you plan any mods. Great data. For example, you'd be hard pressed to see any advantage from boring out the intake manifold; and a HC head by itself provides a tremendous gain over any other single mod.
 
Nothing wrong with .125 over IMHO, but be sure to check your cam bore in the block with that much wear you may wnat to spring for a new cam with oversized journals and have your cam bore line bored. Rod
 
Cam bore is 1.562 all three , I can't seem to find the spec in the book. New cam journals are 1.560
I think the current bore was a machining error. Looks like it was bored sometime in the past but not ran since but now has rust and will need to be bored again
 
How bad is the rust? Do you think it won't clean up at .100?I have had .125 over engines,zero problems.The last one I had bored that big got a BF head and it turned into a little rocket.It was in a 28 RPU.I took an old radiator that looked good the shop I use,he told me it was a cheapie from the 50's but it was clean and flowed well.Never got warm in 100 degree weather.With these high compression heads what little overheating problems I ever had went away.I could sit in a parade at 90 degrees with the spark retarded and never think twice about it.
 
Perhaps it was bored, but never honed with the intentions of going 100 over ---perhaps if the rust is not deep it still can be honed to 100

A stock engine that is well balanced and a B cam will get you 55 and a "little" more, mine with some balance issues is good for 65-67, has been comfortable at 62 for all day trips.
 
trctrdr said:
I just purchased a model A block which has been bored .095 O.S. for some reason. I'm thinking of boring to .125. It looks like the space between number 1-2 and 3-4 will be pretty small. I don't want to have problems with blowing head gaskets as I'm planning on a 5.5-1 head as well as touring cam, model "C" crank, B rods "B" carb. on a bored out "A" manifold and lightened flywheel. Not really wanting to build a "hot rod" just would like to have a little left at 55 MPH.
Also will be installing a F-150 O.D. trans.
Any thoughts?
Click to expand...

When you set it up to bore offset the boring bar away from the thin area.
You should be able to bore to .156 and only take .005 off the center area.
Works for a lot of us.
 
trctrdr said:
I just purchased a model A block which has been bored .095 O.S. for some reason. I'm thinking of boring to .125. It looks like the space between number 1-2 and 3-4 will be pretty small. I don't want to have problems with blowing head gaskets as I'm planning on a 5.5-1 head as well as touring cam, model "C" crank, B rods "B" carb. on a bored out "A" manifold and lightened flywheel. Not really wanting to build a "hot rod" just would like to have a little left at 55 MPH.
Also will be installing a F-150 O.D. trans.
Any thoughts?
Click to expand...
My first question is, would the gasket area be wider than the area between the cylinders? I think not. I have bored many .125 and never blown a head gasket. The gasket is the limiting factor when it is narrower than the deck surface.
 
James Rogers said:
My first question is, would the gasket area be wider than the area between the cylinders? I think not. I have bored many .125 and never blown a head gasket. The gasket is the limiting factor when it is narrower than the deck surface.
Click to expand...

Very good point, hadn't thought of that, thanks
 
Good news. I had a chance to clean the rust out of the bores with a bead ball and accurately measure (with a dial bore gauge) the cylinders. with 99% of the rust out they measure .092 O.S. Should easily finish hone to .100 Thanks for all the advise, now it's off to the machine shop, check for cracks and finish hone as well as new valve seats and a light decking.
 
sucp_1006_08_%2Bbig_block_engine_build%2Bball_hone.jpg
tuneman said:
Haven't heard the term bead ball before?
Could you explain a little about it and how it works?
Click to expand...

AKA dingleberry hone
 
trctrdr said:
Good news. I had a chance to clean the rust out of the bores with a bead ball and accurately measure (with a dial bore gauge) the cylinders. with 99% of the rust out they measure .092 O.S. Should easily finish hone to .100 Thanks for all the advise, now it's off to the machine shop, check for cracks and finish hone as well as new valve seats and a light decking.
Click to expand...

Why new valve seats? Or did you just mean to have them touched up? I would never install new seats unless the original seat in the block is recessed.
 
Seats are pretty wide, one intake is .150, besides don't you think I'll have a problem running unleaded fuel with the original cast-in seats, especially exhaust? I once had a 69 ford pickup with a fresh engine that ate more than one exhaust valve before I had all the exhaust seats replaced with hard ones. Is this not an issue with the model A engine? The old 8N ford tractors which I often repair in my tractor repair business had hard exhaust seats from day one, I have never seen one with a problem caused by using unleaded fuel. The deck need machined (rust issues) which will narrow and raise the seats somewhat.
 
trctrdr said:
Seats are pretty wide, one intake is .150, besides don't you think I'll have a problem running unleaded fuel with the original cast-in seats, especially exhaust? I once had a 69 ford pickup with a fresh engine that ate more than one exhaust valve before I had all the exhaust seats replaced with hard ones. Is this not an issue with the model A engine? The old 8N ford tractors which I often repair in my tractor repair business had hard exhaust seats from day one, I have never seen one with a problem caused by using unleaded fuel. The deck need machined (rust issues) which will narrow and raise the seats somewhat.
Click to expand...

Tractors work much harder than the Model A's and can benefit from harder seats. Many Model A's are using the original cast in seats with no problems. I've heard of many seats coming loose while on a tour, so if you go ahead with inserts make sure the installer knows what he is doing. Where I used to work in the 80's I installed seats. I used a locking fluid, plus I always tapped a rolled edge over the top of the seat.

I don't think lead was in gas when the Model A was built, and lead hasn't been in gas for many years.
 
trctrdr said:
Seats are pretty wide, one intake is .150, besides don't you think I'll have a problem running unleaded fuel with the original cast-in seats, especially exhaust? I once had a 69 ford pickup with a fresh engine that ate more than one exhaust valve before I had all the exhaust seats replaced with hard ones. Is this not an issue with the model A engine? The old 8N ford tractors which I often repair in my tractor repair business had hard exhaust seats from day one, I have never seen one with a problem caused by using unleaded fuel. The deck need machined (rust issues) which will narrow and raise the seats somewhat.
Click to expand...

you do not need harden seat for a model A or any other car. A truck or tractor maybe. I do not run harden seat in my 56 Chev or 66 Vette both have many miles on this crap gas.

You can narrow the seats with a 3 angle valve job. Which is a better way any way.

Just for the record have put in many valve seats in the past 50 years, but only when the seat is cracked. I do have one in my Model A that had a cracked seat and cylinder wall. I have also replaced some that were put in wrong by some one else. Just like every thing else not every one does it right.
 
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RE head gasket. Some head gaskets specifies to what oversize they are good to. You might be wise to put a bevel around the top edge of the piston if one is not there already. Just in case!
 
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