Maximum Bore + Stroke

[Flathead]

On the Model A engine how much, if any, can the stroke be increased? Mainly wondering about space in the crankcase to swing a bigger crank. Would the maximun bore be about 1/8th inch oversize? I am familiar with the V8's but not so much the A. Thanks.

[1930artdeco]

My last engine was bored .125 over which is the max bore. If I use it again it will have to be sleeved.

Mike

[Special Coupe Frank]

Maximum bore probably varies from block to block, depending on water jacket proximity, any core shifting, etc.

Have heard 0.060" overbore is common, 0.080 is "possible", and 0.100" is probably the absolute max IF you have enough meat in the water-jackets. That's still a bit less than 1/8"...

Don't know about stroking... you might achieve 4-3/8" stroke by grinding the rod journals off-center...

Watcha thinking about doing with this engine ?

[Dave in MN]

My inserted bearing engine with just under 50,000 miles is bored .125" over. Zero problems during those miles. The next step would be sleeves if ever re-built. I do not have any problems with it running hot...I added a thermostat to get the temp up.

I've built a few others at this same bore with no problems.
Dave in MN
www.durableperformance.net

[d.j. moordigian]

Flathead,

I have an old race engine, 1950-1960, it's a B, with off set ground rods to work
with A rods. The block is .125 over to .135 over, V/8 60 main bearings and a
reworked V/8 oil pump.

Dudley

[just plain bill]

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Originally Posted by Flathead

On the Model A engine how much, if any, can the stroke be increased? Mainly wondering about space in the crankcase to swing a bigger crank. Would the maximun bore be about 1/8th inch oversize? I am familiar with the V8's but not so much the A. Thanks.

I think they have been bored out to 4.062. 4.000' is actually pretty common. The bigger you bore causes headgasket sealing problems between cylinders. Some have bore the cylinders slightly offset. In a recent issue of S O S S there were photos of engine that is bored into the water jackets and is going to be sleeved oversize. The "B" has much larger bearings so the oil pan has clearance dimples in the pan and this cures one of the problems with stroker cranks. I have read where the use of 12 point nuts on the rods also helps with the clearance problem. I have one, a "B", that is ground offset .156 and that gives a total stroke of 4 .562 or 4 9/16". This is a modification that can't be seen so the PC police won't know. Of course, I must admit, my car only goes 1/4 mile at a time.

[George Miller]

Originally Posted by fordgarage

My last engine was 0.125 oversize on the bore. I would offset grind a B crank to decrease the stroke not increase it, if I was going to change it. Think about it..

I agree with you decrease the stroke. More stroke will give you more torque but less RPM. You do not need more torque, you need more RPMS.
My best running A engine was bored to 4.030.
I have been working on a destroked A engine we will see if it works out.

[James Rogers]

I just finished boring a engine to put sleeves in. I always use the thick wall sleeves that are .125 thou thick each side. This means I have to bore the block to 4.125 to have the sleeve a .002 thou interference fit. I do this all the time and have never hit water. I would say the block could be bored at least to 4.250 with no problems.

[Flathead]

Thanks for all the responses, I was thinking about a torquey touring motor as opposed to higher RPM. Putting dimples in the pan is not a problem, but how much clearance is there between the rods and the camshaft for a longer stroke?

[just plain bill]

Originally Posted by Flathead

Thanks for all the responses, I was thinking about a torquey touring motor as opposed to higher RPM. Putting dimples in the pan is not a problem, but how much clearance is there between the rods and the camshaft for a longer stroke?

I used "Skokie" A rods and had no clearance problems. The engine does have a lot of torque and goes pretty fast 1/4 of a mile at a time.

[Chuck Sea/Tac]

What gasket are you guys using for .125" bore? I'm having a hard time finding a B head gasket for that bore size, and the A head gasket I used before is no longer available.
Chuck

[Jim Brierley]

Just plain Bill is right, he's "been there, done that". Back in the day many racers bored them to 4 1/16" with no problems but I recommend 4" to be the maximum. A 'B' crank can be offset ground to give 3/8" stroke, clearance between the rods and the crank, and between the rods and the pan get real close, so be careful. Guys used to use Pontiac rods, they had to be modified to clear the cam and often the cam was ground to clear them too. The old cam grinders knew right where to grind them.

[Special Coupe Frank]

Just thinking out loud here... stock stroke ( 4-1/4") is already fairly long and torquey; if you're looking for a touring engine with a little extra "grunt", how about a touring cam and perhaps 5.5:1 "police head"... ?

Sounds like "stroking" a Model A might be a complicated and delicate art...

[Flathead]

You're right, a touring cam and 5.5 or 6 head is what I will probably do. However there is that "no substitute for cubic inches" rule that is still valid, especially with a Flathead. Just trying to do my homework on this.

[kelley's restoration]

if you look at the hamb and a guy with then screen name crazydaddyo. you will see that he has had one or two cranks break after doing this offset grinding.
i think you are really just making things more complicated for yourself. just put in a mitchell or volvo overdrive and call it a day.
then its just bolt ons without sacraficing reliability
just my .02
tk

[just plain bill]

Originally Posted by kelley's restoration

if you look at the hamb and a guy with then screen name crazydaddyo. you will see that he has had one or two cranks break after doing this offset grinding.
i think you are really just making things more complicated for yourself. just put in a mitchell or volvo overdrive and call it a day.
then its just bolt ons without sacraficing reliability
just my .02
tk

Those particular cranks were off set to the max and after much discussion it was never clear as to the radius on the rod throws. The radius and finish in the radius are critical. I know of one with a 1/8" off set with 20,000 miles on it. I do use a SBC dampener on my engines.

[Flathead]

I agree that a damper would be a good idea, and of course the crank has to be ground right.

[Chris Haynes]

Originally Posted by kelley's restoration

just put in a mitchell or volvo overdrive and call it a day. hen its just bolt ons without sacraficing reliability
just my .02
tk

An overdrive won't help ya if your engine doesn't have the oats to turn it. Remember the old adages, "There is no substitute for cubic inches". "Speed cost money! How fast do you want to go?

[Smitty]

Dave,
How is your engine with inserts? Is it a much stronger bottom end? Issues with bearing failure eliminated?

Thanks, Steve

[Crazydaddyo]

Originally Posted by kelley's restoration

if you look at the hamb and a guy with then screen name crazydaddyo. you will see that he has had one or two cranks break after doing this offset grinding.
i think you are really just making things more complicated for yourself. just put in a mitchell or volvo overdrive and call it a day.
then its just bolt ons without sacraficing reliability
just my .02
tk

Yes, I have broken two cranks. They both were B cranks ground to A mains and rods. Rod journal offset ground .187" for a total stroke of 3/8". Fillet radii were too small, but even .125" - .187" radii are hard to get with this big of an offset grind. Bore was 4".

As Bill has said, If you are only expecting your engine to go short distances fast, stroking it is advantages. But if your building a touring engine, then changing the stroke is a waste of money.

Head, Cam, And carb are your best "bang" for the buck.

I prefer the T-5 trans. but I will be banned from this sight if I talk any more about "non-stock" alterations.

.

[Jim Brierley]

4" bore with a 1/4" longer stroke + 225 inches, with a 4 3/8" stroke it = 239 inches. The difference in torque is amazing!

[just plain bill]

Originally Posted by Crazydaddyo

Yes, I have broken two cranks. They both were B cranks ground to A mains and rods. Rod journal offset ground .187" for a total stroke of 3/8". Fillet radii were too small, but even .125" - .187" radii are hard to get with this big of an offset grind. Bore was 4".

As Bill has said, If you are only expecting your engine to go short distances fast, stroking it is advantages. But if your building a touring engine, then changing the stroke is a waste of money.

Head, Cam, And carb are your best "bang" for the buck.

I prefer the T-5 trans. but I will be banned from this sight if I talk any more about "non-stock" alterations.

.

I would tend to disagree with that. If I were to build a "touring" engine I would probably go with the 1/8' off set grind. I think the added torque would make a more tractable engine or power band. Too many try for the higher RPM's and end up shaking something loose. Of course not all but most of the amateur, "shade tree", builders have problems when they wind them up too high for too long. My self included.

[Chris Haynes]

I was looking at the new block/crank made by Burtz. They offset the location of the rod caps so the rod wouldn't hit the cam. Very close tolerances. How close do the rods come to the cam in a stock block with a stroker crank?
http://www.modelaengine.com/12.html

[Flathead]

Yes, I think a bigger stroke would help the low RPM power, just where you can use it on the road. No need to rev it up and strain anything. I guess this is pretty much what Bill already said.

[just plain bill]

Originally Posted by Flathead

Yes, I think a bigger stroke would help the low RPM power, just where you can use it on the road. No need to rev it up and strain anything. I guess this is pretty much what Bill already said.

Yes but you said it with less words!

[Crazydaddyo]

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Originally Posted by just plain bill

I would tend to disagree with that. If I were to build a "touring" engine I would probably go with the 1/8' off set grind. I think the added torque would make a more tractable engine or power band. Too many try for the higher RPM's and end up shaking something loose. Of course not all but most of the amateur, "shade tree", builders have problems when they wind them up too high for too long. My self included.

I was referring to the 3/8" stroke in my statment. Sorry I should have made that clearer.

You are right the increased stroke will give you better torque. And as long as you don't go much more then 3/16" you will still have a motor that will hold up to the rigors of touring. In my mind the cost of stroking an engine ($1,500 - $2,000) is a little much to add to your touring engine build cost

.

[1931 flamingo]

If your going to spend that kind of money, a swap to a pinto or chev II with a 5 speed is what i woud do (or a flathead). I know , it won't be 'original" then.
Paul in CT

[Flathead]

Don't want to open up that can of worms. My choice is to keep the original engine. I like the honest simplicity of the Model A. Just looking at some concealable "tweaks".

[Tom Wesenberg]

I agree with Vince and George that you already have plenty of stroke, and adding to it won't increase the cubic inches by much, even if it does give you some more torque AT LOWER RPM's.

I'd use a H/C head and counterweighted crank, and if you want more speed use a 3.54 or 3.27 rear end.