4-1/8" stroke engine

[Jim Nashville]

I am thinking of building an 8BA with a 4-1/8” stroke crank. I have a 4” mercury crank to offset grind and a complete 21A engine that I can pull the rods out of. The rods will use floating bearings and the mains will be inserts. The question is, what pistons do I use? A local old timer told me to use 3-3/4” stroke 8BA Ford pistons. Since I have not disassembled the 21A engine yet I am wondering what the difference is in the length of the 21A rods and the 8BA rods. I need to get this sorted out in my mind before I start ordering parts.

 

[Russ/40]

Both rods are 7", the same. The ford Pistons will not work. You need a special custom piston, built for the stroke. Ford Pistons or Merc pistons would only work in a pop-up situation with a custom cut head. You need to rethink what your doing. You should be looking at Ross for a three ring 4 1/8" stroker piston.

 

[JM 35 Sedan]

Probably more than you want to spend, but if you buy a stroker kit from someone like Speedway, you get all the correct components that you need.

 

[Fordestes]

JM 35 is right,
The Ross forged pistons are overkill for a non supercharged eng. speedway , egge ,many high quality cast pistons on the market, the forged piston will rattle like a jackass kicking a tin barn atleast till they warm up also expect a little oil consumption to go along with the forged pistons ,they have to be fitted with more loose clearances, as for me, on an aspirated build I use a high silicon cast pistons, Patricks in Casagrande Az.
speedway motors,Egge Machine,I think Reds Headers Just to name a few have all done a good job in my street engines, If you go with used rods make shure they are checked for straightness, rebushed and copletely reconditiond ,have the piston pins fitted to the rods and pistons by a reputable rebuilder . The 21A rods have a smaller
Diameter big end to accept the smaller offset ground crank journal/bearings ,as stated the center to center rod lenght is 7" on both style rods.

 

[Ken/Alabama]

My engine is a 59A block with 4 1/8 stroke X 3 3/8 bore. I have Ross pistons in it. You can hear them just a little when cold but it's not bad. No problems with oil consumption. You will like it, it pulls like gangbusters . Pistons for 4 1/8 stroke will be marked 1/16 LC meaning 1/16 Low Crown.

 

[qmdv]

I suppose that for the 3% increase in displacement it is worth the money.

Tim

 

[Ol' Ron]

Yes, It's nice to have the other 9 cubic inches, kinda pricy tho. Why not use a 4" crank and Egge 3 5/16 pistons on 8BA rods. Now I realize this is only 276 cubic inches, BUT, a thousand dollars cheaper.

 

[PeterC]

Probably more than you want to spend, but if you buy a stroker kit from someone like Speedway, you get all the correct components that you need.

Not disagreeing with JM re options - but I chose Ross forged for my 4 1/8th stroke set up (supercharged) - used NOS 21A's and an original Merc crank - happy with the set up.

 

[Ol' Ron]

How much did it cost you to have the cramk cut and balanced.?? Plus floating bearings.

 

[JM 35 Sedan]

Not disagreeing with JM re options - but I chose Ross forged for my 4 1/8th stroke set up (supercharged) - used NOS 21A's and an original Merc crank - happy with the set up.

Peter, when I built my 284ci, 59 series stroker engine (4-1/8" stroke x 3-5/16" bore) I did not use a kit either. Bought a Scat crankshaft for full floating rod brgs, Ross forged pistons, and reconditioned 29A rods. It all went together well, but looking back, the time and cost would have been less if I had gone with a stroker kit. That's the way I would go if I were building one today.
I should also mention that by using the larger/big end 29A rods, I had to cut a slight relief at the bottom of each bore for clearance. If I were doing this today I would use 8ba rods and shell bearings.

 

[PeterC]

How much did it cost you to have the cramk cut and balanced.?? Plus floating bearings.

Mucho Dinaro - but you already knew that ... ported and relieved, line bored, cylinders bored, heavy duty bearing caps etc. Could it have been built with less - sure. Was it overbuilt .. possibly ... but I am a very happy camper as I hear it all singing and feel it in by backside when I manage the throttle.

 

[Jim Nashville]

Thanks for the responses. After thinking about it more I guess I will just stay with the 4” stroke Mercury crank, 3-5/16” bore and mill the heads for an increase in compression. This engine will be in a 41 coupe used as a daily driver. I will stay with a single carb. so the engine will have a stock outward appearance. Guess I am showing my senior age but torque is important to me and not high RPM’s & racing. Suggestions on a camshaft are appreciated. Right now I am thinking I should just use a stock cam. I know most folks like the rumpety idle but the cams I am familiar with are weak at low RPM’s. What do you guys think?

 

[19Fordy]

Don't be afraid.
Use at least 2 carbs, like "back in the day."
You'll be glad you did.

 

[JSeery]

Mucho Dinaro - but you already knew that ... ported and relieved, line bored, cylinders bored, heavy duty bearing caps etc. Could it have been built with less - sure. Was it overbuilt .. possibly ... but I am a very happy camper as I hear it all singing and feel it in by backside when I manage the throttle.

Nice looking block!!

 

[qmdv]

Or at least go with a 48 instead of a 97. Bigger throat.

Tim

 

[Ol' Ron]

I want to say something that will go over like a lead balloon. IF, and I say IF you have a 4" merc crank and rods. You don't have to re balance the assy when Boring to 3 5/16, If you use the rods that came with the crank and Egge pistons. I've buit dozens of these engines with out balancing them. Also non of our stock car engines were ever balance (Exceot one) I know everyone will disa ggree with this, but there out there.

 

[JSeery]

That's because Ford did a fairly good job of balancing the rotating assembly for you.

 

[southfork]

Are Ford flathead rods marked? I mean, If I were to look through a bunch of used rods for the 29A rods, would I be able to see a number indicating which are the 29A rods?

If not, what stock flathead engine should I look to as a probable source for the 29A rods?

 

[Bruce Lancaster]

Big bearing floaters from 239's had 99 forged on them 1939-41, 29 on '42-48.
29's still hve 99 on the caps...
Small bearing ones were 91 and 21, same time divisions.
I've never compared the types, as Joblot only stocked the late ones that replaced all...
I suspect the actual difference may have been metallurgy rather than design, as all through 1941 the Government released regulations banning numerous alloying additives from non-critical uses, essentially reserving them for aircraft. Ford would have had to make many changes in formulas to delete imported alloys, and I'm guessing this is the reason for the new number...but it is a guess, and serious research at Ford archives would be needed to establish the truth.

 

[Straightpipes]

Jim, I built a lowbuck 8BA with the following: EAB heads, Late Merc camshaft, Merc 4 bolt manifold with a Rochester 2G carb (mounted backwards). Ran this setup years ago in the stock car..(many years ago....... If you cut your heads be sure to measure clearances.