Model A Head Mods

[clampdaddy]

Today I pulled the head off my "51 "A" parts tractor so I can have it worked over for my "48 tractor. I"ve seen alot of guys grind the eyebrow back away from the intake valve and I have a couple questions about it.

#1. Will the engine loose any bottom end lugging capability? I"m running a pretty much stock tractor and we have a hard track so my lil" tractor powers out right before I get any real tire slip. I can"t afford to loose any bottom end grunt.

#2. My main reason for doing the head is to mill .200 off it to gain some compression. I"m currently getting around 112 in each cylinder (give or take), and I"m wondering if cutting those eyebrows out of the combustion chamber will negate any compression gains that were gained by the milling.

 

[TiredA]

I"m afraid milling the head isn"t going to gain you enough Hp to notice. I"d swap the first reduction gears out of the "52 to slow it down a bit....then do the head mods. I pulled a "48 for a while and had the same problem as you. So, I traded for a "51 with the lower gears. Then I built the engine up, now I wish I had the taller gears back. Fickle bunch aren"t we?

 

[clampdaddy]

I already swapped the reduction gears. I did gain a little on the bottom but not much, so now I've got to get some more power.

 

[north puller]

Cdaddy, you're not going to get what you want with cutting the head. At the very least, you've got to get a "high compression" aluminum piston rebuild kit. Better yet would be custom pistons or longer rods. If you can get your compression up in the 170-200 psi range you will notice a real difference.

 

[clampdaddy]

Ok, thanks. When I pulled the head I noticed all that extra room at the end of the cylinder and was wondering how much milling the head would even accomplish.

I see that extreme tractor parts has a set of high compression pistons for the "A" running a 5.75 inch bore in a stock block. I have another block that I could have bored but I've always heard the .125 was the furthest that a stock block should be overbored (that's where mine is at now). At 5.75 would I still be able to take my tractor out for a drive or drag a disk with it, or will it become a tractor that is only suitable for short run times and tractor pulling?

 

[Mike N Mo]

I have a PowerBlock that would fit your '48A. That with a set of standard bore high compression G pistons should get you to 60+ HP. E-mail's open if you're interested. Mike

 

[Buster R]

Get a hold of Josh Blackburn he can get u squared away with everything u will need!! Great work and prices.

 

[north puller]

your best bet is to talk to Ray, however if you want power youre gonna end up burning better than pump gas. Would make draging a disk a little expensive (i do plow with my 70 on expensive fuel, just costs a bit more for a plow day). Also i would think that a bore larger than .125 would be less likely to survive excessive heat, and you would have to pay attention to the heat gauge when running. just my 2 cents, i can't really confirm that.

 

[Super Trucker]

Talk to Josh Blackburn for the rocker mod he does and the carb work . He did mine and with a set of .125 over M&W knock offs I have a 50 hp at 540 and I can pull 2-16's in heavy ground in 3rd gear. His prices are very fair.

 

[2-banger]

ive got a..a,60 and 50 ive played with and pull. my 60 has had rods lengthened by josh head cut .150 it blows 220psi i ground brows out of head runs great lugs down good. my 50 we cut hd .200 it has al pistons after it was milled i ground brows out josh did rockers....it only picked up 10 psi runs very strong...but just cutting hd didnt do much..ive got a thats 5.75 bore josh made pistons,rods, cam sounds awesome cant wait to hook it...get ahold of josh have him lengthen your rods and ratio your rockers u wont need to cut your hd..bore it .125 over with al pistons you will be happy

 

[johndeereman]

Why stop at 200? With a head that"s never been milled before you can take .325 off it you just have to regrind the oil galley which takes 2 seconds. As for the 5.75 bore there"s no reason you should have to run better than pump gas. I have a bored pb whith hc pistons and all the bells and whistles done to it running a 93/4 compression and I run high test pump gas. Only thing I"d be worried about with that set up is over heating when running a drag or something I"ve never run that set up personally so can"t tell you if it will run hot or not.

 

[gtx1967jewison]

I seriously would NOT mill a head that far. They were already prone to head gasket leaks & cracking as stock. Its just the wrong way to go about it in my opinion. I want all the iron in my head i can get. a track- only tractor may be a different story. Just my opinion.

 

[Anonymous-0]

I have the 125 over aluminum H/C pistons and also have a flat head which puts me into 110 octain fuel but I still drive it on the local back road jaunts with the other guys on Sundays. Just keep your radiator clean and I see no reason it would over heat.

 

[jd b puller]

Math is a powerful thing...

Mill the head all you want, you"re still not going to get the compression you"re looking for.

With low compression, move something 1/4" and you"ll see a minimal gain. If it"s higher compression (8+), small changes make a big difference.

It"s a lot cheaper to make an engine more efficient than more cubes.

Double the efficiency, you double the power. Or you can double the cubes and double the power (relatively speaking). Efficiency can be gained by minimizing losses from friction, sealing, mass, flow, incomplete combustion, etc.

Stock A was 5.6:1 compression. With +.125, I think it jumps up to about 6.5 ish... Weaken the head and Mill another 0.325 off it and you pick it up to about 8:3. A lot better than stock, but Still not where I"ve found power at.

Put the M&W"s in and eliminate the chamber in the head, pick up the flow a tad and you"re at 9.7:1. pretty close to one of my happy numbers. Take a little off the top or back of the block (when you"re in this range, a little goes a long way) and you"re at 11.

For those that say it won"t lug, they either don"t understand what "lug" means or they believe everything they"re told or haven"t figured out how to make it work, or have unrealistic expectations.

 

[forty40]

Attached is a screen print of the spreadsheet I use to calculate cubic inches and compression ratio for different engines. It has been modified slightly for a 2 cylinder so I could see changes at a glance for some combinations of parts. As talked about in previous replies, it's easy to see that simply milling .150 from a stock JD A head that starts out at approx 185cc combustion chamber reducing the cc to 145 makes a very small change. If I could figure out how to attach the excel spreadsheet, it's a handy tool, but so far I haven't figured out if an attachment is possible

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[nl00sb]

250 over is fine but i wouldnt spend the money on 250 over pistons unless i was going further with the tractor quick easy way to get some more power have someone rework the rods for more compression, just make sure that your block is in good shape and the bore is good further up in the block ray at extreme and josh can do rods

 

[clampdaddy]

(quoted from post at 21:00:35 02/20/13) 250 over is fine but i wouldnt spend the money on 250 over pistons unless i was going further with the tractor quick easy way to get some more power have someone rework the rods for more compression, just make sure that your block is in good shape and the bore is good further up in the block ray at extreme and josh can do rods

That's the way I'm leaning. I think I'll get the head freshened up locally, have Josh do my rockers, and then have him do the rods.

One old timer told me that they used to take a circle cut pieces of half inch plate and attach them to the tops of the pistons with countersunk machine screws and a tack weld to keep them from backing out. Basically adding a pop up to the piston. It sounds a little scary but the price is hard to beat. Lol!