Raising compression on John Deere A

[Jlee2792]

Can I use a connecting rod from a 60 or 70 to raise compression on my A without any modifications

 

[BushogPapa]

Most agree the best way is to have your Connecting Rods Lengthened, to raise compression in these..

If you do, you MUST Hone the cylinders to remove the ring wear at the top of each cylinder, Ridge-Ream as necessary..

Otherwise you end up purchasing New Pistons, etc. to accomplish the same thing, but you will be more limited as to the Compression you can get from aftermarket pistons..

Aluminum Pistons will allow you to deepen the "Fire Slot" on the Spark Plug side of each piston as necessary after lengthening the Rods..

 

[Mike N Mo]

A 60 rod is a direct replacement for an styled A rod. It will have insert bearings instead of babbett, length, crankpin diameter, and wristpin diameter are the same. I'm unsure of the 70 rod length, but the crankpin size is 3.375 verses 3.000" on the A, so that's out. What year "A"? Need more info to give you other options.

 

[buickanddeere]

LP pistons from a 60. Multi angle valve job. Blend in the rough edges in the ports. Port match the manifolds. have the cam re-ground. This will put an A into the HP range of a 620.

 

[Jlee2792]

It is a 48 model

 

[Mike N Mo]

A 1948 A is harder to raise compression with readily available parts from other year "A"s. An early styled A can use late A pistons and heads for a pretty good bump in compression. The best/most reliable solution will be as B&D stated. Try to find LP pistons, or have a set made ($$$$). Longer welded rods can be a viable solution, but they need to be done by someone experienced AND competent. I've seen some really ugly looking rods, some made by guys selling to mainstream tractor pullers. Custom billet rods are also available, but again, kinda pricy. Milling the head will provide minimal results before weakening the head. Is this a dedicated puller, or something you want to plow with? What compression ratio are you wanting?

 

[buickanddeere]

"A" compression of 5.6 to 1 boosted to 7.3 to 1 ain't shabby and should still run on car gasoline even with the side plug and huge open combustion chambers.
There are shops that will CNC a set of any pistons you want.

 

[Jlee2792]

It's gonna be a dedicated puller so is doin any milling to the head a waste of time and money

 

[rick deere]

use airplane fuil you won't beleave how much power you'll get and not change anything else.

 

[buickanddeere]

With the 7.3 to 1 LP pistons the 'A" will operate just fine on 91 octane pump gas.
A reground cam, multi angle valve job, port smoothing and port matching are essential to work with the higher compression.

 

[wilson ind]

If having the crank ground possibly have ground for slightly longer stroke?

 

[BushogPapa]

The combustion chambers are so large that milling the Head makes little change in Chamber Volume..

If this is a dedicated "Puller", opt for a crankshaft change to one with as much Stroke as you can afford...+ find a good Power Block, better Cam timing, Top-Nitch Valve Job, etc, etc and everything improves performance..

Remember...there are fellas running compression pressures at or above 220 lb/sq in and 800 to 900 Cu In...you will not be beating some of these...

PLAN on "Having Fun" and Learning as you go..and don't take being beat personally..there IS a "Learning Curve"...!!

 

[Mike N Mo]

Take just enough off the head to ensure it's flat. Spend your time smoothing the ports, port matching the head to the manifold, grind back the eyebrow above the intake valve. If you stroke the crank, take it to 9", with a 3" crankpin. Doesn't cost any more to go big the 1st time. As far as compression, for a dedicated puller go to at least 10:1. You can put in a bored powerblock, and use standard bore G pistons, makes 398 CuIn With stock stroke. With the right cam, 60-65HP. I have a 6-2 powerblock bored to 6.117" currently, would need to be bumped to 6.125" for the G pistons if you're interested.

 

[Lynerd]

jlee2792 If you could find one of Jerry's old heads or one of Murphy's heads they are flat heads with big valves and large ports. Lynn