Shaving a late 2F head

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SteveH

SteveH

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I have an '82 2F engine from an FJ40 that was rebuilt 25K ago, and then run with mis-adjusted valves, and the compression is a bit low-ish in two cyls. I plan to pull the head, have a valve job done, and get it shaved to bump compression for better performance at my 7000' elevation. The lower end is solid on this engine.

I haven't seen a thread on late model 2F head shaving (in particular) - since this head is rumored to be more 'fragile' than a '78ish head, should I have it shaved less or do anything else along the way? (Paging Mark Whatley!)

Thanks - Steve
 
I'm about to overhaul my '72 F engine (been posting on a thread about backfire issues) and am going to shave, errr, mill the head. Unsure how much just yet, possibly .020"; I'll know more after a detailed inspection, magnaflux, etc. please keep me advised of what you find out and I'll do likewise :)
 
This engine was just honed - not bored. What math formula does one use to determine head milling on a stock 2F? Thanks!
 
A domed piston is not desirable. It hurts combustion performance if the flame front has to wend it's way over & around domes/wedges/valve reliefs. It is also a thermal loss, because the 'finned' aluminum piston pulls heat out of the chamber. Flat or slightly dished piston is most efficient.

CR is calculated thusly:
(pi/4*B^2*S)+C
-------------------------- (divided by)
C

Where b is bore, s is stroke and c is chamber volume.

fill in known data:
(707.8+c)/c=8.3

c=97cc chamber volume.

Using the above equation, it is not necessary to measure & calculate chamber volume, valve dish, HG thickness etc.

The combustion chamber is a simple tapered oval measuring 10cm on the transverse axis and 5.8 & 6.8cm on the vertical axes. The chamber walls are essentially vertical at the gasket face. Calculated area of the chamber face is 59.7cm^2.

If 1mm is removed from the head, it will shrink chamber volume by (59.7cm^2x .1cm) 5.97cm^3, raising CR to 8.8.

Keep in mind the FSM specifically states to remove no more than 2.5mm from the head.
:cheers:
 
just put some bosch +4's in there and call it a day ha ha. this could be a very lengthy debate as far as piston design goes in theory domed would not be as efficient as a flat piston BUT in my opinion that would be combustion efficiency NOT necessarily overall engine effeciency. just like a four electrode spark plug should produce a more efficient burn than a single lol in theory. something to keep in mind during all of this is that increasing your compression ratio is probably going to be pretty negligible anyway. my guess would be you would have the same gain from simply running premium octane gas as opposed to the cheap stuff. if your having low compression readings on a cylinder first and foremost i would recommend to determine if its coming past the rings or the top end of the egine. if you find that its coming from the valves do a headgasket job and take the head to cylinder head shop to do a once over. put some ngk plugs and wires on it and send jim your carb and dizzy. :) and then take it for a spin
 
roma042987 said:
my guess would be you would have the same gain from simply running premium octane gas as opposed to the cheap stuff.
Click to expand...

:lol: Higher octane allows you to increase compression without the nasty side effects, it offers no benefit over a lower octane fuel in an engine that runs properly on the lower octane fuel.
 
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roma042987 said:
I wouldn't recommend milling a head to raise compression. A head is milled to give a true or flat surface. It should be milled until that surface is attained not until some predetermined number is reached.
Click to expand...

I have a 2F in my 81 FJ45, I shaved milled surfaced the head last month when replacing the head gasket..

I was under the understanding that you have to do it like roma042987 says ...
 
No domed pistons for an '82 2F are available. The closed chamber design of this head would not be real happy with any dome either.

Higher octane actually produces less power if everything else is equal. Less energy by volume in the fuel. The only reason to use higher octane fuel is to allow higher compression.

A smaller combustion chamber is always the preferred way to gain higher compression over domed pistons. Engineers put a LOT of effort into designing combustion chambers to work efficiently. throwing a dome into the middle of it is generally not helpful.

Not sure why milling the head would be considered something to be avoided. Never heard that one before. Personally I have lost track of how many I have cut to increase compression.

We routinely remove the full 2.5 mm with no problems.


Mark...
 
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Hey, Pumpkin Troopy... I just noticed your info on your post... did you by chance work the Beaver Creek border crossing in 2010?


Mark...
 
I read my 2F engine manual last night, and I saw no discussion of how to determine how much a 2F head has been milled. What Toyota document might contain this information? How could I measure it?

Thanks!
 
Mark W said:
No domed pistons for an '82 2F are available. The closed chamber design of this head would not be real happy with any dome either.
Click to expand...


Someone needs to let Man-A-Fre know....
 
SteveH said:
I read my 2F engine manual last night, and I saw no discussion of how to determine how much a 2F head has been milled. What Toyota document might contain this information? How could I measure it?

Thanks!
Click to expand...

I've wondered the same thing.
 
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