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I'm looking at decking my block .020" and my heads .010" for a high compression build, but I only have .023" of clearance between the top of the piston and the headgasket.

If I put in EA82 SPFI pistons, and shave off the .020", will I run into issues with hitting the piston on the cylinder head?

And I don't want to shave off too much from the head as I don't want to make it so thin that I have warp issues.

 

So, my official question is, what is the height difference between an EA82 SPFI piston and an EA81 NA piston?

This is obviously measured from the top of the piston to the pin, as that is the distance I'm concerned with.

 

If the piston height is too much, would it be better to convert it to .015" off both sides or just go with .010" off the block and .020" off the head?

The head seems to have a lot more material I could shave off than the block at this point.

 

Twitch

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Shaving the block results in a greater overall volume change than decking the heads.

 

Looking at my photos of my HC ea81 build, it looks like you could get away with .020 off the block.

 

i can post some high-res pics if you want.  Just let me know.

 

 

 

With the block shaved AND heads decked though you are probably getting dangerously close when it comes to piston/valve interference.

 

 

Would probably be a good runner if you didnt have interference problems.  Just so long as you figure out the correct valve train geometry.   I know mine is a bit noisy.  It is slowly working in, but still noisier than I had hoped it would be.  Mine is all hydro.

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Shaving the block results in a greater overall volume change than decking the heads.

 

Looking at my photos of my HC ea81 build, it looks like you could get away with .020 off the block.

 

i can post some high-res pics if you want.  Just let me know.

 

 

 

With the block shaved AND heads decked though you are probably getting dangerously close when it comes to piston/valve interference.

 

 

Would probably be a good runner if you didnt have interference problems.  Just so long as you figure out the correct valve train geometry.   I know mine is a bit noisy.  It is slowly working in, but still noisier than I had hoped it would be.  Mine is all hydro.

 

I've looked at the valve train geometry. This engine won't really be seeing RPM's high enough for valve float, so I'm not too concerned with losing too much there.

After talking to Delta Cam, the torque grind will be taking about the same amount of material off, so my valve clearances won't need to change much or even at all with the decking.

I'm just wondering if I'll be overdoing it if I take .020" off the block.

I should measure the HG to see how much space that adds to the combustion chamber.

If it adds enough, I'll go with my original idea and order the SPFI pistons.

 

Out of curiosity and lack of memory at the moment, do SPFI pistons have valve reliefs in the top of the piston?

 

Twitch

 

PS: This is a solid lifter engine

Edited by Twitch de la Brat

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Ah, adding a cam into the mix changes things.  Sounds like you have the valve train geometry figured.

 

And yes, SPFI pistons have reliefs.  Slight, but there.

 

ea51.jpg

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Ah, adding a cam into the mix changes things.  Sounds like you have the valve train geometry figured.

 

And yes, SPFI pistons have reliefs.  Slight, but there.

 

ea51.jpg

 

Thank you for the picture :)

So with the valve reliefs, I may be able to maintain a safe .025-.030" gap between the piston and the valves.

 

On another side note, did you have to remove any head studs? And if so, what was the most effective method you found without scarring the studs or stretching any threads?

I may just wait until I get to the machine shop to remove the studs safely...

 

Twitch

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Thank you for the picture :)

So with the valve reliefs, I may be able to maintain a safe .025-.030" gap between the piston and the valves.

 

On another side note, did you have to remove any head studs? And if so, what was the most effective method you found without scarring the studs or stretching any threads?

I may just wait until I get to the machine shop to remove the studs safely...

 

Twitch

For the studs, I've heard the double-nut method works well. (Thread one nut on a good ways, then another. Tighten them to each other, then crank on the innermost one to remove the stud.)

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There is a specific tool to do so.

 

If the block is going to the machine shop to be shaved, just have them fool with the studs.

That way if there is any problems with them or threading in the block it can be addressed at the same time.

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Ok, so updates!

I got flat top EA71 Pistons and and on the verge of being ready to put it all back together.

I'll let everyone know how tight the tolerances are between the valves and piston.

Also, the 2 nut method worked fine. I got some extra nuts and studs just in case any are stretched on the threads used to remove them from the block.

 

Twitch

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I do not like the ea71 pistons weak between the ring lands the ea82 piston is far stronger On the ea 81 engines I build for airplanes / hovercraft we used the ea82 pistons shaved block / heads worked very well the ea82 pistons are higher but dident have any clearance problems. Mind you I planed very little of block and heads. At any rate the ea82 pistons are 50 % stronger

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I do not like the ea71 pistons weak between the ring lands the ea82 piston is far stronger On the ea 81 engines I build for airplanes / hovercraft we used the ea82 pistons shaved block / heads worked very well the ea82 pistons are higher but dident have any clearance problems. Mind you I planed very little of block and heads. At any rate the ea82 pistons are 50 % stronger

I know, I know.

Unfortunately in my case, I was unable to source a reasonably priced set of new EA82 pistons, so I went with the EA71's because they were less expensive and readily available.

If it blows a piston apart in the first 1000 miles I'll accept your "I told you so".

 

Twitch

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Don't go over 6500rpms

I don't think my engine will be capable of spinning that fast, even free revving :P

And I know I'll be running out of power somewhere around the 4500-5000rpm range. So the desire to spin it up past that will be negated.

Thank you for the tip though :)

 

Twitch

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Im pretty sure Im running out of carb, but making that little ea81 rev much higher than 4k makes me cringe...

 

The motor I can fix easy.  Im worried about the body panels on this old car if the motor REALLY lets go!   :lol:

 

 

No matter really, this high compression ea81 has enough torque to keep you happy.  It really is a pleasure to drive compared to the old motor.

 I can chug around town all day long in 3rd and 4th  (5-speed) without a problem.  Although, Im sure the 5-speed has a bit to do with it as well.

 

 

 

Twitch, have fun with that motor build.  Go slow, do it once, do it right.   :)

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Well does it run yet!? Sweet to see more people doing the ea81 build up instead of the ever popular ej swap..

Not yet. I have to get back together with my friend who's helping me with reassembly. He does airplane engines :banana:

 

But I should have everything put back together (at least the block) tomorrow. Then comes making sure there are no oddities or clearance issues. I'll have pictures and more updates in the build thread. Check it out. (The Blu Bomb)

 

Twitch

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Don't go over 6500rpms

 

What happens over 6500rpms? Does the piston velocity hit 88 mph, then all the internals go back to the future? (jk)

 

 

Good luck with your build, I wish you many smiles and many miles. Smiles first.

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What happens over 6500rpms? Does the piston velocity hit 88 mph, then all the internals go back to the future? (jk)

 

 

Good luck with your build, I wish you many smiles and many miles. Smiles first.

Thanks man. I'll be nervous as a new father the first time I fire it up, but I'm sure I'll be grinning ear to ear when I hear her roar to life.

 

Twitch

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Didn't go back together today. Crank was groovier than a disco dance floor under the layer of old oil. Amazing what a solvent bath will reveal. So it's in for a regrind (and it's probably going to be goddamn expensive because of the size of the rod surfaces) and possibly I have to go to the junkyard to get a new one if it's going to be too bad.

 

So, for love of all things automotive, change your oil and filter. $25 every 3 months is cheaper than a rebuild.

 

Twitch

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We like pics here Ben!  Come on man all talk and no show what gives?   Good luck waiting to see your happy dance when she lives again!

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Twitch, a BUMP how is this EA71 pistoned EA81 holding up? I have just read of Ivans impression of EA71 flat tops after I have ordered a set - due to their price and availability

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Twitch, a BUMP how is this EA71 pistoned EA81 holding up? I have just read of Ivans impression of EA71 flat tops after I have ordered a set - due to their price and availability

Only thing keeping her down right now is a wobbly disty. Need a new 2WD Nippon disty or at least new bushings for her.

Solid compression and tweaking of the timing and she scoots. Just need to install my dual exhaust to make her a real monster.

 

Twitch

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thanks for the update :)

 

My thoughts aftyer seeing Ivans comment, re EA71 piston strength, not sure if he was commenting on factory or aftermarket slugs. I have some aftermarket slugs for EA82T that have his preferred drilled holes rather than slots for oil ring oil return.

 

Dual exhaust to do some duelling eh ? The most awesome sounding EA I have heard was Willys EA71 with his reijigged exhaust design, called unequal [but so too is the original Y pipe unequal] - sounds like a turbo EJ.

 

I am afraid your dual exhaust, knowing nouhght about what you have done, may sound like the orbital technology I heard running in a BMW 3 ? series about 15 years ago - bit odd it sounded just idling ....

 

here is a link to a story on it ..reckon I was lucky to see it and hear it :)

 

http://www.watoday.com.au/zoom/archive/rnews950713_0155_7797

Edited by jono

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thanks for the update :)

 

My thoughts aftyer seeing Ivans comment, re EA71 piston strength, not sure if he was commenting on factory or aftermarket slugs. I have some aftermarket slugs for EA82T that have his preferred drilled holes rather than slots for oil ring oil return.

 

Dual exhaust to do some duelling eh ? The most awesome sounding EA I have heard was Willys EA71 with his reijigged exhaust design, called unequal [but so too is the original Y pipe unequal] - sounds like a turbo EJ.

 

I am afraid your dual exhaust, knowing nouhght about what you have done, may sound like the orbital technology I heard running in a BMW 3 ? series about 15 years ago - bit odd it sounded just idling ....

 

here is a link to a story on it ..reckon I was lucky to see it and hear it :)

 

http://www.watoday.com.au/zoom/archive/rnews950713_0155_7797

Neat article. So The Bomb has over 20k on this rebuild and while I haven't done a compression check, it is holding up well. As I suspected, it starts to runs out of air around 6k free revving, let alone under load. If I plant it and make it spin under load in any gear aside from 1st, it starts to really drag when it passes 5500, but dumping it into the peak RPM when you shift will make the tires bounce and pull again, so there are times I do over spin it :grin:

 

When I do my compression check, I'll look over the plugs and check pistons with my friends boroscope. See if I have any hot spots, etc.

 

Twitch

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thanks for the update Twitch . The pics below of spfi pistons look just like the mpfi piston tops we got here. And , if I am not mistaken, same as carb 1986 model. I have not measured but observed the pistons in this mpfi block I have, sit near enough to flush with the virgin deck. My machine shop fella took his vernier to the piston from the EA82 mpfi and the new EA71 flat tops to find the flat tops will not rise to same level and his eye of building stuff for 45 years says the flat tops compared to the slight valve relief of the mpfi slugs, will still be higher compression :)

 

. Height-wise with pistons compared side by side, the EA71 have about 10mm more lower skirt than the sleek mpfi slugs which if we can keep the extra skirt should lead to less slap :)

 

Think I need to stick cam on to head and observe just how far valves open to ensure it remains a free spinner.

 

The AE branded pistons came fitted with rings from factory - as is the norm for this company. Top is chrome, lower is cast. And rings are etched with AE as well !!

 

Made in the UK, sold in the US, fitted up in Oz :)

Thank you for the picture :)

So with the valve reliefs, I may be able to maintain a safe .025-.030" gap between the piston and the valves.

 

On another side note, did you have to remove any head studs? And if so, what was the most effective method you found without scarring the studs or stretching any threads?

I may just wait until I get to the machine shop to remove the studs safely...

 

Twitch

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