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Guest Message by DevFuse
 

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EA81 head differences explained - big valve vs. small valve.


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9 replies to this topic

#1 GeneralDisorder

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Posted 22 March 2008 - 11:43 PM

For all of you wondering how to tell apart the different EA81 heads without pulling them off and measureing the valves - I've taken pictures of a few from my collection to illustrate the differences.

For all these pictures, the large valve is on the left, and the small valve is on the right.

First - a shot of the valves. The intake valves on the small valve head (the outer valves on both heads) are 2mm smaller in diameter:
Posted Image

At the bottom of the heads you can see that the large valve head has no holes for the two extra 10mm bolts that the small valve head has. In the picture below you can see that these are very obvious when you are looking at the head from the bottom:

Posted Image

Now - another popular misconception surrounds the shape of the valve covers. Here is a shot of the valve side of the heads, along with an EA71 head to show that the valve covers for ALL EA81 heads are the same. The EA71 valve covers are rounded on both bottom corners, and the EA81 valve covers are less rounded on the left corner, and angled on the other:

Posted Image

In the above picture you will notice that the size/shape of the cross peice in front of the plugs (between the top stud locations) is different. This is NOT an indicator of head type or valve size. I have seen many different sizes of this portion of the casting regardless of valve size or year. I beleive this is related to the actual casting process as it seems to differ on every set of heads.

The ends of the heads are also slightly different in their castings, but this is difficult to rely on as these things changed based on what accesories were availible for that engine:

Posted Image
Posted Image

Hope this clears up some of the confusion on the subject.

GD

#2 P K

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Posted 23 March 2008 - 12:04 AM

Nice work GD.
So the only real indicator is NOT having the extra 10mm bolt holes in casting tubes.
Mods, sticky it. :cool:

r/ PK

#3 mountaingoatgruff

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Posted 24 March 2008 - 12:36 PM

i ordered a set of heads from a jy in seattle a while back, specifically requesting large valve heads, and the guy said that they could do that.

when the heads came, my caliper showed one was a large valve head and the other was not. neither head had the castings for the 10mm bolts - they both had the little "feet" that go over those holes in the block.

btw, when i measured the valves i used a digital caliper and went off the valve margin surface with the valves still installed in the heads. i didn't measure the valve seats.

after returning the heads from seattle, i pulled two sets of heads at a local jy, both off of ea81 d/r 4speed hatch's maked with 83 build dates (prob 84 model year?). one engine had been worked on and the other was virgin. the one that had been worked on had the little "feet" but small intake valves.

so i then pulled the set off the virgin engine (i didn't start there cuz it was completely intact whereas the other had no intake to mess with). those heads had the little "feet" and the larger intake valves. i measured both of these valve sets the same as before.

is it possible to install small intake valve seats in large valve heads (i'd think the larger seats require a larger bore) or to upgrade small valve heads by installing larger valve seats and valves?

i wish i had known this would come up so i could have taken pics, but i think the most reliable way to tell is to measure the valves and from now on i won't settle for anything less that seeing a caliper on the valve to rely on what size it is.

#4 GeneralDisorder

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Posted 25 March 2008 - 12:18 AM

Hhhmmm - well that makes things a bit more salty doesn't it?

Well.... I would appreciate anyone who could assist with pictures of different styles of heads. Obviously I will have a real hard time accomplishing this myself.

GD

#5 mountaingoatgruff

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Posted 25 March 2008 - 01:38 AM

i'll be going back to the same pick-n-pull that those heads are at probably wednesday and if i can manage to get pics i'll definitely post them. i almost took pics of the heads from seattle in case the guys at that jy wanted to make a big deal out of returning them but decided to hope for the best.

hope i'm not hijacking here (just kidding, no hard feelings for deletes:) ) but i've had similar difficulties in identifying part differences on some mopar engines. i found a guy online who accumulated a lot of information by simply taking pics of each set of parts he came across and very specifically labeling each set.

i think its best to just go through the trouble of measuring but if there's a serious enough demand for a way to identify these heads without measuring the valves i'd be glad to submit pics and info of the three or four pairs i have access to.

#6 mountaingoatgruff

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Posted 27 March 2008 - 11:43 AM

haven't made it to pick-n-pull but i haven't forgotten. hoping to go this weekend now.

#7 GeneralDisorder

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Posted 27 March 2008 - 09:25 PM

Cool - that's very helpful.

GD

#8 Qman

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Posted 02 January 2010 - 02:28 PM

Stumbled on this thread. The one real way to identify the heads is that the hydraulic heads have large valves and the solid heads have small valves. '84 and newer should have hydraulic. '83 and newer with automatic also have hydraulic. Keep in mind that this is for an unmolested motor. As miles and head gaskets mount there is a risk that the heads have been mixed and matched along the way.

#9 GeneralDisorder

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Posted 02 January 2010 - 06:41 PM

From taking apart a few that were unmolested, I have found that anything newer than '82 has the larger valves regardless of lash adjuster style. The large valve heads account for a 1 HP increase post '82 model year (73 to 74 HP). The hydro lifters didn't change the HP. They were equipped on all automatic transmission vehicles starting in '83 and all EA81's regardless of transmission type in '85. '83/'84 manual transmission cars were still solid lifter engines.

It is true what you say - that all hydro lifter engines DO have large valves. But so do '83/'84 solid lifter engines. The heads are the same. The block castings are different between the two engine types - hydro blocks have slightly different bolt bosses in some places and are machined to allow the lifters to be removed without splitting the block.

GD

#10 hatchsub

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Posted 18 May 2010 - 08:23 AM

Can a Mod move this to the USRM or sticky it? It took me a little while to find it and knew what i was looking for too lol. This is a commonly asked question on this board and i think it would help out the newer members to know the visual differences rather than just measuring the valves.




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