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Head lapping with sandpaper


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6 replies to this topic

#1 dltrial

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Posted 15 July 2014 - 11:27 AM

I resurfaced my E82 heads following the method discussed here. It took days and hours per day to accomplish.

 

One of the exhaust valve guides was out of place in each head and after trying to press one back into place myself and cracking the guide, I took it to a shop to have those two replaced. They inform me that there are cracks between the valves and that they all have to be ground out and welded, and then the heads would have to be resurfaced since the heat op the welding would warp the heads.

 

After reading up on head cracks on this forum I could see that the cracks went in pretty far so I went to the junk yard and procured two heads with only the beginning of one crack.

 

Now I am resurfacing the heads again and many hours into the process. I start with 150 grit sandpaper and even put about 5 pounds of weight on the head to increase the pressure and it goes soooo slow.

 

I see from the original thread that people were doing a head in just minutes. What the heck am I doing wrong?

 

Also how much of the fire ring needs to be removed? That is the last thing to go and it takes forever.

 

Lastly what else sould I look for on these heads? I never heard of the crack thing until the shop pointed it out (and they didn't look like cracks, they looked like a casting seam or something). Is there something else that I should look for that might render the head bad?



#2 stratman977

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Posted 15 July 2014 - 11:35 AM

It took me an hour a piece. I changed sand paper every 10 minutes. I noticed it didn't take long for the grit to wear out. The only wet/dry paper in that low of a grit I could find locally was gatorgrit brand. I don't know if it was the paper or not but I would have prefered to have 3m paper.

 

I would say mine turned out nice and flat but I would glady pay the local NAPAs machine shop the next time.


Edited by stratman977, 15 July 2014 - 11:37 AM.


#3 Dee2

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Posted 15 July 2014 - 01:10 PM

Unless you're totally bored, I think things like resurfacing heads should be left to machine shops -- right along with turning rotors and honing cylinders, etc.



#4 rdweninger

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Posted 15 July 2014 - 01:56 PM

Dee2, that's like saying you should only take your car to Midas to have the brakes done... because they are 'professionals'.   And honing a cylinder is quite simple as well.     However,  re-boring a cylinder should be done at a machine shop.

   And why not lap your own heads... it's easy.    Tip- Start with 100 or 120 grit.  I spray some wd-40 on the wet/dry sandpaper for lube.  Finish with 200 or 220 grit.   Don't worry too much about slight discoloration about the fire ring.   Use Felpro permatorque head gaskets.   I use half inch glass as my base.



#5 Subruise

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Posted 15 July 2014 - 01:59 PM

in my experience with this method, which is getting up there, ive seen a variety of time needed.

 

it seems the more overheated the engine got, the more warped the heads are, the moer time you spend fixing em.

 

after i hydrolocked and ruined my old bottom end i resurfaced the heads again in preperation for new block in it took around 10-15 minutes each.

 

those same heads took hours the first time i did them after having bad hgs for months on end.

 

If you can fit your thumbnail in the crack between the valves on any EA series engine, thats too big. otherwise put em back on.

 

I feel that it is the duty of the machine shop to research any head in question and see things like, i dunno, factory bulletins about things of this nature



#6 MR_Loyale

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Posted 16 July 2014 - 12:19 AM

There were cracks on my heads but C&D knew Subarus so they said it was no big issue. I think if a shop doesn't normally do Subaru heads, they freak out and say to junk em.



#7 Gloyale

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Posted 16 July 2014 - 12:44 PM

Unless you're totally bored, I think things like resurfacing heads should be left to machine shops -- right along with turning rotors and honing cylinders, etc.

 

+1

 

Dee2, that's like saying you should only take your car to Midas to have the brakes done... because they are 'professionals'.   And honing a cylinder is quite simple as well.     However,  re-boring a cylinder should be done at a machine shop.

   And why not lap your own heads... it's easy.  

 

Not an apt analogy.......unless you are gonna to try to "resurface" your rotors with a hand file.  You don't. even if you change your own brakes you gotta get new rotors or have them turned at a machine shop.......which nearly proves my point.  It's not that they have some title of "professional"  it's that they have the PROPER EQUIPMENT.  That said i would never take a car to Midas but I always do have my rotors surfaced wet on a flywheels surfacer......even better than lathe cut which basically scratches a new finish......I digress.

 

Really you aren't "lapping" the head.....and you are definately not "squaring" it ............you are sanding it like a woodshop project in 7th grade.

 

And it does NOT get the warp out of the head.....if the head is warped....this ain't gonna fix it.

 

At best this method can be very lightly used to remove traces of old gasket......

 

Actually trueing the head to a perfect, square to the bores, surfaced plane, can only be done with the head chocked into a surfacing machine.






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