How to achieve correct piston to wall clearance with forged pistons

[88BB8B]

Hey everybody. I had a question. I currently have a atandard bore 7 bolt N/A block (I think?) which has been hot tanked and honed. The piston to wall clearance measured at the machine shop with a set of used evo 8 pistons was 0.002"-0.0021" if I recall correctly which if my info is correct would be a good clearance to run with those cast pistons and moderate power. However, if I were to get a set of forged pistons, would I need to get a set of +0.25mm or +0.5mm pistons and cut and rehone the block? Or do forged pistons for standard bore come a couple thousanths smaller than stock cast pistons to acheive the looser clearance they require?

The bores are in good condition currently and ready for some standard bore pistons, so I'd like to keeo it that way if possible.

 

[1990TSIAWDTALON]

If you go with forged pistons and require more PTW clearance then you can just re-hone the bores (and make sure to clean, clean, clean them afterwards) to get to the clearances that you want. Just do a little at a time and make sure your crosshatching is good (I move in and out of my bores very quickly during a hone to achieve as close to the correct angle as possible) and measure. It will take a little time, as once you go to far, you can't go back so proceed with care.

 

[88BB8B]

If you go with forged pistons and require more PTW clearance then you can just re-hone the bores (and make sure to clean, clean, clean them afterwards) to get to the clearances that you want. Just do a little at a time and make sure your crosshatching is good (I move in and out of my bores very quickly during a hone to achieve as close to the correct angle as possible) and measure. It will take a little time, as once you go to far, you can't go back so proceed with care.

Same thing with the eagle rods and evo wristpins I'm using. Is honing it carefully okay if I have to take off as much as 0.003"? Does the type of hone used matter? I've always preferred ball hones.

Looks like even though the machine shop charged me for a "final wash" there is still a thick layer of honing grit in the cylinders, so I'll have to clean the block very thoroughly regardless.

 

[1990TSIAWDTALON]

I use the same type of hone for the crosshatching that it gives me and an instant seal of the rings. 320 grit flex hone for deglazing.
I don't care what shop has had what part of mine, they are always dirty. Heads with little curly parts in the coolant passages, cranks with crap in the oil holes, blocks that are hot tanked but definitely not clean enough for assembly so always clean your parts thoroughly! It is well worth it. If you haven't heard of "pulling your crank balls" then see this thread by BogusSVO (Dale).
https://www.dsmtuners.com/threads/pull-your-balls-to-properly-clean-your-crank.472402/
Marty

 

[88BB8B]

I have heard of "pulling your balls to clean your crank" and will certainly be doing that with my remanufactured crank. Good to know that it is safe to hone a few thou off the cylinder walls.

 

[1990TSIAWDTALON]

Yep, that isn't a problem. ADDING to the cylinder walls is a trick I haven't seen yet (except as a sleeve installed).
I wipe my walls down with AFT 5-6 times or until a WHITE paper towel comes out RED, no grey on it, which means you got all of the grit out. If you have any questions on your build, don't be afraid to ask!
Marty

 

[88BB8B]

Thanks for the offer Marty! I definitely do have a few more questions about this build, I know I have tog whipe my cilinders very clean, I was planning on possibly forcing high pressure oil through the motor with a metal pot full of cheap oil and an air fitting to try and force any other bearing material out of the block. Or should the hot tank have taken care of that?

 

[1990TSIAWDTALON]

The hot tank will get most of it but I personally take my blocks to the car wash and WASH THE SHIT OUT OF IT after I have used a rifle cleaning kit in all of my oil passages. The tank sometimes loosens stuff, so I put a circular brass brush (from the gun cleaning kit) and chuck it into my cordless drill and have at it, in and out and all around.
I clean every little hole and passage at the car wash after that and YES I GET SOAKED. I then come home and use compressed air to blow it all dry and clean. I usually feel pretty good (and wet) after that.

 

[92AWDHX40]

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I love these videos i even met him in person, this is clean.

 

[88BB8B]

Power washer sounds like an awesome idea! as long as I dry it quick after. I've gotta get cleaning!

 

[1990TSIAWDTALON]

Thats funny.
I forgot I just bought a power washer so hell yeah, use that. I will too.
And wear a raincoat.....

 

[88BB8B]

Haha! I may invest in a full on poncho.

 

[1990TSIAWDTALON]

You will get wet. I put my raincoat on backwards and then put a face shield on too........