420A 420a forged piston clearance?

[DrewmHolland]

I’ve got my engine pulled apart once again and my question is since I’ve honed the block twice and it’s got over 200,000 miles on it, will I have enough clearance for my forged pistons? I went to measure with a feeler gauge and it seems like my original cast pistons have 0.004” clearance but that can’t be right because they never slapped or anything, am I measuring wrong or something or is that normal to see with high miles…

 

[BLACK'98DSM]

What is the clearance with the new pistons? The old pistons could be worn and that value is irrelevant to using your new ones.

 

[curt-s]

Feeler gauges aren't the most accurate things to use in determining PTW clearance.

 

[DrewmHolland]

well the "old" pistons currently have less than a thousand miles on them so they aren't worn or anything, but with the forged pistons i'm seeing about .004 - .005" depending on the cylinder, i'm guessing the cast pistons have a loose fit because of low silicone content maybe? they definitely aren't hyper-eutectic.
as far as I know the Wisecos should have some clearance built in (only add more for boost) so i'm just gonna send it because two hones might be removing a good bit of material and I really don't want alot of slap

 

[1990TSIAWDTALON]

You need to use a micrometer and measure the outside diameter of the piston then use a bore gauge or snap gauge to measure the inside diameter of the cylinders. IDK if you can rent those tools but you certainly can ask your local parts stores.

 

[Canadian_CD9A]

How To Check Piston To Wall Clearance

Checking piston-to-wall clearance is a critical measurement every engine build should include. Here is a detailed walk through of how to measure your piston-to-wall-clearance.

blog.diamondracing.net

 

[curt-s]

well the "old" pistons currently have less than a thousand miles on them so they aren't worn or anything, but with the forged pistons i'm seeing about .004 - .005" depending on the cylinder, i'm guessing the cast pistons have a loose fit because of low silicone content maybe? they definitely aren't hyper-eutectic.
as far as I know the Wisecos should have some clearance built in (only add more for boost) so i'm just gonna send it because two hones might be removing a good bit of material and I really don't want alot of slap

Honing isn't going to solve anything, especially with potentially tapered or egg shaped cylinders.

Why don't you actually have it properly measured if you don't want to experience adverse effects of putting forged pistons in a cast iron block?

Throwing your shoulders up and shrugging whilst saying "I'm gonna send it" without knowing anything about what's actually going on is a terrible and wasteful way to build an engine.

 

[DrewmHolland]

Eh imma send it anyway but thanks for the advice

 

[BLACK'98DSM]

Well that isn't the best outlook to have

Forged pistons will naturally be noisier on a cold start but once they heat and expand the SLIGHT noise will clear up. If it doesn't, you'll then realize the mistake. At that point stop running it before you ruin the rings, cylinder walls and piston skirts.

 

[Canadian_CD9A]

Well that isn't the best outlook to have

Forged pistons will naturally be noisier on a cold start but once they heat and expand the SLIGHT noise will clear up. If it doesn't, you'll then realize the mistake. At that point stop running it before you ruin the rings, cylinder walls and piston skirts.

That assumes that piston slap is the worst problem an improper clearance has. The rings might not even seat properly here, blowby and premature ring wear are huge problems.

 

[DrewmHolland]

Well I’m finishing up putting everything back together so we will see what happens

 

[jesse12345]

Well I’m finishing up putting everything back together so we will see what happens

Did you at least gap the rings and check bearing clearances? I'd do that at the very least you don't want to tight or to loose tolerances.

 

[curt-s]

I don't think anything was really checked. The impression being given is akin to that slap-it-on single coat of paint before you sell a house.

 

[DrewmHolland]

Did you at least gap the rings and check bearing clearances? I'd do that at the very least you don't want to tight or to loose tolerances.

Yes the top rings are 0.020” and second are 0.023”

 

[jesse12345]

Yes the top rings are 0.020” and second are 0.023”

I wish you the best of luck and hopefully everything works out. I've been down that road of just slap it together. It never really works out but I'll be positive about it.

 

[DrewmHolland]

alright well as far as i know the pistons have minimum clearance built in so i should be alright and i know my cylinder walls are definitely worn down

 

[jesse12345]

As long as you didn't hone the cylinder walls with a brick you should be fine.

 

[curt-s]

Honing is not some sort of magic fix-all, especially not so with consumer level hones. Out of round cylinder walls will prevent proper ring seating as honing removes the tiniest of fraction of material and egg or tapered cylinder shapes can't just be "honed away" with these versions of the tool.
If we had some more information as to why you just don't care to get the cylinders checked properly, maybe we could offer better advice in the future. 420A or not, there IS pride to be had in "I built it right" vs "sending it anyways".
The latter is useful mid-shootout where you just need to have the motor together for another pass, regardless of outcome.

Hey, if this is your only car and you can't afford the downtime of having things checked and done properly, we all understand and are here to try and help. But, when we're missing that information, all we see is a thread asking for advice, all advice being placed in front of you being completely ignored, and then proceeding to make the worst decisions for a motor with forged (or otherwise) parts.

 

[DrewmHolland]

Build is done so I’ll get a cold start for yall when I’m off work

 

[DrewmHolland]

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[BLACK'98DSM]

I don't hear anything excessively unusual. Let's hope it doesn't produce any louder noise in the near future. For now, have fun!

Also didn't you install forged pistons because of plans for a turbo? If so, I'm assuming you used the 8.8:1 compression. Which means it's going to lack some torque running as an NA engine.

 

[Canadian_CD9A]

Wait, is that engine still on stock rods?

 

[BLACK'98DSM]

Wait, is that engine still on stock rods?

I think OP mentioned in a previous thread that he found some forged rods... So I hope not.

 

[DrewmHolland]

Wait, is that engine still on stock rods?

I got a set of eagles and I am running 8.8:1 compression wisecos

 

[jesse12345]

Only time will tell, fingers crossed. Have fun with it once you go turbo is gets alot more fun.