jmrl98

My builder went .035 over - not .030, not .040, but .035 over. We discussed a .040 over, but I decided against it. The reason for the build was an oil ring failure. Not that I'm complaining, but does anyone else have a .035 over bore, or find it odd? The paper work really shows a 4.037 bore, but my pistons are SRP 175993, and shows a .0037 clearance, block .009 decked. Any thoughts? Haven't completed install yet BTW....

C409

..... Competent engine builders will bore and hone a block to the measured piston diameter plus recommended operating clearance ... piston clearances vary quite a bit depending on the specific alloy used to make them ... very few machinists will bore a block without having the pistons in hand .....

Hot Rod Roy

Does your builder have the .035 over pistons? I agree, no competent builder will bore an engine without having the pistons on hand! Does he have a plan?

I went .040 over with my engine 10 years ago, and I'm very happy with my performance.

gkull

You would have to find the man's piston to wall clearance recommendations. But anywhere from .0025 and .0040 are often the numbers given. Did you actually measure .0037?


They are 4.035 bore pistons

Brand:
Sportsman Racing Products


Manufacturer's Part Number:
175993


Part Type:
Pistons


Product Line:
SRP Small Block Chevy 350/400 Flat-Top Pistons


Summit Racing Part Number:
SRP-175993




Bore (in):
4.035 in.


Bore (mm):
102.489mm


Piston Style:
Flat top, with two valve reliefs


Piston Material:
Forged aluminum


Compression Distance (in):
1.560 in.


Piston Head Volume (cc):
+5.00cc


Wrist Pin Style:
Press-fit or floating


Pin Diameter (in):
0.927 in.


Piston Ring Thickness:
1/16 in. x 1/16 in. x 3/16 in.


Quantity:
Sold as a set of 8.

RF1

Although not extremely common, it is done more than you think.
If the pistons are 4.035, the actual piston diameter will be 4.035 minus the published minimum piston to wall clearance.
Increased clearance will be up to the engine builder, and he could hone open the bores as he determines it necessary.

In the old days, engine builders often ordered the pistons, measured them, then honed the cylinder bore to match.
These days, manufacturing tolerances are so tight, that is not required to have the pistons first. They are what they are stated to be, dimension wise.

leesvet

As others have stated, a good builder/assembler will measure each hole and "fit" a piston to that hole precisely. So, the piston for #1 may not be an exact fit for any other hole but its recommended clearance is perfect for #1.

That's how you build an engine right !

And this is where your 5th grade teacher told you that someday your life may depend on knowing how to do math !

cudamax

You decided against it? Did you tell him what to do? and now your not sure?
Your builder wanted to keep the block walls as thick as possible. Thats all. Who cares about the number or size and it sounds like a .030 overbore didn't clean it up.
If he went to .030 over and it was fine and then went more for some other reason or because of a screw up.
Yea I'd be worried and would Question that not the final size number.
Some blocks that are planned for some real high HP numbers or builds shouldn't be used with anything over .030 because they tend to get too thin on a cyl or two. If its a planed mild build, its not a problem but if ur planning on getting anywhere close to 500 horsepower out of that block, it's a problem without sonic checking all 8 cyl bores

jmrl98

I called him today but he wasn't there at the time, and I got too busy to call him back. I didn't want to pay for a sonic test, as .030 usually cleans it up as most will agree. Hence, no .040 over. I was under the impression I was getting .030 over.

C409

..... If the heads are off you can measure the bore ... his paperwork may be a typo ... perhaps he meant 4.0337........

Hot Rod Roy

Several people have asked about your pistons. Until you tell us whether the builder did, or did not have the pistons, this conversation is worthless!

jmrl98

It had to be cleaned up more than .030, so he took it just enough. .0037 is spec clearance. He did have the pistons, and has used them before. May shed some light on why it took so long for him to complete. Thanks for you input gentlemen.

Hot Rod Roy

"He had used them before"?? So these are used pistons? Are these the piston's he's going to put into your engine? Did you okay the installation of these used pistons?

If all this is true, what is your problem??

Hot Rod Roy

This may be true, but there's still the potential calibration tolerances on the measuring tools. When you're talking about a potential engine failure because of a .0002 calibration variation, why take a chance? How many engine builders have you seen that have a temperature controlled shop? Have you asked your builder to show you his calibration certifications to mil spec tolerances?

jmrl98

The pistons are a new part, not used. I meant he has prior experience installing these in other engines that had to go .035 over.

RF1

I am the builder.
If you are suggesting that .0002 variance in piston to bore clearance can cause an engine failure, there is nothing positive I can offer to this thread.

RF1

If the piston is properly sized to the bore, and the rigngs are properly sized to the piston and bore, the only other consideration is balance.
If the piston weights within 10 grams or so of the old, it has to work.

If you don't want it, you're the customer and should have it your way.

Regardless of what you read on forums, engine building is not an absolute.

Removing .0025 (to achieve the .035 overbore) off each side of the cylinder wall will not affect most street or mild performance engines.
Sonic testing will give factual data to qualify, or disqualify my statement above, but again, you are the customer and get the final say.

Hot Rod Roy

Didn't intent to insult anyone. Sorry. You have much to offer here. Thank you for expressing your opinion. There's the rub. Everyone has an opinion. All I was trying to say is the tight tolerances are very critical.

Do you build an engine to the final expected bore and hone sizes, then slide the pistons in place without verifying the dimensions of the pistons? That's confidence!!

cudamax

Hello Mr. Builder. First I wanted to say this is a Forum and everyone has an opinion and opinions are like A-holes. Everyone has one. You sir, need to explain for all of us and the poster what s going on with his .035 overbore. Most all of pistons that can be bought are slightly undersized and have the piston to wall clearance built in the piston. If, say you buy .030 over pistons for a 4 inch bore sbc. The Builder punches out the block and then gets his final hone/cross hatch pattern with the final grit of piston wall smoothness for the planned rings that will be run so as to end up with exactly .030 over from the original 4 inch bore and end up with a final bore size of 4.030. The pistons are slightly undersized for the piston to wall clearance. All of the aftermaket and factory pistons come this way.
Sometimes a builder will decide to run more piston to wall clearance, for whatever reason and will order slightly undersize or a certain size piston to get this or just go bigger on the bore size.
What the heck did you do to this guy? He told you he didn't want a .040 and you went 5 thousands over on his bore size because of what exactly? I've only heard nonsense why his bore size ended up at 35 thousands over. Did you have some odd ball oversize pistons laying around and just decided to fitted them to his block and not tell him? Thats the only thing I can figure.
If you ended up with a bore size of exactly 35 thousands over and used 30 thousands pistons. He is ending up with about .007 thousands piston to wall clearance and it's going to slap loudly and rock badly.

RF1

You misunderstood.
I am A builder, not his builder.
I dont have a dog in this hunt, so I owe you nothing.
Perhaps my post could have been more clear, or perhaps you misunderstood.

RF1

It is much simpler than most make it out to be.

Pistons manufacturered by a reputable manufacturer in this 21st century should match the spec sheet published.
If you create the cylinder bore you want (not what the piston manufacturer recommends), order the pistons, mic them when they come in, you should be good to go.
If they are not within the manufacturers spec sheet, they are rejected, and a new, properly sized set is sent out to replace the defective set sent.

Is having the pistons first helpful, sure. Cant hurt.
Necessary? No.

That is my opinion/fact/voodo statement.
Choose the one that you like best.