Piston to cylinder wall clearance!

[EZ28]

Well my dart shp, sbc, 427 short block came in. I bought this from a very high profile engine manufactuer. It has eagle forged crank and rods with Mahle forged pistons. Question is you can move the piston around in the block. I admit I am not a pro. With the piston to one side you can insert a .034 feeler gauge between the piston and cylinder wall. The cylinder diameter is 4.126. The part no. on the pistons are correct for that bore according to the Mahle website. I called the short block manufactuer and he ASSURED ME that was normal and to go ahead with the build. I simply have never heard of this. Any suggestions, advice or help will be very much appreciated as I cannot sleep.
Thanks,
EZ28

[CNC BLOCKS]

If your measuring above the top ring that measurement is probably fine as the ring land area is smaller then the skirt area, If your Mahle pistons are for a 4.125 bore and the bore is 4.126 you should be fine.

Get some sleep now I beleive from what you wrote that every thing is fine!!

[CLAYTONRACING]

If your measuring above the top ring that measurement is probably fine as the ring land area is smaller then the skirt area, If your Mahle pistons are for a 4.125 bore and the bore is 4.126 you should be fine.

Get some sleep now I beleive from what you wrote that every thing is fine!!

X2 everything sounds fine. If your still worried you can measure the bottom of the piston skirt, but like was said ring land area is smaller.

[Awesome Bill]

The top side of the piston above the ring land is always .030 or so smaller. I don't know why the block is 4.126" in bore size, this means he most likely did not plate hone. If you plate hone the block with bolts down to 70 or so, this pulls the metal inwards and makes the bore larger. Here is something to remember, if you check your bore just as this engine was shipped to you and it measures perfect round, it is wrong, it only becomes round when the 5 head bolts pull the bore back into honed specs. My saying is if it measures right its wrong, you can only measure when plate honing. If you don't think so, you will have an engine that has blow by like a few others here on the board.

Did you get any specs from this well known engine builder on how to put the bore back round? If you did not, then he does not care how his engine does after it leaves the station. Its your baby and it most likely will be down on power.

We ship or give the customer in detail how and what to use when installing their heads and torqueing the head back down.

1. We give you gasket recomendations for your applications, we ask this first then hone with them.

2. what fasteners you are using, studs or bolts and even washers!

3. lube we use, molly or oil or several others out there

4. then specs on torquing, lbs or lbs then torque angle.

On every short block assembled unit we sell, the customer gets this information. The bore size will change from studs to bolts, molly lube to oil, torque wrenches to torque angle. We torque angle after base torque is used on every complete engine we do, even stocker rebuilds. This assures as a perfect bore size when your heads go back into the equasion. Also, your a full .001" larger on bore size than what Malie recommends. Your bore size should of been 4.125"! People put more clearance in the bore when this only leads to more piston rock and closer rebuilds. If this is a street engine, we keep them to .004-.005. If this is Nitrous applications, we put them @ .006-.007". This gives the piston a little more room to expand rapidly when all that heat is put into the piston @ one time. We also put .002-.003" more bore size on all marine engines because most marine engines have a very large water supply and the block runs .002-.003" smaller than any street engine.

I could go on and on. But if your block is perfectly round right now, its wrong! It won't get better and there is not enough ring to rub off to make the cylinders round. This is why blow by happens with these large bore engines. The bore finish is critical and takes time to achieve a good ring seal. It is in no way just the stone's finish, it is the procedure of bringing the bore up to size and in a running state as close as possible. I put all bores @ .0003 max taper and the finish is a babies butt smooth. Hope this helps.

[EZ28]

Thanks to CNC blocks, Clayton Racing and Awesome Bill for your response.
I appreciate the Info.. Relating to your response Bill, You know what they say hindsight is 20/20. Wish I had done more research before before I purchased. They also say, Live and learn. I learned a valuable lesson.
To CNC Blocks, I am sleeping better.lol
EZ28
GETCHASUM RACING

[CNC BLOCKS]

Don't know much about your build but 4.126 is certainly fine as Mahle says in there guide they send with their pistons on severe duty applications such as drag racing,nitrous, forced induction, filled blocks or any endurace racing may require an additional .001-.003 clearance.

If you ever need another block preped put let us know as we have 2 Sunnen line hone set ups, line boring equipment, Sunnen 616 Cylinder king for cylinder honing, torque plates and we machine our blocks in a HAAS 4-axis CNC machining center ETC.

We are Master WD and WD with all the top companies

Here is a link to some of the work we do.
http://www.chevelles.com/forums/showthread.php?t=93124

[3V Performance]

Not to mention but CNC's attention to detail is spot on. We have had the opportunity to use some of his block.

[Awesome Bill]

With today' cnc Equipment as everyone hollars about, it is expected to be dead on every time. When making pistons years ago, when we honed the block it was not out of the ordinary to have .001-.004 from piston to piston, this is where larger bore sizes come from.

With today's CNC mills and lathes, you can hold that tolerance to .0001-.0003 with no problem. So if we squeal about aline bores being .00025 - .0005 out, when that is really still dead on, then we should raise hell about piston bores being oversized .001.

I find that pretty funny coming from Carl saying the bore size and this clearance is "ACCEPTABLE" from the manufacture. Its always going to be acceptable, they don't care and another .001 is just a little more room for the pistons to rock back and fourth and unload under real conditions.

It really depends on the assembler in this case and maybe you have a larger std size piston and the block needed the .001 bigger bore? Any street engine or even race engine is good @.004" clearance with today's fully CNC machined finished pistons. If we are going to hollar about machine work within .0001 and then say .001 is acceptable, that horse has 2 faces!

You most likely will be fine, you just have .001 less to go now on your next hone. That means second time around will be .003-.005 larger, this means a ton of piston to wall and maybe an early overbore and fresh pistons. But if your piston manufacture can't hold .0001-.0003 change brands while your at it!

[CNC BLOCKS]

With today' cnc Equipment as everyone hollars about, it is expected to be dead on every time. When making pistons years ago, when we honed the block it was not out of the ordinary to have .001-.004 from piston to piston, this is where larger bore sizes come from.

With today's CNC mills and lathes, you can hold that tolerance to .0001-.0003 with no problem. So if we squeal about aline bores being .00025 - .0005 out, when that is really still dead on, then we should raise hell about piston bores being oversized .001.

I find that pretty funny coming from Carl saying the bore size and this clearance is "ACCEPTABLE" from the manufacture. Its always going to be acceptable, they don't care and another .001 is just a little more room for the pistons to rock back and fourth and unload under real conditions.

It really depends on the assembler in this case and maybe you have a larger std size piston and the block needed the .001 bigger bore? Any street engine or even race engine is good @.004" clearance with today's fully CNC machined finished pistons. If we are going to hollar about machine work within .0001 and then say .001 is acceptable, that horse has 2 faces!

You most likely will be fine, you just have .001 less to go now on your next hone. That means second time around will be .003-.005 larger, this means a ton of piston to wall and maybe an early overbore and fresh pistons. But if your piston manufacture can't hold .0001-.0003 change brands while your at it!

Mahle give a bore size for their pistons and depending on the applications you may want to go .001 to .003 over

All the Mahle pistons we have check for size have been right on the money.

I find that pretty funny coming from Carl saying the bore size and this clearance is "ACCEPTABLE" from the manufacture. Its always going to be acceptable, they don't care and another .001 is just a little more room for the pistons to rock back and fourth and unload under real conditions.

We machine and hone blocks for a lot of other shops out there and its comon for another builder to want a cylinder bore .001 over on the bore size.

Not to mention but CNC's attention to detail is spot on. We have had the opportunity to use some of his block.

Tom and I use to work together till he went south to work in the top CUP Engine shops like DEI, Roush and Toyota and knows his way around engines and has worked with latest tecknology and has run our blocks for years with great success and his stuff still sets track recoards.

Glad to see you over here Tom