Best way to clean carbon off piston tops

Pulled the heads and wanted to clean up the piston tops and the small carbon ring at the top of the cylinders. What's the best way to do this? Cylinder walls look great. Smooth and nice visible cross hatch. Just some carbon build up on the top of the pistons and a small ring of carbon around the top edge of each cylinder. Dont want to pull the pistons if I don't have to. Also. These are obviously not stock 73 pistons. Anyone recognize them?

without pulling pistons.. carb cleaner and a scruff pad.. can't think of the real name of them but they come in a package and most likely multi colors too..

They look like "rebuilder" pistons to me. Perhaps Ohio Pistons or Badger Pistons, 8:1 with OC heads. If you are going to run them just leave them alone. BTW, 9:1 (CC Aussie heads) and aggressive cams don't mix well, just saying. Chuck

They look like "rebuilder" pistons to me. Perhaps Ohio Pistons or Badger Pistons, 8:1 with OC heads. If you are going to run them just leave them alone. BTW, 9:1 (CC Aussie heads) and aggressive cams don't mix well, just saying. Chuck

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Just curious as to why you say that about the Aussie heads and the cam? This set up was recommended by a very reputable builder as well as comp cams and confirmed by another builder in the area. 

On the pistons did some checking they are sealed power cast piston #425np

You can use WD-40 and a wire wheel on a drill. Looks like engine is already .040" over.

I also agree that it's a pretty big cam for your combo. Those low compression pistons wont be doing you any favors. Would be better to run a smaller street cam. It will just all around perform better. I did big valves in my old Aussie heads. Really didn't help. Roller cam only marginally better vs a comparative street grind HFT or SFT cam. You could save a lot of money just installing a HFT camshaft. Even going with a custom HFT/SFT camshaft would be notably cheaper and perform better than a off-the-shelf roller cam setup. Especially since the combination of parts is so unique.

I had a smoking issue with my 302. I went to the local garage and talked to the guy I know and trust about doing a leak down test to see if it was rings or valve guides. He said he'd be able to do it but to try DELCO (?) top engine cleaner first. He said they used to use it when he worked for GM to free carboned up piston rings back in the day. 

I pulled the plugs and used a syringe to squirt enough cleaner into the holes to cover the top of the pistons and let it sit a couple days. I then cranked to engine over to get the cleaner out of the cylinders to avoid hydraulic lock, and reinstalled the plugs and started the engine. It smoked like hell for quite a while then calmed down. I don't know if it'll smoke again, but it's good now. 

You might be able to do this too, and it will be easier because you have access to the piston tops.

Anyway, that's my story and I'm sticking to it. It looks like my rings may have been stuck, but are better now. It beats a total teardown if you don't need it.....................

I agree with Chuck, leave the piston tops alone. Anything you remove can wind up down the sides of the piston on top of the top compression ring and scratch up your nice smooth cylinder walls when you start it up.

When you get it running right it should clean up some just by driving it.

9:1 compression is not enough compression for a big cam. I wouldn't go any bigger than a 270° - 275° cam.

"Just curious as to why you say that about the Aussie heads and the cam?"  It is not the heads or the cam.It is the pistons. They have a large dish and if the block has not been decked the the piston is probably .015-.020 down the bore at TDC. All of which combines to reduce static compression ratio.While the CC of the Aussie heads helps it is optimistically 9.0:1. The timing events of the cam, most importantly where the intake valve closes, in large part determines what the dynamic compression ratio is. Dynamic is what the engine actually "sees". Low dynamic compression ratios produce poor idle quality and lower power and torque. Search on Wallace dynamic compression calculator to run your particular numbers to see what you come up with. Chuck

Just curious where you guys are calculating 9:1 static compression?

4.040 bore

3.5 stroke

Dished piston volume of 3.6cc based on dish dimensions from Federal Mogul site and checking with a syringe

Finished chamber volume on the heads is 60cc

Compressed head gasket of 0.040

Piston at 0.020 below deck

Calcs out to static compression ratio of 10.65:1

This is why I did not even plan to with flat tops as I was concerned the compression would be too high.

Ran the dynamic calculator on Wallace. Not 100% sure what it all means but here is what it gave me.

I do remember reading somewhere that it should not top 8:1 if you want to run pump gas and iron heads.

Thoughts on these figures?

Camshaft, Rod Length, Boost and Altitude Correction to Compression

Static compression ratio of 10.65:1.

Effective stroke is 2.54 inches.

Your dynamic compression ratio is 7.84:1 .

Your dynamic cranking pressure is 155.73 PSI.

Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 7.84 :1.

V/P (Volume to Pressure Index) is 122

Pulled the heads and wanted to clean up the piston tops and the small carbon ring at the top of the cylinders. What's the best way to do this? Cylinder walls look great. Smooth and nice visible cross hatch. Just some carbon build up on the top of the pistons and a small ring of carbon around the top edge of each cylinder. Dont want to pull the pistons if I don't have to. Also. These are obviously not stock 73 pistons. Anyone recognize them?

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73 Pony, I used spray on oven cleaner, let it sit for about 5 minutes and rinse it off. Works well, but I had my pistons out of the engine. DO NOT get it on the skirts if you go that route.

I did a very light cleaning. Used some carb cleaner and a hand brass brush. Rotated to get the cylinder at TDC to clean each one. When done I wiped down all the cylinder walls with some fogging oil.

I used the Sealed Power dimensions of the 425NP piston of 0.080" (0.203cm) deep dish and 2.770" (7.036cm) diameter dish to come up with a dish volume of 7.9cc. The 3.6 sounds more like the cc of the valve reliefs. I wound up with a static CR of 9.76:1. This is probably good enough for a cam in the 280 to 290 degree advertised duration range.

I don't have your cam particulars, so I ran the numbers with a 290 degree advertised duration cam I have the specs on and came up with 7.37:1 dynamic CR, which is a little below the desired 7.5:1 minimum. 8.3:1 dynamic CR is about as high as you want to go with pump gas.

I'm still not sure here. I used a formula online to calc the dish volume based on measurements provided but who knows if that was a correct formula. I also used one of my wife's syringes and some plexi glass and was able to put just under 4 cc of fluid in the dish.

That being said I believe 7.9 cc dish was stock in 73.

Running a static comp calc with the following....

4.040 bore

3.5 stroke

60 cc cylinder head volume

7.9 cc piston dish volume

0.020 deck clearance

0.040 compressed head gasket

I get static of 10.14:1 this is using several different online calculators.

Using that number in the Wallace Racing site I get a dynamic of 7.47:1

Am I calculating something incorrectly here?

If I run the calculation with flat tops or 0cc on the piston I come up with 11.13:1 static and 8.19:1 dynamic. This tells me that flat tops are not really an option if I want to run pump gas. Occasionally I can find no ethanol 93 octane but not often. More common here is 91 octane no alcohol.

Did you use anything for the valve relief volume?

The desirable dynamic CR range I use is 7.5 to 8.3:1. You could also go with a little more cam or with different LSA or LCL specs to lower the dynamic CR.

Well. Wife Is tired of me scratching my head on this. We are going to stop by her office and grab some more accurate measurement devises to figure the actual volume of the dish in these pistons. I will update later tonight from the garage.

Ok. Got some better equipment and had my wife assist me. Took 5 separate measurements. The volume of the dish including the valve relief were as follows.

7.67cc

7.71cc

7.70cc

7.73cc

7.71cc

Average of 7.704cc. Given there was still a little carbon build up there I think the 7.8 to 7.9 cc is prob accurate giving a static of 10.14:1 and a dynamic of 7.47:1. I'd say it is right in the ballpark to run on pump gas.

I used the Diamond Piston compression calculator and the data from the Sealed Power site. Originally I used a chamber volume of 65cc. I also added 2cc for the valve reliefs that Sealed Power does not address. If the chamber volume actually is 60 cc, then I get 9.7 static compression (5.78 rod, .020 down the bore, 4.100 gasket bore, .041 compressed gasket, .275 to top ring, 4.040 bore, 60cc chamber). If that is all correct you should be good to go. Sorry if my comments distracted or annoyed you. I really was trying to be helpful. Chuck