Say, could anyone please give me the dimensions and recommended piston side clearance for either the TRW or Sealed Power 455 +.030 forgings, also their weight as compared to a stock piston. Am helping out a friend over here. He has a '70 block that has been bored about +.030 with bores measuring out at 4.344''. Trying to establish if we can use either the TRW or Sealed Power or the block will have to go .038 over and purchase some more expensive pistons. Thanks in advance.........
Ian, you will need to measure the pistons to calculate the piston to wall clearance. I believe the manufacturer reccommends a minmum of .0035 piston to wall clearance. They can be run looser. They will make a littel more noise whn cold if installed looser. Jim Burek
Ian, Just pulled a few fresh ones out of the box and threw the Mic on them for you. Measured 4 pistons at the spec point for this piston, which is right near the bottom of the skirt(3.24" from the top), 90* to the pin. This is different than say a JE piston, where the spec is measured .500 from the bottom of the skirt. They measured 4.3407 to 4.3408.. Fed Mogul recommends .002 to .0025 with this piston, I run those at .002 on a true street motor, and just a touch looser at .0025 with a motor that is going to be a little stouter. Their recommended bore size is 4.3425- 4.3435, as their spec for the piston is 4.3410, but we typically find them to be a few tenths under. Manufacturing tolerance with this piston, which is no problem if you fit each piston to the individual bore, the more expensive JE/SRP stuff is typically right on the nuts. With your bore size, you should go to the .038 over piston. You could run the TRW's, but piston slap is probable after break-in on a cold start, and that's mighty annoying on a new motor. I would recommend TA's version of the SRP piston at around $600.. while a little more $$ than some offerings on the market in that size, the features of this piston warrant the price difference, IMHO. Honing with a deck plate installed is also highly recommended. JW
Ian, Were ALL of the cylinder bores checked by a professional? Was the block sitting at room temperature for a few days before the bores were checked? This is all very important before you make this sort of decision. Running a piston to wall clearance of .002-.0025 seems a bit tight to me. Engines rarely blow up because the specs are a bit on the loose side but they will melt down in a heart beat if things are too tight. But both Jims would have much more experience than I on this subject but do your homework. Here are a few links to some nice articles about pistons.... its worth a read. http://www.carcraft.com/techarticles/77899/ http://www.federal-mogul.com/cda/content/front/0,2194,2442_2905_6800,00.html Good Luck
- The block has been instorage for over a year in my buddy's shop. Everthing good and clean and at room temperature. I measured the bores myself. The previous over-bore was done in this country and I would think almost certainly without torque plates in place. All cylinders measured round and all within .001. However there were no pistons used or otherwise supplied and being on a tight budget I just wanted to know if we could use this block as is. It would be primarily for street use. - I'll go and check some of my other blocks to see if something measures up to get him a motor built without spending a fortune. - Thanks to you all for the info. - Happy New Year!!! :TU:
I run TA's SRP piston, 38 over. They reccomend a 4 thou clearance (double checked with JE/SRP) and this is sheer nonsense IMHO. The engine is quite noisy, not a problem given my street/strip use but a street car would sound awful. They need to rethink that clearance, 2-3 would be better.
- Spoke to my buddy. Have come to the conclusion of getting a motor built right. To that end he will be speaking to a few of you guys out there that do it for a living. He's looking for about 500 horse to get his 3600 Skylark into the 11's reliably without incuring the national debt, while we carry out the big block conversion work. Thanks again guys...... :TU:
I did my own machine work on my engine. I used the sealed power forged pistons. Like Jim W said they are not all real close in size so I honed each bore for a certain piston and went with .002 clearence and pistons still looked like new last time I reringed it. I am glad it was on the tight side to start with because after many years of running I was able to touch up the bores with a hone when I rebuilt it and still have about .003/.0035 clearance. If I had set it up at say .004 to start with they would be way loose by now. I had to rering it after loosing a fanbelt on a pass and didn't notice till it was to late, it got to hot and killed the rings, it ran ok but had alot of blowby and blew oil smoke out of the headers at high rpm but never scored a piston at .002 clearence. Also when honing a block for that close of clearence I found that I had to let it set after honing to let the bores cool or they will be to tight even with alot of honing oil running in them when honing. On the machine we had I found the bores would would shrink up about .00075 when I left it set a while after honing. Boring and honing was one of my jobs when I was working in a machine shop so I had plenty of expiriance with this stuff. Just my two cents. Tom
Clint.. Using the actual JE pistons, or the SRP versions. I can assure you that the SRP versions dictate .003 piston/bore clearance, and the biggest difference is actually the point of measurment on the piston that this is taken.. You measure that piston .500 from the bottom of the skirt, you measure the TRW right near the bottom. Measure the pistons in the same spot, and you will come up with the same number, for a relative piston/bore clearance, within a few tenths. Now, the JE piston did call for more clearance, have not used a set of them for a while, they are more of a race piston. And in race motors, I have run the piston to wall out as far as .009. I put together six motors this last season with SRP pistons, put 4 of those in the cars.. none of them had any piston rattle at startup. JW
Thanks Jim, These are teh SRP pistons...mistakes on my part, just looked over my sheets again. ou: TA's sheet reccemended wall was 0.003, measured .5 from the bottom. The spec'd out 4 thou was a decision my idiotic machine shop made based on the reace use of the Wagon. According to my spec sheet it came out at 0.005 when I measured it out myself. Just my opinion but from the sound that clearance with the SRP's is way too high for pure street use. Maybe I'm too high for the street/strip use of the car now??
Clint, If you measured the SRP piston near the bottom of the skirt, like the TRW pistons call for, you would find the SRP's, set at .003 (measured at .500) are right around .002-.0025, when the lower measurement is calculated. The piston skirt is slightly tapered, and it is the reason that piston manufacturer specifies a measurement point, for their recommended specs. We have no noise issues with those pistons, in pure street applications, after being set to the recommended piston/bore clearance, at the .500 measuring point. Did they use a torque plate when setting the piston to wall, and to do the final hone? If not, then I suspect you have more piston to wall up at the top of the bore, than you might think. The bores will pull in an unfilled block, anywhere from .0005 to .0025. depending on the particular block, and it's wall thickness. This get's more pronounced, as the block gets overbored larger, and the wall thickness is reduced.
I did indeed measure from the bottom 0.50 as specified. The shop in question did indicate that they used a torque plate, and the local shop that supplied it told me on a check up call that they had sent it over. There was less than a thou top to bottom on the bores. I think the noise involves my allowing a clearance of 0.004 and the shop dialling in 0.005... ou:
