Need Piston Cylinder Wall Clearance Specs "Old School" NOS TRW L2262 30
 

Reference: For my 1968 400 Engine. I have an old School "NOS" set of TRW forged pistons part number L2262 30 that I'm looking for the cylinder wall clearance specs on. I bought these NEW in 1993 and am first using them now. The problem is that I no longer have the spec sheet for these and I need the piston to cylinder wall clearance min and max spec. Again, these are for a 400 Engine, .030 over Forged pistons that I purchased in 1993.

While I dearly need the help of this forum, I'm humbly asking everyone to please carefully examine what I'm looking for before you give me an answer. The L2262 part number is still being used to produce "standard" size pistons today, I "think" under the Sealed Power name and the pistons being made today are of a different grade of material with different expansion rates that those of 1993. Not the same as the Old School TRW pistons I have.

There are also new pistons listed as part number L2262F (The F) at the end is a totally different piston again because of the material.

So, if you have knowledge of the cylinder wall clearance for the era of my pistons, I would be thrilled to hear from you. This was a fairly common piston. I'm not sure what year it started being made, but if you have specs from the mid 1980s until at least 1993 for this part number, I'm thinking the cylinder wall clearance would be the same. So please help if you can.

It's been a long time since I posted. I moved cross country 5 years ago and it took me a long time to get back in the groove.

Thanks
OJ :usa2:

use 69-70 Ram Air IV specs, basically same piston

I rebuilt my RAIII engine in 1980 with 30 over TRW "Power Forged" stock appearing pistons--probably the same piston. If I remember correctly, TRW did not call for as much clearance as the factory RAIV used--due to the nature of these pistons.

I have a number in my head, but I'm a little hesitant to throw it out since this was 1980. But I do know that if this is the same piston, you can build the engine a little tighter than the RAIV factory specs because these pistons did not have the same expansion rate.

You said you have a number in your head. I won't lock you into this since it's from memory, but so far, I have half of my (non-forum) references giving me clearances of .002 to .0025 and the other half telling me it's in the .005 to .007 range. What do you remember using for your rebuild? My pistons are likely similar to yours. Thanks OJ:old:

.005-.007 .002 -0025 is for cast pistons

KO,

I appreciate your help and I know you are one of the gurus here, however I'm going to push for a little more of your wisdom.

Where does this information come from? If it's the original Pontiac specs published for the RA engines, then how do you know the piston material is the same as those made in 1993 (25 years later)? If it's different, they are going to have different wall clearances.

I actually now have a spec sheet that lists this piston part number with .002 to .0025 wall clearance, BUT there is no date code on it. It does have a publication number of 9288174. It was sent to me by a member of another forum. It is definitely old, but I don't know if it was before or after my pistons were made...

Again, I appreciate your wisdom.

Ive built many many TRW piston engines. TRW was to OE supplier for Pontiac for the 69-70 Ram Air IV engines as well as the 73-74 SD 455. Those pistons haven't changed one bit form 69 through the 90s at least when TRW name was dropped and Sealed Power/Speed Pro name was used. The best thing to do is have the skirts coated and run them on the tight side @ .0045-5, one because they will be quieter, two rings seal will be better and three the skirts won't scuff. I have removed these pistons from very low mileage engines and all show significant scuffing on the skirts. Im sure lll the fine iron filings from breaking in a flat tappet camshaft doesnt help plus the old school method of washing a block w soap and water isn't ideal either .

piston to wall clearance
 

I have had several 389-400-428 engine combos built for me using TRW pistons including 3 400s using the L2262s style you are contemplating using, over the last 40 years. I have always used a clearance setting of 5 to 5 1/2 thousants on all my forged piston motors. The engines always sealed and Never locked up due to too tight clearance. Use 2 to 2 1/2 thousants on cast pistons and 5 to 5 1/2 thousants on forgings. Use a Double Moly ring set or double plasma moly with your pistons -thats what Pontiac fitted in all its high perf engines-the low performance combinations (usually 2 bbl 400s) used a single moly ring on the top rail with a cast iron derivitive ring on the bottom ring rail. That low po combo would seal almost immediately but would not have the long term durability of the double moly combo.