Old TRW piston clearance.

[gn69z28]

Old L2300 427 chevy pistons. Slightly used so no paperwork. Naturally aspirated street car. How much clearance should they have.

[BillK]

.0015" according to my 2005 catalog.

[Old School]

For them to be quiet .005 to maybe .006. A little noise on start until it warms up .007-.0085. If you have to use them because that is all you have .0085 to .012.

I don't recommend really running more that .065 on a street engine. However, when you are young and poor and that's all you have run them. I have run them at .012 in bracket engines of my own. I rolled the top edge of the piston with a file, smoothed it with sandpaper so it wouldn't tear up the cylinder when it rocked and run it. It lasted a long time, until a used cast crank broke. It was a lot of fun back then.

[Old School]

.0015" according to my 2005 catalog.

Bill, are we talking about the same piston? I am talking about the old forged pistons that did not have the lightening bolt. I am 99% sure that TRW recommended .005. Maybe it was the max but I will look it up. I have an old instruction sheet if I can find it. Those old TRW expanded a lot. The newer ones made in India or wherever takes less clearance than the old forged ones.

[BILL-C]

Do the skirts have drilled oil return holes or a big slot?

[gn69z28]

They have a big slot.

[BillK]

People dont realize that a lot of the old TRW / Sealed Power forged pistons that were the same as the factory pistons all ran very tight clearances. I have three different old catalogs here and they all show the same clearance, .0015" which is the same as the Chevy oem spec for the 390 horsepower 427 The factory spec is actually .0009 to .0015

Measure them and see what you have ?? Pistons are designed to be run in a particular bore size and the clearance is built into the piston. I have been doing this for aver 30 years and very very rarely has a piston been made wrong as far as size goes. If those pistons are standard bore (4.250) then I would expect them to measure somewhere near 4.248 near the bottom of the skirt or wherever the largest od is. If they were meant to be run at .005" clearance they would measure 4.245"

I have an even older TRW catalog at home and I will look at it tonight but I will bet it will be the same.

[mag2555]

Here you go, from a 1986 TRW catalog.
On motors with short rod ratios ( under 1.72) I always added another half a thousand to the factory piston to bore clearance spec to releave the scuffing I would always find at the bottom of the bores!

[racear2865]

I dont care what catalog said. We tore several down from dyno at .004 and would be scuffed. You better run .005 to .006 or you got to look at it early.
reed

[Ks Fats]

L2300F piston calls for a 4.251 finished bore; it is the factory replacement piston. The L2268F is the high performance piston and also calls for a 4.251 bore. The 2268 was happiest at .006 if memory serves correctly; since the finished bore diameter is the same for both the clearance would be in the piston diameter. The slotted oil drainback piston would require less clearance and have a larger skirt diameter than the 2268.

[rebelyell]

https://www.gmheritagecenter.com/docs/g ... rvette.pdf

take a look along about page 132 of GM-published specs for 1969 Corvette motor

L36 390hp @ 10.25:1 w/ QJet has OE CAST pistons w/ skirt clearance 0.0012"-0.0020"
L68 400hp @ 10.25:1 w/ 3 x 2bbl has OE CAST pistons w/ skirt clearance 0.0012"-0.0020"
L71 435hp @ 11:1 w/ 3 x 2bbl has OE FORGED pistons w/ skirt clearances 0.0040"-0.0046"

L2300F is FORGED (Not Cast); VMS-75 is a high-silicon forging alloy and is much like 4032 alloy

[Ks Fats]

Don't believe I said it was cast; most know that the L-2000 series were all forged. The L-2300 was indeed forged, it was also listed as a non performance piston. At no point did I say set it up with cast clearances; if both pistons require a 4.251 finished bore (TRW Cat.E-178 1978) the clearance is compensated for in the skirt diameter. Since the recommended bore is known put a mic. on the piston; (L2300 @4.247 and the L-2268 @4.245). The slotted return in the oil groove of the L2300 allows for less heat to the skirt and more expansion through the pin boss so it will be tighter than the 2268 and looser than the cast piston. Tolerance on both pistons was usually around.0005 so the recommended finished bore is adjusted according to size and projected heat load. The L2300 piston will scuff if the pin is too tight in the pin boss also. Sorry for any confusion caused by the initial post.

[BillK]

L2300F piston calls for a 4.251 finished bore. . . . . . . The L2268F also calls for a 4.251 bore.

Just curious where you see that ? All three of the TRW /Speed Pro books that I have say 4.250 ?

[Ks Fats]

Bill,
The L2300 is on page 642 in the 78 book; also has "Except High Performance & Special performance" in bold print below it. The L2268 is on page 644 0f the same book. Both pistons are listed as 66 to 69. Just noticed the L2308 for the ZL1 and L88 is also listed as 4.251; they all list the oversize's accordingly. +.030 is 4.281,+.060 is 4.311 etc.. The pages are yellowed but still readable after 40+ years. I must have "loaned" my interchange, haven't been able to locate it. The truck pistons are listed @4.250 for recommended bore.

[BillK]

Bill,
The L2300 is on page 642 in the 78 book; also has "Except High Performance & Special performance" in bold print below it. The L2268 is on page 644 0f the same book. Both pistons are listed as 66 to 69. Just noticed the L2308 for the ZL1 and L88 is also listed as 4.251; they all list the oversize's accordingly. +.030 is 4.281,+.060 is 4.311 etc.. The pages are yellowed but still readable after 40+ years. I must have "loaned" my interchange, haven't been able to locate it. The truck pistons are listed @4.250 for recommended bore.

Interesting. I have never seen that before. The oldest book I have is 84 and it shows 4.250 bore. Learn something every day