Hey I bought a 1974 ford f100 2wd from my uncle with a 390 for the engine to rebuild, He bought it almost new and the motor has never been apart and when I got into the engine and looked at the pistons they said 410 on them and I compared them to another 390 truck piston and they were alittle different, The title on the 74 says 390 and the valve covers say 390 to.DID FORD EVER PUT 410 PISTONS IN A 390 ? OR IS IT POSSABLE IT IS A 410 ? OR AN ACCIDENT? THANKS

 

Seems to me like I heard that 410 pistons were used in 390 truck engines to lower the compression ratio. 360s used 390 pistons for the same reason. 410 has a longer stroke-3.98, same as 428- and 4.05 bore-same as 360-390.
Many pistons from 360s are marked "390 4V"

 

Lets just move this down to the FE forum where you can get the local FE experts to chime in for you.

 

I can feel your excitement, I got a big ol woody one day when tearing down a truck 390 and finding 410 pistons. Found out later that it was a common install. Using up old parts I guess.

At least you got a 390.



John

 

There should be a code on the crankshaft, "2U" for 390, "1U" for 428/410, etc... Find that and see what it says and post back here.

But yeah, I've heard of low-compression truck 390's coming with 410 pistons from the factory because it was the easiest way to get the compression WAY down... The higher pin height makes the piston sit lower in the bore.

 

does anyone think it could be a 4.100" bore piston? maybe another possibility

 

Check the crank, you never know if someone was in there, but yes, Ford used the 410 pistons with 390 rods and cranks to lower compression ratios in the pickup engines. Some of the earlier engines came with pistons that were actually mercury leftovers, then when they saw that they did what they wanted, they didn't change the outside of the mold. If you use the 1139 silvolite or sealpower 381p you will duplicate this problem when you rebuild, and if you use felpro 1040 gaskets you'll get 7.8 to 1 compression. Thankfully, we have better options now. Wanna know about them ? DF, and I really am at Dad's

 

old post i know..but...
WHERE is this located?

 

Don't remember exactly - rear most counter-weight? Second from the back?

GUYS!?!?!?!?

 

ok, i think i found it. 3rd from the front. 3U.

 

3U is a 390