Just bought my first truck last week and was told it had a 390. Using a VIN Decoder it looks like it might be a 360. How does one tell the difference.

Here's the code:
F25YRD69929
131 E F254 2381 (6? or G) 37

Also What's the difference between F150,F250 and F350
BTW mines a 1968 F250 Camper Special, 4 speed, manual brake, no power steering,2wd.
Thanks in advance,
Neil

 

Y=360
H=390

I know for sure your truck didn't come with a 390, because (a) the Y in the VIN and (b) because the 390 got power disc brakes standard in '68. Keep in mind these engine codes in the VIN are only correct if the engine is the original equipment. It is a very common practice for someone to change a 360 into a 390. The fundamental difference is that the 390 has a different crank with a longer stroke. The 390 rods are slightly shorter and the 390 pistons have skirts as well.

To answer your question on how to distinguish, you must measure the stroke. The 360 has a 3.5" stroke while the 390 has a 3.78" stroke. Pull the #1 plug out and measure piston travel from bottom to top.

 

[font size="1" color="#FF0000"]LAST EDITED ON 27-Mar-01 AT 09:48 PM (EST)[/font][p]I'm aware of another visual cue between 360s and 390s. On the crank flange, where the flywheel or flexplate bolts to. The 360 has a rather larger half moon shaped cutout (thinking about the diameter of a half dollar). The 390 has a smaller square notch. So you say: but I don't want to pull the engine off the tranny just to see this. Well I've seen the crank flanges, both kinds w/o the flexplate or flywheel w/ engines on engine stand or at least separated from tranny w/ flexplate off. Having familiarized myself w/ what they look like, I've experimented at wrecking yard w/ peaking up the bellhousing inspection cover. When lucky, the crank is in a position that I get a good idea which cutout it has, but I'd say look at some cranks that you can see clearly to get an idea what they look like. I've never tried the dowel trick, I'd be nervous that if the dowel went in at any kind of angle, that you don't get a factual measurement. I had heads off of a FE in wrecking yard and my digital caliper w/ end measure tool. The engine was too rusty to turn over. I was unsure till I actually separated the engine from tranny. Part of the measureing dilema for me was that apparently on the 360 (which it ended up being) the pistons don't come up to zero deck height. So not being positive if piston was totally TDC or BDC and not knowing the deck clearance, the difference in the crude measurement between 3.50 and 3.784 wasn't conclusive to me till I saw the crank cutout.

BBT

PS after thinking about your situation.... I'd say do the dowel measurement, and also try and peak up your bellhousing access. Since you have a running motor, you can rotate engine to compare tdc w/ bdc and when I got to think that on 390's 3.78 stroke that you'd clearly have a measurement exceeding the 3.50 of a 360 (or a 352 for that matter). So many years, and opportunities for someone else to have swapped in a different motor. I have a 390 that when I first had heads off, I measured the stroke and was confident it was well over 3.50. The difference was I could rotate my motor, and the junkyard motor I couldn't. Add .16 deck clearance or so and it clouded the issue for me in the frozen junkyard motor.