I have a 390 FE out of a '66 Thunderbird that I am tearing down to see what condition it is in. I have a '55 F100 that I was thinking of putting it into. I have been reading all I can find on here about FE's and I think I have most of it figured out. The bore measures 0.040 over the 4.05 spec, Pistons are stamped 040, the stroke measures just under 3.8" and the crank is stamped 2U which I have read means a stock 390 crank. The heads are casting C6AER, the block is casting C6ME- and the heads and block are all date coded 5L13 which I see translates into late Nov 1965 castings. So everything seems to add up matching the VIN that said that it is a 390. Obviously given the over bore the engine has been gotten into sometime in the past. My question is that I see a lot of welding on the balance holes and cheeks of the crank. I read on here that the 390 FE is internally balanced. The crank measures stock diameters on the journals. Is it normal to have that much rebalancing? Sent from my iPad using The H.A.M.B. mobile app
No, that's not normal! Is the car it came out of still around? The only thing I can think of would be if whoever rebuilt/replaced the motor may have had it rebalanced but used the 428 flywheel/damper. '66 was the first year of the 428 and it was available in the 'Bird. Maybe somebody at the machine shop wanted the 428 enough to substitute (rebalanced to work) a 390 to the unsuspecting owner...
They must have rebalanced it when they did the bore job. Replacement pistons were evidently heavier than the stock ones. Actually is a sign of a quality rebuild, a lot of shops would just drop in the new heavier slugs and call it good. I had Ernie Hashim rebuild my 331 hemi into a 354 with a 1/8" bore and he did the same thing to my stock 331 crank.
Is it me or does it look like someone ground off a bunch of material and then welded more on? I had a 66 Tbird with a 390 btw and they are a great motor. Sent from my SM-G920V using The H.A.M.B. mobile app
Ah yes I see that now, I thought I saw grinder marks but it's just the a shadow on the rough casting. Sent from my SM-G920V using The H.A.M.B. mobile app
Sorry I forgot to include that in the t-bird the engine was mated to a C6 automatic so it just has a flexplate (no weights on the flexplate). Sent from my iPad using The H.A.M.B. mobile app
"the stroke measures just under 3.8" - that is all you need to know. That is a 390 crank and as such is internally balanced. The long stroke 428 (and 410) was the only externally balanced FE, but with the 3.98" stroke it is easy to identify the difference. I agree, the 0.040" pistons (or possibly the rods) must have been quite a bit different in weight than the originals, requiring the re-balance job. Not a bad thing, just something that often gets overlooked. I would be more concerned about the 0.040" boring job if it is in need of another cleanup. 0.050" is typically max on a 390 since the FE motor pioneered thin wall casting techniques and Ford fought core shift problems with the new processes during the FE's entire production run. Please get some one to sonic check it and see exactly were the wall thicknesses are at if another bore job is needed. I am sure someone will jump my shit and say they have a 390 punched out 0.080", but blocks that can take that are few and far between and don't last long bored to that level without additional support such as hard block, hence the need for a sonic check.
The real early 352 blocks could take the big overbores (I recall seeing one punched to the 4.13" 428 bore), but by '66 that was no longer true. .040" over was the end of the line in most cases....
Ok thanks guys. I will have it checked. It looks to me like the rebuild doesn't have much mileage on it. No measurable cylinder wear, the bearings look new etc. but I will have a professional shop check it for me and I will ask about a sonic check. Sent from my iPad using The H.A.M.B. mobile app
Just to close the loop on this one. The block checked out fine. Sent from my iPad using The H.A.M.B. mobile app
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