Another 340 J & O head thread (what do i have?)

[EL5DEMON340]

if i can tie the engine to the vin i'll be happy. i'm pretty sure my dad didn't replace anything internal like that back then.

Yes check the numbers on it, the stock 10.5 to 1 pistons look exactly like yours down to the two orientation notches that face the front of the engine. Plus I see some orange paint which is a clue if original paint to it being a pre April 71 10.5cr engine.

 

[Infecteddog]

Those look more like aftermarket pistons to me. You will want to do some measurements rather than guess on the compression ratio. It may be higher or lower than you think depending on the machining done on the block previously. It's not worth it to guess, and there is no such thing as a "10.5:1" or "8.8:1" piston. There are just pistons of differring designs that get put in a block with a head gasket and head combination. Whatever that combo yields is what that piston "is". So you have to do a little measuring, do a little math, and then you know what YOU specifically have in that engine.

Very true. Most of these compression ratios were with thin head gaskets no longer commonly used and honestly most 100% stock heads I've had cc'd at the stock ratings. We actually did a set before/after and IIRC one set grew 2ccs after getting cleaned up by the machine shop. On the other hand, it's about as common to see them shaved down to 3-5ccs below stock. Most simple rebuilds will end up shy of the factory CR for that combination.

if i can tie the engine to the vin i'll be happy. i'm pretty sure my dad didn't replace anything internal like that back then.

Should be on the side of the block low down. IIRC you get two of the VIN that tell you what car it came from and then you get the serial of the VIN. The last two I saw were a Duster and a Dart Sport/Demon. The Duster is likely the most common by far.

 

[moper]

Yes check the numbers on it, the stock 10.5 to 1 pistons look exactly like yours down to the two orientation notches that face the front of the engine. Plus I see some orange paint which is a clue if original paint to it being a pre April 71 10.5cr engine.

Not sure I agree. As I remember all the pre '72 340s I've had all had flat tops with no valve reliefs. They were taller giving them more compression but the never had valve reliefs. I haven't seen any new ones of that style for years though. The later ones ahd the 4 valve reliefs. and those are what you see everywhere.

 

[eduardostewart]

so i'll check for casting numbers on the passenger side, but i think i just read that there will/could be numbers on driver side front of the block below where the head would sit?

 

[crackedback]

J, O, U, N, 915 heads are all the same basic casting.

The 915 J head appeared in regular production for 1970 model year 340's.

 

[eduardostewart]

pardon my newbness, we have all the accessories off the engine. so, in regards to missing the balancer on the front, can i put the crank bolt back in and turn it to move the piston(s) to TDC? clockwise, correct?

 

[txstang84]

You can if you don't have a crank nut, but be sure to use the washer too...seeing that the heads are off, you can probably turn it by hand with the balancer on just enough to engage the key...

 

[Marcohotrod]

the stock 1968-71 pistons had 2 valve reliefs with a compression distance of 1.84" and protruded above the block about .015 and used a thin head gasket and 2531894 or 3418915 heads with about 70 cc chambers for about 10:1. 1972-3 pistons had a comp distance of 1.74" and below deck about .085" for about 8:1 with heads of about 70 cc

 

[EL5DEMON340]

Not sure I agree. As I remember all the pre '72 340s I've had all had flat tops with no valve reliefs. They were taller giving them more compression but the never had valve reliefs. I haven't seen any new ones of that style for years though. The later ones ahd the 4 valve reliefs. and those are what you see everywhere.

You might be mixing it up with the 383hp they had no valve releifs.

 

[eduardostewart]

alright guys, we got the engine out. we mounted it to the engine stand, and myself was worried about breaking off the "ears" of the bottom holes. so we mount it using the 10,11,1, & 2 o'clock threads on the block. Are those 3/8" bolts strong enough to hold all that weight? when we rolled the stand around the floor one of the wheels when over a bump/ditch in the concrete and the engine/stand kind of waved up and down, made me cringe a little.

 

[krazykuda]

alright guys, we got the engine out. we mounted it to the engine stand, and myself was worried about breaking off the "ears" of the bottom holes. so we mount it using the 10,11,1, & 2 o'clock threads on the block. Are those 3/8" bolts strong enough to hold all that weight? when we rolled the stand around the floor one of the wheels when over a bump/ditch in the concrete and the engine/stand kind of waved up and down, made me cringe a little.

Yes 3/8" bolts will be fine. Use at least grade 5... grade 8 is better...

 

[Bad Sport]

alright guys, we got the engine out. we mounted it to the engine stand, and myself was worried about breaking off the "ears" of the bottom holes. so we mount it using the 10,11,1, & 2 o'clock threads on the block. Are those 3/8" bolts strong enough to hold all that weight? when we rolled the stand around the floor one of the wheels when over a bump/ditch in the concrete and the engine/stand kind of waved up and down, made me cringe a little.

They do spring a little, quite common. I agree on the grade 8 bolts.

 

[eduardostewart]

thanks guys, we used grade 8, actually had to run to TSC since i didn't have any long enough on hand. just got nervous and decided not to use the 9 & 3 o'clock ears since they made me nervous.

i also did some more vehicle/engine decoding. if any of you want pics let me know. this is all new to me so it was exciting detective work to me.

 

[Bad Sport]

Not sure which stand you have, but I will throw this out there. Be careful when wrenching on it, as sometimes pulling in one direction could cause it to tip over. Just think it through.

 

[eduardostewart]

got the biggest one HF has - the 4 wheel/leg one. was warned about the "T" stands, thanks for the concern though!