340 engine repair/build questions

[Inertia]

Most of us would rather trust a 318 bored .130 over than a boring a 340 .070 over/4.110.

I know i do.

Yeah, there's a always book theory vs real life experience .

Costs a lotta bucks to tool up for 340 + .060 pistons, different ratios, from different manufacturers.
Musta been a demand .

 

[FlamesAreWicked]

This is what i did with a similar engine. Im putting it back together now. The pitted bore builds compression turning by hand the same at the nice bores.
I think it had a weeping head gasket ever since rebuild by previous owner perhaps.

The pitting will still be there after a ball hone.
I would’ve had this bore sleeved but the machine shop isn’t taking new work.

The pic makes it look worse than it is.

View attachment 1716428365

Just gonna let’r eat as is? Interesting..

 

[cookietruck]

Just gonna let’r eat as is? Interesting..

Yep.
That bore tested the same psi as the other bores. 185psi.
That’s what made me think the head gaskets were ok. Then a few years later noticed a bit of coolant weeping from the gasket by the header.

Should’ve just replaced the head gaskets and put it back together a few years ago…but let it sit in the garage thinking this is trash and all the bores got rusty.

Then got to the point I need to get it running and I’m curious how it will do.
So tore it down and ball honed it, figured out all that was in it. Reground cam and better heads.

If it runs terrible or burns or blows tons of oil I will build a fresh short block.

 

[Dartswinger70]

I think with a 340 block its makes sense to take the chance that the rings will seal and seat, especially on a cruiser. If its a race engine maybe I'd reconsider etc. but the worse that could happen is it burns oil etc. then if so, pull it back out these engines aren't hard to swap etc.

 

[FlamesAreWicked]

After some talking with the guy I bought it from.. we agreed on some money back on it.. so I’m gonna go through it to make sure it’s 100%. Now to see what the machine shop will say it’ll need. My 68 Dart will be getting a 340.

 

[cookietruck]

Thats cool. Congrats on the 340. Theyll want to bore it and replace pistons. Get some mahle pistons.

 

[FlamesAreWicked]

Thats cool. Congrats on the 340. Theyll want to bore it and replace pistons. Get some mahle pistons.

I was thinking the same.. figured .040 would still be okay. Hopefully that’ll do the trick. I’ll have to see what’s available and affordable

 

[FlamesAreWicked]

Thats cool. Congrats on the 340. Theyll want to bore it and replace pistons. Get some mahle pistons.

Best I can tell online.. they don’t have a .040 over option

 

[TheRacerDave]

Had this same issue with a SBC I was working on. Ball hone first as it won't increase the bore diameter.* A little discoloration won't hurt anything, but using magnification look for pitting. If necessary go to a rigid hone and take the absolute minimum to remove the pitting, no more than .001" with those cast Silv-O-Lites.

Going +.010 over the current 4.070" (std +.030) would most likely clean it up; unfortunately the only way to get a 4.080" (+.040) piston is with a custom Diamond, Ross, etc. $$$

* My ball hone is 400 grit for moly rings; coarser grits may remove metal.

 

[Inertia]

Had this same issue with a SBC I was working on. Ball hone first as it won't increase the bore diameter.* A little discoloration won't hurt anything, but using magnification look for pitting. If necessary go to a rigid hone and take the absolute minimum to remove the pitting, no more than .001" with those cast Silv-O-Lites.

Going +.010 over the current 4.070" (std +.030) would most likely clean it up; unfortunately the only way to get a 4.080" (+.040) piston is with a custom Diamond, Ross, etc. $$$

* My ball hone is 400 grit for moly rings; coarser grits may remove metal.

Imagine my surprise, I didn't know they had stopped making .060 pistons for 340.

I gotta coupla sets of .060 pistons sitting on a shelf, and a few in engines.

I'ma gonna start collecting worn out +.040 - 340 blocks .

Just for reference, going an additional .020 is a removal of only 0.010 of material from the cylinder wall.
10 thou off the wall. . . - alum foil is 6.5 thou.
So you'd be removing alum foil thickness from the wall .
Things are relative . .

Good luck .

 

[cookietruck]

I was thinking the same.. figured .040 would still be okay. Hopefully that’ll do the trick. I’ll have to see what’s available and affordable

Ahhh.

The Racetec catalog says they can minor adjustments to bore, ring pack, pin height etc. at minimal cost.
Try calling them?

 

[Illahe]

Those are Silvolites. They are the cast replacements for the 68-71 2 relief pistons. Compression height is different than the oem 72-73 models.

The deck height of the silvolite pistons will get you near 9.5:1 with a decked cylinder head on a good day...I have a set in my 340 build. You may be able to save the short block, the cylinders look stained far more than compromised.

 

[FlamesAreWicked]

Had this same issue with a SBC I was working on. Ball hone first as it won't increase the bore diameter.* A little discoloration won't hurt anything, but using magnification look for pitting. If necessary go to a rigid hone and take the absolute minimum to remove the pitting, no more than .001" with those cast Silv-O-Lites.

Going +.010 over the current 4.070" (std +.030) would most likely clean it up; unfortunately the only way to get a 4.080" (+.040) piston is with a custom Diamond, Ross, etc. $$$

* My ball hone is 400 grit for moly rings; coarser grits may remove metal.

Summit does show some 4.080 piston options. Low cost silvolites all the way up to DSS and beyond in price.. $1300+. This car will be just a driver, cruiser, with some occasional “spirited driving”. There’s options depending on how much a person wants to throw at it. The shop may look at it and say we can hone that out.. or they may say it’ll need to be cut.. we shall see. I haven’t called them yet.

 

[Illahe]

Imagine my surprise, I didn't know they had stopped making .060 pistons for 340.

I gotta coupla sets of .060 pistons sitting on a shelf, and a few in engines.

I'ma gonna start collecting worn out +.040 - 340 blocks .

Just for reference, going an additional .020 is a removal of only 0.010 of material from the cylinder wall.
10 thou off the wall. . . - alum foil is 6.5 thou.
So you'd be removing alum foil thickness from the wall .
Things are relative . .

Good luck .

View attachment 1716429132

View attachment 1716429133

Can you post the compression height of the pistons for reference.

 

[Illahe]

I get that the pistons are above the deck. I have done a few. Looking for the Piston deck to pin bore dimension. My silvolites are coming io at .014 above the deck and the old forged 2 valve relief seem to have a higher compression height.

 

[Inertia]

I'll check tomorrow.
There a set of +60 over on eBay right now, didn't know how rare they are getting

 

[Illahe]

Had this same issue with a SBC I was working on. Ball hone first as it won't increase the bore diameter.* A little discoloration won't hurt anything, but using magnification look for pitting. If necessary go to a rigid hone and take the absolute minimum to remove the pitting, no more than .001" with those cast Silv-O-Lites.

Going +.010 over the current 4.070" (std +.030) would most likely clean it up; unfortunately the only way to get a 4.080" (+.040) piston is with a custom Diamond, Ross, etc. $$$

* My ball hone is 400 grit for moly rings; coarser grits may remove metal.

DSS piston lists their 6300-4080 replacement piston +.040 2 valve relief forged piston with 1.802 compression height at roughly $650.00

 

[Swinger 340]

The guy I bought it from did say he’s willing to pay back some cash on it.. just need a game plan. I told him I’d be in touch and depending on what the shop says it needs. If I was a betting man, the shop will wanna open it up some more. I can handle disassembly. Organized and thorough.. I dunno, I would think 10 more over would do it but.. I’m hopeful at this point.

I would disassemble it yourself, sometimes your parts are switch out for another inferior part. If the car is going to be a "KEEPER", I would bore it 30 over, if needed and have the rings set a little tight, for the motor to give you years of good service. I use TRW Forged 30 over on all my two 340's and that has been over 35 years ago. On your discount, a good core 340 should be around $2,000- $2,500 with the 2.02 "J" heads. A 360 2 bbl, "J" head motor should be around $800.00 to $1,000. Check the driver side of the block and make sure it is a true 340 block with all the goodies. The motor mounts are the same, so you can't go by that.

 

[Woody500]

I had the exact same situation.

Bores cleaned up @ .040 but one needed 1 sleeve. I used the exact same new Silvolites that you currently have. They are a cast piston that installed at .017 above my deck. I redid my stock rods and used the original forged crank and did not balance. Engine runs strong and smooth. Like you, this is a punchy cruiser engine.

If it were me, I'd try cleaning the rust off with solvent and a scotch brite or some other mild abrasive. Any pits in the "stroke zone" and it would be off to the machine shop for me.

Good luck.

I've told on here before about a Slant Six Marine engine in '56 Higgins 17 Utility boat. Bought whole boat for $800 with stuck engine. Before doing anything filled cylinders with Knocker Loose & soaked it
while I looked it over & noticed a crack on the head. Went to Wrecks and got another head, non marine.
Took head off & 1 cylinder was very rusty so I sanded off the rust, wiped out the crap & re Knockered it to soak over night. Piston over half way down.Next chance I cut the corners off of a 4x4 so it would fit snugly in the bore and started hitting the 4x4 with a sledge hammer until piston moved. Then re-oiled & moved it down with a socket and then wiped & sanded. Then up & down, oiling & wiping until clean, then with 30w ND & wiped some more.
Then reassembled & it never smoked in the years I water skied with it.
And The Higgins was the finest Ski Boat I ever owned, hull very light, built like an Aircraft Spar, & Slant Six pulled hard out of the hole.
Long story but shows how excellent Chryslers Metallurgy was then, so previous post may've been joking, but is actually correct in saying you might be able to sand it off and get away with it.
Be very clean for reassembly.
Bet others have done the same.

 

[FlamesAreWicked]

I’m gonna get the machine shop check it out and come to a game plan.. you can tell it had miles on it but there was some cross hatching left and I didn’t feel and ring ridge..they may only need to hone it and put new rings.. which would be ideal. Also gonna have then put new bearings.. the crank journal surface looked really good but the bearing on the #1 rod cap didn’t look amazing so.. no reason to not do that as well while we’re at it.. ought to be a peppy engine once it’s done..

I'll have to rethink my carb for it.. my original plan was to put a performer intake and a Holley 670 that I picked up from a close friend on the original 318 but with the new found engine, I scored a rpm air gap from a fellow member here and I may step it up to 750-800 maybe? I know a lot of Mopar guys like the new AVS carbs.. I’m not a guy who only uses certain brands.. I’m not lookin for max effort but something that works.. the edel is a little more affordable brand new..

 

[gzig5]

I’m gonna get the machine shop check it out and come to a game plan.. you can tell it had miles on it but there was some cross hatching left and I didn’t feel and ring ridge..they may only need to hone it and put new rings.. which would be ideal. Also gonna have then put new bearings.. the crank journal surface looked really good but the bearing on the #1 rod cap didn’t look amazing so.. no reason to not do that as well while we’re at it.. ought to be a peppy engine once it’s done..

I'll have to rethink my carb for it.. my original plan was to put a performer intake and a Holley 670 that I picked up from a close friend on the original 318 but with the new found engine, I scored a rpm air gap from a fellow member here and I may step it up to 750-800 maybe? I know a lot of Mopar guys like the new AVS carbs.. I’m not a guy who only uses certain brands.. I’m not lookin for max effort but something that works.. the edel is a little more affordable brand new..

AVS2 650 worked great on my 340. Lots of good options.

 

[Illahe]

I’m gonna get the machine shop check it out and come to a game plan.. you can tell it had miles on it but there was some cross hatching left and I didn’t feel and ring ridge..they may only need to hone it and put new rings.. which would be ideal. Also gonna have then put new bearings.. the crank journal surface looked really good but the bearing on the #1 rod cap didn’t look amazing so.. no reason to not do that as well while we’re at it.. ought to be a peppy engine once it’s done..

I'll have to rethink my carb for it.. my original plan was to put a performer intake and a Holley 670 that I picked up from a close friend on the original 318 but with the new found engine, I scored a rpm air gap from a fellow member here and I may step it up to 750-800 maybe? I know a lot of Mopar guys like the new AVS carbs.. I’m not a guy who only uses certain brands.. I’m not lookin for max effort but something that works.. the edel is a little more affordable brand new..

Spread-bore carb works really well on a 340 that doesn't have some deep gears behind it.

 

[FlamesAreWicked]

Spread-bore carb works really well on a 340 that doesn't have some deep gears behind it.

I have a 3.55 gear.. so it has a little bit of gear in it.. I just don’t wanna under carb it..guess since I have it already and it’s not super small, I could use it until.. just food for thought I guess

 

[273]

I have a 3.55 gear.. so it has a little bit of gear in it.. I just don’t wanna under carb it..guess since I have it already and it’s not super small, I could use it until.. just food for thought I guess

When you get it running put a vacuum gauge on it do some full throttle runs and see if vacuum is excessive at full throttle then decide if you need a bigger carb.

 

[TheRacerDave]

DSS piston lists their 6300-4080 replacement piston +.040 2 valve relief forged piston with 1.802 compression height at roughly $650.00

Seems the aftermarket likes to shorten compression heights from the original design - I ran into that with the Silv-O-Lites in the 327/275HP SBC too. It was originally 10.25:1 compression ratio, but now it's only got 9.2:1 - and that's thanks to milling the heads!

Early 340s were 1.840, although some sources say 1.820. So that 1.802 compression height will put the piston near zero deck to .020 in the hole. Stock 340s have the piston .018" out. It will drop compression ratio about by about .8.

I know...... it's a street ride and compression ratio is less of an issue.