340 timing

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Tjhduster

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Hey guys I just replaced the push rods, rocker arms, and valve seals and I’m having trouble getting the timing right on the motor. This motor is upper end 340 with a 360 crank bottom end. I’ve tried it at 2,6,9, and 12 degrees above dead center and it still runs like crap. Any ideas?
 
You Didn't do any work to the engine that would require moving or removing the distributor. I would check the firing order first.
 
did you use longer pushrods that could hold valves slightly open?
 
As almost said, check that the rocker arms are correctly oriented (lefts and rights), and that your lifter preload is in the working range of the lifter.
Also make sure your rockershafts are correctly oriented. There is a notch on one end of each shaft; it goes down and to your left. On the Passenger side this would be towards the firewall. On the Drivers side toward the rad.
And finally, 340 springs require 340 rocker arms. The arms are clearanced on the underside so they don't push the springs over to the side, or ,I suppose, as said,hold the valves open a tiny bit

Then if all is correct,wait for the lifters to self adjust;at least 5 minutes at idle.Maybe 1 minute at 2000 rpm
 
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Tjhduster said:
Hey guys I just replaced the push rods, rocker arms, and valve seals and I’m having trouble getting the timing right on the motor. This motor is upper end 340 with a 360 crank bottom end. I’ve tried it at 2,6,9, and 12 degrees above dead center and it still runs like crap. Any ideas?
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"Above top dead center" ? I hope you mean BDC - Before Top Dead Center. I dont know your engine spec's but normally you should be looking at 10 - 12 degrees of crank rotation BDC @ 800 - 900 rpm idle. I set my engines timing "all in" which for the current 340 is 36 degrees BDC @ 3000 rpm.
 
That's interesting , I didn't realise that the 340 engines had different rocker arms to other LA engines. Are you talking about factory 340 springs? And which years did they have the clearanced rocker arms? I have never read anything about them, except for the T/A AAR heads of course, which are significantly different.
 
My factory X heads all have the clearanced arms and red springs.
When I installed the red-boys on a 318 back in the 70s, is when I discovered this. The 340 springs are a larger diameter.
The left and right rockers center the pushrods in the tunnels.
Orienting the notches provides oiling at the heavily loaded bearings.
 
AJ/FormS said:
My factory X heads all have the clearanced arms and red springs.
When I installed the red-boys on a 318 back in the 70s, is when I discovered this. The 340 springs are a larger diameter.
The left and right rockers center the pushrods in the tunnels.
Orienting the notches provides oiling at the heavily loaded bearings.
Click to expand...

Interesting. I also have some X heads on a 68 340 but it had been played with by the time I got it (about 14 years ago) and no idea if the springs were factory installed, I highly doubt it. Also the rockers on it, no idea if they were the original. So these notches allow the rockers to clear the larger diameter springs but also allow better rocker oiling? When you say 'bearings' do you mean the load bearing area of the rockers on the shaft? As it is just smooth metal to metal there. Would you by any chance have any photos of those rockers, as I have had 3 x 340s over the years and would like to look through my rockers to see if I can see any of them there. They are all mixed up now, 273, 318, 360 etc ! Thanks
 
70Hardtop said:
Interesting. I also have some X heads on a 68 340 but it had been played with by the time I got it (about 14 years ago) and no idea if the springs were factory installed, I highly doubt it. Also the rockers on it, no idea if they were the original. So these notches allow the rockers to clear the larger diameter springs but also allow better rocker oiling? When you say 'bearings' do you mean the load bearing area of the rockers on the shaft? As it is just smooth metal to metal there. Would you by any chance have any photos of those rockers, as I have had 3 x 340s over the years and would like to look through my rockers to see if I can see any of them there. They are all mixed up now, 273, 318, 360 etc ! Thanks
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No photos but the machining is very easy to see It's the shiny cut-away part. All you have to do is eyeball that area on your loaded heads, every rocker. If you have smaller than stock diameter springs or beehives, it will not be a problem.
This is the only mod to the otherwise stock rockers.
Yes the bearings are the load-bearing areas. If you get the shaft notches upside down they oil the valve covers real nice. If you put them in backwards the oil goes to the wrong place. In either case,the interface galls
 
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Oh, ok, I must have been not fully concentrating, yes I know about the shaft notches and the oiling now. I was reading your post as the notches (reading as cutouts) on the rocker arms for the springs and wondering how they could possibly affect the oiling. So it's just the rocker arm differences I was interested in. I will check all mine and see if I can see any. There would have to be at least one. I'm sure it would have only been the 2.02 valve 340s that had them. I wonder if the 340 J heads that were on 70-71 340s had these larger springs and modded rockers, I would assume they did.
 
all 1968-1973 340s had the same cam and valve springs and rockers etc. (and the 1974 360 hipo
 
Marcohotrod said:
all 1968-1973 340s had the same cam and valve springs and rockers etc. (and the 1974 360 hipo
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Not "all the same cams" according to the info in this link which seems fairly comprehensive: The Mopar 340 V8 high performance engines

Which states that the 1968 340 camshaft for manual cars was more aggressive than the cam used in autos. 1969 they all used the automatic camshaft.

1972 saw the 340 detuned via lower compression (from 10.25 to 8.5:1), milder camshaft, smaller intakes (2.02 to 1.92) and sometime during 1972 went to a cast crankshaft also.

If then, the 340 had different rocker arms to the other LA engines they should have a different part number. I have never seen this mentioned anywhere, I thought the 340 shared the same rocker arms as the others. Unless the factory clearanced the stock ones for the larger springs. And if the springs were also larger then the retainers may also have been different and I have never seen or read about that either.

Question for AJ is perhaps on this engine, someone machined the rockers to suit those springs? And wasn't a factory mod?
 
forgot about the 1968 manual trans 276/284 cam. the 1969-1973 340s all had the same 268/276 cams. 1972-3 had 1.88" intake valves.
 
Marcohotrod said:
forgot about the 1968 manual trans 276/284 cam. the 1969-1973 340s all had the same 268/276 cams. 1972-3 had 1.88" intake valves.
Click to expand...

So then, looks like the info in that link is a crock... Here it is cut and pasted directly from that page, with those parts in colour:

(however I would still be ready to believe that the camshaft profile was changed in 1972, inline with the vastly reduced CR and the new emissions requirements. But until that's proven somehow I will accept that it wasn't)

1968 - 340 released, rated at 275 horsepower, with:
  • forged crank
  • four-barrel Carter AVS carburetor
  • hydraulic cam (a more aggressive cam was used in the four-speed cars in 1968)
  • “X” casting cylinder heads, with 2.02” intake, 1.88” exhaust valves
  • 10.5:1 compression ratio

1972 - The 340 four-barrel dropped to 240 horsepower:
  • Compression dropped to 8.5:1; the compression height of the piston via wrist pin location changed by 0.10”
  • The crankshaft was switched from forged to cast somewhere in the production cycle, believed to be in early April 1972, with engine 39118000 (thanks, Karl Thomas); a milder camshaft was used
  • 340/360 were moved to “J” casting heads with 1.92” intake valves; exhaust valves remained the same
 
Well I thought Marco would be back.
Stated another way; the X heads always had 2.02s in them.
The Js,Os and Us could have had intakes of either the 2.02 or 1.88, depending on the years.
AFAIK the exhausts were always 1.60s
The castings are all AFAIK the same.My knowledge ends in 74.
Mind you most of that is based on period information, and the couple of dozen period heads I have, or have had.
AFAIK there never was a 1.88 exhaust.
I have read that the 1.88 seats can be opened up to fit the 2.02s.
I sell my Xs to stock-class racers. They will sometimes accept a 1.88-J. Nobody wants the 1.88-Us. I only ever had one pair of 2.02-Os. I'm almost out of 2.02 heads.
As far as the cam is concerned, I only know what I have read, and that is; that the 68 manual-trans cam was a one-year only deal.
 
thanks for post. Yes that is what I know too. I was just pointing out the errors in that Allpar page. I even looked up the B/RB eng specs for valve size to see if they had mistakenly put in one of those valves, but no. So I wonder how many other errors they have in other parts of that site. Just goes to show that you can't believe everything that is written. However as I said, I am still open to the idea that they changed the cam profile in 72, for the reasons I gave. The 68 cam profile was quite "hot" even for the "racy" '60's and it would make sense to use a smaller cam to comply with the more stringent emissions in 72. CR and cam are the first things they change. But I'm not in a position to ever know for sure, unless I hear it from someone who DOES know for sure.
 
the 1968 autom. 340 and all 1969-1973 340s and the 1974 360 hi po had the same 268/276 cam, double roller timing set , and valve springs and windage tray. the 1972 340 and 1973 had .100" shorter pistons, 1.88 intake valves, and good thermoquad carbs. anyone that thinks the 1972+ detuned 340s had a different cam-please provide specs and a part number
 
Marcohotrod said:
the 1968 autom. 340 and all 1969-1973 340s and the 1974 360 hi po had the same 268/276 cam, double roller timing set , and valve springs and windage tray. the 1972 340 and 1973 had .100" shorter pistons, 1.88 intake valves, and good thermoquad carbs. anyone that thinks the 1972+ detuned 340s had a different cam-please provide specs and a part number
Click to expand...
That about agrees with my memory.
And lest anyone should think the low-compression 340s were slugs,
Hah!
Yeah they lost some compression, but with a little timing changes,that TQ about made it up once she was on the pipe.
 
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