What to set valve lash w/o cam card?

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DustyEd

DustyEd

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Here's my dilemma ....I want to check the valve lash on my '70 duster 340, but don't know what gap I should use. As far as I can tell, the factory cam was a 276/284/52 high lift, high overlap, long duration. However, the previous owner changed this stock set up to an even longer duration cam, adjustable rockers and solid lifters back in 1975. He doesn't recall the cam specs or even the brand of cam.
So, what is the "best educated guess" for the lash gap in this situation? And, will the intake and exhaust gaps be different?
I know there's not much to go on here, but it's all I've got!
 
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Go .012 intake and .014 exhaust. If it seems not to run well, then try .018 intake and .022 exhaust.
 
1975 was b 4 tight lash cams most likely
what's the lash now? should give you a clue
using rusty's method you will not hurt anything
staring of at 30 30 or .028 you could
what''s your compression?
engine been rebuilt? (1970 pistons)
recent timing chain?
70 is a good motor
 
Wyrmrider said:
1975 was b 4 tight lash cams most likely
what's the lash now? should give you a clue
using rusty's method you will not hurt anything
staring of at 30 30 or .028 you could
what''s your compression?
engine been rebuilt? (1970 pistons)
recent timing chain?
70 is a good motor
Click to expand...

Just getting ready to pull the old aluminum Mr. Gasket covers off (hopefully later today), so I'll find out then.
Have not checked the compression. I have all the engine wiring out, so it will be awhile before I can check each cylinder's compression. Factory compression ratio is 10.5 :1 for the '70 duster 340.
Engine never rebuilt, just the above changes I mentioned (that I know of from speaking to all three previous owners). The front cover does have a small trace of silicone oozed out, so "maybe" on a new timing chain. (?) It has 79k actual miles on the car with all #s matching.
This thing runs strong for being close to original.
 
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damn silicone
if it's squeezing out one side it's squeezing out the other
factory iron rockers?
 
1975 vintage cam?
I’d start out at .025”.

If it seems abnormally noisy tighten it up a few thou.
Then, if that seems to numb up the bottom end a bit, you’ll know you’re in the ball park.

You’re likely going to be balancing noisy operation vs low end response and tq.
 
Set it to .024/.028 cold and then see what it is hot.

NO cam will require more lash than that.

You may be able to and want to work it down a little from there.
 
Personally, I'd want to know what was in it before possibly messing something up with incorrect adjustments. If it were mine, I would invest in a timing cover gasket set & pull the front of the motor down to see what cam is in it.
 
Isky recommends .020/.020 for their E 4 cam in the 273. I set mine to that and it's perfect. A little solid lifter rattle when cold and quiet when it warms up.
 
Dusty Ed; First verify that you have solid lifters.

The 1967 273 motors had solid lifters. The valve lash was .013 for the intakes and .021 for the exhaust valves. Adjusted while hot. That's what I'd do.
 
Demonracer said:
Personally, I'd want to know what was in it before possibly messing something up with incorrect adjustments. If it were mine, I would invest in a timing cover gasket set & pull the front of the motor down to see what cam is in it.
Click to expand...
I did exactly that when I bought my 69 Dart many years ago that was built by a fellow that past away.
 
Pulling the front cover to see what cam is in there is an option.

I still say set it to .024/.028 cold

lets say the cam is 20/20 cold like the isky above. The lash I'm recommending isn't going to hurt it. Let's say it's an MPP purple shaft. (.028/.032) My recommended lash specs are still fine.
 
roccodart440 said:
Set it to .024/.028 cold and then see what it is hot.

NO cam will require more lash than that.

You may be able to and want to work it down a little from there.
Click to expand...

With iron heads and block, shouldn't hot and cold lash remain pretty much the same?
 
Well, I got the chance to remove the left valve cover today.
Wow, as Gomer Pyle says, "Surprise...surprise...surprise!" Standard rockers! Must be hydraulic lifters. What a disappointment. The owner of this Duster 340 back in the '70s had two of these cars. He MUST have gotten the two mixed up.

O.K., now I got another question for you guys. Below is the #s stamped on each rocker from the front of engine to rear of engine (Left side....1,3,5,7).....
710 LT 710 T ........710 LT 78 RT........710 LT 78 RT.........710 LT 78 RT

Are these good to go, or do I need to find the "correct" ones? And should I pull the arm and check the rods and surfaces while I'm here? How do I decide if each rocker is in usable condition (where it pivots on the arm)?
 
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put the valve cover back on and change the timing chain much more chance that it's bad
but you could remove the shafts and keeping everything in exactly the same order inspect the rocker bearing area and the push rod cups and see if the rocker pads are worn by the valve stems
remember where the bolts went so you can get them back in exactly the same place or your rocker shafts get no oil
and remember which way the notch on the shafts face
btw i agreed with the early advice to start with tight lash from Rusty Rat Rod
first you did not know which cam you have so stock lash is irrelevant, so is the Isky E 4 cam or Purple shafts which can be .028 or more
and ruining loose lash on a tight lash cam really bangs the valvetrain as you are starting past the clearance ramp you would know from the racket
 
oldkimmer said:
He just said he has stock rockers and hydro lifters. Kim
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Hey, Kim,
What do you think of the "mismatch" rocker #710 T on cylinder # 1 (see my previous post)? Do I need to find another #78 T rocker to match the other cylinder's rocker setup?

Another question: Should I be concerned that only one(1) rocker had oil pooled on the valve end of the rocker? And, I could not compress any of the lifters when I pushed down on the rod side of the rockers.
 
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I'll get a photo later today. The engine did have a very slight tick on this side, so I'm wondering if someone put a LEFT rocker in a RIGHT rocker position.
 
curious why you wanted to check lash? is it the tick? did you check for an exhaust leak?
 
DustyEd said:
O.K., now I got another question for you guys. Below is the #s stamped on each rocker from the front of engine to rear of engine (Left side....1,3,5,7).....
710 LT 710 T ........710 LT 78 RT........710 LT 78 RT.........710 LT 78 RT
Click to expand...
If the 710T is the same shape as the 78 RT's then you are good. But I can never remember the relative position of the 'lefts' and 'rights'; I need to see it.

Not being able to compress the lifters is normal and a good sign. It means they have filled with oil and are not leaking down. Some of the ones that are partially opened may have leaked down, with the lifter plunger now setting in the bottom of the lifter body. So you can really only test lifters for leakdown like this when they are on the base circle of the cam lobes.

You can pull the rockers off and apart and inspect the wear in the bottom of each rocker for excess wear. Excess wear on one will be pretty obvious; there is no spec to measure this to AFAIK.

When re-installing the rocker shaft bolts, many/most of the book specs are wrong... too high! Torque these bolts 15-18 ft lbs.

As far as oil in just one rocker, I am not sure that has any significance. Was it at or near the back? Did the other rockers have oil around the shaft? Were the notches on the ends of the shafts facing down and to the left, as you look at each side of the engine?
 
billsdartgt said:
curious why you wanted to check lash? is it the tick? did you check for an exhaust leak?
Click to expand...

My initial concern was the tick, but since the previous owner thought it had solid lifters/adj. rockers I wanted to check lash, anyway. Who knows how long had it been since lash was checked?

Yes, exhaust leak was my FIRST thought. However, since I thought there was adj. rockers I was hoping readjustment would fix the tick and save me from removing (maybe breaking) the old header bolts in order to replace the gasket. Those bolts have been in there a long time!

Now, I'm still wondering if the 710 T rocker on the #1 cylinder intake (right side rocker) is incorrect. (Cylinders #3, 5,7 all have the 78 RT rocker on the right side. And if I replace the entire set, what is the correct HD rockers to buy?
 
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