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343 Pushrods

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pacerman View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Topic: 343 Pushrods
    Posted: Jan/02/2019 at 11:30am
I have posted about this before, I am finally preparing to put 090 cylinder heads on my factory shortblock 343.  I know about the step dowels etc.   I have a seemingly new set (actually several sets) of the correct 343 pushrods but I was reading an old Dick Dotson publication today and a guy named Don Wright advises that one should use the later 360/390/401 pushrods if one is installing a dogleg head on a 343 block.

True?  Why?

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/02/2019 at 2:25pm
imho too many variables at play to know for sure what is correct pushrod length.
Would suggest using a pair of adjustable length pushrods to determine what length
works best with your specific assembled parts...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2019 at 3:23pm
Ok I am pretty sure I need the "short" 343 pushrods (with the length I have seen posted several places).  I will inspect how they fit to the best of my ability. 

New issue today, and this is just a comment.  I don't expect any help with the issue really since I suspect that few if any on this forum have dealt with this.  The factory 343 short block I am using was created in 1973 (original sale date on the invoice) from a "28" block which is a post 1969 360 block.  AMC used inserts (helicoils or equivalent) to convert to the 7/16 head bolts so it would indeed be a service placement block for a 343.  I am using new ARP 7/16ths head bolts and they were/are a very tight fit in the holes---so tight in fact that I questioned their size. The compare favorably to the tap I mentioned below.  

There is no obvious corrosion in the hole threads I am using a 7/16ths snap-on tap to "clean" the threads.  It is a regular tap, not a thread chasing tap, but that's all I have.  I have noted that some of the holes are a little more "loose" than others but all are tight enough that I could not spin an ARP bolt down into them with my fingers.  I am just chalking this up to the manufacturing process and trying not the let it bother me.  I too have the 70 ft-pound torque issue the the ARP bolts mentioned in another thread here on the forum.  I am going with the ARP spec of 70 foot-pounds using the ARP thread lubricant lightly on the threads and on the washer and under the head of the bolt, vs. the factory spec.   Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/08/2019 at 6:54pm
On-hand Stock AMC Push Rod Length info:
7.767" = '66-'69 Stud Mt Rocker Arm
7.800" = '70 &Up Stud Mt Rocker Arm
7.820" = '72 &Up Brigded Rocker Arm

PushRod "Goal" = Lifter Plunger approx .030" +/- below or "off of" Retaining Ring...
Stock Rocker Studs have a Positive Stop Shoulder for the Ball and are non-adjustable.
As long as they are not to long and over-preload the Lifter Plungers, or too short and leave lash.
Deck, Gaskets, Heads, Valves, Seats, Lifters, Cam Base Circle, etc can all effect Pushrod length.
Do you know the length of the existing Pushrods that were in it?
If possible, with Intake Manifold off, one can actually SEE and confirm Pushrod Length & Lifter Preload.
Which is pretty strait forward with stock shouldered positive stop rocker studs
but a little more involved with replacement aftermarket Studs and adjustable Poly-Locks.. 

Boy, sounds a little "worrisome" about the Bolt Thread to Thread Insert Fit...
Do the Stock 7/16 Bolts screw into the Inserts as they were?
There are different "Grade" Thread production specifications, 2A, 2B, etc...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Jan/09/2019 at 8:19am
The length of the pushrods increased for the 1970 model year because the deck height of the block increased, thus pushing the rocker arms that much further away from the cam. It sounds like the block you have is the raised deck version so, all else being equal, I think you need the 70 up pushrod length.

This assumes the cam you are using has the same base circle as the OE cam, and you are using OE rocker arms and studs. As already mentioned, there are many variables, so the best approach is to measure the length required with an adjustable pushrod.

I have 6090 heads on a low deck 390. The stock length 67-69 pushrods worked just fine for me even with a vintage Crower cam. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Jan/09/2019 at 5:40pm
What bigbad69 says about the pushrod lenght makes sense.  I have set of those 7.80 pushrods and I used them today.

I am using the clay method to check for piston/valve clearance and I have a problem.  The exhaust valve measures approximate .175 inch clearance without a head gasket in place.  So that's plenty.

The intake valve hits the piston with no gasket in place and only has about .020 to .030 clearance with the head gasket in place (not completely compressed, just with the several head bolts real snug).  Not enough. 

I will discuss this problem with my machinist and might take the engine to him to have him check my measurements and possibly fly cut the pistons.  I hate to have to load that engine in my truck and haul it to him though.  What a pain.

The cam is an old Sig Erson Viking 100 with .480 valve lift intake and exhaust (per the cam card).  I am just wondering what could be the problem.  The block is factory "28" block and the pistons are slightly recessed at TDC but are factory flat top pistons.  I don't think the heads were shaved much when the valve job was done but I have no records now.  Maybe I should try the shorter pushrods (in case the factory did actually deck the block to convert it to a 343).  
Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jan/10/2019 at 10:26am
I may be wrong but pretty sure Pushrod Length and Piston-To-Valve Clearance are not related...
Unless the PR is too long and holding the valve open off it's seat not allowing it to fully close?
May also have this backwards, but Cam may be "too advanced", opening the Intake too soon?
Retard the Cam and do another Clay Test ?
I assembled only 3 AMC V8's, but I used some Solid Lifters to "figure things out"
and used careful measurements to "transfer" dimensions for correct Pushrod Length
from "testing / measuring / claying solid lifter" to "final assembly hydraulic lifter".



Edited by PHAT69AMX - Jan/10/2019 at 12:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Jan/10/2019 at 11:42am
Originally posted by PHAT69AMX PHAT69AMX wrote:

I made be wrong but pretty sure Pushrod Length and Piston-To-Valve Clearance are not related...
Unless the PR is too long and holding the valve open off it's seat not allowing it to fully close?
May also have this backwards, but Cam may be "too advanced", opening the Intake too soon?
Retard the Cam and do another Clay Test ?
I assembled only 3 AMC V8's, but I used some Solid Lifters to "figure things out"
and used careful measurements to "transfer" dimensions for correct Pushrod Length
from "testing / measuring / claying solid lifter" to "final assembly hydraulic lifter".

  Understood and thanks.  I am using a solid lifter to do the modeling clay tests.  I am trying to figure things out and might retard the cam.  Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Jan/11/2019 at 6:31am
I'm surprised you're seeing piston to valve contact with just a .480 cam,
even with flat top 343 pistons, they have decent valve cutouts and they usually end up pretty far below deck.


I tried to look up the duration and lobe centers for a
"Sig Erson Viking 100"
 and the answers were all over the map,
depending on where I looked.

Hopefully someone else who's put together a 343 piston engine will jump in here,
but I know when I checked my .550ish cam with 108* lobe centers against my low cr 401 pistons there was still miles of room.

IIRC,
tighter lobe centers, and/or advancing the cam will give tighter PtV clearance on the intake side.

Did you also degree the cam at the same time you were checking for clearance?
Did you try checking a different intake lobe and piston?

It just seems strange to have that tight of PtV with short compression distance pistons and a mild(ish) .480" cam.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pacerman Quote  Post ReplyReply Direct Link To This Post Posted: Jan/11/2019 at 9:18pm
Thanks for the comments guys.  Here is the rest of the story.   I am using the raised deck (post 1969) pushrods for this block and they work fine.  I was not able to get zero lash with the short pushrods, so that was a major clue about that.

The piston/valve clearance problem was mostly operator error in the early going.  I misread or misunderstood the timing marks on the Rollmaster crankshaft gear.  If you have used one of these gears, I think you could realize that it is easy to do.  I downloaded the installation diagram from the Rollmaster website and made the correction today.  So with the crank installed straight up (not retarded or advanced) and the head gasket in place, I had .050  P/V clearance on the intake valve, which is still not enough.  Research told me that retarding the cam would increase piston to valve clearance on the intake.  I retarded the cam two degrees and got .100 - .110 clearance which  is satisfactory.  I had a huge amount (.200 or so) on the exhaust valve in my earlier attempts so I did not remeasure that clearance today.  

Why didn't I use a degree wheel?  Well the modeling clay test told me what I needed to know and this is a street engine.  I do not own a degree wheel but may get one for my next engine project.    Thanks again for the comments.  Now to finish this engine .  Joe
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