Moparts

340 Engine... How to determine pushrod length??

Posted By: cuda_tim

340 Engine... How to determine pushrod length?? - 09/03/09 12:56 PM

Guys!

I'm preparing my 340 for reassembly and I've been searching (somewhat casually) for the proper method in determining push-rod length. (BTW: I've been known in the past to skip this step and just slap an engine together and see what happens... )

I didn't see anything in the tech area, and even many of the guys at the machine shops aren't sure (unless it is a chevy ).

My 340 has the stock cam, lifters (hydraulic), and non-adjustable rocker shafts/arms. They all mention using a black or blue felt marker to mark the tops of two valves, assembling with two push rods & rocker arms/shaft and rolling the engine over a few times.

Then check the affect that the rocker arm has on the top of the valve.

I can't see how affective this method is with non-adjustable rocker arms, although I think I understand the intent of the procedure.

They also mention using a solid lifter & the adjustable push-rods, to determine the proper length. But they say that the stock lifters can be used (some-how) also.

Basically you lengthen and shorten the adjustable push-rod to achieve the correct imprint on the top of the valve. (Then use that length to order new ones of that length).

Has anyone used this method with non-adjustable rockers?

Any advice would be appreciated.

Thanks!

Tim...
Posted By: mopars4ever

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 01:06 PM

Did you have machine work done to the block? If not and everything is stock I personally would not bother but that`s me.
Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 01:08 PM

Yep sounds like chevy builders doing that will tell you if your rocker to valve tip geomerty is correct but the length of the pushrod will NOT do anything for it since you have a SHAFT MOUNTED system and once you bolt it down and torque to spec it is what it is. You have to use spacers under the shaft OR remove material from the cast stands to change that relationship.

Has the block been decked alot ? heads shaved alot , head gasket thickness vs. original ? These are things that aeffect the pushrod length on big block and small block mopars .
Posted By: cuda_tim

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 01:11 PM

Quote:

Did you have machine work done to the block? If not and everything is stock I personally would not bother but that`s me.



Yes, heads were shaved significantly. In fact, I need to use a shim...

But more importantly, I think I'd like to know the best way to do this...

Tim...
Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 01:15 PM

Quote:

Quote:

Did you have machine work done to the block? If not and everything is stock I personally would not bother but that`s me.



Yes, heads were shaved significantly. In fact, I need to use a shim...

But more importantly, I think I'd like to know the best way to do this...

Tim...



what do you mean ... I NEED TO USE A SHIM ????
Posted By: RapidRobert

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 01:46 PM

From Dave Hughes & co: At 60% of total valve lift (50% if BB) the centerline thru the pushrod and adj screw should be a straight line viewed from the front of the eng. Shorten/lengthen the pushrod and or saddle shims (or milling) to achieve it. 1-2 threads showing and include the lash if it's a solid cam/lifters & if hyd use a junk hyd lifter w the cup welded solid. Then rocker tip side alignment & shims on the shaft to correct that then check the wipe pattern.
Posted By: cuda_tim

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 02:18 PM

Quote:

Quote:

Quote:

Did you have machine work done to the block? If not and everything is stock I personally would not bother but that`s me.



Yes, heads were shaved significantly. In fact, I need to use a shim...

But more importantly, I think I'd like to know the best way to do this...

Tim...



what do you mean ... I NEED TO USE A SHIM ????



Ok, my machine shop performed a valve to piston clearance check for me and they advised using a 0.020 shim, in addition to the normal Fel-Pro head gasket.

I don't remember the numbers exactly (I'm at work), but I think that the numbers fell out like this:

Using the Clay method, the clearance between the intake valve and the piston valve relief was 0.036. They recommended 0.100 on the exhaust side.

If you figure that the Fel-Pro head gasket compresses to 0.039 and the shim is 0.020, this should get me to 0.095.

0.036 + 0.020 + 0.039 = 0.095.

Anybody?

Tim...
Posted By: Challenger 1

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 02:30 PM

Quote:

Quote:

Quote:

Quote:

Did you have machine work done to the block? If not and everything is stock I personally would not bother but that`s me.



Yes, heads were shaved significantly. In fact, I need to use a shim...

But more importantly, I think I'd like to know the best way to do this...

Tim...



what do you mean ... I NEED TO USE A SHIM ????



Ok, my machine shop performed a valve to piston clearance check for me and they advised using a 0.020 shim, in addition to the normal Fel-Pro head gasket.

I don't remember the numbers exactly (I'm at work), but I think that the numbers fell out like this:

Using the Clay method, the clearance between the intake valve and the piston valve relief was 0.036. They recommended 0.100 on the exhaust side.

If you figure that the Fel-Pro head gasket compresses to 0.039 and the shim is 0.020, this should get me to 0.095.

0.036 + 0.020 + 0.039 = 0.095.

Anybody?

Tim...



Never heard of a head gasket shim?
Posted By: repad

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 02:32 PM

I had the same problem when I had the heads shaved .070. The machine shop could not tell me how much shorter my pushrods needed to be. You would think there would be a formula similar to the one used in shaving the intake to fit. I found it easier to get new custom cut pushrods and adjustable rockers.
Posted By: 65vert

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 03:03 PM

End result on 69 340-Chrome moly pushrod through chrome moly rocker arm. Hamburger sells or used to sell adjustable rocker arms which was my net result.
Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 03:19 PM

Quote:

From Dave Hughes & co: At 60% of total valve lift (50% if BB) the centerline thru the pushrod and adj screw should be a straight line viewed from the front of the eng. Shorten/lengthen the pushrod and or saddle shims (or milling) to achieve it. 1-2 threads showing and include the lash if it's a solid cam/lifters & if hyd use a junk hyd lifter w the cup welded solid. Then rocker tip side alignment & shims on the shaft to correct that then check the wipe pattern.



doning my firesuit ...

That's some BAD info from Hughes , I'm surprised ... really , I am ...

Hughes bootlickers , don't waste your energy ...
Posted By: patrick

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 03:21 PM

Quote:

Quote:

Quote:

Quote:

Did you have machine work done to the block? If not and everything is stock I personally would not bother but that`s me.



Yes, heads were shaved significantly. In fact, I need to use a shim...

But more importantly, I think I'd like to know the best way to do this...

Tim...



what do you mean ... I NEED TO USE A SHIM ????



Ok, my machine shop performed a valve to piston clearance check for me and they advised using a 0.020 shim, in addition to the normal Fel-Pro head gasket.

I don't remember the numbers exactly (I'm at work), but I think that the numbers fell out like this:

Using the Clay method, the clearance between the intake valve and the piston valve relief was 0.036. They recommended 0.100 on the exhaust side.

If you figure that the Fel-Pro head gasket compresses to 0.039 and the shim is 0.020, this should get me to 0.095.

0.036 + 0.020 + 0.039 = 0.095.

Anybody?

Tim...



use the standard fel-pros (Q8553PT) they're actually .054" compressed. that'll get you .090" clearance. if you're still concerned, try retarding the camshaft 2 degrees.
Posted By: DUFFMAN

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 05:23 PM

Quote:

You would think there would be a formula similar to the one used in shaving the intake to fit.



P2 = 7.500 - D/Cos(14)

P2 - Desired (new) push rod length
7.500 - Stock small block pushrod length
D - Amount of height removed; Amount milled from heads + Amount shaved of the block deck + head gasket compressed height difference
Posted By: Anonymous

Re: 340 Engine... How to determine pushrod length?? - 09/03/09 09:42 PM

YOU DO NOT ADJUST PUSHROD LENGTH BASED ON VALVE TO PISTON CLEARANCE!!!!!!!!!!!!!!!!!!!!!!!!
Posted By: cuda_tim

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 02:38 AM

Quote:

YOU DO NOT ADJUST PUSHROD LENGTH BASED ON VALVE TO PISTON CLEARANCE!!!!!!!!!!!!!!!!!!!!!!!!



Ok, so when does the pushrod length need to be considered? And how it is verified without adjustable rockers?

My original post only suggests that I would like to determine the length... since I want to make sure it is correct.

Especially since I know that when using the stock cam, (per my machine shop guy) I need to add a shim, since the valve to piston clearance is already tighter than normal.

And especially since I know that (when I disassembled the engine) the intake manifold mounting holes had previously been "hogged out" a great deal in order to get the intake to fit correctly.

Anybody?

Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 01:17 PM

Quote:

Quote:

YOU DO NOT ADJUST PUSHROD LENGTH BASED ON VALVE TO PISTON CLEARANCE!!!!!!!!!!!!!!!!!!!!!!!!



Ok, so when does the pushrod length need to be considered? And how it is verified without adjustable rockers?





when you deck the block and the head A LOT , which sounds like the case here since you don't have enough piston to valve clearance now , take one of your old pushrods put it in place with head on the block and pick a spot in the valley that you can easily get at with wrenches and cut about an inch and half out of it , thread the inside ... FINE THREAD .... get a piece of threaded rod and 2 nuts , wala ADJUSTABLE PUSHROD ... find out the length you need with it .
Posted By: Anonymous

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 03:39 PM

Some of you guys are confused. PUSHROD LENGTH is adjusted to maintain VALVE CLEARANCE "lash" when adjusting valves AND to maintain decent rocker arm geometry. IT HAS NOTHING TO DO with piston to valve clearance. Pushrod lenght is set WITH THE VALVES CLOSED

Piston to valve clearance is determined by cam lift, by valve timing, by the type and height of pistons and deck. Unless I mis--read the type of cam you posted you have very little valve/ piston clearance.

If you need more valve / piston clearance you need to

go to a lower lift cam

go to lower ratio rockers which also lower the lift

Buy different pistons with deeper reliefs

Figure a way to cut deeper reliefs--not a backyard project for the usual shadetree--these must be milled, the pistons re--balanced and quite possibly the engine rebalanced


I'm starting to wonder if this entire question is not mis construed. Maybe you have more piston / valve clearance than you were told?? In any case pushrod length is NOT the answer
Posted By: patrick

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 04:28 PM

Quote:

Some of you guys are confused. PUSHROD LENGTH is adjusted to maintain VALVE CLEARANCE "lash" when adjusting valves AND to maintain decent rocker arm geometry. IT HAS NOTHING TO DO with piston to valve clearance. Pushrod lenght is set WITH THE VALVES CLOSED

Piston to valve clearance is determined by cam lift, by valve timing, by the type and height of pistons and deck. Unless I mis--read the type of cam you posted you have very little valve/ piston clearance.

If you need more valve / piston clearance you need to

go to a lower lift cam

go to lower ratio rockers which also lower the lift

Buy different pistons with deeper reliefs

Figure a way to cut deeper reliefs--not a backyard project for the usual shadetree--these must be milled, the pistons re--balanced and quite possibly the engine rebalanced


I'm starting to wonder if this entire question is not mis construed. Maybe you have more piston / valve clearance than you were told?? In any case pushrod length is NOT the answer



another way to change valve to piston clearance is to change the cam timing. moving the ICL around can drastically change V-P clearance.
Posted By: B G Racing

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 04:31 PM

Using stock non-adjustable rockers and hydraulic lifters you need only bolt on the rocker assembly,find the distance(adjustable pushrod ball&ball ends)and at rest,valve 100% closed add your desired preload(start the plunger downward)Lock your adjustment on the pushrod and you have your proper length.Make sure you are on the(bottom) of the cam lobe at true basecircle.
Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 07:11 PM

Quote:

Some of you guys are confused. PUSHROD LENGTH is adjusted to maintain VALVE CLEARANCE "lash" when adjusting valves AND to maintain decent rocker arm geometry. IT HAS NOTHING TO DO with piston to valve clearance. Pushrod length is set WITH THE VALVES CLOSED





The only person confused here seems to be YOU , no one said anything, anywhere, in this thread about adjusting piston to valve clearance with the length of the pushrods till you brought it up .

If you go back and reread you'll see he was told to use a HEAD GASKET SHIM to regain his piston to valve clearance .
Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 07:11 PM

Quote:

Using stock non-adjustable rockers and hydraulic lifters you need only bolt on the rocker assembly,find the distance(adjustable pushrod ball&ball ends)and at rest,valve 100% closed add your desired preload(start the plunger downward)Lock your adjustment on the pushrod and you have your proper length.Make sure you are on the(bottom) of the cam lobe at true basecircle.



Posted By: Evil Spirit

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 08:02 PM

Quote:

Using stock non-adjustable rockers and hydraulic lifters you need only bolt on the rocker assembly,find the distance(adjustable pushrod ball&ball ends)and at rest,valve 100% closed add your desired preload(start the plunger downward)Lock your adjustment on the pushrod and you have your proper length.Make sure you are on the(bottom) of the cam lobe at true basecircle.



And now for the real wrinkle.If whenever the valve job was done, if the heights of the valves weren't equalized (across the tops of the valves) you will have to check every rocker. If you drop a straightedge across the top of the valves and the heights are all over the place, you would either need different length p/rods for each rocker, have to have the ends cut to the right height, or adjustable rockers.
Posted By: patrick

Re: 340 Engine... How to determine pushrod length?? - 09/04/09 09:11 PM

Quote:

Quote:

Using stock non-adjustable rockers and hydraulic lifters you need only bolt on the rocker assembly,find the distance(adjustable pushrod ball&ball ends)and at rest,valve 100% closed add your desired preload(start the plunger downward)Lock your adjustment on the pushrod and you have your proper length.Make sure you are on the(bottom) of the cam lobe at true basecircle.



And now for the real wrinkle.If whenever the valve job was done, if the heights of the valves weren't equalized (across the tops of the valves) you will have to check every rocker. If you drop a straightedge across the top of the valves and the heights are all over the place, you would either need different length p/rods for each rocker, have to have the ends cut to the right height, or adjustable rockers.



aren't we overcomplicating things here? Isn't that part of what the hydraulic lifter's function is for, to soak up the tolerances in the valvetrain? yes, check every position with a length checking pushrod like johnahhahh suggests making (or just buy one) for 0 preload on the lifter plunger, and then look through the summit catalog to find the nearest length pushrod not shorter than that number, and you'll be fine. on a mild hydraulic cam, you won't have aperformance difference if you have .010 preload or .080 preload. it's just not that critical.
Posted By: Evil Spirit

Re: 340 Engine... How to determine pushrod length?? - 09/05/09 01:32 AM



aren't we overcomplicating things here? Isn't that part of what the hydraulic lifter's function is for, to soak up the tolerances in the valvetrain? yes, check every position with a length checking pushrod like johnahhahh suggests making (or just buy one) for 0 preload on the lifter plunger, and then look through the summit catalog to find the nearest length pushrod not shorter than that number, and you'll be fine. on a mild hydraulic cam, you won't have aperformance difference if you have .010 preload or .080 preload. it's just not that critical.



The one time you don't check it is the time it bites ya. I've seen heads that were converted to 2.02's that the intakes weren't set deep enough in the heads - they were .080 lower (from the top side) than the exhausts. Exhaust valves were used, and the seats were deep. It's not that hard to toss a straight edge across the tops and at least see if more attention is needed.
Posted By: Anonymous

Re: 340 Engine... How to determine pushrod length?? - 09/05/09 03:22 AM

Quote:

Quote:

Some of you guys are confused. PUSHROD LENGTH is adjusted to maintain VALVE CLEARANCE "lash" when adjusting valves AND to maintain decent rocker arm geometry. IT HAS NOTHING TO DO with piston to valve clearance. Pushrod length is set WITH THE VALVES CLOSED





The only person confused here seems to be YOU , no one said anything, anywhere, in this thread about adjusting piston to valve clearance with the length of the pushrods till you brought it up .

If you go back and reread you'll see he was told to use a HEAD GASKET SHIM to regain his piston to valve clearance .



!!!! REALLY?????!!!!!

From the OP's very own words:

"Basically you lengthen and shorten the adjustable push-rod to achieve the correct imprint on the top of the valve. (Then use that length to order new ones of that length)."
Posted By: JohnRR

Re: 340 Engine... How to determine pushrod length?? - 09/05/09 01:03 PM

Quote:

Quote:

Quote:

Some of you guys are confused. PUSHROD LENGTH is adjusted to maintain VALVE CLEARANCE "lash" when adjusting valves AND to maintain decent rocker arm geometry. IT HAS NOTHING TO DO with piston to valve clearance. Pushrod length is set WITH THE VALVES CLOSED





The only person confused here seems to be YOU , no one said anything, anywhere, in this thread about adjusting piston to valve clearance with the length of the pushrods till you brought it up .

If you go back and reread you'll see he was told to use a HEAD GASKET SHIM to regain his piston to valve clearance .



!!!! REALLY?????!!!!!

From the OP's very own words:

"Basically you lengthen and shorten the adjustable push-rod to achieve the correct imprint on the top of the valve. (Then use that length to order new ones of that length)."



You still aren't seeing it ... ... he said the imprint on TOP OF THE VALVE , meaning ROCKER TO VALVE TIP GEOMETRY ... which is the wrong line of thought for pushrod length because that doesn't move anything on a SHAFT MOUNTED SYSTEM ... I'm still trying to figure out how him saying rocker scrub across the TIP OF THE VALVE is being TRANSLATED into PISTON TO VALVE CLEARANCE ???

Reading is funDUHmental
Posted By: cuda_tim

Re: 340 Engine... How to determine pushrod length?? - 09/07/09 06:20 PM

Ok, I think I finally got an answer. Thanks, guys!

Just to reiterate, by using an adjustable pushrod, I can determine the length that I need. I do this with the valves completely closed (lifter on the true base circle of the cam lobe). I just need to make sure that the lifter has some pre-load.

Then I use the measured length and buy new ones at least "that" length.

BTW: My machine shop did make sure that all of the valve tips were at the same height (cutting was necessary in many cases). I probably should still check the length of one push rod on each head.

Just to be clear, the valve to piston clearance was not the reason for getting new push-rods. I only want to make sure that the push-rods that I'm using (or need to buy), are the correct length.

Thanks!

Tim...
Posted By: menomoniemopars

Re: 340 Engine... How to determine pushrod length?? - 08/14/10 08:44 PM

Got the same issue right now , need to find proper length pushrod
© 2024 Moparts Forums