[250-CI AL H] Measuring pushrod length with adj. pushrod

[62Ranchero200]

Greeting Ford Six Fans:

My 250 block was decked .030 to achieve near zero deck height, and I am using a composite head gasket, which varies from the compressed thickness of the original steel shim gasket. As noted elsewhere, am using the CI aluminum head, which I have been told has the same external dimensions and rocker arm geometry as a stock head.

While this is a straightforward concept - use the adjustable pushrod from CI to measure the correct pushrod length, then order the pushrods from CI - there are a lot of variables here:

I'm using 1.6:1 stamped steel adjustable rocker arms
Soaked the hydraulic lifters in break-in oil and pumped them up about 30 times each with a pushrod, but it's hard to say exactly how pumped up they are compared to normal operation
The measuring pushrod itself is adjustable

With all of these variables, how would you approach this measurement?

Thanks
Bob the Builder

 

[bubba22349]

I think your on the right track except you will need to use a solid lifter to get your push rod measurement. Or you can also gut out a used hyd. lifter check that the face dose not have excessive wear (remove the spring) stack washers in it or make a some type of spacer, JB weld etc. Good luck

 

[62Ranchero200]

I think your on the right track except you will need to use a solid lifter to get your push rod measurement. Or you can also gut out a used hyd. lifter check that the face dose not have excessive wear (remove the spring) stack washers in it or make a some type of spacer, JB weld etc. Good luck

I thought, also, that I should use a solid lifter, because that's what Mike says to use when degreeing the cam. Have done that before, and have a couple of solid lifters I used for that purpose. However, Mike told me not to use a solid lifter for pushrod measurement, because the length of the solid lifter is different than the length of the hydraulic lifter. I guess this is OK for degreeing the cam because you're measuring relative lift, not permanently installing pushrods of that length.

Thanks
Bob

 

[CNC-Dude]

You actually need to preload the lifter just as you would in the engine when you adjust the valves or the pushrods will be too short by however much the lifter is preloaded. You also need to take this opportunity to verify and correct your pushrod geometry, as simply adjusting your pushrod to zero lash rarely gives you the right pushrod length as far as that is concerned.

 

[62Ranchero200]

So if I understand correctly, I need to modify a hydraulic lifter by stacking washers inside or otherwise fixing the plunger at the top of its travel, to simulate a fully pumped up lifter, when I measure the pushrod length. That way, the pushrod will never be too long when the lifter is fully pumped up, which would hold the valve open and result in a burned valve.

Thanks
Bob

 

[bubba22349]

Sorry about that, no that will only give you zero lash you will then need to add about .030 to .060 length for preload and also make sure that when you are measuring with your rocker adjusters so they are set high enough so you still have enough adjustment left (about 1/2 of the threads showing above rocker) With Engine at TDC on compression stroke. Or you can do as CNC-Dude suggested he is a machinist and is being much more accurate, you will be putting the correct preload into the measurement (1 full turn so lifter is compressed to its preload) with the rocker set to correct height. if I remember right the Hyd. lifter piston has about .125 to .150 of travel. Another way you could ball park it, you said that you cut the block .030, plus the comp head gasket depending on brand about .050 minus original steel head gasket about .025. So .030 - .025 = .005 difference not enough to worry about over stock length push rod. With the aluminum head measuring the same dimensions as a stock head then a .005 shorter length push rod would be right for a 170 or 200 but the 250's never came with adjustable rockers and cup type push rods so you would also need to add the 250's extra block deck height too the 200 push rod length. Good luck

 

[jahearne]

There are only 2 or 3 available pushrod lengths for the our motors. Just by all three and return the sets that don't fit. (Sorry Mike, just kidding).

 

[62Ranchero200]

Sorry about that, no that will only give you zero lash you will then need to add about .030 to .060 length for preload and also make sure that when you are measuring with your rocker adjusters so they are set high enough so you still have enough adjustment left (about 1/2 of the threads showing above rocker) With Engine at TDC on compression stroke. Or you can do as CNC-Dude suggested he is a machinist and is being much more accurate, you will be putting the correct preload into the measurement (1 full turn so lifter is compressed to its preload) with the rocker set to correct height. if I remember right the Hyd. lifter piston has about .125 to .150 of travel. Another way you could ball park it, you said that you cut the block .030, plus the comp head gasket depending on brand about .050 minus original steel head gasket about .025. So .030 - .025 = .005 difference not enough to worry about over stock length push rod. With the aluminum head measuring the same dimensions as a stock head then a .005 shorter length push rod would be right for a 170 or 200 but the 250's never came with adjustable rockers and cup type push rods so you would also need to add the 250's extra block deck height too the 200 push rod length. Good luck

Decking the block brings the pushrod end of the rocker arm closer to the lifter, requiring a shorter pushrod (all other factors remaining the same), is that right? A thicker head gasket brings the pushrod end of the rocker arm farther from the lifter, requiring a longer pushrod. It seems to me that these two mods - a .030 decking and a .025 thicker gasket - should nearly cancel each other out, resulting in only a .005 net change. Am I thinking of this incorrectly?

Also, I have an adjustable pushrod made for the 250, so it's already the correct length for a 250.

As @jahearne noted, there are only two sets of ball and cup pushrods (for adjustable rockers) for the 250, from CI: stock length and 1/8" (.125") shorter. It seems to me that I'm extremely likely to end up with the stock length, since the .125" shorter would be way too short. Because the 250 never came from the factory with adjustable rockers, no one else is going to make a cup and ball pushrod for that engine.

Thanks
Bob

 

[bubba22349]

62Ranchero200 wrote: Decking the block brings the pushrod end of the rocker arm closer to the lifter, requiring a shorter pushrod (all other factors remaining the same), is that right?

"Yes"

62Ranchero200 wrote: A thicker head gasket brings the pushrod end of the rocker arm farther from the lifter, requiring a longer pushrod. It seems to me that these two mods - a .030 decking and a .025 thicker gasket - should nearly cancel each other out, resulting in only a .005 net change. Am I thinking of this incorrectly?

"Yes"

62Ranchero200 wrote: Also, I have an adjustable pushrod made for the 250, so it's already the correct length for a 250.

As @jahearne noted, there are only two sets of ball and cup pushrods (for adjustable rockers) for the 250, from CI: stock length and 1/8" (.125") shorter. It seems to me that I'm extremely likely to end up with the stock length, since the .125" shorter would be way too short. Because the 250 never came from the factory with adjustable rockers, no one else is going to make a cup and ball pushrod for that engine.

Thanks
Bob

Your right that the stock length would be the best way to go

 

[xctasy]

I'm a bit upset, can't find my old Breakfast in America post on this. Our Aussie non cross flows had adjustable rocker gear with an approx 8.920" pushrod

1. The adjustable rockers and whatever push-rods you get have to be the right type. There are I guess your on the right track now.





They have to clear the rocker cover





See https://fordsix.com/forum/viewtopic.php?f=3&t=67977
The Aussie forum has some 200, 221 and 250 Aussie info


It's been 7 years since I've had a 221 apart, and I think that from 1968, the 221's got earlier adjustable valve gear, not the same as the US 250. One of addos posts confirmed it. This means the 221 has a "cup to the rocker gear, and a ball to the hydraulic lifter" pushrod. The rockers were designed to have a 3/8" (9.525 mm, 0.375") ball, while the 250 had a ball on the pushrod and a cup on the rocker, to arocker mounted ball.

Stock factory log and 2v 250's are quoted as 8.920" std (ball a lifter, cup to rocker ball for adjustable rocker gear)