custom length pushrods are needed for a hybrid

[923.4v6]

Just to let everyone know when doing a hybrid you will need custom length pushrods. I had a hybrid with 3400 heads and I ordered custom pushrods for it ( they were probably milled ). When I went to my 3500 heads I installed the same pushrods and they had a little tick but the engine would show 97 mph in the 1/4 in my datalogs. My knock counts kept rolling so I ordered pushrods for a 92 cavi and the were on long side even after I installed shims under the rockers. They brought my mph down to 85-86 and would not crank over 5400 when it was cranking 6200. Since they didn't help the knock count from rolling the shorter ones will be put back in untill I can order some custom length ones.

[SappySE107]

Did you measure how long you need them to be? Shimming rockers isn't how I would go about it and basing length off mph in the 1/4 doesn't make any sense at all to me.

[923.4v6]

Did you measure how long you need them to be? Shimming rockers isn't how I would go about it and basing length off mph in the 1/4 doesn't make any sense at all to me.

No, but I can get a good estimate based off the custom ones I have that has a little tick. I figured since they make shims for the ford pedestal rockers I could shim mine a little (only about .030). The engine was cranking 6200 in 1st, 6000 in 2nd, and 5800 in 3rd now it will only crank 5400 in 1st, 5200 in 2nd, and 4900 in 3rd and thats with a crane 272 cam. After installing the shims the rockers still tighten down 1.5 turns from 0 lash. I pefer 1/2 a turn.

[SappySE107]

you are changing the geometry of the rocker arm when you raise it, and it is now riding on a different spot of the valve stem tip. This could potentially be bad, but you would have to check.

You need to measure the length you need, based on proper preload.

[923.4v6]

just checked the ones I custom ordered the exh are 6.300 so I'd say I'll be ordering 6.320-6.325 stock appears to be around 6.390. The stock int. seemed to work with .030 shims. Here are the ones they offer for ford's http://cgi.ebay.com/ebaymotors/Ford-...Q5fAccessories but I wouldn't even think of going up to a .060 though.

[SappySE107]

how much preload are you giving them?

[ForcedFirebird]

Did you measure preload? How do you know if they are too long? New cam(they also can vary from mfgr)? I measured .050" preload. When I get back to the shop monday, I'll measure a stock 3500.

Also don't forget the 3500 heads could have different rocker bolts depending on the year of the 3400 heads.

Ben, think adjustable rocker arms help? If so, you will need to modify the 3400 pushrod guides, of grind the head for them to be used. I'm going to be swapping to the full rollers and measure the contact point of the roller tip.

Here's a good article about valve train geometry...

http://www.circletrack.com/techarticles/ctrp_0611_rocker_arm_valvetrain_geometry/index.html

and

http://www.compcams.com/information/Products/Pushrods/

[923.4v6]

With the 3400 heads I tried to go with .025 preload. Crane cams told me to shoot for .020-.040 and I like mine on the loose side. Looks like using the same length pushrods with adjustable rockers would be the same as using shims since your adjusting the rocker highth with the nut. Force I think .050 is on the tight side but like I said I like mine on the loose side.

[923.4v6]

well I just called comp cams and they said between .030-.060 preload and sais it would be about 1/2 turn. After shimming mines going 1 1/4-1 1/2 turns which is way to tight. And forced I would stick with your .050. Crane must have told me wrong?

[ForcedFirebird]

http://www.holley.com/data/Products/Technical/INST150.pdf

On engines with non-adjustable rocker arms, you must have a lifter pre-load of .020” to .060”. (See “Setting Lifter Pre-Load” in this instruction sheet.) Use the same sequence as above.

Setting lifter pre-load in hydraulic lifters on engines with NON-Adjustable rocker arms:
Lifter pre-load (the distance the lifter plunger is depressed by the pushrod) should be between .020” and .060”. Too little
load or no pre-load will result in very noisy operation while the engine is running. Too much pre-load may cause the engine
idle rough, have very low manifold vacuum, and/or poor low-RPM throttle response.
With all adjusters fully backed off, torque all bolts for rockers, shafts or stands to proper specs. As always, NEW LIFTERS

[923.4v6]

There all different
crane cams .020-.040
comp cams .030-.060
holley .020-.060
but my 6.300 only makes 0 lash no preload which puts me about 6.330. But like someone said all cams will vary and they will vary from one lobe to the other or at least on my cam.

[ForcedFirebird]

You have over .080" preload if you are counting the turns just after the pushrod will stand up on it's own. 10mm1.5 threads, so 1.5x1.5/25.4=.080" You valtrain should be exceptionally quiet?

[923.4v6]

You have over .080" preload if you are counting the turns just after the pushrod will stand up on it's own. 10mm1.5 threads, so 1.5x1.5/25.4=.080" You valtrain should be exceptionally quiet?

O its quite it just doesn't want to crank very many rpms now. From my experience I wish I had went with adjustable rockers also. And if thats .080 with 1 turn i'm probably at about .100-.120.

[ForcedFirebird]

OK. I miss-understood that you were getting longer than stock Cavi pushrods, but you are getting longer than the other custom ones you have. I'm at a loss, though because there shouldn't be that much of a difference, even if the heads were shaved to the max. You're sayin the pushrods that worked on the 3400 heads are at 0 preload, and the stock flat tappet pushrods are .080" preload. Since the pedistal is non-adjustable on both heads, and the valves are canted (with straight lifters), I can't see this being possible.

[923.4v6]

Well the 3400 heads had a stock cam so there may be a differance. The 6.300" gave it around .025 preload. Those same pushrods with the 3500 heads, same head gaskets,and the 272 cam only made 0 lash no preload.I ordered a set of stock 92 pushrods from advance auto and they were 6.389, which should give me .089 preload give or take. Both also were pedistal rockers. Everyone that does a hybrid needs to check there preload since it will vary engine from engine and can effect performance extremely.