89 Mustang Pushrod length question - Ford Mustang Forum
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post #1 of 17 (permalink) Old 02-03-2013 Thread Starter
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89 Mustang Pushrod length question

Ok so I have a comp cam p/n 249-35-351-8, gt40x turbo swirl heads, crane 1.72 roller rockers and I need to know if the stock push rods are too long? The lift is .512" intake and exhaust, duration 270/276, with a 114 degree lobe seperation. I think the push rods are too long because the valves are not closing all the way to build proper compression. With 1.6 rockers there are no problems. Has anyone else ran into this problem before? If so, what size push rods are you using?

Thank you in advance.
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post #2 of 17 (permalink) Old 02-03-2013
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Pushrod Length, Question answered.

Many factors come into play here. It all depends on if the block was resurfaced the heads were resurfaced, head gasket thickness. ETC. I would buy or borrow a pushrod checker that way no mather what is going on in your engine you can dial in the correct pushrod length and get the most power out of the engine.
Call Comp Cams (1-800-999-0853 Cam Help) and tell them exactly what you have they may have an off the shelf pushrod to get the job done. Too many times a guy will put an engine together using a mis/mash of parts and the clearances are all over the place. This is one area you want to be right on so that the valve train stays together. Hope this suggestion works for you. Good Luck.
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post #3 of 17 (permalink) Old 02-03-2013
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You need a pushrod length checker (and a 8 in. calipers to accurately measure what it determines):

Trick Flow® Adjustable Pushrod Length Checkers TFS-9000 - SummitRacing.com

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post #4 of 17 (permalink) Old 02-03-2013 Thread Starter
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The block is stock, I used fel pro gasket set for a stock 302. I was doing some research and I think since there rockers are pedistal mount, I may have tightened the bolt too tight? I was reading turn 1/4 to 1/2 turn past zero lash. I will try to properly tighten the hold down bolts first and if that doesn't work, I will buy or borrow a pushrod length checker. Thanks fellas.
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post #5 of 17 (permalink) Old 02-03-2013
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how would you tighten the bolts too tight? they torque to 24fp....YOU NEED TO MEASURE!
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post #6 of 17 (permalink) Old 02-03-2013 Thread Starter
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I tightened the p### out of them. With the cam set up and 1.72 rockers there is very little clearance on the valve springs from keeping the valvs open. I think they are just too tight keeping just enough tension on the valve springs to keep the valve open. I hear air out of the headers on the exhaust side, but when I put my finger over the spark plug hole no air comes out.
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post #7 of 17 (permalink) Old 02-03-2013
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Quote:
Originally Posted by cindys_sn95 View Post
how would you tighten the bolts too tight? they torque to 24fp....YOU NEED TO MEASURE!
+1, you want to tighten the bolts to ~20 ft. lb.; nothing more, nothing less. The 1/2 to 1-1/4 turn equates to 0.020-0.060 in. of preload on the lifters, which is what you want.

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post #8 of 17 (permalink) Old 02-03-2013
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Quote:
Originally Posted by YLDPONY View Post
+1, you want to tighten the bolts to ~20 ft. lb.; nothing more, nothing less. The 1/2 to 1-1/4 turn equates to 0.020-0.060 in. of preload on the lifters, which is what you want.
Don't mean to hijack here but I don't want to needlessly start a new thread since we're already on this topic. My trickflow pushrod length checker has little white dashs on it. The instructions say that every time they line up while you're unscrewing the checker is equal to .050". Couldn't I get close enough using that method combined with checking the contact pattern on the valve stem? I'm using scorpion 1.6 pedestal mounted roller rockers now so I should be able to see the pattern better then with the factory stamped rockers. I don't have a set of 8" calipers so that's why I'm asking.
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post #9 of 17 (permalink) Old 02-03-2013
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that would do it.
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Quote:
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that would do it.
Cool beans thanks
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+1, I'd probably trust Trick Flow's denoted measurements. Just be sure you know where you're starting (if you're starting at 5.950 in. or 6.000 in. etc.).

With pedestal mount rockers the contact pattern is second hand, and you don't have a lot of room to adjust it. At least the way I see it, it's almost fixed (correct me if I'm wrong). Pedestal rockers usually have a few shims you can change the height they're mounted at, but they are small measurements (0.090 in. max for my case) and that's it.

If you have a pushrod length that gives you 0.020-0.060 in. of preload on the lifter while using no shims, one shim, or maybe even two shims under the pedestal your contact pattern better be good.

I say this for two reasons:
  1. In the instructions that came with my Crane 1.7:1 roller rockers they didn't not say anything about checking the contact pattern
  2. Given the adjustability (when compared to stud mount rockers) it makes perfect sense to me

'94 Laser red 'vert. Still a 5-oh... for now
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post #12 of 17 (permalink) Old 02-04-2013 Thread Starter
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Ok so further checking, I loosened them and retourqued to proper spec, it fired off but ran like crap. It turns out that I am experiencing coil bind. I am going to just sell the 1.72's and get some 1.6's. It's cheaper to replace rockers than the springs, pushrods, etc.
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Well I had to reread this all over.....so how do you know that the 1.6 rockers will work?

The problem is the pushrods not the springs.

2014 V6 Deep Impact Blue Mustang, Borla Type S, 2.73 (Uughh need 3.73)
1989 Sonic Blue Mustang LX Coupe, 349 ci,
392 rwhp 424 rwtq....Mustang Dyno
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Somehow, I have a very bad feeling about these proceedings...

Quote:
Originally Posted by Smurf stang View Post
how do you know that the 1.6 rockers will work?
302/351W "X-HEAD" ALUMINUM ASSEMBLED 58CC

According to FRPP, even with 1.72:1 roller rockers (0.552 in. net lift) the springs that the heads come with should be good.

'94 Laser red 'vert. Still a 5-oh... for now
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I am more concerned about pushrod length.

Plus using stock pushrods is another recipe for disaster.

2014 V6 Deep Impact Blue Mustang, Borla Type S, 2.73 (Uughh need 3.73)
1989 Sonic Blue Mustang LX Coupe, 349 ci,
392 rwhp 424 rwtq....Mustang Dyno
"There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." -Will Rogers-
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