No compression with rocker arms torqued

[snowbrd84]

Recently replaced camshaft and had 135-145 psi in cylinders 1-7, 180 in number 8 before.

Boat still seriously lacks power. New compression test today.

1 145
2 145
3 90
4 0
5 150
6 140
7 0
8 145

If I loosen the rocker arm bolts on a bad cylinder all the way, it goes to 145 ish psi.

Tried retorquing to 40 ftlb with cylinder at tdc. Back to zero. At my witts end with this boat. Any thoughts?

 

[stresspoint]

what motor?

did you pre soak the new lifters before fitting?.

were the heads machined.

could you have possibly mixed up the push rods from another motor .

 

[snowbrd84]

7.4 454 flat tappet hydraulic.

Push rods never left the motor and were labeled by cylinder.

Did not soak the lifters but did prime the motor before break in

 

[tpenfield]

Are you following the proper procedure for adjusting the rocker arms to 0-lash? Are the pushrods all the same length?

IIRC, for rocker arms it is not about torque, it is about zero-lash

 

[snowbrd84]

This motor is non adjustable - you are supposed to just torque the rocker arm bolts to 40 ft lbs.

Intake push rods are shorter than exhaust.

 

[tpenfield]

I would double-check the procedure . . .

I may have a service manual that covers the Gen 5 454. Typically you tighten the rocker arm to zero lash and then go about 1/2- 3/4 turn. IIRC, on the Mark 4 it was a full turn past zero-lash.

 

[tpenfield]

Yup, the manual says to torque to 40 ft-lbs. You might want to try setting to zero lash and then go 1 turn on the problem cylinders, to see how that compares.

How far past zero-lash are you having to tighten to reach the 40 lbs?

 

[kenny nunez]

I wonder if the previous owner installed a longer pushrod trying to compensate for the worn cam lobe. It would be worth the while to check and also compare the rocker arm in question with a known good one.

 

[snowbrd84]

All the rocker intake rods are same and all exhaust rods are some. Exhaust posts are further outbound, so longer rods I assume.

Turns out it was only the intake rockers. I was able to tighten them until they lost compression, then back out a little bit and get 150psi on each cylinder. All exhaust torqued to spec.

Now when I start its popping at the carb like crazy.

 

[alldodge]

Suggest,
Pull cam and place on blocks then use dial indicator or lobes to verify lift

Or could try to measure lift at rocker

If lifters where replaced check dimensions in

 

[kenny nunez]

ARP makes a kit that converts your rocker arm bolts to adjustable studs. They are available at either Summit or JEG’S.

 

[alldodge]

Just a thought
swap lifters with one of the other cylinders to see if its stuck lifters

 

[snowbrd84]

ARP makes a kit that converts your rocker arm bolts to adjustable studs. They are available at either Summit or JEG’S.

I'm going to buy these because torque method doesn't work. Setting valve lash the classic way worked. Just redid it and it started without any popping or other sounds.
After setting lash plus 1/3 turn, some would be loose again after cranking to check compression. I basically set them again. The rocker bolt would be finger loose if not.

 

[QBhoy]

All the rocker intake rods are same and all exhaust rods are some. Exhaust posts are further outbound, so longer rods I assume.

Turns out it was only the intake rockers. I was able to tighten them until they lost compression, then back out a little bit and get 150psi on each cylinder. All exhaust torqued to spec.

Now when I start its popping at the carb like crazy.

Definitely set to the correct rotation? She’s not 180 degrees out ?

 

[kenny nunez]

Be sure to get the self lock nuts. If you know any Chevy gurus in your area for any extra advice.

 

[snowbrd84]

Thought u was good but fired it up after buttoning up and lifter tick and then popping through the carb again.

The cam I took out was .310 lift and this one is stock spec .286. Could that make a difference.

Def not 180 out. I have put 10 hours on it before today after the cam swap. It was low on power but ran

 

[QBhoy]

Thought u was good but fired it up after buttoning up and lifter tick and then popping through the carb again.

The cam I took out was .310 lift and this one is stock spec .286. Could that make a difference.

Def not 180 out. I have put 10 hours on it before today after the cam swap. It was low on power but ran

Ah. You might be onto the issue there. Is it a marine cam ? Don’t suppose you’re taking water in with that cam in there ? You could have bent a push rod or tuliped a few valves. This would account for the compression and/or current running condition perhaps.

 

[snowbrd84]

Yes it's a marine cam. Compression all back up to 150 one those intake valves were loosened.

I'm guessing retightening some of them set them too tight once lifters pumped up.

 

[snowbrd84]

Can anyone verify spec push rod lengths for Mark V hydraulic tappet? The ones in here are

Intake: 8 1/4
Exhaust: 9 1/4

 

[alldodge]

Everything you should need to know and more
https://garage.grumpysperformance.com/index.php?threads/big-block-pushrod-guide-plates.4596/