New Cylinder Heads = No Compression???


FATHERnSON

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Hey - New user here and looking for some help

I have a 2000 Mazda B4000 with a 4.0 OHV V6... I blew a head gasket and decided to just do a whole rebuild on the heads. I replaced valves, rocker arms, and pushrods on those old heads, but could not get the compression to start. Come to find out, my heads are cracked and valve seats are sunk, so I replace the heads and move all the parts onto the new ones. When I install those, the engine will not start, and I had no compression in four of my six cylinders whereas before it was just low. Once I backed off my rocker arms shaft support bolts down to 15 ft. lbs. from 50 I got compression back. Can I run the engine on that loose of bolts and if not what should I do? After cross-referencing casting numbers on the block, old heads, and parts supplier info I know these new heads are indeed correct. Our current plan is to buy a rocker arm pedestal shim kit so we can torque it to spec while keeping compression. Any thoughts or advice is appreciated!
 


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adsm08

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Which two cylinders had compression?
 

FATHERnSON

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Purchased the shim kit and should be arriving tomorrow... Another thing I forgot to mention is that currently there is a gap between the rocker arm and valve stem on the exhaust valve on cylinder four. If that does not clear up with the kit, what is my option? I know its probably a dead lifter, but I do not want to replace that; possibly a different pushrod that is long enough to close that gap?
 

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Putting a longer pushrod on a collapsed lifter is like putting make up over melanoma. Take it apart and see what's going on, it may be a worn out lobe and lifter and not just a collapsed lifter. If you don't have time to do it right will you have time to do it over?
 

FATHERnSON

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That's a good point... Are there any risks if I just leave it as is and fix at a later time???
 

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If it's a worn lobe or lifter it's shedding metal particles into the oil, the longer you run it the more damage you'll have.
 

55trucker

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Are you sure the new pushrod lengths are correct?
Are you also sure that the valves you installed into those replacement heads are 1. the proper installed height & 2. seated properly?.....you didn't make any mention of either.
Have the lifters pumped up & are not draining?
 
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RonD

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Remove rocker assembly and put a straight edge on the valve stems to make sure they are ALL the same height

Pull out all the pushrods and do the same, lay them flat with a straight edge at each end to make sure they are all the same length, and yes I think 5.5" was stock length, 5.475

Something is wrong, done many 4.0l OHV heads and never ran into this issue
 

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The shim kit won't work. To my knowledge, I installed the valves correctly. It seemed rather simple and I followed the manual: compress spring, remove keepers, remove valve, replace valve stem seal, then reassemble it. I am not aware of any height adjustment of the valves on these heads. I believe them to be seated properly as the heads are brand new, but I am not currently looking at them (they're on the truck). I will do the straightedge test tomorrow. All of the lifters are rather stiff. Had one totally shot and replaced it. Should I replace all of the lifters; we decided not to, but I am not familiar with how much they are supposed to compress. I know the issue is not the pushrod length because I swapped out my new rods with my old ones and the problem did not change. I was thinking I may have to just pull the heads again and replace the lifters. If the valves are seated all level is that what I should do???
 

FATHERnSON

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to 19walt93's bit about the pushrod gap; would replacing the lifter fix that if the lifter is worn close up that gap?
 

55trucker

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There is no *height* adjustment of the valves, the height is a predetermined value that is calculated into the valve train geometry, one will not find the value in a ford service manual, one would have to approach a machine shop & ask the employee what the specs are for this particular cylinder head.
If the valves are new as in *unused* then their overall length, margin, face diameter will be in spec, if the heads have had the seats reground sometime in the past & whoever did the job opened the seats up too much then the installed valves will be *sunk* into the head & possibly the stems extending too far above the spring seats. If this is what has happened then the *installed height* will be out of spec & the valve might be staying open when the rockers arms are tightened down to the proper torque spec & putting too much pressure on the valve stem tip.

To check the *installed height* one does so with the head on a bench, springs removed, one slides in a valve & bottoms it, making use of a vernier caliper one extends the caliper slide to measure the distance from the end of the valve stem to the valve spring seat surface. That is the installed height.

Valve stem installed height.
 
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FATHERnSON

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The valves and heads are brand new so then the installed height is correct. I tested that the heads were sealed with the valves in by pouring brake clean into the grooves; it did not leak
 

55trucker

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Please define *Brand new*?........as in 20+ year old Ford castings that have never seen use at all?........the only way to know for sure what the installed height is ....is to measure it, don't assume,
You've lost me on *pouring brake clean into the grooves*

the way to test for leaking valves is done on a bench, assemble all of the valve train, to test the intakes turn the head on it's back exhaust ports down, place a block of wood if needed under the casting so the intake port openings are horizontal........now pour warm water into the ports & fill them up completely....now you wait...if after approx 3 mins you do not see any sign of dampness around the valve head you can safely assume that valve is sealing, if you DO see dampness then that valve is not sealing.
Now drain out the water & flip the head over & do the same for the exhaust valves......after you've completely finished disassemble everything & high pressure air spray all that was wet & then some WD-40 on the parts.

Everything that didn't seal needs work.............
 

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The valves and heads are brand new so then the installed height is correct. I tested that the heads were sealed with the valves in by pouring brake clean into the grooves; it did not leak
"New heads" to me, means heads came completely assembled, valves installed

Did you install the valves in the head?
and if so you need to do a "Valve job", i.e. grinding seats to match valve angles, Google: valve seat angles
 


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