4.2 Rattling top end problem

City
Halifax
State
UK
#1
Best off watching the video but does anyone know how much sideways movement there should be on a rocker arm?.
I ran the engine for 10-15 seconds to make sure the lifters were primed before taking the video.
The engine was rebuilt 4ish years ago and has only done about 2500 miles but its had a tick for a while, sounds worse when warm and increases in clattering noise with the revs.
Thought i had a dodgy or sticking lifter so put some thicker oil in just to try that but it made no difference so took rocker cover off and found this.
Lifters, Push rods, Rockerarms and bearings were Melling and brand new, valves and springs were new and installed by an engine shop, there is no play in the lifters or push rods that i can tell just this side to side movement!.
Engine runs great and sounds amazing from the exhaust but the top end clatter is doing my head in as it reverberates around the half cab and i assume this is whats causing it.
I dont have another 4.2 to compare it with so maybe its normal for a bit of noise but would appreciate some input from you lot who own them please!

 

Kane

CJ-8 Member
CJ-8.com Member
City
Berlin
State
ct
#3
In the chevy world the lifters need a minimum .020 preload. I woukd venture this would be a good start when checking yours.
 
City
Halifax
State
UK
#5
Thats an excellent video,
So f the preload was right then i guess it wouldn't be so easy to do the side to side movement as the slack should be taken up by the lifters or is that me just hoping its simply an easy pushrod fix???
 
City
Halifax
State
UK
#6
Well i have done some digging out of the original engine parts and it appears the new push rods are longer (but possibly just less worn on the balls) than the originals and the rocker arms themselves have a far more pronounced curve to them on the original ones than the new ones.
Bit hard to tell from the photo but the left hand rocker is original.
I trial fitted an original rocker arm on a new pushrod and its nice and tight on the valve with minimal sideways motion.
So would it be a good idea fitting the original rocker arms after leaving it a couple of days for the lifters to leak off a bit or am i asking for bent push rods and valves????

Edit to this- Reading up and watching Moses video i hadn't realised how important the clearances are for this and looks like i have wrongly just assumed the lifters would take up the clearance required as there is no adjustment on the rocker arms.
There appears to be a lack of pushrod information for the 1981 year of engine that i have too to tell me what should be in there so looks like i had better do the job properly and get measuring.
I think its the new rocker arms that are causing my rattling issue but i dont want to start bending parts by installing the old rockers on the new pushrods but there is a clear difference in shape and appearance with the new arms against the old ones now i have them side by side.
 

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Kane

CJ-8 Member
CJ-8.com Member
City
Berlin
State
ct
#7
Buy an adjustable pushrod from summit racing and use that to find out your length. I had to do that in order to get thr right size for my 4.0 head conversion. There was too much mixed info on the web for me to trust it.
 
City
Halifax
State
UK
#8
Buy an adjustable pushrod from summit racing and use that to find out your length. I had to do that in order to get thr right size for my 4.0 head conversion. There was too much mixed info on the web for me to trust it.
Thanks for that Kane i think i am going to have to do just that to be certain as you are right it is very murky indeed is all the information but i think i may of sussed out whats going on.

If anyone's still interested in my tip tapping woes then here is the continuing saga of what i have found by a bit of measuring with some quite large micrometers.
The old push rods are 9.627ish long or thereabouts so 9.622 is nearest as a standard size and the new ones are 9.696ish so 9.700 is nearest as a standard size.
This does mean that there is quite a large 0.078" difference between the two, so it may be very fortunate for me that the new rocker arms are definitely a different shape and arc to the old ones that were taken out.
Even so That 0.078" extra on the push rods seems to still not be quite enough to give me enough preload on the valves due to the rockers differences.
So i have come to the conclusion that the engine i have is either an early 81 or possibly pre 81 and uses different rockers and pushrods than the ones that were supplied for my rebuild..

I wont know for sure without an adjustable pushrod but i am thinking that the original pushrods and rocker arms would be exactly whats needed for this engine and that the new rocker arms and pushrods are now scrap metal.
Just glad i hoarded the old parts or i would be clueless now!
Just kicking myself a bit for not checking all the parts against the new ones when i fitted them all ages ago, really should know better owning a Jeep :oops:
 

Kane

CJ-8 Member
CJ-8.com Member
City
Berlin
State
ct
#9
There are a couple other factors that can mess with your pushrod length, head gasket thickness, how much the block was decked and how much was the cylinder head machined. If you had a valve job how deep did they cut it? All of this will mess with that final measurement and require custom pushrods.
 

Mancunian

Basic User
CJ-8.com Member
City
Bridgeport
State
WV
#10
Suggest you measure the difference between the rocker arms,
Try measuring the height of the valve face with the rocker down on a flat surface, use something eg 0.25 x ~1" bolt with threads up (round the end if you can, or make it a point) to set push rod side height, measure from flat surface (table) up to the valve face with a shim stack. You need to set it so that the rocker arm is roughly horizontal.

I'm wondering why it's not possible to remove push rod ends and shorten them - maybe pressed on?

Also it should be fairly easy to make an adjustable pushrod if you have access to a lathe and are cheap like me, that's where i'm headed as you have me worried about my engine now.

Another thought, is it possible to back off both arm capscrews until there is no pre-load on the pushrod(s) and then determine how many turn(s) required to tighten down? Quick and dirty - but my guess is that there should be ~1/2 turn for 25 thou preload. Make sure both lifters are on the heel of the cam.....
 
City
Halifax
State
UK
#11
There are a couple other factors that can mess with your pushrod length, head gasket thickness, how much the block was decked and how much was the cylinder head machined. If you had a valve job how deep did they cut it? All of this will mess with that final measurement and require custom pushrods.
The head was stripped and cleaned but no machining was done at all at the shop so there is the head gasket, new valves along with a little bit of valve grinding in that could make a bit of difference to it all.
I still think this is my fault this for buying and installing the new parts not thinking to check them against the old or if i did then i just assumed the push rods were worn or the lifters would do the rest of the job for me.
It was a while ago now when i did all this it isn't 4 years like i put in the first post its more likely 6 years!.

Suggest you measure the difference between the rocker arms,
Try measuring the height of the valve face with the rocker down on a flat surface, use something eg 0.25 x ~1" bolt with threads up (round the end if you can, or make it a point) to set push rod side height, measure from flat surface (table) up to the valve face with a shim stack. You need to set it so that the rocker arm is roughly horizontal.

I'm wondering why it's not possible to remove push rod ends and shorten them - maybe pressed on?

Also it should be fairly easy to make an adjustable pushrod if you have access to a lathe and are cheap like me, that's where i'm headed as you have me worried about my engine now.

Another thought, is it possible to back off both arm capscrews until there is no pre-load on the pushrod(s) and then determine how many turn(s) required to tighten down? Quick and dirty - but my guess is that there should be ~1/2 turn for 25 thou preload. Make sure both lifters are on the heel of the cam.....
You forget this is a Jeep engine Mancunian and there is no adjustment available to make the only way to adjust is change the pushrod for a different one.
But yes i am cheap so think i need to butcher one of these pushrods and make an adjustable one to get me a measure of where i need to be to double check my theory before i go any further.
 

Kane

CJ-8 Member
CJ-8.com Member
City
Berlin
State
ct
#14
Yeah I didn't know your location. Got it. Well they are hollow so taping and dropping some threaded rod in one should me easy enough.
 
City
Halifax
State
UK
#15
Hadnt realised the location thing wasnt on the forum anymore but you read my mind Kane!.
Took 10 minutes in the engineering shop to whip one up in the lathe or should i say it took a man who knows what he is doing 10 minutes, i would still be there now with a broken drill and a tap wedged in it if it were me doing it!!.
 

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City
Halifax
State
UK
#16
And adjusted to take up the slack it read 9.606.
so if i add the 0.020 for preload then it gives me 9.626 which is 0.004" off what i think my push rods are (9.622) and 0.001" off what i measured the push rods as with the micrometer so i think i can live with that bit of rough measuring.
Wont know without putting it all back together for sure but hopefully the rattling problem is solved and no damage has been done.
Just need to wait for some new 9.622 push rods to appear now as the old ones have carbon issues, the rockers will clean up nicely though.

Just for comparison here are the rocker arms next to each other with the only straight edge i had to hand, there is quite a lot of difference now i look properly :o
 

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City
Halifax
State
UK
#17
Just a quick update after i have installed the new 9.622" (standard) push rods with the original rocker arms.
Only done about 10 miles but i would say that the rattling noise that was annoying me is no more.
Feels to have a bit more power too, but i may be imagining that as its possible i am just throttling it more as its now quieter.
Will be interested to see what its like with a few more miles on it, hopefully its now cured of the noise and i can get to drive it in the sunshine for a while.

Thanks for the advice and suggestions everyone!
Dave
 

sxer

Legacy Registered User
City
Little Falls
State
Mn
#19
In 81 there were two different length push rods. When I rebuilt my 81 4.2 I ordered new push rods. When I started it the first time, it ran ok but had a miss at idle. After scratching my head for awhile and checking all the obvious things, I did a compression test. A couple cylinders had no compression. I found the valves were never fully closing on those cylinders. Long story short I measured the old push rods and found they were slightly shorter. Ordered correct ones and it now runs perfectly.
 

BigAl

Basic User
City
Prattville
State
AL
#20
Just rectified this problem on mine. Way whole lot easier for an old man to install push rods while on an engine stand than when in a Scrambler. I can't raise my arms. Well, enough to drink a beer, not enough to change a light bulb. Mine ran good, just rattled.my push rods were .027 too short.
 
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