Broken valve train

[Gearhead]

Mystery to me why this happened ?





Just south of longview , just cruising along sunday , a shudder , no real noise , a loss of power. I pulled each spark plug wire , one at a time to find the dead cylinder , #4 was dead. Compression check  revealed the following , #1=185,#2=185,#3=185,#4=30,#5=185,#6=185 . I followed that up with a leakdown test on #4 , that showed 4% leakage , an acceptable number as would be on an otherwise VERY healthy engine. Suspecting a bad lobe on my cam , I removed the valve cover to check for rocker arm movement on the #4 intake valve , it obviously was not drawing in air to compress. What I found is shown above in the pictures.

We'll see if I can get warranty , all chrysler parts are guaranteed for a period of one year , as printed on my reciept. What else is kind of eye opening is , the wear on some of the roller tips of the other rocker arms.

Should I have stayed with the standard rocker arms that were replaced 10,000 km ago ? when the engine was rebuilt. The Mopar roller rockers were installed less than 6,000 km ago and NOT cheap. This , and many other 4.0 engines I've listened to have a slightly rattley sounding valve train , I'm told that this is normal , the roller rockers were intended to quiet the valvetrain somewhat , due to the adjustable nature of the design , allowing the installer the ability of controlling the amount of lifter preload . Standard rocker arms are torqued down , fixed length pushrods are used as well , the technician simply bolts down the rockers and lives with whatever preload that happens to be there , a generic fit but it works.

I should mention , this is a 4.7 , lovingly hand crafted and has been equipped with - - -

+ .060" sealed power pistons , a 4.2 high inertia crankshaft , a rubicon 62mm throttle body , Accell 24 lb/hr injectors , Banks full exhaust system , a professionally ported & polished cylinder head w/3 angle valve job , back cut valves , Mopar roller rockers , Flexolite extreme electric fan , balanced reciprocating group , new ARP fasteners where required , the best of gaskets, new oil and water pump , Comp Cams #68-232-4 valvetrain kit .

I'm sad   , it will get fixed shortly , even if I have to put the standard rocker arms back in.

[Bnine]

What else could it be other then a defective rocker?

I broke a set once. Well, not me actually, but a freind when I swapped my 283 out for a 327. He was helping me get my rig together while I was in class.

 He torqed them all to tight and I snapped 6 of them within the first two days after assembly.

Anyways, long story short is that in my limited experience, when they are torqed to tight, they break almost immediately. Not 6000k down the road..............

Seems strange, I hope it gets covered bud.

[Gearhead]

I had a fast Camaro years ago , back then , it would not be unusual to see that car doing donuts on dry pavement. Pretty much a dukes of hazzard style of driving . I busted a roller rocker on that too , those were cheapo mr gasket brand , the previous owner of that car believed that , being outfitted with roller rockers upped the rev limit to 17,500 rpm. Tough engines , them small block chevy's.

That was then , this is now , I'm a little more refined and mature , and inclined to be nice to this Jeep / engine. I rarely rev this engine over 3500 , feeling there's no need to , it makes all it's power down low and quite happy doing so.

Other possible causes , all of which I've ruled out

  Installer error ? nope  , the other eleven are still working , and the       adjustment ofvalve lash is a no brainer.

  Stuck / seized valve ? nope , I can open the valve with a prybar with no need to use the pry bar to close the valve.

   Broken valvespring ? nope , these are quality springs with lots of life left in them.

Did a valve hit a piston ? , nope , there's enough clearance , there's enough spring , this engine is blueprinted.


bottom line is  ppffffffffffffffff , this engine may be a little messed up but it'll live to see many more adventures.

[Gearhead]

An update and some additional comments...........

Funny no one has mentioned , the pushrod in the above pic looks bent ?

The pushrod is not bent , I have a granite surface plate , it rolls nicely , the picture makes it look bent and there are some rub marks where it had been rubbing after the arm snapped. Preload was set at 1/2 turn from zero lash , each cylinder being set near tdc on the compression stroke. I'll be taking the roller rockers off tonight , inspecting them and temporarily putting the stock rockers back on , the roller mentioned in the first post Is the #4 exhaust , so far I've not looked closely at the others. At first , before I got home and began looking into this , I had suspected a bad cam lobe , not so after checking travel , a visual inspection of the lifter when viewed from the top appears to be normal as does the action of the lifter while cranking , smooth and consistant as it would normally be . The roller tip spins freely on both of the rockers I did remove , even the busted one.

I ordered another pair of roller rocker arms , discussed warranty with the partsman at the dealership , this will be decided soon .


My gut feeling on this is the rocker arm was bad , it failed .When new , I noticed a few nicks here and there , right out of the box , suggesting they had been handled roughly.

My pushrod length as measured on my hieght guage is 9.645" , they are slightly long for this engine , I'll be ordering some that are shorter. The block has been decked , the head has been resurfaced. The stock rockers are back in now , using a dial indicator , I measured the amount of preload at one of the lifters , .050" is what I saw there. Using the 9.645" pushrods the roller rocker arms are at the very begining of the range of adjustment , just scraping by would be an acurate statement , it worked though , each pushrod could be spun with my fingers before preload begins , a little bit of slack would have been better.

The plan is this ........
I had my parts guy order me six oversize intake valves and six oversize exhaust valves. These are to be used on my spare cylinder head. I'm going to port this head and do the necessary seat work to go to + .060" valves . I am ordering some shorter pushrods , the roller rockers are going on this head when it's ready and installed. there's not a thing wrong with the head thats on there right now , It's simply an upgrade , this Jeep being somewhat of a lab rat. I've got a high volume oil pump coming too , the theory on that is , I'm still wanting to have a quieter valvetrain , not that this one is unacceptable , I just think it should be quieter.

Looking at the remaining roller rockers , the # 3 exhaust had some scoring on the roller tip , a few others had some slight wear , When I've got time they'll get checked to see if any are out of round. It would be nice to find some replacement parts for these , the trunion bearings shouldn't be hard to find if ever needed , I'm a little concerned about their method of retention on the roller tips too . If asked to do a product review on these parts , they'd get a low score on quality , though I've not heard of any other failures , I can see weaknesses in the design. This is not the first engine I've built using roller rocker arms , I've used several brands too , choices are limited when shopping for 4.0 hi po parts.


I should mention , with the stock rocker arms back on , the compression is back up to 185 on the # 4 cylinder.

I'll finish up the engine repair part of my weekend carnage tomorrow , follow that up with some welding ( front shackle mount replacement ) , and get my compressor running again ( if it's not pooched  ) , that should get me ready for days off and more wheeling in a few short days.

[Bnine]

oooohh!!!!

I cant wait to see how the bigger valves do. Think it will take anything noticeable of the bottom end?

How did I know you would go and build all new chains after you came over the other day    

[hps4evr]

i thought i read somewhere that roller ockers from a 304 v8 will fit a 4.0L? might want to confirm this. along with that was the point that the 304 roller roskers were cheaper, and you get a spare set of 2... just a thought.

[Gearhead]

I'm not expecting losses on the bottom of the powerband , the ports on these head castings are small enough that velocity will be maintained. the next cylinder head may end up going on another stroker build , somthing  built for higher rpm. or forced induction. The current engine was built for low rpm grunt. A plan is starting to develop .

The chains , umm    ,  I built three , we chained up once we started seeing more ice flows and had crossed a couple of frozen creeks , then it started getting hilly , most of us chained up on the rear axle only , the pair from you went on Dom's XJ for a short time . I think Dom appreciated the use of them . We'll settle up our chain deal here asap .
C'mon over , I have gifts

[Gearhead]

i thought i read somewhere that roller ockers from a 304 v8 will fit a 4.0L? might want to confirm this. along with that was the point that the 304 roller roskers were cheaper, and you get a spare set of 2... just a thought.

I think the mounting stud on those is 3/8" , a  4.0 is 5/16" with not a lot of room for upsizing the hole.

[Gearhead]

It's fixed  :twisted:

Runs nice again  

Standard rocker arms back on til the Mopar roller rocker issues get resolved , I've ordered a replacement pair , possibility of those being warrranty ??

Frame fixed , the right front shackle was only being held on by a small speck of pidgeon poo weld and a slight up draft at highway speed. New shackle installed and welded properly  

All that's left for repairs is the compressor , it's on a 30 amp circuit breaker which trips as soon as the switch is turned on , hmmmmmm , warranty less than six month old Viair 450C , I think I've aired up maybe five times and inflated an air matress three times.

Should I have gone for the York instead ?

[Bnine]

Denise's Viar has run well for a good 2 years now. She has on occasion aired 4 jeeps in a row.

Should be warrenty. They usually hold up pretty well.

I wonder if that breaker is just worn out, and its tripping to easy during start up spike?

You working tomorrow (friday)? Give me a shout. Im in the shop all day after about 2pm.

[Gearhead]

Compressor fixed  

Irocs back on , now they need to be tested  :twisted:

[hps4evr]

did you finally get wheels for your irocs... i hope so...

[Gearhead]

did you finally get wheels for your irocs... i hope so...

Yup ,    Allied rockathons 15 x 10 , black , 32 bolt beadlocks

[Gearhead]

Update / comments on roller rockers / possible warranty


Warranty denied

As relayed by Chrysler partsman ( a bit of a pencil neck)

His call to Mopar performance tech support / help line resulted in "support person" saying the rocker arm was "misaligned " on installation.

My thoughts ? ,  person is a suit , has never built an engine before , didn't give a damn and NOT a good candidate to have in a help line / support position , in otherwords , a dickhead.  Too bad I couldn't have spoken to him directly , the out come may have been more favourable or ......... we could have hurled insults back and forth on the phone , that would have been at the least , entertaining.


Misaligned ?    pppffffffffff  6000km trouble free says otherwise.

Another pair of rocker arms will be here next week , I'm a little nervous about using these rocker arms anymore , the roller tips appear to be quite soft .


My oversize valves are here , as well as  the high volume oil pump and double roller timing chain. All Mopar performance items , my way of supporting Chrysler and showing product loyalty , too bad the support part is a one way deal !

The standard rocker arms , installed last week are just fine , engine runs great.

[hps4evr]

throw some pics up of your yj on the irocs!!! they fir nice? any rubbing?