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wae
wae PowerDork
1/5/23 12:51 p.m.

1993 Chevy P30 motorhome chassis with a TBI 454.  Miles are unknown for sure - I was told that when I bought it "it had a new motor 12k miles ago" but no corroborating paperwork.  There are some heat tattles on the heads, though, so maybe it got a used engine?  I don't know for certain.  Anyways....

On the way to the Rolex last year, it developed a lifter tick.  I tried some Risoline, but that didn't fix it.  Assuming it was a collapsed lifter, I put a total of 1,200 miles on it to get to Daytona and back and then waited until the last minute to swap lifters.

When I went to put the new lifters in, though, I noticed that one valve stem was significantly shorter than the others.  It stuck out half as much over the retainer compared to its neighbors and then I found a hunk of metal in the top of the head that was roughly valve-diameter.  So I decided to replace that valve. 

With the head off, I'm taking a closer look and noticing that a couple of the valve stems look a little beat up.  One of the rocker arms actually has a hole in it where it is supposed to sit on the valve. (It was bolted down, I just set it next to another rocker for comparison purposes)

Wtf causes that to happen?  I'm going to have to go back and look at the other head, but I don't recall that those valve stems looked worked over at all.  My plan is new valves, new rocker arm, new lifters, and send it.  Am I in bigger trouble than that?

Appleseed
Appleseed MegaDork
1/5/23 1:04 p.m.

The only thing I can think of is extreme seat pressure.  Can you compare the busted rocker's spring height and pounds with one that isn't broken?

Professor_Brap (Forum Supporter)
Professor_Brap (Forum Supporter) UberDork
1/5/23 1:19 p.m.

That's wild. +1 on high seat pressure. 

Asphalt_Gundam
Asphalt_Gundam Reader
1/5/23 1:46 p.m.

The lack of chamfer on the clearly touched up valve tip says the rebuild was a "cheap/quickie" job. 

It could have made a cut into the rocker that lead to failure, IF it contacted in a way to cut into the rocker.

I have seen this before and it was with aftermarket stamped rocker arm set. The arm material was just weak and failed. Basically turned the valve tip and spring vs cam lobe into a hole punch. So if they're a cheap set of replacement rockers that's likely why.

Spring pressure seems unlikely unless one really stiff spring ended up in a set. 

Another possibility is if the valve stuck (guide too tight - it is an exhaust). It's not like the stamped steel rockers are make to handle huge loads. Usually the pushrod would bend but perhaps it wasn't the weak point. This could also be from poor quality control on a replacement valve where the stem ended up big. Typically only two valves are used to set a gauge for measuring clearance.....if it was even measured at all (see no chamfer on valve tip for indication of low quality job). 

L5wolvesf
L5wolvesf Dork
1/5/23 5:54 p.m.

Many years ago I had a Pontiac wagon for towing to races – very similar valve train. On the way to RIR I heard a loud ticking and then a loss of power. When we got to the track I pulled the rocker cover and saw a somewhat similar thing. In my case the push rod had worn through the rocker and firmly wedged itself into the rocker. I pulled the other rocker out and went V7 for quite a while.

As I recall it seemed like that rocker wasn’t getting any oil.

Carl Heideman
Carl Heideman
1/5/23 9:19 p.m.

+1 on oil to the rocker. 

wae
wae PowerDork
1/5/23 10:25 p.m.

I don't recall that any of the rockers seemed especially dry.  I can check the pushrods, though, to make sure they're all open.  If the lifter was bad, that could cause a problem with oiling up the pushrod, couldn't it?

I'll have to check the rockers for stampings that might indicate if they're original or aftermarket.  I have no idea if that's been opened up before, but the head gasket just sort of looked more like a Fel Pro to me.  Again, I can check it for markings.

Several of the valves were a bit mushroomed on the tip of their stems when I took them out.  I had to hit some with a file to get them to slide out of the guides.  I'm not sure any of them were machined deliberately.  The other side's valve stems all looked perfect, which is kind of weird.

wae
wae PowerDork
1/6/23 9:13 a.m.

I went over and checked the valve stems on the left head this morning.  They all look fine to me - mostly squared off edges and no indication that they've been beat up:

I forgot to grab the pushrods to see if any were clogged. 

Would this be a plausible theory: the lifter failed in such a way that it is fully "lifted" which made the effective length of the pushrod too long, beat up the rocker, and then the bits of metal flying around in the head damaged the other stems?

My only interest in the "why" is that if there's a high-probability that whatever caused that rocker to generate a hole is some bigger issue, then I'll start trying to figure out how I get the block out.  But if it's more likely that cleaning things up, replacing the lifters, pushrods, and (some of) the valves will take care of things, then I'm fairly good to go.

Although, what's up with exhaust valves?  I can get intake valves all day for $5 each, but exhaust valves are either not available or $30 each....

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/6/23 12:36 p.m.

What beats up the valvetrain is lash.  You may have indeed had a stuck lifter, but driving it with lash in the system beat the hell out of the valve tip and the rocker 

 

Your carnage looks similar, although not as extensive, to a Pontiac 400 that I worked on that someone had installed Rhoads lifters.  You know, the ones with long travel and fast bleed-down to make a cam seem smaller. 

All of the rockers were trashed, all of the valve tips were mushroomed over (no hardened tips in a '69 GTO), and when we realized that, and that the valves were all at different heights, we pulled the heads to replace the valves and found that the exhaust seats had receded almost a quarter inch.  Yes, half the lift was wasted in just opening the exhaust valves past the "seat"!

Asphalt_Gundam
Asphalt_Gundam Reader
1/6/23 3:45 p.m.

I can't tell from the pic but is the bad rocker beat up on the pushrod side too. metal looks like its fatigued (shiny half moon). If it is then the failure was likely a collapsed lifter that made extra lash and was then having a good head of steam on the cam lobe when it slammed into the rocker/valve tip until something failed.

Those expensive exhaust valves are sodium filled. Hollow stem with sodium in it that will become liquefied and increase heat transfer away from the head. Replacing with a quality stainless steel valve would be just fine.

For the overall fix...If it was me....pull the heads, rebuild with new guides and valves and get all new valve train. cam, lifters, rockers, springs, and even pushrods if there's damaged ones

Appleseed
Appleseed MegaDork
1/6/23 7:09 p.m.

In reply to Asphalt_Gundam :

Or check the rebuild cost against an aftermarket budget head.  

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/6/23 7:11 p.m.

In reply to Appleseed :

....that will probably need new springs, and definitely new valve seals, because all of the cheap ones including brand E come with white Nylon garbage and the valve springs are usually way wrong for what you want.

Streetwiseguy
Streetwiseguy MegaDork
1/6/23 8:08 p.m.

Big block Chevs don't really have the finest valve train in the world at the best of times.

ShawnG
ShawnG MegaDork
1/6/23 9:37 p.m.

Ugh, that's the L19 454. 

Too early for roller lifters. 

You're going to break exhaust studs off when you pull the heads, might as well make fixing them somebody else's problem. Just toss on a set of parts store reman cylinder heads with new rockers and pushrods and drive it.

Motorhome service means those exhaust manifolds are probably shot or at least warped to hell too. 

When I had to replace the exhaust manifolds on my tow-beast 460 Ford, it was cheaper to put on a Banks system than it was to replace factory iron manifolds and install a new exhaust.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/7/23 7:52 a.m.

In reply to ShawnG :

The exhaust rockers need to come off to pull the heads?

bentwrench
bentwrench UltraDork
1/7/23 8:37 a.m.

Sorry but, The inside of that motor is filthy, I can't hang.

 

It needs a rebuild.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/7/23 8:41 a.m.
bentwrench said:

Sorry but, The inside of that motor is filthy, I can't hang.

 

It needs a rebuild.

That engine is clean as a whistle inside!

 

I remember pulling valve covers off of some engines and finding a jellymold/sand castle of sludge with the rockers running in little channels in the glop.

Years later I remember scraping a full quart of sludge out of Range Rover oil pans, because when the task before you is so epic the human response is to quantify it for future storytelling.  Powerwashing jelly out of engine blocks and heads at the machine shop before allowing them to go into the parts washer (picture a walk-in dishwasher that has a tank with 250gal of boiling lye).

 

wae
wae PowerDork
1/7/23 9:01 a.m.

...Actually, I was able to get all of the exhaust studs out without breaking a single one.  Didn't even need heat or P'Blaster.  And it already has the Banks headers on it - although I seem to recall Banks telling me that they didn't use an exhaust manifold gasket, but I'm fairly certain that one was baked on there.  The valves have GM part numbers on them but I'm not sure where the rocker arms are from.  They have a stamping on them that sort of looks like a double "E"?

I measured and inspected all the valves.  I'm going to put 4 new intake valves in and replace two of the exhaust valves - two of the originals look perfectly fine while one was used to hole-punch the rocker arm and had to be filed to clear the guide and the other is pitted and beat up a bit.  I've got a rocker arm coming as well as new stem seals.  Just in case anything got bent, I'm putting new pushrods in on the right side as well.  16 new lifters are already in the valley.  Hard parts are Melling, sealing parts are Fel Pro.  Oh, and a new electric fan switch since I broke off the old one when I slipped with a wrench.  Oops.

The lobes on the cam don't look bad and getting the cam out would be quite the challenge.  If this was something that I intended to keep for a long time, I'd very seriously consider a new cam and at least gasket-matching the exhaust ports.  My plan is to go to the Rolex, bring it home, sell it, and buy a travel trailer.  As it is, I'll finally be able to get the timing adjusted a bit since the clamp bolt was a bit stuck and I didn't want to risk breaking anything before.  I'll also be able to ensure that the EGR passages are fully cleaned out in the intake - replacing the EGR valve solved the performance issue I was getting, but I still get a soft code that pops up after running for a while at highway speeds.

Some of the crud that is in there was transferred from the sheet I had over the hole-in-the-floor, but the holes are plugged up to keep anything from falling in.  I figured cleaning things up would be my last step before putting the valve covers on.  I'll agree that it isn't pristine inside, but I have seen way worse.  I've got the head taken apart at the shop and parts should arrive starting Monday.  The most difficult (and expensive) thing to get has been the exhaust valves - more expensive than the ones for the Mercedes!  I'll get it cleaned up, chase all the threads, and get it all put back together.  Fingers crossed.

ShawnG
ShawnG MegaDork
1/7/23 10:07 a.m.
Pete. (l33t FS) said:

In reply to ShawnG :

The exhaust rockers need to come off to pull the heads?

No, but the exhaust manifolds do...

Appleseed
Appleseed MegaDork
1/7/23 11:22 a.m.

In reply to wae :

The fact you didn't snap a bolt ON AN EXHAUST MANIFOLD means you've already won.

A 401 CJ
A 401 CJ SuperDork
1/7/23 2:26 p.m.
L5wolvesf said:

...I pulled the other rocker out and went V7 for quite a while....

I hate digging up tired old tropes and platitudes but it bears repeating: large displacement, low revving, domestic V8s will run poorly longer than most engines will run.

Nockenwelle
Nockenwelle New Reader
1/8/23 12:51 a.m.

Regarding root cause of the original problem, I'll cite two factors already listed: shortage of adequate oiling, and bad valve tip condition. The motor appears to be one of the bastard Mark V (or at least the heads are), cursed with all of its predecessor's issues and none of the later fixes with a sizable helping of new mid-90s GM cost-saving E36 M3 to deal with. It's true that the Big Chevy has a weakness in the valvetrain layout, but mostly just due to mass. It also requires dilligence in setup if you're at all outside the bounds from factory geometry. The design is actually very good, and a large part of why the BBC continues to be a contender in horsepower battles even today with contemporary competition.

For a third: the non-adjustable Mark V rocker bolts are also a very likely conspirator. The premise requires a very specific valve tip height to establish correct lifter preload, and I'll bet that dollar-store valve job didn't get it there. The direct effect using factory-length pushrods is lifter preload, and low tip heights will result in low preload and probably some free lash. The rockers are stamped with the window symbol, which is a GM mark. Not great, but not particularly soft and terrible, so probably not the real problem. You can easily swap to studs with adjustable rocker nuts. Aftermarket roller rockers are widely available. I run steel-bodied Comp Pro Magnum rollers lifters on all of my BBCs.

The valve tips look terrible. Even in the marginal cell phone photos I can see they're not true and very coarse, although maybe flat. The factory valves have hardened tips, and if dressed correctly should last the life of the engine. If dressed improperly and not perfectly aligned to rocker plane, they will become an angry hardened rotary file and easily chew through even an adequate stamped rocker. Remember they rotate. Roller rockers will show uneven witness marks on the tip roller in the same scenario. You might also have some bent rocker bolts.

The springs appear to be completely stock and completely adequate, but should be measured for seat and open pressure. I'd be taking a real hard look at the one that punched through for retainer or lock damage since that was what the business end of the rocker was pounding on. 

Asphalt is correct about the sodium-filled exhaust valves, as well as the suitability of a quality aftermarket stainless replacement, but they also have an oversize 3/8 stem which can be hard to source a replacement for. Good stock valves are the easier option.

I would also be inclined to check out the oil pump. GM only put minimal effort into the oiling on BBCs. The short block will survive a surprisingly long time with poor oiling, but the valvetrain won't. If the pump is in good shape and makes at least 50 psi before bypass, it should be OK. Use a priming tool to verify, and make damn sure you're getting oil thru all 16 pushrods. If you do put a pump on it, don't use a high-volume unit, just increased pressure. If the standard volume pump isn't enough, the motor has an internal leak.

Check out all 16 cam lobes 360 degrees with bright light and the help of an assistant to slowly turn the crank. Easy to see thru the drain-back slots in the valley. Be absolutely sure you're not putting effort, money, and new lifters on a cam with a bad lobe. It's very common. I have refused to built flat-tappet motors since the 90s because I'm tired of lifter mysteries.

If it was mine, the heads come off and get completely gone thru no question. Also not much faith in a short block built by the same shop as the heads.

 

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
1/8/23 7:46 a.m.
ShawnG said:
Pete. (l33t FS) said:

In reply to ShawnG :

The exhaust rockers need to come off to pull the heads?

No, but the exhaust manifolds do...

Chevy uses bolts, not studs.  Anyway that matters little when the head is already on the bench smiley

 

When they break they break in service from the exhaust manifold growing/shrinking with heat, and the bolt or stud being constrained by rust packed in the hole or from some doofus overtightening them or using the wrong hardware so the manifold can't move around under them.  They generally come right out when you put a wrench to them if they are intact.

wae
wae PowerDork
1/8/23 9:53 a.m.

In reply to Pete. (l33t FS) :

This motor had bolts-with-studs-on-them, so I can understand the confusion there.  According to the Banks installation manual, you're supposed to re-use the factory exhaust bolts so I'm assuming that's what these are.  Four of those bolts have a stud on them that holds the spark plug heat shields in place.  I've never seen a brand-new one, but with the layer of rust and whatnot on these, they kind of do look like a stud, rather than a nut.

The more I've been thinking about this, this may not have been the sudden failure that I thought it was.  It always had a little bit of a light "tick-tick-tick" to it, but maybe all my years of being around Triton engines mal-conditioned me to just assume it was an exhaust leak.  It was pretty hard to hear, typically you'd only pick it up when driving next to a wall.  Perhaps that was valve lash noise and after a long while of doing that the rocker arm had enough.  I'll get in there and take a closer look at the cam to be sure it's not wrecked.

If I had better access to this thing, I'd be approaching it very differently.  While getting to the intake, lifter valley, heads, and even the header bolts is incredibly easy through the doghouse, getting to anything on the front of the motor is damned-near impossible.  And getting the motor out whole would probably necessitate removing a $1,000+ windshield that would probably break in the process.  Maybe I could remove the front seats, build a gantry that would go through the side windows, pull the intake and heads, and then lift the block onto a rolling stand sitting on a plywood path to the door, then maybe I could get it through that door after also removing the swivel chair.  Maybe.  Other options include cutting the front cap off or finding a way to lift the coach about 24"-36" to be able to drop the motor down.  Also, if this were my dream coach, or if it was at least sufficient for my needs/wants, I'd be more inclined to be very thorough.  Actually, my fantasy would be to make it a FRED via a Duramax swap.  But, frankly, this coach is just too small for a family of 5 with 200 pounds of dog spread across two units. 

wae
wae PowerDork
1/8/23 12:04 p.m.

Observations from this morning's inspection work:

  • The old head gasket is definitely a Fel Pro, so that thing has been apart in the past at least once.  I don't know if it just got new heads, if the original motor was rebuilt, if it got a whole second motor that was rebuilt, or a used motor was put in, but they took it through the door and had to pull the heads off to make it fit.  There's also an exhaust manifold gasket in place.  That's notable only because Banks says you don't need a gasket with their headers.  I plan to put a gasket on because I'm not sure how clean and flat I'll get everything and it was fine with the gasket before, and it'll match the other side.
  • Turned the engine all the way around to look at the lobes.  They don't look rounded off and the wear patterns look normal.  I'm not saying that the cam looks brand new or anything, but I've seen much worse called good.
  • Pushrods are all clear all the way through and don't appear bent.  No unusual wear.
  • Old lifters have normal wear patterns with halos on the flat tappets.  The tappet for the #3 exhaust valve (the hole-y rocker) has a faint triangle pattern inside the halo
  • There's a bunch of coolant in the oil pan, but I'm assuming that most of that got in there from taking the intake manifold off.  I checked the oil right after we got back from the last trip and there was no milkshake.  I did pull off some oil though to check it and there's no grit and no glitter in it.
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