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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Mike Phillips on November 10, 2009, 07:53:51 pm
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No compression in #8 cylinder - 454 Magnum
***Update***
More engine problems.
As most of the regulars on this forum know I put a 454 Magnum Marine engine in a 1975 GMC Jimmy in June. Bought it from a friend that had it rebuilt for a boat then junked out the boat and I bought the motor. Long story short, after 500 miles 2 rocker arms failed on passenger side. Had mechanic friend replace them and since then the engine has ran great until about 3-4 weeks ago.
Now engine is starting to running crappy again so I had a local reputable shop diagnose and they said there is no compression in #8 cylinder.
Truck has about 1000 miles on engine. Starts and runs okay, runs only mildly rough at idle and runs rougher over about 55 miles per hour.
I'll pull the valve passenger side valve cover tomorrow and do a visual inspection. Anyone want to guess what the problem is? Could it be another failed rocker arm?
Here's the engine,
(http://www.showcargarage.com/gallery/files/1/454MagnumInstalled034.jpg)
(http://www.showcargarage.com/gallery/files/1/454MagnumInstalled036.jpg)
Thanks,
Mike
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Are the rockers standard? If so is the lift on the cam higher than stock rockers can take? It may need a different ratio rocker arm? Don't know if it applies to BBC at all just know I had a problem with a SBC 400 back when I was 16 and didn't know anything. Just starting the dialog, please omit if I am out in left field. My $.01
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All I know is that it's a rebuilt 454 Magnum engine. I don't know and don't think it has a larger than stock camshaft.
:-[
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Mike, A couple questions. You mentioned 2 rockers going before...What 2 (same cylinder, 2 intakes, 2 exhausts) & what happened to them (pushrod push through the cup)? How much running time was on the engine when you got it?
Not to pick on you & compared to the new problems, it's trivial...Paint that steering shaft! That's too nice of engine compartment to have that sticking out there. Keep us posted, Lorne
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Mike, A couple questions. You mentioned 2 rockers going before...What 2 (same cylinder, 2 intakes, 2 exhausts) & what happened to them (pushrod push through the cup)?
It was one rocker on cylinder 3 and 5 I think. I'll have to dig up the bill to confirm but it wasn't cylinder #8
In both cases I believe the pushrod pushed through the cup. My mechanic and friend had to do some research as he'd never worked on this style of engine before and this led him to a performance Marine shop and the owner of the shop said these rocker arms for this engine were known to be weak and break.
How much running time was on the engine when you got it?
Never been fired before. I fired it up new.
Not to pick on you & compared to the new problems, it's trivial...Paint that steering shaft! That's too nice of engine compartment to have that sticking out there. Keep us posted, Lorne
I'm all over it man...
;D
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Oh yeah... the Jimmy flies the Jolly Roger and sports 2 - 9' Surfboards...
(http://www.showcargarage.com/gallery/files/1/1975JimmyPiratesFlag1.jpg)
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Sounds like a new set of roller rockers are in order. You may have bent a valve this time or if your lucky, just bent a pushrod and wedged it enough to keep a valve open. I'll keep my fingers crossed for you.
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Doesn't jive with me....failed rocker arms? Hollow pushrods should fail first. Do a leak down test. Do you have rocker arm studs or bolts?
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Mike P, looks like you live pretty far from the ocean with that desert background....sand surfing?
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Doesn't jive with me....failed rocker arms? Hollow pushrods should fail first. Do a leak down test. Do you have rocker arm studs or bolts?
(http://www.showcargarage.com/gallery/files/1/454JimmyProject015.jpg)
I'll remove the valve cover tomorrow after work and do a visual inspection, couldn't get to it tonight.
If it's another broken rocker arm then I'll be in the market for a some top quality roller rocker arms.
:)
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Doesn't jive with me....failed rocker arms? Hollow pushrods should fail first.
I've seen this several times with stock type rockers on a couple different BBC's...A couple pushrods looked like they could allmost be re-used, just slight deforming around the oil hole & light scuffing on the sides. One just like what Mike is describing...One here & there shortly after a re-build, after several (3-4) the whole set was replaced & no more problems for years.
I agree with you though...The first time I heard/saw it I was going ??? WTH. This was back many years ago (20 or so), before the market was flooded with the cheap off-shore stuff that is out there now. I believed them to be stock, used pieces.
The ones I've seen looked as if the cup was made of plastic or something & the pushrod just popped through, the rest of the rocker was just like normal...One or Two had a crack running down toward the pivot out of the "hole".
I agree on the compression check & look at everything around the rockers closely at & near full lift. Keep us posted, Lorne
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I've seen this several times with stock type rockers on a couple different BBC's...A couple pushrods looked like they could allmost be re-used, just slight deforming around the oil hole & light scuffing on the sides. One just like what Mike is describing...One here & there shortly after a re-build, after several (3-4) the whole set was replaced & no more problems for years.
Valve covers will be coming off in about 8 hours and I'll update this thread with what I see, hope it's fixable without removing the head.
Any suggestions for a quality set of aftermarket rocker arms?
:)
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Are they rocker arm studs or bolts?
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I removed the passenger side valve cover and found the problem... now I'm looking for a great set of roller rockers as well as the root cause of the problem. The local NAPA store has a brand new one in stock I'm going to pick up tomorrow and then I'll baby the engine till I get the root cause of the problem figured out and the new rocker arms to install.
(http://www.showcargarage.com/gallery/files/1/454brokenrocker001.jpg)
(http://www.showcargarage.com/gallery/files/1/454brokenrocker002.jpg)
(http://www.showcargarage.com/gallery/files/1/454brokenrocker003.jpg)
(http://www.showcargarage.com/gallery/files/1/454brokenrocker004.jpg)
(http://www.showcargarage.com/gallery/files/1/454brokenrocker005.jpg)
(http://www.showcargarage.com/gallery/files/1/454brokenrocker006.jpg)
Ouch!
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Wow! that would do it. Have any salvage yards near you?
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Wow! that would do it. Have any salvage yards near you?
Local NAPA store has a brand new on in stock. I'll pick it up tomorrow and install it tomorrow night and baby the engine till I figure out the root cause.
:)
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Local NAPA store has a brand new one in stock.
Brand new and fresh from China.
Once you sort out what is causing it, why not upgrade to these (http://www.summitracing.com/parts/CCA-1411-16/)? They're cheap, strong (as long as open spring pressure is under 350 lbs), and reduce wear on valve guides. Of course, you would have to switch over to studs as well.
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Go with a full roller.... The heads you have allow for no rocker arm adjustment. Are your pushrods the correct length? did you swap in a bigger cam?
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***Update***
First, I was recommended to a local machine shop that works on a lot of marine engines. I explained what happened to the owner of the shop and showed him the broken rocker arms and the first thing he said was, (after looking at my truck),
What kind of valve covers are you running?
I said, some tall Ansen aftermarket valve covers.
He then said that was the problem, the factory engineered valve covers were designed to keep the rockers well lubricated and the tall valve covers I installed were reducing the proper oiling of the valve covers.
He told me to go to the local auto parts store an order a replacement rocker for a newer Gen VI 454 and put the stock valve covers back on.
I called Tim Briggs, one of the best engine builders I've ever known and he said what the shop owner said was probably true. Tim's going to look into a high performance replacement option for my valve train because if the tall valve covers are the root cause then it's likely even though not all rockers have broken they may already be affected. He'll make sure they'll fit under the stock valve covers.
I did order a single replacement rocker arm kit from Advanced Auto parts and also one from NAPA here in Stuart, Florida basing off a 1998 Chevy Suburban with a 454. Keep in mind, I have know idea what this motor came out of but I do have a picture of what it was slated to go into and it could be it came out of this boat too, I just never received a concrete answer to that question.
(http://www.showcargarage.com/gallery/files/1/454JimmyProject016.jpg)
Here's a shot of the stock valve covers, I still have them but they're in Apple Valley, California and I'm having them shipped to me.
(http://www.showcargarage.com/gallery/files/1/454JimmyProject015.jpg)
Anyone agree with the shop owner's assessment that the root cause is the tall valve covers?
Anyone disagree?
:)
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As you can see there is plenty of oil on the rocker arms. I disagree that your valve covers are the problem. You didn't answer my previous questions. Please answer them. Lack of lubrication in these points would cause galling and I see very little from your pics. Either your rocker arms were over tightened or you have a binding condition. You have a roller cam, but is it stock? What valve springs are on there? Are the valve rotators installed? Keep in mind they will be UNDER the spring. Rotate the engine by hand and watch the actuation of the rocker arm. The torque spec for the rocker arm bolts is 40lb-ft
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As you can see there is plenty of oil on the rocker arms. I disagree that your valve covers are the problem. You didn't answer my previous questions.
Usually I'm pretty good about breaking posts up via the quote format and answering questions, it was along day yesterday so after my previous post I logged-off and hit the hay... sorry...
Please answer them. Lack of lubrication in these points would cause galling and I see very little from your pics.
Correct, everything looks clean and smooth.
Either your rocker arms were over tightened or you have a binding condition. You have a roller cam, but is it stock?
This is a non-adjustable rocker arm system, you torque the rocker arms down to 40lbs and all the play is adjusted by either grinding the valve stems or changing the push rod length. At least that's what I've been told. I've only worked on adjustable valve trains myself so this is new to me. I actually wrote a how-to manual called,
"How to adjust the Chevrolet Valve Train using the EIOC method.
So I'm very aware of how to adjust the normal or old school style Chevrolet valve train both hydraulic and solid lifters. This Gen VI engine is alien to me.
What valve springs are on there? Are the valve rotators installed? Keep in mind they will be UNDER the spring.
I bought this from a friend that was storing the motor and the boat for a friend that flaked-out and left the state. He sold the boat to someone else and I bought the motor. It was supposedly rebuilt in a SoCal engine shop with a good reputation but that's about all I know. I'll send the link to this thread to Steve, the guy I bought the motor from but in the past I haven't got much more information about the engine than what I've already posted. As such, I don't know what valve springs are on the engine, I don't know if the rotators are or were installed, the engine was wrapped in plastic and a new rebuild when I bought it.
I tool this photo when I was looking at the motor initially. Steve is a reputable business man and a car guy like the rest of us.
(http://www.showcargarage.com/gallery/files/1/454Magnum001.jpg)
Rotate the engine by hand and watch the actuation of the rocker arm. The torque spec for the rocker arm bolts is 40lb-ft
I'm going out of town for the weekend for some car guy stuff, when I get back I might have the following Saturday off and at that time I can probably get my hands dirty and get some work done.
Thanks for the follow-up, I appreciate your help. I need to get this engine bullet-proof.
:)
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Show a pic of the bottom the rocker arm too please
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I disagree that the covers are causing your problems also. It looks like it binded up and broke in two.
Are there any numbers on the cylinder heads?
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I disagree that the covers are causing your problems also. It looks like it binded up and broke in two.
Are there any numbers on the cylinder heads?
Maybe too much cam for the stock valvetrain
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Yes I am aware you have non adjustable rocker arms, that is why I initially asked what you had and gave you the torque value. Yes they can be overtightened still. You do not adjust the clearance by grinding the valves, you need the correct push rod length. Once you determine that you do not have coil bind and that the rocker arms are correct along with the pushrods you won't have any issues. The Gen V BB's and crate motors also had this style cylinder head.
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Mike, I also don't buy the valve cover theory. Not all BBC's had the drippers, plus MANY BBC's have been run without them on non-factory valve covers. One of the ones I saw this happen to had factory covers...One had Aluminum M/T's without drippers.
Have you done a compression test yet?
I would also like to see the bottom, the pivot, ect. from that rocker & a few other rockers, pivots, ect. from a couple other cylinders also. It's hard to tell for sure in the pictures because of the shadows/glare, ect. but I see no signs of gulling, ect. from lack of oiling. I would take apart a couple "unfailed" cylinders & look for witness marks. It would be helpful if you knew if all of the failed rockers were intakes. Are the springs single or dual? I'd be checking allot more just to be safe before just sticking another rocker on there. Lorne
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Hey everyone,
Thanks for all the ideas and questions, I'm in Dallas, Texas for the next few days so I can't get any picture or doing any wrenching till I get back home, as soon as I do I'll pull a couple other rocker arms off and get some good close-up pictures.
Mike
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Hey Mike whats up with the BB
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Hey Mike whats up with the BB
Sorry for such a late reply... my job keeps me very busy... here's the update...
***Update***
One of my mechanic friends said he was told by that there were some rocker arms Chevy put out that were defective and/or weak and that breaking like mind did is a known problem. I don't know if this is accurate or not and quite frankly don't care as I've found out the root cause of the problem.
The problem is the non-adjustable Chevrolet design for their modern heads. My boat mechanic Tim Briggs said this design is used so valve trains can be assembled at speed on assembly lines without the need for a second step, (valve adjustment). While this might be fine for assembly line work it doesn't work anytime any modifications to the engine are made that affects the valve train.
Here's what I know. I'll never buy a Chevy Mark VI engine again unless a Pro shop has went through it and upgraded the heads to quality aftermarket heads as the stock heads are JUNK due to the thread size for the "bolt" that holds the rocker arm in place. The thread size that hold the rocker arm in place for the Gen VI engines is a 3/8" diameter thread hole while old school heads, (the good stuff), is 7/16" diameter threads.
There's a conversion kit by Comp Cams to install a 3/8" stud with a 7/16" diameter stud on top for "Normal" high performance parts. So I'm going to order the bolt to stud conversion kit and a set of Pro Magnum Roller Rocker Arms and this should solve all the rocker arm problems and fix the Chevrolet Engineer's mistake. While this engine is in a Pavement Pounder, you would never want to use a head like this in any kind of performance situation, including High School Drags. So learn from my experience, spend the money up front for a quality engine with quality heads. My next engine will be built by Tim Briggs. Whatever the cost, it's a money saver, not a money pit.
Pro Magnum Roller Rocker Arms
(http://www.showcargarage.com/gallery/files/1/CompCams1320ProMagunumRollerRockerarms.jpg)
The Good News and the Bad News!
The Good News is it will be easier to install the conversion kit and the new rocker arms after I remove the engine.
The Bad News is on December 10th my truck was rear-ended by an young man with a suspended driver's license in a 1996 Ford Truck. The Allstate Adjuster has evaluated the condition of my truck after the accident and has totaled it.
Thanks for everyone's help....
You can see pictures of the damage and the crime scene here,
Just was rearended... 1975 Jimmy RIP (http://"http://forum.73-87chevytrucks.com/smforum/index.php?topic=14415.0")
Mike
(http://www.showcargarage.com/forums/images/smilies/smile.gif)