No compression in #8 cylinder - 454 Magnum

[Mike Phillips]

Originally Posted by HotPursuit

Do a leak down test. If the readings are good with both valves closed you may have rocker arm problems again.. Pull the covers. What brand of Rocker arms

Stock Chevy rocker arms. Leak down test is out of my ability to do right now.

Originally Posted by whoya

If a rocker arm failed or loosened you still would have compression, If it was to tight you would not.

Checked and noted. Will be interesting to see what things look like under the valve cover.

Don't mind pulling the heads and having a valve job done, whatever it takes to get it right.

Originally Posted by OutlawMan

If they were reputable they should have done a leakdown test to show weather the problem is the bottom or top end.

They're a very good shop but after seeing my truck and its height, they decided that they're really not into the hot rod scene and would rather work on normal cars and trucks. I don't blame them, this is a beast to work on. To get the driver's side valve cover off you have to remove the brake booster and it's also easier to do all of this with the hood off, so it's more complicated and extra work as compared to a normal car or truck. Lucky for me I don't mind turning wrenches.

Originally Posted by OutlawMan

If the rockers arent broke and still move showing no signs of a wiped lobe on the cam could be a burned exhaust valve.

Checked and noted.

Originally Posted by Strip Poker 388

Ok after ya figure it out we need to paint the steering shaft.clean up the wiring.the heater hose on the intake, change to a 90,it will run behind the alt,cleaner look.

Here is how i ran my heater hoses,the wires are also under the finder,same as the fire wall I ran them behind the fire wall,box and could by heater.I just making suggestion,not being negative

Rob

Thanks for the suggestions Rob, appreciate the suggestions. Nice engine and engine compartment you have there!

About 8 hours from now the valve cover will start coming off and I'll update this thread with what I find out.

[ezstriper]

don't think it's a rocker issue this time....no compression...pull the head...

[whoya]

Originally Posted by ezstriper

don't think it's a rocker issue this time....no compression...pull the head...

I agree, Hate to say it but it sounds like its going to be worse then a rocker. Valve or Piston.

[Mike Phillips]

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.















Ouch!

[mrfixxall]

How much lift on the cam? stock? make sure you use arp rocker studs,ive seen other brands brake so spend a little extea cash,its worth it..

[Mike Phillips]

***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.




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.



Anyone agree with the shop owner's assessment that the root cause is the tall valve covers?

Anyone disagree?

[picklenjim]

Don't agree with it being the valve cover. You had a rocker not even there but that doesn't explain no compression. That valve is either bent or stuck in the guide partly open or both. Is that one of the rockers that your friend replaced earlier? Either way if there is no compression in that cylinder with that rocker arm off the head is going to have to come off.

[Mike Phillips]

***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


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


Mike

[ezstriper]

sorry to hear that !!!!! you may have to buy it back to get your $ back...Rob

[Griff]

Stock Gen V BBC's use the same rocker arm/shoulder bolt set up as well. I highly doubt the failure was due to the lack of drip tabs on the underside of the valve covers. More than likely, just a bad rocker arm. From the pics, there is no evidence of a failure caused by a lack of oil. There is no color change or signs of heat. The 3/8 hole can be an issue, but the adjustablle valve train stud kits with the 3/8 bottom and 7/16 top are good to about 450# of valve spring pressure. Merc uses the same stud kits on 500hp's.