No compression in #8 cylinder - 454 Magnum

Hi all,

First post here,

I put a 454 Magnum Marine engine in a 1975 GMC Jimmy in June. Bought 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 engine ran great.

Now, 2 months later, engine starts 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 rough and runs rough 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,





Thanks,

Mike

Mike, We better wait until you pull the valve cover, that way we will have alittle more info. I really had to laugh, I think this is the first time I have seen a under the hood truck pic in the boat engine tech. It does look pretty clean, those valve covers look like they are for a hemi.

check the rocker adj.

nice job,looks really clean. when it was running right,how did it go? Guess???? another rocker arm failure. good luck.

Check. Will remove it tomorrow and take some pictures if there's anything to seel


Sorry about that, just trying to find some knowledgeable guys when it comes to Gen VI Roller Cam 454 engines.

Here's a boat I owned for 20 years with a 402 BBC

1970 Super Sanger Flat Bottom Drag Boat - V-Drive
National Title Holder - 1976 Super Modified Class 1/4 Mile in 9 seconds at 122 mph.
Owner/Driver: Rick Baker




Here's my son Rand about one and a half years old sitting in dad's boat before I sold it.

Note the stereo bolted to the passenger's side head on the engine, (just behind the passenger seat) and if
you look you can see a 76 Gas Station Ball on the tip of the stereo antenna behind the Indy Champ air scoop.




1966 Chevrolet Milk Truck
My favorite rig of all time, I kick myself every day for selling the Milk Truck. This had a 396 big block Chevy in it with a turbo 400, Lokar Shifter, Pertronix ignition, mild cam etc. It's a 1-Ton dually, the front end is a steel clip joined to a custom built fiberglass back end that was insulated to keep the milk cold. Yes Sir folks, this is a real Milk Truck.





1959 Cadillac Coupe DevilleThis was my 1959 Cadillac right after we installed and fired up the 462 big block Chevy engine for the first time. This car went from sitting in a barn for over 20 years to back on the road in less than 5-weeks. Note the Milk Truck parked in the street, and the other 1959 Cadillac is a Flattop that we owned at the time also.





That's not everything I've put a BBC into but a good start...

Just need to get this current project scienced out and bullet-proof....

I'll update tomorrow...

Thanks!

When it was running right it was a true beast. Just way too much fun!

It will turn the 35" Boggers over without hesitation. Reminds me of driving the Drag boat, point it straight where you want to be in a few seconds and then hold on because it will jump when you bury the gas pedal.

Wish it got 30 miles per gallon...

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

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

1959 Cadillac Coupe Deville wow thats the shet!!!

Ok after ya firure it out we need to paint the sterring 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 sugestion,not being negitive

Rob

If they were reputable they should have done a leakdown test to show weather the problem is the bottom or top end. If the rockers arent broke and still move showing no signs of a wiped lobe on the cam could be a burned exhaust valve.