No compression in #8 cylinder - 454 Magnum

[Mike Phillips]

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,





Thanks,

Mike

[zieg85]

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

[Mike Phillips]

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.

 

[HAULIN IT]

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     

[Mike Phillips]

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...

 

[Mike Phillips]

Oh yeah... the Jimmy flies the Jolly Roger and sports 2 - 9' Surfboards...

[zieg85]

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.

[VileZambonie]

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?

[beastie_3]

Mike P, looks like you live pretty far from the ocean with that desert background....sand surfing?

[Mike Phillips]

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?

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.

 

[HAULIN IT]

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   

[Mike Phillips]

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?

[VileZambonie]

Are they rocker arm studs or bolts?

[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!

[Lt.Del]

 Wow! that would do it.  Have any salvage yards near you?