Thread: Heavy Isolated Misfire Under Load

still missing on cylinder one?

Check the pushrods, if that is good, you may have a collapsed roller.

Yes still cyl 1

Ill check the push-rod again it looked straight last time I looked at it.



Collapsed roller? On the rocker arm? Im thinking maybe a bent valve.

Pretty bummed out about this.

The more I think about it. Something had to bend because of the lower pivot point of the rocker.

When I pulled the rod out a few days ago. It looked straight. But maybe I didn't look at it well enough.

I really don't want to pull the head to inspect the valve. Ill open it up again tomorrow. If the rod is straight, I guess I'll be pulling the head.

take the rod out roll it on something that is dead flat. kitchen counter, table. it has to be smooth and flat.

That's what I was planning on doing. First thing in the morning.

Here's a picture comparing Cyl1 exhaust rocker (left) Cyl3 exhaust rocker (right).

There was some damage to it from sitting on the shim but it should be fine.





Cyl1 exhaust pushrod on top ( markings are from the push rod rubbing on the head gasket ) vs Cyl3 exhaust pushrod on bottom

Straight as an arrow.



I tried to get a picture of the valve stem / guide. Let me know if you guys see anything.







At this point what else can it be besides a bent valve?

I even switched both pushrods and rocker arms. The miss did not move.

I can't even see them.

sounds like a bent valve then.


do a compression test on that piston. see if it makes peressure.

yeah this isnt the first time someone has tightened down high ratio rockers without letting the lifter bleed down...most of the time it just kill sthe valve seal and you get oil burning.

on those instances where the piston is at tdc....you can open the valve right into the piston...as if you had .7 valve lift.

even oem rockers could do this.

do a leakdown test, compression test might not be very helpfull.

just use the spark plug portion of the hose and blow into it with it at tdc compression

rotate the crank 30* of either side of a cylinder TDC and all your pistons will be ~3/4"+ down in the hole to keep you safe....or just tighten a half/full turn and move to the next to allow the lifter to bleed out the oil from the plunger

Originally Posted by Turbocharged400sbc

on those instances where the piston is at tdc....you can open the valve right into the piston...as if you had .7 valve lift.

I appreciate the detailed post. Thank you.

However, you're scaring me. Youre saying that the piston could have kissed the piston?

When it misfires it sounds almost as if the valve isn't opening enough to exhaust the gasses.

At this point I feel as if the head needs to come off. I've checked everything else and I feel anymore diagnoses may be a waste of time, which I have none of.

DONT PULL THE HEAD WITHOUT A LEAKDOWN

you need to find out which valve hit, yes the valve head may have hit your piston...however it likely didnt do anything other than leave a cosmetic mark on the piston, but tweaked the valve...

air hissing out the exhaust or intake/both will tell you wheterh bboth are bent or just one.

how the hell was the #1 rocker sitting low enough to hit the HS stands/shims?

that right there probably led to the exh valve being opened far enough to bend as the fulcrum was moved closer to the piston, changing the geometry for the worse.

some how he was missing the pedestal, either forgot to install in under the rocker, or it broke and fell in the engine. either ways he was one short till he got the new one.

likely the exh valve is bent

Pretty positive it was the valve with the missing rocker pedestal.

So my piston should be alright?

yeah...dunno...without the pedestall...its likely your valve could have been in the postion of having up to 1" valve lift....at that point its possible there may be more damage than just kissing it....

At this point who knows.