Engine miss? do I have a bigger problem!!

[69candy]

So a while back I broke a roller rocker on my 428. Mild build in my 69 mustang. Had to drive it home. upon pulling the covers I discovered the broken rocker and bent pushrods. Put a new set of pushrods in and put the original rocker shafts back on. Took it for a drive and felt fine. went for a longer drive the other day and it has developed a miss. Pulled the plugs and sure enough 2 fouled. Same cylinders as the bent rods. Put new plugs in and no diff. checked plug leads and cap, got spark at the plug. Still misses on that cylinder. No funny noises!! Is it possible it may have bent a valve? or something more serious? will put a bore scope in tomorrow? maybe a crook cap? They are BBM heads, 40tho over cam etc. Was reving it when the rocker broke.

[machoneman]

A leak-down test may be a better way to determine if you've bent a valve. I'd swap on a good rocker to that cylinder and carefully check the clearances, cranking the engine over by hand, checking for a weak/broken valve spring or rocker witness marks. One other way to check for a bent valve is to pull the shaft on that side and lay a straight edge across the valve tips. A bent valve should show a short(er) tip than the others.

W/O a leak-down tester, doing a compression test, using a swapped on rocker, may also show if a valve is bent. Lacking either tool, making or buying a special air chuck that can screw into the plug hole and adding air pressure to that cylinder literally allows one to hear air escaping from a bent valve. 

[Blueoval77]

More often than not this is a wiped cam if its a flat tappet......Need to check compression and roll the engine over with the cover off to see whats what.

[69candy]

managed to get a compression tester in there today, 30psi!!!!! something is not good. Will pull the motor out this week, numbers matching car so hopefully not to bad!!

[jayb]

Probably a bent valve, might have had piston to valve contact when you got on it.  Hydraulic lifters?

[69candy]

Bent valve in number 5. Only a very small one but enough to hold open about .25/ .5mm. Straight edge over the valve train confirmed it was a little low. Rest of the motor is fine, no big marks on the piston, Engine builder is gonna check it all out to be safe. Just got to order parts once he works out what we need, BBM heads still look fine!!!.
 

[Blueoval77]

Man how do you get P to V contact with "A mild build" ?   

[jayb]

Hydraulic lifters can pump up and leave the valve hanging open after it is supposed to be closed, leading to contact with the piston.  I've seen the spring clips that hold the plunger in place on hydraulic lifters pop out, so that even if they were adjusted properly (1/2-3/4 turn down from contact), there is nothing preventing the lifter pumping up.  Also a spring that is overtaxed can "loft" the valve at peak lift, or allow it to bounce on the seat as it returns.  Anything like that can lead to P-V contact, even with a mild build.