Technical Bent Valve when turning by hand?

I was adjusting the roller rockers on my Ford Fe, using a breaker bar to turn the engine by hand, when it suddenly became very difficult to turn. In hind sight, I'm certain the valve was hitting the piston. How likely is it that I bent a valve? I was trying to turn it pretty hard.

 

only way to check is back it off and pull the cover and look at the height vs the others ( as it will be shorter ) and then do a compression check of the cylinder .

 

do a compression test. Although that might or might not reveal a slightly bent valve (I had 3 slightly bent intake valves in my car, it was running ok)

 

As likely as the valve timing being a tooth off at the sprocket (or the valve adjustment being too tight: by .120"+/-)
In multiplicity with the length of the handle on the breaker bar, some leverage plus existent factors can add up to a compromisal in the integrity of the most hardy of valves.

 

I don't think you can do a compression test without being able to spin the motor....maybe squirrel meant a leak down test. I'd think it's ok...valves are pretty sturdy...you probably just gouged a piston when you kept forcing the two parts together. It's probably fine...but you'll have to pull the head and look. I would think you need piston speed to bend a valve....not by turning it over by hand....unless you were standing on the breaker bar...

 

Look at it this way...if the valve is hitting the piston...(it'll probably happen to more than one id assume) you just found out your cam is too big for your setup as is. Youll either need a smaller cam...or bigger reliefs in your pistons....

 

Maybe you could provide a little bit of explanation of why you think the valve was hitting the piston...then we could figure out for sure what might be going on? If the rocker adjustment was way tight, then it could happen.

If you think about where the piston is when it's close to the valve, and the leverage you get to move the piston up in the bore by turning the crank when it's near TDC, I think that it's probably pretty easy to bend one turning the crank by hand.

 

and when they touch, they touch on one side, not across the whole face, will they bend turning by hand? hell yes.

 

The valve wouldn't hit the piston just because you turned the engine by hand. Unless it was frozen in its guide, or you cranked it down way too tight.

 

Is there any chance that the push rod would bend before damaging the valve?

 

Rusty....could be too big of a cam hitting a high compression piston or some other scenario. ....hopefully it is a rocker too tight...

 

maybe ya cracked the piston and the valve is fine.

 

A few of you asked me what makes me think a valve was coming into contact with the piston.
I am in the process of re-assembling my engine, and everything was turning fine until I bolted on my rocker shaft with adjustable rockers. When it got to where it was too hard to turn, I rotated it back in the opposite direction, then heard a metallic sounding "TINK". My best guess is that the pushrod wasn't properly seated at either end.
The engine is still out of the car, and is now married up to the tranny. I installed special $$$ head gaskets and don't really want to pull the heads back off and have to re-order new head gaskets unless I really have to.
I think I will pull the rocker shafts off, and set a straight edge along the top of the valve stems. If that checks out, I'll bolt the starter on and do a compression test.
Back to the question in my original post, I'm wondering how likely, or easy it is to bend a valve when turning an engine with a breaker bar. Has anyone else bent a valve in this manner before?

 

only from a stuck valve from a long sitting motor .

 

You'll need the rockers back on and articulating the valves to get a proper compression reading...could be that one pushrod (or two) wasn't all the way in the lifter. Maybe you can pull the intake and see what's what before you back the rockers off...that way you'll know for sure...

 

I have bent a pushrod when barring an engine during assembly. The push rod was not seated in the lifter.

Maybe the Tink sound was a pushrod contacting the head as it bowed under compression? Or maybe the pressure forced it off the edge of the lifter and into the socket where it belongs?

 

Like Squirrel mentioned above, when the piston is near the top of it's stroke close to where it would come in contact with a valve adjusted too tight, or a pushrod not seated, you have one hell of a lot of leverage given the crank position. There isn't a lot of piston movement per degree of crank rotation near TDC, but the leverage is multiplied. I agree it would be pretty easy to bend one, especially since you said you tried pretty hard to turn it.

Sounds like you have a good plan though, with measuring valve height. While you have the rocker shaft off you could do a leakdown test. If that looks OK, bolt it together with the rockers backed way off, adjust and do a compression test.

Hope the "tink" you heard was just a lock washer falling off the workbench.....

 

Little miss sunshine...

 

What push rods are you using with the adjustable rockers ?

I think you will find a standard push rod is too long. If so this will keep your valves in the open or partially open position.

 

these guys must all run tiny little cams straight up...

 

very tiny little cam it was in a ford 300-I6 in a big lincoln welder ... thing sat for 10 years before the company got it , dummy me forgot to open the top and tap the valves with a hammer to see if any were stuck , and it bent , wound up pulling the head as several others were sticking too , thing looked like the oil never been changed ,

other bent valves were from a U joint saying bye! on a 3-4 shift at the end of the season and went from 6000 to 9000 ( no rev limiter ) by the time I got the clutch back in and the motor sputtering took out 4 EH and left marks in the tops of all the pistons from both sides, ( ross pistons are Great ) some heavy some light . if it was earlier in the year the springs would have saved them , but at the end of season they were ready for recycling .. valve notches wouldn't have saved them from the valves floating.

now I am trying to figure out how someone bent a valve in a flathead ! should be impossible but seen one ( think it was a prank )

 

Just so guys know, the intake valve is the most likely to hit, as it opens at the end of the exhaust stroke as the piston is approaching TDC. In other words, they are heading straight towards each other at the end of the exhaust stroke. If you combine an early intake opening (big duration, narrow LSA) with a lobe that is aggressive off the base circle, and add some cam advance to the mix, its not only possible to run the intake valve into the piston, its a fair to middlin' possibility.

 

May not be a valve. I would drop the pan and use a bore scope to see if any foreign material is in there.

 

That "tink" could be a rod nut landing in the bottom of the pan...

 

I thought they were more of a "thunk" because of the oil in the pan ..

 

Depends on if theres any oil in the pan...

 

???

 

You could stick a boreascope through the plug hole and if your valve hit the piston (assuming the pistons are aluminium), the valve will leave a dent in the piston (hopefully not).

 

As a raw youth l bent a whole head full of valves when shimming a twin cam head. No one told me l had to remove one cam before l shimmed the other. They bend real easy!

 

Update. As best I can tell without having pulled the heads off, the valves do not appear to be bent. I pressurized the cylinders and did not have any air coming out of the intake or exhaust manifolds. So next, I removed the valve springs and set up a dial indicator on the outer circumference of the valve stem tips and rotated the valves while measuring for lateral and radial movement, with virtually none detected. I also set a straight edge along the tops of the valve stems (they're all inline and not canted), and all of the Intake valve stems were perfectly along the same plane as each other, BUT to my surprise, all exhaust valve stems were .033-.038" below the intake valve stems. These are brand new, out of the box, fully assembled Edelbrock heads, so I was expecting to see all valves stem tips line up perfectly along the same plane. Anyway, I am fairly satisfied that the valves are ok, and not bent. The pushrods were all ok too. Hope this info is useful to somebody else one day. Once I have the engine installed and fired up, I will update again if I find any related issues. Thanks for all the feedback.