The Stovebolt Site Forums The Shop Area Engine Shop Bent pushrod - freshly rebuilt 261. Why?

Hi All,
Not a truck, a 41 Chevy sedan.
I have a freshly rebuilt 261, .30 over, Delta camshafts RV2 grind, resurfaced lifters, and slightly stiffer valve springs (both Delta cams). Fenton headers, stock intake (for now).
Original rocker-arm assembly and original pushrods (11 1/4").
Also had the (848) head rebuilt at the same time. It already had hardened seats.
Tank, fuel line, fuel filter and fuel pump all new.

It's been through its 20 minute @2500rmp cam break in (8 minutes at a time). I've ran it two other times since then, just for a few minutes. So on about its 28th minute of life, it bent the pushrod on #6 intake.

What do I need to check to see if it was just a "bad" pushrod, or if there is something else wrong.

Thanks in advance for your help.
Joe

Picture of the bent pushrod:
https://plus.google.com/u/0/photos/110536946680808097477/albums/5834818645841593441

How old is the gas you are using? That may sound like a funny question to ask but consider this, if the gas sat in the tank for a long time to the point it's turning to varnish, when you shut the engine off it can harden on the valve stem and stick the valve shut. That is what can bend the pushrod. That happened on my '38.

2 weeks old. Tank, fuel line, fuel filter and fuel pump all new.
Thanks.

I'm sure it is not related but I don't think the 20 minute run in is supposed to be done 8 minutes at a time.

Check for piston-to-valve interference (which should have been done on assembly). Get the piston to exact top dead center by either probing into the cylinder through a spark plug hole with a piece of soft wire as you slowly turn the engine as the exhaust valve closes, or using a degree wheel. The intake will be opening at that time, and if the clearance is too close the valve will hit the piston. Once the piston is at TDC, use a pry bar on the intake rocker arm to check how much travel it takes to make the valve touch the piston. If it's less than 1/16", tear the engine down and use a flycutter to put a slight eyebrow in all the pistons at the potential contact area. Been there, done that, on hundreds of racing engines!
Jerry

Thanks for the ideas.
I did NOT check the rods for straightness.
The valve guides are new.
I did adjust the lash both cold and after fully warm.
The lifter is not stuck (moves as smooth as glass).
Just looking at the valve, spring, etc., it looks just the the others (nothing obviously wrong).

The "8 minutes at a time" break-in was because I couldn't keep the engine cool.

That's a good idea. Is this possible even though the engine has 30 minutes on it? Wouldn't that happen rigth away?
Thanks.
Joe

Could it be possible that the valve guide in not installed to the correct height and the valve spring retainer is hitting the top of the valve guide?

How could you install the spring retainer if the valve guide was so far out that it allowed the retainer to hit it?

I don't see how that would go unnoticed even if you were able to.

The valve guides are pressed into the head after the old ones are bored out. If the mechanic didn't cut it back down to the proper height, there could be contact between the spring retainer, seal, and the guide. This engine should have plenty of valve spring clearance, but it doesn't mean something was over looked.

Using a dial indicator, measure the valve lift on the next valve over. Then take the indicator to the bent push rod valve and move that rocker by hand the same amount. Does it travel the whole amount? ( Doesn't matter where the piston is at this point as long as its down the bore) Now, pry down on the rocker till it bottoms out to see how much total valve lift you have. If you can go past the original valve lift by at least .050" or more, you have plenty of clearance and no coil bind or guide trouble.

Pull the lifter out of the block and check for cam damage of crap in the lifter if they are hydraulic. Check the bottom for scuffing or gouges.

You should also figure a way to cool that engine and give it a real break-in. A few minutes at a time is not doing it any good. Use a garden hose in the heater hose inlet and regulate the flow to keep it cool. I have run engines with out radiators for 20-30 minutes this way, just the let the water run into the yard and have a thermometer in the outlet stream to keep tabs on the temp. Keep it warm, not hot, not cold.

I vote for a sticky guide. It doesn't take much to hang one up and doesn't always show up right away. The way it was broke-in was likely a factor, lack of oil, the guides need to break in as well.

Joe

What Joe said .

I vote for a sticky guide . Have you really got adequate oil supply to the top. Is the guide / valve clearance ok.

I would agree with Joe H: Sticky valve guide is common with new rebuild and almost certain when they get hot. Not a lot of lubrication at the guide on a good day. New guide and new valve should have had a lot of assembly lube all over it when it was installed. That would have been cleaned off real soon after starting up. Intake would be washed off from fresh air fuel mix coming in and exhaust would have been burned off just as fast. If the valve will move now you may have no real issues just keep it cool while running it. Look at the lifter as has been suggested If it is good then find a push rod and see what happens.If the valve hangs up when you push on it then you need to get it fixed. But if it moves you may be OK.

Thanks for all the ideas.
The rocker arm moves freely. I haven't figured out how to push on the valve yet. I'll keep you all posted.

This should be a link to a photo of the bent pushrod:
https://plus.google.com/u/0/photos/110536946680808097477/albums/5834818645841593441

UPDATE: The valve is 100% stuck. Was able to exert force with a pry bar and it won't budge. So take the head back to the machine shop???

They say if you have the head planed more than a certain amount you should recess the intake valve seat an equal amount to maintain intake valve to piston clearance.
Valve guides should be reamed for valve stem clearance after they are installed.

John

Take the head back to the machine shop. They didn't make sure the clearance was right between the valve and the guide.

It sounds like the machine shop didn't put enough clearance in the guide when they installed the valves. Yes, take the head back to the shop- - - -if they're reputable, they should fix it free, and provide you with a new gasket set. Any shop I've owned or managed would handle things that way.
Jerry

I"ll take the head back.
Thanks to all.

It is true you should check for valve clearance after having the head machined, but on this type of engine, there should be no need to worry. If it was a racing engine, I would worry. A few thousands here or there is not going to change much, heck the new gasket is probably thicker then the originals. You sure don't want to cut anymore then needed to clean up valve seats. Cut to deep and the next rebuild will require new seats installed which means big money.

Joe

Possibly, but he does have an 848 head on a 261, with a somewhat modified camshaft. Once the stuck valve is repaired, I believe a check with modeling clay or some other method of measuring piston/valve clearance would be the prudent thing to do during reassembly. I usually bolt up the head without a gasket installed, and if there's even a little clearance that way, the thickness of the head gasket is enough of a buffer to assure safe operation.

On the round track engines with radical cam profiles and high RPM, we used .060" clearance as a bare minimum. One engine we ran had such a radical cam profile that the closest piston/valve point came 20 degrees AFTER TDC. The intake valve was outrunning the piston for the first 20 degrees of the intake stroke!
Jerry

The head is back at ths shop. The owner is out of town this week, so it will be next week before I can talk to him.

Here are two pictures (I hope):
https://plus.google.com/photos/1105...47603064934864977?authkey=CKrsvqqA5Z-CMQ
Click on "All Photos"

If you click on the first pick and look real close at numer 3 piston, you can see a very light smiley face. The rest of the pistons, show no sign of the valves hitting.

#6 cylinder, (the one with the stuck valve) was stuck open, so you can see where it was hitting the piston.


So do I need all the pistons fly cut? Or, was this just an installation issues with #'s 3 & 6 valves?

Thanks.

No need for a cut, the valve was stuck open so the timing of the piston to valve was off. With everything working right, the piston follows the valve, or chases after it. At Top Dead Center, the valves should be closed or just starting to open, yours was wide open.

Joe

Probably wouldn't be a bad idea to check it as Hotrod suggested for clearance just to make sure.

John

When i was in the process of rebuilding my 1954 261. Patrick trucks ,said there are two different length of pushrods available for my engine.
Not sure if this maybe your problem.

The length of the pushrod doesn't change the amount that the valve opens. The camshaft dictates the amount the valve opens.

What do the think about #3 hitting? Not enough to worry about?

Well it quickly becomes a what came first issue, "The chicken or the egg." If the valve stuck in the guide, the piston hit the valve because it was open when it should have been closed, and the guide is at fault(too tight). If the piston hit the valve because of inadequate P to V clearance due to machine work causing it(head milled a lot, or valve seat too high in head, etc...), then yes, reliefs in the pistons will need to be cut to compensate. You just need to determine which infraction is occurring to make the correct fix.

If the valve is still stuck open, you probably have a bent valve now as well.

I understand about piston #6, the one with the stuck valve.
But other picture is piston #3, and it has a smiley face from the valve. This valve is not stuck, just seems to be hitting.
I guess I'll just wait to hear from the machinist. But I really appreciate all the info.

I've seen several of the 235/261 come in with stuck valve or two after someone rebuilt the head. Didn't allow enough clearance between the valve stem and the guide.

Could very well be bent now if it kissed the top of the piston.

The machinist will find out when he gets it out.

#3 likely stuck too, but the piston popped it back into place before any real damage was done to it. I would make sure the machinist checks all the valves for being straight, and the clearance between the stem and guide.

This is getting to be a rather common problem these days. Machine shops think 60 year old machines should operate at the clearances of modern engines and they never bother to look at the old books. Whenever I work a head, I shoot for the big end of the spec. Using a quart of oil every thousand miles ain't nothing compared to valves seizing when they get hot. We even went for the big end of the speck back when we were expecting to get another 100k out of a head. These old engines will never be driven like that and with today's lubricants, the guides aren't going to get any bigger with a lot of miles.

One of the wise old sayings I picked up from a race engine builder- - - -"Oil is cheaper than engine parts!" If it uses a little oil between changes, at least things are getting lubricated. A too-tight valve guide is going to overheat and start galling things long before it has a chance to "wear-in".
Jerry

OK. That makes sense to me. I'll be sure to tell the shop I want plenty of clearance in the valve guide.
Thank you all again for your input.
Joe

Two photo's of clay added. All six cylinders looke like this:

https://plus.google.com/photos/1105...6680808097477/albums/5834818645841593441

Thanks again to everyone.
Joe

looking GOOD! plenty of clearance there.
Jerry

Update:
Just wanted to thank everyone for your help on my project.
After much hair-pulling-out, ulcers, etc.... I'm on the road. The 261/T5 is running great (knock wood) and I'm enjoying the car. There is much left to do, but at this point, I couldn't be more please with the outcome.
And I could not have done it without alot of help from friends both local, and online.
Thank you!
Joe