Bent 6 pushrods.... All Exhaust?!?!

[rking]

Thats right, fresh rebuild, bent all 6 exhaust pushrods...

This combo was running just 2 weeks ago. The only changes were new engine bearings. So my question is what the hell is going on!!

Timing marks are set dot to dot on the crank and cam, stock pushrods, stock rocker arms, bent only exhaust pushrods; the intake pushrods are perfect...

So anyone please help with some ideas... My brain is hurting from thinking so much, and I cant come up with a good explanation to why only the 6 exhaust pushrods bent, particularly when the timing chain marks are aligned dot to dot..

Please help!!

 

[powerhouse]

check for coil bind on the valve springs or piston to valve contact. You say installed dot to dot but were the actual valve timing events checked, ( cam degreed?) sometimes when parts are made they are made wrong. These should be your first areas to check. Andy

 

[Chuck Leeper]

Cam is off location..
Does the chain system may have advance and retard markings? If so, you installed the chain, using the wrong 1's.
AIRC, the pistons chase the exh valves, and the intake valves chase the pistons. Chain on wrong, and the pistons just caught up w/ the exhaust valves....

 

[boostingbuick]

Sound like you went with the wrong crank dot. One dot should line up with the crank keyway at the 2 o'clock pistion and the other should like up with the cam gear. If you get the wrong one then the pistons could make contact with the pistons.

 

[Chuck Leeper]

An echo???

 

[rking]

check for coil bind on the valve springs or piston to valve contact. You say installed dot to dot but were the actual valve timing events checked, ( cam degreed?) sometimes when parts are made they are made wrong. These should be your first areas to check. Andy

I had this engine together and running just two weeks ago. When we put it together the first time, we degreed everything, and have an entire build sheet on it. That is why this is troubling me so much... I just screwed up somewhere and cant figure it out. It has to be timing related...

Cam is off location..
Does the chain system may have advance and retard markings? If so, you installed the chain, using the wrong 1's.
AIRC, the pistons chase the exh valves, and the intake valves chase the pistons. Chain on wrong, and the pistons just caught up w/ the exhaust valves....

This is my same guess also, but I just have a double roller timing chain in there, nothing fancy. The only way to advance or retard the timing would be to install it differently on the crank gear. The crank gear has a DOT, and TRIANGLE, and a big U on it. I installed DOT to DOT... DOT at top on crank gear, and DOT at bottom on the cam gear... I thought that this was straight up, just like I previously had it???

Sound like you went with the wrong crank dot. One dot should line up with the crank keyway at the 2 o'clock pistion and the other should like up with the cam gear. If you get the wrong one then the pistons could make contact with the pistons.

I just have a standard double roller timing chain in there. I have everything lined up like I noted above, however, when I line the dots up like above, the crank keyway is more in like the 4 or 5 o'clock position??

 

[boostingbuick]

What brand timming chain did you get? Mine is a rollmaster with dots. And is ajustable with a keyed crack gear. No echo, just tring to help.

 

[jpwalt1987]

the crank keyway is more in like the 4 or 5 o'clock position??[/QUOTE]


There is your problem.... as said above..the keyway should be at the 2 o'clock position. Dont feel bad , i did this on a BBC motor and bent all the xhaust pushrods.:smile:

 

[rking]

UPDATE: When installing the crank gear and aligning the dots between the cam and crank gear.... THE KEY IN THE CRANK NEEDS TO BE AT THE 2 O'CLOCK POSITION!!! I installed the key in the retarded crank keyway, but lined up the dots for straight up... Not good! I remember it being about 3 in the morning when I put that together... Luckily, no other damage.

 

[jhanson1750]

Well glad to see you found the problem. I always try to remember others problems when I work on mine so Thanks for posting and I will pay better attention when putting mine together. Jon Hanson

 

[JayC]

Cam is off location..
Does the chain system may have advance and retard markings? If so, you installed the chain, using the wrong 1's.
AIRC, the pistons chase the exh valves, and the intake valves chase the pistons. Chain on wrong, and the pistons just caught up w/ the exhaust valves....

+1

I know other people who have done the same thing before. Have fun pulling the heads off.

 

[JayC]

Luckily, no other damage.

You're delludinig yourself if you think there was no other damage. Think about what caused the pushrods to bend?

Hello Mr Piston, meet Mr Valve

Do a leakdown.. you'll change your mind.

 

[boostingbuick]

You better believe the valves are bent. The valves stop moving and the pushrods didn't. The only way the valves stop moving is if they hit something, like above, Mr. piston.

 

[rking]

Oh, yeah, I know, the piston met the valves. Of course I pulled the heads, had them taken straight to the machine shop and had them checked. Everything was good. No bent valves... I guess fortunately I was running stock pushrods, so I guess not the strongest things ever!

 

[JayC]

I find that REALLY hard to believe as Ive never seen anyone escape with the valves unscathed when that happened but if the machine shop gave you the green light, I guess it was your lucky day.

 

[boostingbuick]

WOW!! Guess you needed some good news somewhere. I hope to hear you have it running soon. Good luck.

 

[rking]

Oh I know!! I bent some pushrods on my first LT1 that I built years ago... I still have the valves as souvenirs . I was completely surprised, but so relieved, sometimes you just need good news! Should have it fired up tomorrow, hopefully no popping !!!

 

[TurboKen]

UPDATE: When installing the crank gear and aligning the dots between the cam and crank gear.... THE KEY IN THE CRANK NEEDS TO BE AT THE 2 O'CLOCK POSITION!!!

might be a stupid question, but it the engine in the upright position or upside down?
just trying to learn
Ken

 

[Blown&Injected]

Dots will line up 2 times - once will be right, the other time will be 180 out. So just making sure the dots are lined up is not enough, must be lined up on the #1 compression stroke.

 

[turbodave231]

If your valves hit the pistons hard enough, you may have damaged the top piston ring land.

Be sure to check the spring retainer didn't hit the top of the valve guide (or valve stem seal if you run one on the exhaust). This is just as bad as coil bind and will cause bent pushrods without bending valves.

When degreeing a camshaft, I use the timing dots as a starting point, but after that, I pay no attention to where the dots are in relationship to each other. I am watching the degree wheel and the dial indicator to find the right keyway on the crank sprocket. When I get the intake opening and closing event at the .050" lift number, I engrave my own marks on the timing gears.

You might want to check the exhaust timing events at .050" lift to make sure the cam manufacturer didn't screw things up. I have never found a cam that was ground wrong, but I've heard horror stories.

Checking valve to piston clearance with checking springs and some Playdough after the cam is degreed can help avoid these problems. Better to find and correct the problem on the engine stand.