Loud Knock- Where to start?

[jeremy92555]

Fresh 302 with maybe 1500 miles on it. Was getting on the freeway yesterday about 1/2 throttle and all of a sudden a loud knock and loss of power. I was able to keep it running to get off the freeway but it has lost all power and will barely start and run. Oil preasure never changed, no smoke and no oil anywhere. I have assumed the worst but figured I would ask if there may be any other possiblities. I am not a motor guy so any help on where to start would help.

 

[methcat]

fresh? is it modified or have anything unique in it? heads stock?

if it's modified (high compression) that'll get you..

if everything is norm, start checking the standard stuff like timing and vacuum leaks

edit*** after re-reading, "suddenly" is probably not most of the above. you check compression yet? i've had valves blow out in holley carbs before but from what i remember it winds up with a rich condition, not lean...

 

[Viperwolf1]

Look at the oil. It should be fresh and not full of sparkly bits of metal. If that looks ok pull the valve covers and look for a problem there.

 

[jeremy92555]

not sure what compression the motor is. It has pro comp heads, comp cam, double roller timing chain. That is about all I know about the internals. Towed it to my In laws cause it was closer and dont want to go over there today and mess with it. I guess I will start by checking compression and pulling valve covers off and go from there. I guess i am hoping for a miracle but doesnt seem likely.

 

[Broncobowsher]

Where to start...
Pull the valve covers. Willing to bet you will find something in there.
If you don't see anything, compression test.
99.9% sure you will find something after looking at those 2 things.

My guesses...
Bent pushrod, broken rocker, broken rocker stud, broken or dropped valve. Fore me I was real good at hanging valves open then having the rocker/lifter/pushrod beat themselves up until I could get it stopped. That was nearly 20 years ago and the best I can tell they didn't properly size the new valve guides to match the valves. From as drastic as you describe it, I am guessing intake valve.

 

[jeremy92555]

It sure would be easier to do myself if it is in the top end. If something did go wrong with valves does that typically ruin the heads?

 

[2horsegarage]

I had a similar problem in my mustang, 302, fresh, new heads--- Broke a rocker arm. Sounded just terrible. I ended up changing the studs, rocker arms and push rods because the rocker arm studs looked damaged and i assumed the push rods were too long.

No other problems other than the broken rocker arm...

 

[jeremy92555]

ok I pulled the valve covers off today finally an you guys were right. I have a badly bent pushrod that looks like it was stretched and the other one is just bent slightly. So my question now is what the heck may have caused that? How do I prevent if from happening again. Am I being naive or am i as lucky as I feel and all i have to do is replace the pushrods and adjust valves?

 

[Broncobowsher]

Too much to list...
Are the heads stock or aftermarket?
Are the pushrods the right length? Did you check the geometery?
Running guideplates? Are the pushrods hardened? are you running guideplates and rail style rockers together?
Look at the valve tips, are they galling up/mushrooming? Rocker side as well.

 

[jeremy92555]

I am probably way over my head here. I am not much of a motor guy so I will tell you all I know. The motor was built by the previous owner, He said it has Pro-comp 215 heads aldo fit 351W. Comp cams E303 Hyd. 2.05 intake valves. Double roller timing chain. I noticed today that it has 1.6 ratio roller rockers. I do not believe that the push rods are hardened. I searched the number on them and they are not hardened and are 6.876 in long. The tips do not look like they are mushrooming at all. They look normal. I am running guide plates as well. I have not checked geometry, I would need some help for that it would be over my head. I have no idea if the push rods are the right legth or even how to tell.

 

[Viperwolf1]

If you look carefully at the tip of the valve stems you will see a mark where the rollers were running. If the mark is across the center of the stem the geometry is correct and the pushrods are the right length. If the mark is closer to the intake side of the stem the pushrods are too short. Closer to the exhaust side and they're too long.

These are just a hair on the short side.

 

[jeremy92555]

I will check that tomorrow, thanks that is good to know.

 

[blubuckaroo]

I'd like to see photos of the rockers, pushrods, & guide plates assembly.

 

[ochretoe]

Another potential cause is week valve springs. I broke 5 rocker studs befor I figured out I was ripped off on springs.

 

[blubuckaroo]

Pics of Jeremy's valvetrain

It looks like the builder used standard pushrods. It also looks like some heating on the guide plate. I'd say measure for the correct pushrods and buy a set of hardened ones. You should be good to go unless the builder cheaped out in other places too.

 

[av bronco]

Something dont look right on those rockers, I would say the pushrods are too short but from the stud to the tip the rocker arms look too long. can you move those up or down to center the roller on the valve?

 

[jeremy92555]

no, I cannot move the rockers up or down. The wear mark on the valve is more towards the exhaust side, would that mean the push rods are a little to long? There are 6.876" long. I also pulled the manifold and the lifters seem to be in good shape from what I can tell. The

 

[Viperwolf1]

Yep, a little too long. You can cut an old, straight one and thread it to make an adjustable length checker. Then coat the valve tip with a marker, assemble and turn the engine over a few times to see where the mark ends up. When you get the length correct measure it and order some hardened ones in that length. It's a good idea to measure on both banks, front and back.

 

[Broncobowsher]

It looks like slightly too long pushrods to me as well.
The "heat" to the guideplate may simply be the friction from the pushrod.
Pushrod may have skipped the heat treat process or had a bad process or the wrong one used. Maybe the box was short one so another one was grabbed from another (incorrect) set. Who knows. Just the pushrod is toast. That guideplate is now bad as well. Since I am nit-picking I don't like the self locking adjuster nuts either. I prefer the poly-locks. But that is a personal preference.

If you can pick up an adjustable pushrod and try a few different lengths and see if the geometry can be dialed in a little better before ordering new pushrods that would be good as well. Too bad pushrods are such a pain to accurately measure. They are sold in "gauge length" which doesn't really match up with sticking a nice big digital caliper on them and taking a reading.

 

[blubuckaroo]

I just use an adjustable pushrod (available from Comp Cam) to find the correct length then measure it with a 12' vernier micrometer. Then you can order the correct length HARDENED pushrods from Comp Cam.
Jeremy, you said it has only 1500 miles on it? Were you pushing it a little hard for the first time? What is the valve spring pressure? May just have been too much for the stock, non-hardened pushrods.