Hello,

I've got a problem with my 350 build. First off, I was told by my machine shop that I should not be at all concerned about piston to valve clearance due to my mild cam (lifts in the .480's with 1.5 rockers). It's a good thing I did check, however.

I'm using hydraulic roller lifters and lightweight checking springs with an adjustable pushrod. My rockers are full roller, 1.5 ratio. I thought I could hear it hit, then I checked it out with some modeling clay. It's cutting right through the clay to the top of the piston.

I have no idea what's going on. The heads were slightly shaved, but only like 0.008 inch. My machine shop said there would be no problems here.

Please help!

 

Someone correct me if im wrong but if its not timed correctly like the cam sprocket and the crank sprocket lined up correctly the valves could hit the piston regardless of the lift. I would say check the chain make sure its lined up correctly because witht tha little of lift i cant see it hitting the piston

 

My chain is definitely lined up, I checked many times because I was worried about that myself.

 

Sounds like your sprockets aren't lined up.

Specifically, parts from different sets, parts that aren't made right, you're lining up the triangle when you should be lining up the square, etc.

Only way for some weenie stock-ish street non-performance cam with .4xx" lift to hit pistons is for the valves to be about 40 - 50° off from the crank. If it's exhausts hitting, the cam is retarded by about 40° (exh is still WAY open, like .200", when the piston reaches TDC and the exh is supposed to be closing and the int opening).

 

Here is a picture of the clay. I'm 99% sure I lined up the dots. Plus I've already put my timing cover and harmonic balancer on...

 

I don't doubt the clay.

Check some valve events with a degree wheel. I suspect you'll find they're out in the ozone somewhere.

 

This is so frustrating...I know I lined up the dots. It's a Cloyes timing set, but I guess that is the only thing that could be wrong? Now I'll have to rip of my harmonic balancer and timing cover.

Is there any other possible explanation?

Thanks for the help.

 

Lining up the dots only ensures the camshaft is timed to the crankshaft. Does the gear on the crankshaft have 3 keyways? If so then it will have A, O, R markings over each keyway to advance or retard the cam timing up to 4*. If you advanced the cam and the cam you use has advance built into it, it's very easy to have piston to valve clearance issues.

Unless you're after specific timing for a performance situation, always install the cam in the straight up position.

What thickness head gaskets are you using?
What pistons are in the engine? Are there any valve reliefs?
Are you sure the rockers are 1.5 ratio?

 

The crank gear did have three key ways on it. Head gaskets are stock FelPro. Pistons are Speed Pro -10cc with 4 valve reliefs. I'm definitely sure the rockers are 1.5, stamped right on them.

Wouldn't be such a big deal except I have to loan out the balancer installer/remover, and now I'll need a new timing cover gasket. But I'm very thankful I didn't just installer the rocker arms and not check the clearances. With a .480/.487 lift cam, there is no way I should be hitting the piston correct? And I can't imagine not selecting the correct key way for the crank gear!

edit: just quickly googled Cloyes keyway info...apparently the curved keyway is the one for 0 degree advance. I think I may have assumed the square one was the stock setting...if this is the case I'm an idiot and probably shouldn't be rebuilding motors...

 

Hey it happens Just double check alignment of the timing marks and like others said, check the degrees on a degree wheel for opening and closing. This will definately let you now if you are off or not.

Only other thing I can think of is that the cam dowel pin is drilled slightly off its standard location. I believe my last cam I got had this rare problem, and caused all the valve events to be significantly off. Thankfully I have a degree wheel and use it for my builds.

Also, you sure the cam you have is only .480's lift?

 

Unfortunately I do not have a degree wheel, this is my first build (can you tell...?). At any rate it is a relief to know what the problem likely is. The bad part is that I'll have to wait a few days before I'm back working on the engine.

I don't know for certain regarding the cam, I bought it second hand. Those are definitely the specs given by the seller though.

Thanks!

 

If you can, invest in a degree wheel kit. Its a good tool to have to know you are getting the cam in right. Cam is no good if the valve events are not timed right.

 

Not hard to get REAL CLOSE on the cam timing, without a degree wheel...

At TDC (not the firing one of course, but the other one) the exh valve is closing and the int is opening. At EXACTLY TDC, they should be open very close to EXACTLY the same amount. Won't be "perfect", but you can tell to within 10° or so, if the cam is aligned to the crank.

Find TDC. See if that lines up with the point where the #1 or #6 exh is just closing, and that same cyl's int is just opening.

I'm betting you'll find that when the piston reaches TDC, the exh valve is no where near closong (like ,is still .200" open and has at least 40° more crank rotation to go before it gets there), and it isn't anywhere close to the int opening point. Meaning, the cam is WAY behind the crank (retarded). Meaning, no matter what you think those dots are telling you, it's not right.

 

Alright, so I ripped the balancer and cover off, and it was the wrong keyway! Thanks for the help guys. One more thing, any issue in reusing the crankshaft keys? This is a new crank. Everything fits nice and tight.

 

If it's not sheared, you can use it as many times as you like.