Aluminum Head Damage...

Just got AFR heads back from machine shop. First trip out with the new combo this year, things went terribly wrong, and all exhaust valves ended up bent. I mic'd the clearance before ever firing the engine, and knew that I had enough piston to valve clearance.

Upon delving deeper, I discovered that the camshaft sprocket dowel pin had sheared off, allowing the cam to rotate a bit...enough to apparently retard the cam enough to smack all of the exhaust valves! At least none broke, only kissed the pistons and bent enough to make a difference!

After talking with folks, it sounds like the bolt holding the sprocket in the center probably loosened up some, allowing the pressure to be transferred to the pin. The pin is only an alignment dowel, and is not designed to keep the sprocket from turning.

All in all...it cost me around $1400 for new valves, pushrods, gaskets, and heads repaired.... I went to EBN and bought a replacement pin for 58 Cents!!! OUCH!!!!!!!

Anyway...the cam bolt now has RED loctite securing it, and I hope to get the engine installed back in tonight. Maybe this weekend will be a little better outing!

 

Yep done that myself. Cost me a nice 302. Mine was much worse. Before the pin broke the cam walked back and the cam lobes hit the lifter next door,took chunks out of the lifters which found there way into my oil pump and stopped it dead. You may want to have a peak at your cam and lifters if its still apart. Hopefully your cam didnt walk back like mine did.

 

Duuude that stinks! I am trying to understand how it could shear.. The only load to the cam is the valve springs isn't it? Otherwise it would just turn ..?

 

Cam and lifters looked fine. Solid Roller cam and lifters .614 lift IN/ .621 Ex. I'm gonna guess that with the bolt not holding pressure against the sprocket...the "slack" in the timing chain was enough to allow them to hit. I'm running dome pistons, with about 13:1 compression, so there wasn't a whole lot of clearance to begin with. I checked it again yesterday as I was putting it back to gether and had .121 on the exhausts...which is enough...but it ain't much lol. Intakes had more...but they don't necessarily need as much.

 

Bummer, Guess that is the reason some double pin their camshafts.

 

Man that sucks, I red loctite everything on my car.

 

Good luck this weekend, would love to hear how you do Tom.

 

Thanks Ward...I suspect it will run much better without the valves hitting the pistons ...that's been my experience in the past anyway

 

ITs pretty common Gene. Seen many Hemis do it. Lots of load on that little pin on accell and decel if the bolt is loose.

 

Glad your cam is OK.

 

Be careful I've machined several lately for double pins. And honestly I don't think the bolt has much to do with it. The last one I did had already been machined for a 3/8 bolt and was using an ARP stud with a hardened ground washer and it wasn't loose when it sheared. It's double pinned now with 2 unbreako brand dowels. This motors springs are 700 psi open pressure and .730 lift.

 

Wow...that's not very encouraging lol. I'm planning on switching to a bigger cam over the winter, and will have it drilled for double pins...or can you order them like that new? Never checked...I've never had this happen...or even knew anyone that it happened to actually. Will definitely be in the back of my mind for a while though.

 

Surely you can order them that way. I understand that all of the Pro 5.0 guys double pin but they are definitely the most extreme in the small block world. I don't know how extreme yours is. It may be fine. These engines I've been helping with are 650+ hp to the ground. No power adder.

 

Hope all goes well for you.

 

Now this has got me thinking about if i used loctite or not.