Im trying to find out why my brand new, freshly assembled and built 6 bolt exploded one single valve on the first 30 seconds of idle.

Brian crower 272's (brand new) are the only add on to the head right now.

I was using a cometic MLS, the head is definetly nowhere near "service limit" in terms of overall height, the valvetrain was stock but the head is a new remanufactured unit. Piston to valve clearances were fine.

After idling for a minute it died, and i found this:










Timing was dead on. Motor started up very first crank, then this happened.

I guess i really dont know what would cause this valve to snap at idle after 30 seconds. Everything on the car was brand new?

How can i tell/find out if the BC 272 cams caused this?

You measure the lift, duration and degree to their specs.

Just something to look out for, I have seen something similar before and it ended up being the crank TIMING off. The tin plate that has the marker on it can go on 2 different ways: the right way and the wrong way. If it went on the wrong way, the marker would say the motor was at TDC when in fact it was not. Just check for your own sake before you begin to point any fingers.

Thanks Tim, i am definetly not looking to point fingers right now, im more or less trying to find out why this happened before i start to rebuild this mess.

i did not think about the crank plate being on wrong. If i put the crank plate on and when the marks line up, it would/should be a TDC in #1, correct? If i put it on backwards, it would line up (mark wise) but not be at TDC? Simple as that?

Im pulling the lifters and cams out tonight, so i'll see if the lifter froze up, or if the cam is scarred at all..

The valves were hitting the pistons. Its not the cam's fault, you have to check that kind of stuff when you put an engine together.

Kevin

How are the other valves?

If your timing was off, I would think you probably have at least 3 other valves that are bent or broken/scarred.

If it's just that one valve, I would lean towards a frozen lifter or something that could affect just one valve.

Someone feel free to correct me if my thinking is off here

You can see marks showing contact on all the pistons and also the intake valves are shined up where they were hitting (adjacent cylinder). It was a basic piston-valve clearance problem, nothing froze up or anything like that.

Kevin

Agreed, the timming was off. It happens, live and learn. Kinda sucks it's such an expencive lesson.

I dont see any marks on any other piston. If the timing was off he would of had valve contact the second he started it.

Ya it wouldnt have ran for 30 seconds. Let us know what you find.

He ended up putting the crank plate on backwards which showed his timing as being right but it was actually off. His car is back together.

Ouch, expensive lesson learned

wishihadatalon said:

He ended up putting the crank plate on backwards which showed his timing as being right but it was actually off. His car is back together.

Click to expand...

Was I right... or was I right?

fwdeclipse said:

I dont see any marks on any other piston. If the timing was off he would of had valve contact the second he started it.

Click to expand...

Not true. I've seen it with my own eyes. The car runs relately well actually. It's not until you rev the motor up, that pistons HIT valves.

Soo the best way to avoid this is by having the balance shaft sprocket on the crank as well, as you can't line that one up wrong correct? If the trigger plate and balance shaft sprocket are aligned together, and the balance shaft sprocket is on the right way, you won't run into that problem... I think.

Best way to avoid it- permanently mark the timing plate before you take it off. Etch "this side out" into it with a dremel or something. I remember being freaked out by this very possibility when I was putting my engine together because I hadn't marked it.

SO how do you check this after the fact? seriously, I'm paranoid now.

It's pretty evident. If you put it on the wrong way, it bends because it doesn't have a perfectly flat profile. Secondly, the crank sprocket and balance shaft sprocket are usually etched into the plate. Thirdly, put a screw driver into cylinder #1 and when it stops moving up when you turn the crank, it's at TDC.

why not just rotate your motor and see if the crank mark is lined up with the other mark and if the 1st piston is at tdc.

Egh... looks like he tweeks the Valve a little bit... The only way I knew which way the crank plate went back on was by looking at the debris shadow on the surface of the plate... Tech Tip: The best time to clean your parts is after they are installed.