Engine Problem. Help!

Hey guys -- I've got a 454 in my Supra Saltare that only has about 150 hours on it since the last rebuild (which I did myself.)

Yesterday... which was the last day of the season anyway.... I was pulling a rider and the engine went POP and just died. Wouldn't restart and there is def. something inside the block rattling around when I try to turn it over.

No shavings on the dipstick and the oil looks good. I just pulled off the valve cover on the side that seems to be making the noise (I was hoping to discover a bent pushrod or evidence of a bad valve) and when I go to turn it over, none of the valves move. The engine cranks but NO VALVETRAIN activity. WTF? Is it possible I broke the cam? What should my next step be?

Thanks!

Broken timing chain would be my guess? Maybe a cam? Did you replace the cam? If yes I would assume you replaced cam bearings, maybe too tight?
That sucks!
sorry
G

Yeah, when I rebuilt it I replaced the cam and cam bearings. I'm trying to remember if I have to pull the harmonic balancer to get the timing chain cover off to check it out....

balancer: not sure on a chevy. Is there a hole (crank) in the timing cover? If not, you could leave it on.

Sounds like a timing chain to me too. If the cam was broken, you would have valvetrain action to the point of the break.

Anything else to be aware of? I'm assuming that if I can find TDC and align the gear markings, this should be a fairly straightforward fix. THANK GOD the boat isnt a v-drive... this would probably be an engine pull for sure!

Well..... Not sure how this happens.



??????

Looks like your cam froze up or something haulted it VERY quickly?

Yep. But.... how does a cam freeze up?

improper cam bearing's installed how did you put them in and you must line up that rear bearing with the oil passage Joe

You need to have a machine shop install them or you need to buy the cam bearing installation tool which I bought but its 200.00 so its cheaper to go to a machine shop You also need a cam shaft handle to install the cam without scaring the bearing. usually lack of oil to the cam You should have noticed it on your oil pressure gauge. Joe

Did also break that cam in properly you need to run that engine at 2000 rpm for a min. of 20 minutes the cam is lubed by splash of the oil. it will not break in the cam properly. if it just idles. this is the biggest cam failure on a small chevy. usually lobe wear.

Looks like the bolts were over torqued and failed.

Joe -- My machine shop installed the cam bearings and I used the comp cams installation instructions to install the cam. Break in procedure was followed to the T. This engine had 150 hours on it before this failed... I'm still so confused. If there was a torque problem or a break-in issue, it would have happened much sooner.

I am confused also. I have drag raced all my life and had a lot of failures. looks like you were running a double roller timing chain. I have seen engines grind up rocker arms bend push rods in "U" shape and never sheer those bolts off. other than a cam bearing failure. you need to pull that engine out and remove that cam. we run gear drives and dry belt systems now with cam buttons to keep the cam from walking. but this has nothing to do with your failure. most the time if you have something come apart that iron gear will just chew everything up like a grinder. why don't you contact comp cams great company I have dealt with them for years. maybe they will be able to tell you what kind of failure your engine had, Joe

I called comp cams right after it happened and the tech I talked to on the phone had no idea... said he's never heard of this before. I've personally bent pushrods, wrecked distributor gears, and had other maladies happen... but this is still a REAL PUZZLER!

I dont know about your build but if it was a zero tolarance build (domed pistons, no valve reliefs ect....) I'm pretty sure you toasted some pistons and valves. Sorry but good luck

I wish I lived close to you I would love to help you tear it down. We could sit here and guess all day, You won't know until you tear into it. I have never seen that happen before Joe

In the pic above I see 3 broken bolts but no dowel pin???

Loosen the rockers and pull the push-rods, cam should rotate with little effort if bearings are ok. But usually, a bad bearing will cause the cam to twist in half right i front of the bad bearing.

(Message edited by chpthril on October 06, 2008)

Yeah -- I have no idea where the damn dowel pin went. It either fell into the oil pan when this went south or it was never installed. Unfortunately, it was so long ago that I dont remember if there was one there or not. I'm going to try and snake a magnet into the oil pan and see if I can come up with it.

I posted this same thread to hotrodders.com and those guys seem to think it was either caused by that missing dowel, or overtorquing/undertorqing the bolts. I myself think it's possible that the gear was worn so badly that it caused a big impact everytime I stopped and started. Right now my plan is to drill out those bolts, install a new timing set and see if I can turn it over by hand. If the cam isn't seized (and I don't suspect it is) then I'll do a leakdown test and try to diagnose how the valves faired. It doesn't have domed pistons, so I really don't think the valves got hit -- but we will find out soon enough.

Thanks for all of the help!