Broken Timing Chain?

[wotan2525]

The saga continues....

Last Friday was the last day of the season for us (better to happen now than on the first of next season!) and I was pulling a rider at about 3400RPMs when POW! loud noise and engine quit. I was able to flag down a tow from a drunk guy in a dingy.... put the boat on the trailer and dragged it home.

I expected the worst due to the sound the engine was making when I tried to turn it over. Sounded like metal parts against metal parts. I pulled the dipstick and there wasn't any shavings.... good sign! I pulled off the exhaust risers and the valve covers to discover that I don't have any valve train activity at all.

Since I've rebuilt this engine before, I'm not too worried about the process of replacing the timing chain and gears, but I don't really know how to degree in the cam and get everything lined up correctly. Anyone have any advice or resources on how to do this?

Thanks!

[Seabeejamie]

You dont have to degree the cam. If you run manufacturer parts (for a chevy) just line up the two dots. dot should be at the top for the crankshaft and the bottom for the camshaft. aside from cleaning the gasket maerial off and draining the oil, 20-30 minute job.

[wotan2525]

Any benefit to degreeing in the cam? Do I even need to find TDC or just line up the dots?

Sounds easier than I thought it would be! I looked on the comp cams site and the instructions mentioned a CRAP LOAD about how to advance or retard the timing...... It confused the hell out of me.

[Salty87]

i changed my timing chain a long time ago. i think you just need to line the dots up.

any chevy manual should say, doesn't need to be marine.

[Seabeejamie]

There are benefits to degreeing a cam, but to do this mods must be made to intake, exhaust and ignition timing. Manufacturers do a pretty good job of dialing in the cam for a good all around power band. If you REALLY want to go this route, I would recommend that you call the manufacturer direct, tell them what it is you want exactly, and they will custom grind you one for about $100.00 more than what you would pay for an "off the shelf cam".

[wotan2525]

Well.... How in the EFF does this happen?

Any ideas what the next step should be for me?

http://img145.imageshack.us/img145/4015/10404520zr6.jpg

[Salty87]

help me out here, wotan....am i not seeing the end of the camshaft? i've seen the inside of mine before but i was watching. i'm no mechanic. i sent mine to a shop for rebuild. i don't even have a garage at home, did everything outside.

[wotan2525]

Yep. That's the end of the camshaft and the three bolts that are sheared off. I can't imagine a force that would cause the camshaft to stop that suddenly.

I've got my fingers crossed that it wasn't actually a seized cam that caused this (I'll know more when I'm able to extract those bolts and give the cam a spin) -- hopefully it was some kind of issue with the bolts being under or over torqued. Sigh.... Boats.

[Salty87]

you're up north, aren't you?...don't know how you guys deal with short seasons.

i know that feeling of dread though...best of luck!

[DKJBama92Mariah]

Who did the rebuild? I have never seen or heard of anyting like this. My first two guesses are that either the rebuilder used substandard hardware store bolts on the cam sprocket that just snapped, or one of the bolts just worked its way loose, causing the sprocket to wobble back and forth and shear off the rest of the bolts. When you put her back together, a bit of loctite on those bolts sure couldn't hurt.

Hopefully one of the valves didn't smack into a piston.

Keep us posted,
DKJ

DKJ

[wotan2525]

<sheepishly>

I did the rebuild. It was my first one. I think I've discovered the problem and it's exactly what you suspected. I drilled out those bolts and one of them only had about 3 threads left in the cam. There was no loctite on any of them. I'm going to reassemble it dry, pull the spark plugs, and see if I can get it to turn over by hand. Assuming the cam isn't seized, the next order of operation will be a leakdown test to see if the valves were roached.

[DKJBama92Mariah]

Oh man bud, that sucks. I just shed a tear for you. Live and learn i guess. Sounds like you've got the plan for dealing with it though. Good luck and may all your valves be straight.

DKJ

EDIT: Also, when you go to turn it over by hand, have the valve covers off so you can make sure all of them are opening. Keep an eye on your pushrods too to make sure one of them didn't bend.

I'm not sure a cams normally seize. Usually when something seizes up in the valvetrain it ends up being a lifter getting stuck inside its bore. This usually just ends up making a helluva racket and wears off that particular cam lobe.

[Seabeejamie]

If you didnt use loctite and one backed out, this can be enough of a balance issue to vibrate and hence shear the remaining bolts. Some good news here, if you didnt go with an extended lift cam, your valves should be fine. The 350 has a semi hemispherical chamber (wedge) that JUST allows for the valves to be fully open and the piston at TDC. most people alter duration of intake and exhaust rather than lift, so you are probably OK.

[DKJBama92Mariah]

Wotan,

Is that a chevy or a ford motor?

[Salty87]

wotan's running a 454

[DKJBama92Mariah]

wotan's running a 454

Yup, that's out of my territory; I'm a Windsor man. Good luck with it.

[wotan2525]

I don't have the light to get this figured out during the week, so hopefully on Saturday I will know a lot more. From everyone I've talked to, I really don't think there is going to be an issue with the valves interfering with the pistons -- but I'll give it a once over and make sure I'm ok.

I bought a cam locking plate, new cam bolts, and a bunch of other goodies to upgrade while I have it taken apart. I'd almost forgotten what a joy it is to remove and reinstall those exhaust manifold risers. Grrrr!

[wotan2525]

And she's back... 2 oil changes... a compression test... it doesn't appear like there is any lasting damage. Wahoooo! You never get lucky on these things!!!!

[Seabeejamie]

glad to hear it Wotan....still have time for a last run or two!