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Old 02-28-2006, 11:28 PM
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Broke the fresh BB

The motor is pretty much a stock Corvette L36 427 BB with everything new except crank & rods. 10:1 compression. It was professionally built (so I'm told), never ran, and sat for many years, so I took it apart to replace seals & gaskets, relube, and just give it the once over, and also replaced the Pete Jackson gear drive with a Rollmaster timing chain set. Cleaned up all the threads and replaced head bolts, etc with ARP stuff if it didn't already have it.

I started it to break in the cam and oops, had the distributor out 180. Kaboom thru the Qjet. Fixed that and restarted. The motor ran fine and was smooth. I did hear some ticking noises. Lifter preload was 1/2 turn, so went to check it out. Pulled the valve covers off and crap... 3 broken guideplates (all exhaust side) and one slightly bent pushrod (exhaust). With my vast experience (this is my first BB) I didn't pay attention to the fact that the pushrods are different sizes. That can't be a good thing. I didn't realize it until after I removed all the pushrods, and now don't know if I had them mixed up. The other head was ok as far as pushrod location, but it also had a broken guideplate (exhaust). Guide plates are Manley, but no idea on the pushrod brand or if they're even heat treated. They are the 3 piece type with welded balls. The rockers are Comp Magnum 1.72. Don't know about the studs. I've ordered all Comp Cams brand stuff to replace everything on top, except the rockers, and got the Magnum pushrods.

Ok, that's it. I have no idea what caused this, so looking for some help in understanding the problem so I can avoid it happening again. Should I pull the heads to check the valves? I ran a vacuum test on one side (for now) and all cylinders act the same. It's not airtight and can only pull 10 lbs before leaking down and holds at around 5 lbs.

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Old 02-28-2006, 11:41 PM
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with the 1.72 ratio rockers did you factor that in when you ordered the cam, valve springs and pushrods? if you were trying to lift that motor more then the heads will allow you'll get that problem. dont quote me on this, but the pushrods for the exhaust will be slightly longer in length then the intake pushrods. im pretty sure thats how it is without looking it up.

IMO it sounds like when you took the engine apart to replace the gaskets you put the wrong pushrods back in the wrong holes.

but thats just my opinion. maybe somebody else can say different......
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Old 03-01-2006, 05:58 AM
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Have you pulled the heads? Look to see that valves hit the pistons and see if they match the broken parts. If you reversed the push rods you had some real lift there for a short time. If your lucky you may not have hurt anything you can't replace with a few bucks, depending on the cost of the pistons.
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Old 03-01-2006, 07:53 AM
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I haven't pulled the heads yet. The pushrod was just slightly bent. When it was all together, the depth of the nuts on the rocker arm studs were all the same. The pushrod that bent was in the correct location. Any ideas why the guide plates snapped?
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Old 03-01-2006, 08:15 AM
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It's highly unlikely that you had the pushrods in the wrong positions. The difference between the two is about an inch. An inch too long and you'd never get the rocker on and an inch too short and it wouldn't reach the rocker no matter how far you screw it down.

Sounds like too much lift/duration for either the valve spring/retainer stack or piston to valve clearance. When contact was made the pushrods bent/broke and the side load took out the guideplates.
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Old 03-01-2006, 09:44 AM
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not uncommon with bbc engines that sit for a while. they have iron valve guides and the valves will frequently be stuck and the pushrod crumples under lift, possibly taking out the guide as collateral damage. you should be able to free up the valve and replace the pushrods if it did not run for any length of time. check the cam for wear.
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Old 03-01-2006, 12:25 PM
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Here's the cam info... Lift I/E is .502/.527, Duration 292/303, Duration @ .050 214/224. Not sure about the springs, but I would think even a stock set of springs would handle this cam.

As far as a sticking valve, wouldn't that have been obvious during the rocker adjustment?

The motor ran very smooth during and after the break-in. Took it on a couple test drives while fine tuning stuff. Great throttle response, etc. Then the ticking noise started. One thing that happened is that the distributor hold down, well, didn't hold, and at one point it rotated a bit and I was at 12 degrees ATDC. Don't know if that relates but just throwing stuff out there...

Tnx!
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Old 03-01-2006, 04:42 PM
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yeah that's a pretty mellow cam. I noticed this on my 454 prior to rebuilding. It ran fine, but had a broken pushrod. I did not adjust the valves prior to firing up the core, but sure enough the valve was stuck from some moisture getting in the valve guide. I don't know how you set up the valves (what method) but assuming it was stuck in the closed position, it could be missed. check the action on the valves with a lever type spring compressor to verify their movement.
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Old 03-01-2006, 05:02 PM
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Doc here,

Another thing that is extremely rough on a fresh cam and valve train, with little or no lube in the valve train..Is a backfire..

Imagine if you will the force of the engine rotating clockwise and within milliseconds dead stop and be forced to "Kick" backward..

On an older set up, chain slop will buffer a lot of the impact, but not so forgiving on a new set up.

You may want to keep that in mind when you repair it this time.

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Old 03-01-2006, 05:16 PM
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Hey tnx, ratlover... I'll give it a try with the valve compressor. That makes sense to me. On top of everything else, the #5 exhaust rocker was overheated as well (blued). I still haven't run the vacuum check on the driver's side but getting ready to go out there and do that. How did you free up the valve? Was compressing it enough? I didn't build the heads. I bought the motor already built, but one that had been sitting for several years (8 I believe), which is why I tore it apart to replace stuff, relube, fresh thread sealer, etc.

Docvette... Tnx for that info. No, I won't be out 180 again. That was an amateur move. Oh wait... I am one...

It's actually a good thing I tore it apart since one of the piston compression rings was in the wrong spot. Plus the honing job was less than, well, it sucked.

If you guys want to see the engine, I have some pics on our clubs gallery. It should be the 1st album. Gallery
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Old 03-02-2006, 08:37 AM
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This was just prior to disassembly and rebuild on my motor. I did free it up by squirting some penetrating oil underneath the umbrella seal and working the valve up and down. It would probably be best to pull the head and inspect for any damage, but you could get by this way. If there are no domes on the pistons, the 454 with this little lift is a non- interference engine (piston hitting valves) so I think you are ok there. I have also heard of some guys running a little tranny fluid in the gasoline to help lubricate the valves. I think so long as you check the lobes by pulling the intake and putting a dial gauge on the lifters to verify and record lift you would have a good idea if there are any problems existing that may affect performance down the road. good luck.
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Old 03-05-2006, 07:22 AM
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Just wanted to let everyone know that the motor is well again. I pulled the valve springs to check the valve movement, and they were fine. I replaced several things with Comp Cams stuff, plus using their Magnum pushrods. Those things are sweet... They're the chromoly ones with hardened .080 walls. Fired her up and no incidents. Ran smooth, no odd noises, perfect, started breathing again...

What was the cause? Still dunno, but it could have been a temporarily stuck valve, the 180 out backfire, or bad karma.... Tnx for the help, guys.

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