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  #91 (permalink)  
Old 12-09-2007, 07:14 PM
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Quote:
Originally Posted by Joshua Lee
Bogie...

All that would be true if the engine hadnt been running for so long WITHOUT this issue... See my point?

The motor has been the same for 2 years without an issue before the 1st bent valve... Now another....
Then your back at square one, assuming a main or rod bearing isn't going out allowing the crank or the rod to get away with abnormal movement, I'd of course sustect a rod bearing before the main. Or a rod is stretching because it's in failure mode, or the pin or piston have distorted to make it longer in the bore than it once was. If not that, then we're back in the head and or looking for damage to the cam or its drive mechanism. If the cam is coming retarded or is excessivly advanced there can be problems with the piston and valves being in the same space.

Back to all I said and you discovered about the valve train. Anything from the valve floating or sticking to your discovery of the rockers coming in contact with the head bolts is back in play and all needs to be carefully inspected.

Bogie

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  #92 (permalink)  
Old 12-09-2007, 08:38 PM
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me ~>

I just hate having a problem just come up from nowhere.. Even before the 1st bent valve I had 20 passes without a hitch....
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  #93 (permalink)  
Old 12-10-2007, 05:59 AM
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Did you replace the valve springs the last time you had the heads off?
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  #94 (permalink)  
Old 12-10-2007, 11:07 AM
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No... The "guy" said they were fine

What about timing chain stretch Bogie?
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  #95 (permalink)  
Old 12-10-2007, 01:33 PM
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Quote:
Originally Posted by Joshua Lee
No... The "guy" said they were fine

What about timing chain stretch Bogie?
Springs can't be totally ruled out because they pass a compression test. That puts the possibilities that the spring has control on your side but is not a guarantee. Truly odd things happen with springs, they move like made from jello. You can always get into unpredictable symbiotic vibrations that cause the the spring to surge and shake out of control.

The timing set can be a source of problems with too much advance initially set into it or as the gears and chain wear the cam timing will fall retarded. Either situation can get you into collisions between the valves and pistons. It's always a good idea when first setting the engine up to mark the distributor's position retaliative to a fixed point on the engine. That becomes on indicator that if you've not made any timing case changes yet the distributor needs to be advanced to maintain the proper timing, the timing chain or gears are wearing allowing the cam to fall retarded and you're compensating for the resulting lost spark timing. This of course can also indicate problems with distributor and cam gear wear as well, but it serves as an early indicator that something is happening.

Bogie
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  #96 (permalink)  
Old 12-10-2007, 02:51 PM
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Springs sound suspect with that much time on them. Do you know how the guy checked them? You may have posted but what are the cam specs? My engine is a brand new build and the builder is concerned with them sitting for any period of time with pressure on them 650# open. What are your spring pressures?
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  #97 (permalink)  
Old 12-11-2007, 05:47 PM
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Any suggestions on steps I need to take??? I dont want to pull it apart and miss something...
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  #98 (permalink)  
Old 12-11-2007, 07:17 PM
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Quote:
Originally Posted by Joshua Lee
Any suggestions on steps I need to take??? I dont want to pull it apart and miss something...
How apart is apart going to be?

At this point I'm pretty concerned about everything from machining to parts.

- I'd be interested in rocker cover to rocker, girdle, and retainer nut clearance.

- Back to your old friend rocker to head bolt clearance

- Rocker to stud and rocker to retainer clearance.

- Sweep pattern of rocker tip on valve stem.

- Coil clearance when the spring is compressed to max lift plus say .050 over. The coils should have .050 between them, that's good for the inner as well as outer springs.

- Clearance of the retainer to the top of the guide including any oil seal. .050 is absolute minimum but with a sudden jerk, high lift cam .060 to .070 would be better.

- Putting the head in a press and depressing each valve in turn to max lift, looking to see what the casting is doing around the spring pocket.

- You do have a hard shim between the valve spring and pocket?

- Check for proper guide to stem clearance.

- Check to insure the seat is normal (90 degrees) to the guide and is concentric with the valve.


For the timing set, you can go thru the drill to see if timing has slipped by doing the installation thing with a degree wheel and a positive piston stop before you rip the guts apart. A number of sneaky racers use the factory nylon coated cam gear and silent link chain instead of the "racers" stuff to reduce the transference of dynamic crankshaft forces into the cam; elimination of bad, bad, bad vibrations. They change up the timing set frequently. Leave gear drives for the pros, cause if you have a shaky crank they'll cause all sorts of mischief with the cam.

The piston that hit the valve should be pulled, you just can't trust it. While there check for looseness in the bearings that could allow the piston more movement than can be tolerated.

If you don't have a rattler or viscus damper on the crank get one. You need to soak up wild vibes on the shaft. Check the number one main. If it's carved out on the front edge, that's tell you the crank snout isn't damped enough and isn't running on center.

Bending moments on the block induced by the alternating forces of the pistons can twist the block and bend the heads as well. For a competition engine this can become a real problem when using production components, especially when the block is overbored and or relieved for a stroker crank. The only hope here is a real race block whether GMPP or aftermarket to gain the necessary strength and stiffness.

Four bolt caps do a lot for holding the crank in place and spreading the loads out. A bottom end girdle can help a lot to keep them reacting forces in the directions of max strength. Cast iron heads add to overall bending strength as well, but if the block is strong enough on it own, i.e. racing grade stuff, aluminum heads are fine, but they contribute little in the way of stiffness to the block which often isn't enough for a production block gone racing. Another help is a valley girdle in a stock block. This helps retain and react the loads that want to lift the cylinder block both up-wards and out-wards causing all sorts of distortion in the block which it shares with the heads. Keep in mind that SBC heads bolt to the cylinder walls, distortion there is transmitted up the bolts into the head.

The clearance of the lifters to their bores needs to be checked as well as their alignment to the cam. At this point I rather think the cam's gotta come out. If the lifter is lofting then it's quite likely to have damaged the cam. The cam must have a stable retention button or other means of reacting it's lateral movement besides hoping the lifters can do it with a 2 degree twist in the lobes, for a high spring pressure high turning engine with flat tappets it ain't enough. If you're using a button then you've got to use a cast timing cover or if sheet metal a bolt and lock nut arrangement from the water pump back against the timing cover to provide a way for lateral forces to be reacted into something stiff and strong enough that it can't be pushed around.

You'll find I use the work "reacted" a lot. This is engineer speak for the need to transfer forces and loads from one place to another. Forces and loads always cause distortion even if you can't see it, it's there. With a strain gauge and a swing, I could have you sit on the swing while it's attached to the biggest, heaviest beam you've ever made, and it will bend enough to tell your weight within a few thousandths of a pound.

The crank needs to be carefully balanced. As power goes up an externally balanced shaft becomes a liability. A race engine needs it's balance by the main bay. This takes a lot of load off the shaft which is reacted into the block thru the main bearings and their webs. However, balancing never eliminates all the loads because you can't counter balance the power stroke that tries to accelerate the shaft nor the exhaust stroke where the piston and rod going over the top want to lift the shaft, and the other strokes want to slow the shaft, while others still want to drive it out the bottom; but if you can at least get the weight of the piston and rod offset in the counter weights, a great deal of load is thus neutralized reducing the forces being pushed into the block's structure.

Bogie
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  #99 (permalink)  
Old 12-11-2007, 07:38 PM
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<~me
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  #100 (permalink)  
Old 12-11-2007, 08:10 PM
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Quote:
Originally Posted by Joshua Lee
<~me
OK, I finally went to the map to find Justin, Texas. Probably been close if not in it. I've spent several business trips in Corinth and Louisville. Lived in Houston but that's about 300 miles from you. Was stationed at Ft. Wolters back when there was a Ft. Wolters out there by Mineral Springs. A long, long time ago. Was in the Waco airport the day JFK was assassinated.

Bogie
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  #101 (permalink)  
Old 12-12-2007, 03:42 PM
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I live in Sanger now it's about 20 miles north of Justin..

OK BOGIE.... Answer me this

I do a small (street) burnout behind my house... Bring up the rpm's and launch...Bring it to 6200 and shift and bring it back up to 5000ish and let out... TWO TIMES

Not broke....

Take it to the track and do a single burnout and it breaks??? Why would driving it up to 6k rpm's not break it but a track burnout (5-5.5k) break it?
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  #102 (permalink)  
Old 12-12-2007, 05:10 PM
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Quote:
Originally Posted by Joshua Lee
I live in Sanger now it's about 20 miles north of Justin..

OK BOGIE.... Answer me this

I do a small (street) burnout behind my house... Bring up the rpm's and launch...Bring it to 6200 and shift and bring it back up to 5000ish and let out... TWO TIMES

Not broke....

Take it to the track and do a single burnout and it breaks??? Why would driving it up to 6k rpm's not break it but a track burnout (5-5.5k) break it?
This I can't really answer. "Luck of the Irish"-"Third Time's the Charm"; who knows. It might hook up better at the track snapping the driveline back thru the engine which triggers some of the deformation events I was talking about.

How are the engine and or transmission secured to the chassis, with a torque plate, factory rubber mounts, same idea as OEM but with a solid mount?.

I know this seems weird, but some of these problems come at you from strange directions. So I'm cogitating as to whether a bending load is being introduced from the chassis reaction back into the engine.

Bogie
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  #103 (permalink)  
Old 12-12-2007, 05:19 PM
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stock location steels up front and stock location poly on the transmission..
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  #104 (permalink)  
Old 12-12-2007, 07:14 PM
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Quote:
Originally Posted by Joshua Lee
stock location steels up front and stock location poly on the transmission..
You might be at the point where you need to go full pro and mount the engine with mounting plates. This will move the reaction load from the mid side water jackets to the front and rear of the block.

See: http://www.jegs.com/webapp/wcs/store...10002_56706_-1

and http://www.jegs.com/webapp/wcs/store...10002_12466_-1

Bogie
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  #105 (permalink)  
Old 12-13-2007, 06:32 PM
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I have allready thought of that..But... At the moment I need to fix this damn #5 issue, lol... Would you go "all in" on the timing chain and cam springs? or what at this point? I am pulling it back apart this weekend...
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