My step-dad has a '66 427. It has been an absolute nightmare to get anyone competent to work on it. He had the car partailly restored, including having the engine gone over. Two months later, it blew. Total rebuild was done. A few weeks go by and a stud snaps and a rocker arm puts a severe dent in the valve cover. Got that fixed. Three months goes by and the motor blows again. He never even jumped on it. Ok, another total rebuild. Last week another stud snapped on the other side and the rocker arm darn near came through the valve cover. Here's the question:

The mechanic says that stud girdles should be installed, also requiring tall vale covers. I'm no mechanic, but I think the guy is full of :bs . How many 427's are out there that run just fine without girdles? :rolleyes: What could be the problem?(besides having a crummy mechanic) The specs on the motor I don't know. All I know is that it made 514hp on the engine dyno. That is healthy, but shouldn't be so harsh as to snap what are supposedly the strongest studs available. Any ideas? Thanks, Classic

 

Here is a link talking about the need for stud girdles.
http://forums.corvetteforum.com/zero...212563#2212563

John

 

I don't know what your dad's cam specs are, but if it's a pretty mild cam there should be no need for stud girdles. I'm running a 294 Duration solid flat tappet cam in my 468 without stud girdles. After all of this trouble with the 427 your dad keeps going back to the same engine builder :confused:? I would have ditched him after the first engine failure.

 

Sounds like you have some coil bind issues of some sort. Either springs are stacking solid or pistons are hitting valves etc. If all that is happening, a stud girdle is not going to help.

How much cam is in it and what springs? Tell us the rest of the combo... pistons, heads etc.

What actually "blew" each time? Did it drop valves, spin bearings or what?

Sounds like we need to start back at square one and slowly look at everything. Something ain't right!

Jim

 

Ok, the motor was done by a restorer, after which is spun the bearings and a bunch of other bad stuff. Took the motor to a different guy to be rebuilt. Then a rocker arm breaks. Shortly after that, the motor gave up the ghost because coolant had made it into the oil. The mechanic said a lifter broke and that caused the radiator to be entirely drained of fluid. So the motor was totally rebuilt again. Now another stud breaks on the other side. The specs for the engine are:

Cleaned and degreased, Align bored and honed, decked block, machine block for cam thrust plate.

.060 TRW forged pistons
9.75 to 1 comp ratio
Forged steel crankshaft, rods + Mains machined .010
connecting rods bushed and reconditioned
balanced rotating assembly

Heads, big block rectangular port, open chamber
bowl ported and gasket matched
resurfaced
pressure checked
4 angle valve job
bronze valve guides
manley intake and exhaust valves 2.25+ 1.88
Isky valve springs,locks and retainers
comp cams guide plates, studs and push rods
Harland sharp roller rockers
Isky roller cam kit, .620 lift, 290 duration, 108 lobe center

750 holley dbl pumper, 4 corner ideling

Supposedly this engine made 514 on the engine dyno. Does that right either? Thanks Classic

 

From first read, the thing that stands out is pistons, valves and cam. You have a relatively healthy cam there and I'm assuming the 9.75 pistons are the small dome ones with around .100 dome.

Something you really have to watch on those pistons is the edge of the valve pockets. The pockets are pretty shallow anyway, but the real issue is they were designed for 2.06 valve heads. 2.19's get real close when you get near .600 lift. 2.25's have got to be tight if no work was done to them.

They typically hit around the upper edge of the pocket. If you look at them close you can see the shiny spot worn into the piston.

I can also tell you that stainless valves don't take the side bending loads very well when they are touching pistons. Not too bad if they hit squarely, but edge hits hurt them quickly.

I'd roll the motor by hand and watch the valvesprings for stackup. You need AT LEAST .030 between coils (.060 much better) at full lift. Don't forget to check the inner one by itself. Also check retainer to guide clearance. Usually no problem on big blocks, but with new guides there's no telling how much clearance there is... depends on who set them up.

If studs break, something is stacking solid. Either springs, retainer or piston. They just don't die often unless this happens.

The Hp level is OK, but nothing drastic with a solid roller cam and rectangular port heads unless it was made without headers. That much cam needs much more compression.


Jim



[Modified by 427Hotrod, 11:44 PM 6/5/2002]

 

Thanks for the help. The car has the original exhaust manifolds. I keep trying to talk him into going with headers. He is going to need all the help he can get if he gets to run against my 327. ;) Thanks again, Classic

 

I don't think the mechanic is full of it at all. You are making 514 crank horsepower. If you're revving this engine up pretty high, and it's that wild, you should have stud girdles and tall valve covers. I know this creates a clearance problem on Corvettes with power brake boosters, but you could try getting a cheap set of chrome valve covers and ding them with a ball peen hammer for clearance, just to see where it's at. You would be surprised how much flexing is going on in the entire engine.

There are a couple of things you really need to check though. You have to make sure if you're running roller rockers, that the pushrods are the correct length and the rollers are perfectly centered over the valve. You also need to make sure you have the correct springs for your cam, and make sure there is no coil bind. These are things you have to check first.

I agree that if you had a mild 427, you would not need any of this. But at 514 horsepower, you obviously do NOT have a mild 427. Stud girdles seem like they cost a lot, but they are good insurance. Also, consider buying ARP screw in studs. As you increase the performance of an engine, you must respond with the right parts to make it live.

 

I run L88`s on the street and they never required stud girdles. They produce over 500 HP correctly set up. If your braking engines at the rate you say, the assembly is incorrect. If you use the right parts with your combination it should be good for 20,000 miles not three months. Contact a racer that uses a big block engine in your aera and have him assemble it and that should solve your problems as he would know if your clearences are correct. All they are, are pumps. But whom ever is building the engines appears to be inexperienced with high horsepower. Camshaft, springs and guide clearences have to be checked. Just adding parts to an engine sometimes causes the trouble. Not everything is compatible. :)

 

I agree with a number of guys here. There is no need for a stud girdle but it is cheap insurance. If you are breaking studs something is binding. Either the spring is going solid or the retainer to guide clearance is off. If you are running into binding the lifters will soon be destroyed along with the cam nose.
If a lifter went bad the last time is also is pointing to something going solid. Most normal shops aren't too swift at checking these clearances.
Good luck