Bent valves on new rebuild

[Clem Z.]

Re: Bent valves on new rebuild

The other choice is self aligning rockers - one or the other, but definitely NOT BOTH!

Duke

make sure you have enought valve stem tip above the keys to do this.

[Joe L.]

Re: Bent valves on new rebuild

make sure you have enought valve stem tip above the keys to do this.

clem-----


At least the 2 valves shown in the picture of the engine in question have PLENTY of stem length beyond the top of the valve locks. If all the valves are the same, which is likely if they were all replaced at engine rebuild, he should have no problems, at all, if he wanted to use guided rocker arms.

[Steve V.]

Re: Bent valves on new rebuild

SUCCESS. Taking advantage of Jack's keen eye on the push rod slots, Duke and Joe's advice on parts and the many other essential tips, the engine was reassembled today with new push rods, guided rockers and new rocker studs and she fired right up, apparently no other damage. A week or so late I was able to take my 20 mile shake down drive with no problems.

I am very grateful for the invaluable help getting things fixed as well as the education on guides/springs/dampers. All in all one of my lesser expensive educations. BTW, most all push rods were bent and all of the rocker studs were deeply scarred, up to .040" deep.

[Duke W.]

Re: Bent valves on new rebuild

The one remaining question is why were the pushrod holes opening up and the engine assembled without guideplates?

Some consider the above an "upgrade". I don't. In fact, I never understood why GM used pushrod guideplates on some production engines as the previous method of guiding the pushrods with the oblong pushrod holes in the heads never caused any problems that I am aware of.

This is a good lesson for all. DON'T let the machine shop do these kind of "upgrades". In addition to being unnecessary and adding to cost, they can lead to these kind of problems.

The only real design weakness in 283/327s is weak connecting rods. Beyond replacing the OE rods all OE equivalent parts should be used and most of the valve train parts will likely be reuseable.

As far as machining is concerned, most will only need a rebore - no block deck or head machining unless appropriate flatness checks demonstate that it's required, and the same applies to the main bearing saddles. Most will be in alignment and no align boring or align "honing" is necessary. Bearing condition on disassembly and measuring alignment with a machinists bar and .0015" feeler gage is all that's usually needed to determine that bearing bore alignment is in spec.

Duke

[Joe L.]

Re: Bent valves on new rebuild

The one remaining question is why were the pushrod holes opening up and the engine assembled without guideplates?

Some consider the above an "upgrade". I don't. In fact, I never understood why GM used pushrod guideplates on some production engines as the previous method of guiding the pushrods with the oblong pushrod holes in the heads never caused any problems that I am aware of.

This is a good lesson for all. DON'T let the machine shop do these kind of "upgrades". In addition to being unnecessary and adding to cost, they can lead to these kind of problems.

The only real design weakness in 283/327s is weak connecting rods. Beyond replacing the OE rods all OE equivalent parts should be used and most of the valve train parts will likely be reuseable.

As far as machining is concerned, most will only need a rebore - no block deck or head machining unless appropriate flatness checks demonstate that it's required, and the same applies to the main bearing saddles. Most will be in alignment and no align boring or align "honing" is necessary. Bearing condition on disassembly and measuring alignment with a machinists bar and .0015" feeler gage is all that's usually needed to determine that bearing bore alignment is in spec.

Duke

Duke------


I agree that the 283 connecting rods and the early 327 connecting rods were a weak point. Even the later 65-67 small journal 327 connecting rods were marginal. However, one thing that Chevrolet did that many folks don't know is that all 1955+ Chevrolet V-8 connecting rods were forged steel. Many other GM V-8 engines, particularly Buicks, used cast iron connecting rods.

[Duke W.]

Re: Bent valves on new rebuild

The problem with the early rods was not material, but design - a sharp corner and not enough mass at the bolt seats. This leads to fatigue failures.

The second design 327 rod with the extra little hump of material adjacent to the bolt seats was a vast improvement. In fact, I can't say that I've ever heard of one failing, but for $250 you're better off buying new a new set of rods because it will cost about that much to qualify/rework a used OE set, and the new design rods are better than any OE rod. Fifty years of experience and better analysis tools gets you better parts.

Speaking of "design problems" I just finished reading the recently published What Really Sank the Titanic by two PhD metalurgists - Jennifer Hooper McCarty (somewhat of a babe, I must say after looking at her website) and Tim Foecke. They lay out their ten years of research on Titanic structural artifacts and blow away all the previous "explanations" like "brittle steel", and the coal bunker fire.

I think their research has finally solved one of the greatest engineering mysteries of the 20th Century - why did the "unsinkable" leviathon sink, and sink so fast, after mildly sideswiping an iceberg. It's a facinating investigation and conclusion.

If your local library doesn't have this book, they should!

Duke

[Clem Z.]

Re: Bent valves on new rebuild

The problem with the early rods was not material, but design - a sharp corner and not enough mass at the bolt seats. This leads to fatigue failures.

The second design 327 rod with the extra little hump of material adjacent to the bolt seats was a vast improvement. In fact, I can't say that I've ever heard of one failing, but for $250 you're better off buying new a new set of rods because it will cost about that much to qualify/rework a used OE set, and the new design rods are better than any OE rod. Fifty years of experience and better analysis tools gets you better parts.

Speaking of "design problems" I just finished reading the recently published What Really Sank the Titanic by two PhD metalurgists - Jennifer Hooper McCarty (somewhat of a babe, I must say after looking at her website) and Tim Foecke. They lay out their ten years of research on Titanic structural artifacts and blow away all the previous "explanations" like "brittle steel", and the coal bunker fire.

I think their research has finally solved one of the greatest engineering mysteries of the 20th Century - why did the "unsinkable" leviathon sink, and sink so fast, after mildly sideswiping an iceberg. It's a facinating investigation and conclusion.

If your local library doesn't have this book, they should!

Duke

another reason not to do thing piece meal having some work done at a shop and doing some work yourself. the best thing to do is have one shop do it all including assy of the engine parts that way if there is a screw up they are responsible. on this deal here you got off lucky as a lot more could have went wrong.