Tom Dingman's busted rocker spring

[Tom D.]

Here's a view of my 1960 (Altoona Registered) Corvette 283, as of today. This happened yesterday and I expect to fix it ASAP.

[Michael H.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Here's a view of my 1960 (Altoona Registered) Corvette 283, as of today. This happened yesterday and I expect to fix it ASAP.

Your lucky the valve didn't drop into the engine, I would put some air into that cylinder to keep the valve up. I assume the keeper failed ? Were you turning high RPM's ? Good luck.

Mike

[Tom D.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Cylinder #7. Only about 1500 RPM (FI's choke was on after a cold start). The startup was normal, so I got out to open the garage door. About 10-20 seconds of normal run time and then suddenly very noisy. Probably only ran about 10 seconds in this condition.

New spring is in. Rocker seems ok, as does the pushrod. However, the valve now appears to be slightly longer than its neighbors. (Crude straight-edge measurement and visible threads on the stud are less than before.). Compression testing tomorrow.

[Michael H.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Cylinder #7. Only about 1500 RPM (FI's choke was on after a cold start). The startup was normal, so I got out to open the garage door. About 10-20 seconds of normal run time and then suddenly very noisy. Probably only ran about 10 seconds in this condition.

New spring is in. Rocker seems ok, as does the pushrod. However, the valve now appears to be slightly longer than its neighbors. (Crude straight-edge measurement and visible threads on the stud are less than before.). Compression testing tomorrow.

I assume you got a new keeper as well as spring. Are your studs just pressed in or pinned/screwed in ? I had a pressed in stud back out on my L79 motor. I bought a .001 over size stud cleaned up the hole and used some special Loctite ( I think its green ) and primer for close tolerance holes and pressed it back in. I replaced all of my original 50 year old rockers and pushrods and installed new Comp cam roller tip rockers and push rods, I've never had anymore problems knock on wood.

Mike

[Dick W.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

I assume you got a new keeper as well as spring. Are your studs just pressed in or pinned/screwed in ? I had a pressed in stud back out on my L79 motor. I bought a .001 over size stud cleaned up the hole and used some special Loctite ( I think its green ) and primer for close tolerance holes and pressed it back in. I replaced all of my original 50 year old rockers and pushrods and installed new Comp cam roller tip rockers and push rods, I've never had anymore problems knock on wood.

Mike

Loctite 640 sleeve retainer. Will hold the world together Used it in the past on sleeved engines that the sleeve was loose in the bore and on press in valve seats.

[Gene M.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Tom, seeing racing equipment rocker arms I would be concerned the correct geometry is not in effect and the cause of the failure. My direction if it were me would be to use the original style rocker arms and push rods to insure I had correct geometry.

The springs and set height also an effect on proper geometry. Personally the I’m of the opinion that those roller tips does nothing except add problems in street use.

I would pull both heads and make some reversals back to original configuration and be sure nothing else has happened that is not visable.

The longer stem height is not a good indicator.

[Tom D.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Yes. Thanks very much. I plan to take the heads off after Altoona. I will replace the rockers then, or perhaps now...

Forget the longer stem height. I make a mistake in measuring it.

Cam is "097" replica. Going with 0.018 gap on Exh. valves and 0.012 on the intakes.

[Joe L.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Yes. Thanks very much. I plan to take the heads off after Altoona. I will replace the rockers then, or perhaps now...

Forget the longer stem height. I make a mistake in measuring it.

Cam is "097" replica. Going with 0.018 gap on Exh. valves and 0.012 on the intakes.

Tom------


The Comp Cams rockers seen in the photos are investment cast rockers. In general, investment cast rockers will offer more precise dimensional accuracy than the original stamped steel type. The roller tips may or may not offer any benefit but I don't see any real downside to them.

By the way, stock rocker arms on Gen III and Gen IV small blocks are investment cast.

[Dean B.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Maybe my old failing eyes are not seeing correctly but looks like I see a broken coil on the valve spring. Was this the initial failure that started this whole event? When piston is down, does the valve freely travel in the guide as in not bent? How did the compression test go? Will be interesting to hear the outcome.

[Dick W.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

There is no guarantee that with stock rockers and pushrods that the geometry is correct. I have a set of these that I use to determine what the correct length pushrods need https://www.summitracing.com/parts/cca-7705/overview/

[Tom D.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Maybe my old failing eyes are not seeing correctly but looks like I see a broken coil on the valve spring. Was this the initial failure that started this whole event? When piston is down, does the valve freely travel in the guide as in not bent? How did the compression test go? Will be interesting to hear the outcome.

Don't know if the coil broke first, or the keepers didn't keep. I suspect a bad spring, which has been replaced (with the head on).

Cyl. #7 now has about 130 pounds of compression, so a winter teardown is planned. All springs to be replaced then, along with at least one intake valve.

[Gene M.]

Re: Mid Atlantic Regional- Altoona, PA Concours Judging

Roller rocker arms are not typical on a stock valve train. I suspect the cam, push rods and springs are not typical GM pieces in addition those rocker arms. Not being screw in studs and guide plates a ‘Racing type” valve train is less durable in normal street use. There are many factors that go into the geometry of the valve train outside of push rod length. Some are coil set length, caps, valve seat depth, rocker ratio, cam lift and base circle, & head machining, to cover just some. A good engine shop should be able to advise you. But as a general rule a stock valve train is very slow acting and has a lot of forgiveness even if not optimum geometry.

[Roger W.]

Re: Tom Dingman's busted rocker spring

Tom,
What brand are the valve seals?